Lecture Notes(5)

Lecture Notes(5) - BICD 150 – Endocrinology...

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Unformatted text preview: BICD 150 – Endocrinology (Summer 2011) Dr. George Fortes Teaching Assistant: Ni Mo Table of Contents Lecture 1 (8/2/11)………………………………………………………………………………………………………2 Lecture 2 (8/4/11)………………………………………………………………………………………………………6 Lecture 3 (8/9/11)…………………………………………………………………………………………………….11 Lecture 4 (8/11/11)…………………………………………………………………………………………………..15 Lecture 5 (8/16/11)…………………………………………………………………………………………………..19 Lecture 6 (8/23/11)…………………………………………………………………………………………………..23 Lecture 7 (8/25/11)…………………………………………………………………………………………………..27 Lecture 8 (8/30/11)…………………………………………………………………………………………………..31 Lecture 9 (9/1/11)………………………………………………………………………………………..…………..36 Disclaimer: These notes are intended for you to supplement your studies. It is absolutely by NO means a substitute for going to lecture! Lecture 1 – 8/2/11 Intro + Overview Organs that secrete hormones Types of hormones: proteins + peptides, amino acid derivatives, fatty acid derivatives, steroids Hormone- receptor interaction Types of receptors: membrane receptors, G- protein coupled, growth factor, guanylyl cyclase Some Important Info: - Midterm Exam (40%, short answers): o Thursday – 8/18/11, 3:30- 4:50pm - Final Exam (60%, comprehensive MC): o Saturday – 9/3/11, 3- 6pm - Dr. Fortes’ email: [email protected] - Course website: ted.ucsd.edu à༎ this is pretty much where you’ll find anything associated with the course - Sections start on Thursday Hormones - Means of chemical communication - Secreted by glands and ducts Types of Signals - Paracrine – local secretions that influence nearby cells (e.g. prostaglandin) - Autocrine – secretions where it binds to receptors in the membrane of the same cell à༎ self stimulation - Juxtacrine – secretions that influence adjacent cells - Endocrine – secretions by ductless glands (main focus of this course) - Exocrine – secretions into ducts that leads to outside of body (e.g. sweat gland, mammary gland) Figure 7- 2 from Silverthorn: Anatomy summary - Pineal gland – type: gland. Secretes melatonin - Hypothalamus – Clusters of neurons. Secretes the hormones that target the anterior pituitary to release tropic hormones - Posterior pituitary – extensions of hypothalamic neurons and peptide hormones. Secretes ADH and oxytocin - Anterior pituitary – the “master” gland. Secretes tropic hormones: ACTH, TSH, FSH/LH, GH - Thyroid – secretes T3/T4 - Parathyroid – type: gland. Involved with calcium homeostasis (PTH) - Heart – type: cells. o Secretes atrial natriuretic peptide (ANP), which increases sodium excretion. This in turn increases urine output and decreases blood volume à༎ lead to decreased blood pressure - Liver – type: cells. Involved in various metabolic activity - Stomach and small intestines – type: cells. Secretes various hormones involved with digestion (mammphys 2 stuff) - Adrenal cortex – type: gland. Releases corticosteroids (e.g. cortisol), and mineralocorticoids (e.g. aldosterone) - Adrenal medulla – type: gland. Secretes amines (epinephrine and norepinephrine). - Kidneys – type: cells. Secretes erythropoietin (EPO) - Skin – modifies vitamin D3, which is involved in calcium homeostasis - Testes – male sex hormones (testosterone, DHT) - Ovaries – progesterone, estrogen - Adipose tissues – releases peptide hormones such as leptin, adiponectin, and resistin. Figure 7- 6: Steroid hormones - Steroid hormones are modified from cholesterol. This process occurs in the mitochondrial matrix. - Rate limiting step is the transport of cholesterol from intermembrane space into the matrix. Once in the matrix, the side chains are cleaved. - In the adrenal cortex, cholesterol can be converted into either aldosterone or cortisol - In the ovary, cholesterol can be made into estradiol (a type of estrogen) Types of Hormones - Proteins and Peptides – synthesis takes some time (because it has to go through transcription, post- transcription modifications, translation, etc.) o Once activated, the half- life is relatively short (a couple of minutes) o Peptide hormones can also be stored in membrane bound vesicles - Steroid hormones o Regulation is activation of their synthesis o Since they are lipid soluble, they can freely pass through membrane, and cannot be stored in vesicles. §༊ Because of this free passage, steroid hormone receptors are located inside the cell o Steroid hormones have slower effects because they alter transcription, and lasts for hours. - Fatty acid derivatives – ex. prostaglandin o PGs are a type of eicosanoids. Hormone- Receptor Interactions - Hormone binding to a receptor will result in a conformational change. Sometimes may cause protein dissociation. - Binding reaction: Hormone (H) + Receptor (R) <- > H- R (forward reaction has a formation rate constant k+1 or kon, while the reverse reaction has the dissociation constant k- 1 or koff) o The change in [H- R] over time is equal to kon[H][R] – koff[H- R], which is 0 at equilibrium o Therefore, at equilibrium the rate of forward reaction is equal to the rate of reverse reaction. In other words, kon[H][R] = koff[H- R]. Rearranging the equation gives you: [H][R]/[H- R] = koff/kon = KD o KD is also known as the dissociation constant, which is the concentration at which half ot eh sites are occupied by the hormone (same thing as the Michaelis Menten constant KM for enzymatic reactions). o KD measures the affinity of a given hormone. Lower KD (i.e. lower koff) à༎ higher affinity) o Lower KD can be achieved through 2 ways: either have a high formation rate constant (kon), or have a low dissociation rate constant (koff). o Antibodies have very low koff à༎ low KD à༎ slow dissociation of antigen from antibodies. Neurotransmitters, on the other hand, will want to have a very quick dissociation: high koff à༎ high KD (otherwise, slow dissociation would render neurotransmitter useless). - Agonist – elicits same effect on receptor - Antagonist – prevents binding of hormone or neurotransmitter, and does not activate receptor. (Does NOT elicit opposite effect!! That is the job of an inverse agonist) o Example: Naloxone – opiate antagonist, used to treat opiate overdose. Types of Receptors – 2 main categories: on plasma membrane (extracellular) or inside cell (intracellular) - Membrane Receptors o G- protein Coupled Receptor (aka 7- helix receptor, or serpentine receptor) – transmembrane segments where the protein crosses the membrane 7 times. §༊ Ligands bound: β- adrenergic agonists, PTH, LH, TSH, GHRH, TRH, ACTH, MSH, glucagon, etc. §༊ Upon binding of a ligand, the GPCR undergoes conformational change §༊ Inside, the receptor is bound to a G- protein, which consists of 3 subunits: α, β, γ. The G- protein essentially acts as a switch. In the “off” form, GDP is bound to the subunit. To turn it “on”, GDP is displaced and GTP binds instead. §༊ Sequence of events: • 1. H + R à༎ H- R (receptor now undergoes conformation change) • 2. H- R* (receptor now activated and binds to G- protein) + Gαβγ- GDP à༎ H- R*- Gαβγ- GDP (this is the complex in the “off” form) • 3. H- R*- Gαβγ- GDP à༎ H- R* + Gα - GDP + βγ (the G- protein now undergoes conformational change where interaction between the α subunit and βγ subunit weakens, causing the α subunit to dissociate from the βγ subunit) 4. Gα- GDP + GTP à༎ Gα - GTP + GDP (GDP dissociates from Gα, and GTP binds. Now it is in the “on” form) • 5. The ON form will then proceed to activate its respective phosphorylation cascade: o Gαs à༎ activate adenylyl cyclase o Gαi à༎ inhibit adenylyl cyclase o Gαq à༎ activate PLC- β There are 3 different kinds of G proteins (all undergo the same mechanism) • Gαs à༎ activates adenylyl cyclase. This enzyme catalyzes the conversion of ATP into cAMP. cAMP will then activate protein kinase A by releasing the inactive regulatory subunit of PKA. PKA will then phosphorylate serine and threonine residues on various target enzymes. o Ex: epinephrine on adrenergic receptor, or glucagon acting on liver. • Gαi à༎ inhibits adenylyl cyclase, and reduces cAMP. • Gαq à༎ activates PLC- β (phospholipase C- β) à༎ hydrolyzes phosphoinositol bisphosphate (PIP2) into diacylglycerol (DAG) + water soluble inositol triphosphate (IP3) o DAG remains in membrane and serves as a 2nd messenger to activate protein kinase C o IP3 is present in the inner layer of the phospholipid membrane. §༊ IP3 opens certain calcium channels, which will increase the concentration of calcium inside the cell. This allows for smooth muscle contraction, and it is the mechanism for vasoconstriction (α1 adrenergic receptors) §༊ In addition, IP3 will also increase the activity of calmodulin. The calcium- calmodulin complex (CAM) will activate CAM- kinase. How to turn the G- protein signaling off? • 1. Hydrolysis of GTP into GDP + Pi by GTPase from the α subunit of G- protein (the enzymatic activity is slow enough to allow for the G protein to do its thing before turning it off). • 2. Dissociation of hormone based on its rate constant koff • 3. Dephosphorylation of proteins by phosphatase • 4. Hydrolysis of cAMP to AMP by cAMP phosphodiesterase What are some things that can go wrong? • Cholera toxin – main target: cells in the intestinal mucosa and colon that can secrete ions. Targets Gαs o The toxin ADP- ribosylates (covalently adding an ADP- ribose group to) Gα, which will inhibit GTPase activity. This prevents Gα from being turned off, which results in the overproduction of cAMP. o CFTR (cystic fibrosis transmembrane regulator) – functions as a gated ion channel for Cl- . It is found in pancreatic duct cells, intestinal cells, and respiratory tract. When the channel is open, Cl- ions will freely leave cell into the intestinal and colonic lumen. This channel is gated by cAMP (i.e. cAMP will open the channel). o Therefore, with the overproduction of cAMP as a result of the cholera toxin, the CFTR will always be open, and Cl- will constantly be flowing into the lumen. This generates an electrochemical gradient, which will then draw Na+ from the basolateral side of the cell into the lumen as well. Once in the lumen, Na+ will react with Cl- to form salt, which will then increase the osmotic pressure in the lumen. This osmotic pressure will then draw water from the basolateral side into the lumen as well. As a result, the person will get massive diarrhea and may die from dehydration and electrolyte imbalance. §༊ The opposite effect, where CFTR is non- functional due to genetic defects in the synthesis of the channel, is cystic fibrosis. • §༊ §༊ §༊ Pertussis – targets Gαi o The toxin adds an ADP- ribose group to Gi, inactivating it. This will also increase the production of cAMP (essentially you’re inhibiting the inhibitor) o In the lungs, the CFTR channels are thus open for a longer period of time, and water and salt are drawn into the alveoli, resulting in chronic cough. o Growth Factor receptors §༊ Ligands bound: insulin, insulin- like growth factor (IGF), epidermal growth factor (EGF) §༊ The receptor is a single α- helix across the membrane. However, since α- helices are rigid (i.e. no conformational change), the signal must be passed through another way: • Once a hormone binds to the receptor, it will combine with another hormone- bound receptor (process called dimerization) • The inside portion of the receptor is a receptor tyrosine kinase (RTK), which can phosphorylate other receptors. The phosphorylated tyrosine (Y- P) binds to proteins with SH2 domain. This triggers a phosphorylation cascade, which will affect transcription and other functions. • Note: RTKs from growth factor receptors have innate autophosphorylation capabilities, but those of cytokine receptors do not. o Cytokine receptors §༊ Ligands bound: GH, prolactin, erythropoietin §༊ Cytokine receptors for the most part are similar to growth factor receptors, except in 2 ways: • These receptors do not have innate receptor tyrosine kinase activity (and thus must recruit another form of tyrosine kinase, called JAKs, as you will see below) • Cytokine receptors take the form of a dimer, even when inactive §༊ Upon binding of a ligand, cytokine receptors recruit soluble tyrosine kinases, called JAKS (aka “just another kinase” or “Janus kinase”, they refer to the same thing). JAKs are inactive unless bound to active receptor. Once they bind to cytokine receptors, they will then cross- phosphorylate the opposite intracellular portions of the receptor. This will then induce the transcription of STAT (signal transduction and transcription) proteins. STAT proteins then proceed to diffuse into nucleus where they alter gene expression. o Guanylyl cyclase receptors §༊ Ligands bound: atrial natriuretic peptides (ANPs) §༊ ANP receptors have intrinsic guanylyl cyclase activity §༊ ANP increases Na+ excretion in the kidneys (and thus increases urine output) §༊ Upon binding will activate guanylyl cyclase, which will convert GTP into cGMP • cGMP inhibits vasoconstriction, and plays an important role in erection. Intracellular Receptors o Cytoplasmic receptors – steroid hormones: glucocorticoids, progesterone, and androgens. NOT estrogen! §༊ All of these hormones have specific receptors in the cytoplasm. §༊ Structure of receptor: has both –NH2 end and –COOH end. Contains 3 domains: ligand binding, DNA binding, and transactivation domain. The –COOH end has the ligand binding domain (specific for the different types of the receptor to recognize the type of hormone), and the –NH2 end has the transactivation domain. Hormone binds to the hydrophobic binding site (usually inside protein) §༊ Heat shock proteins (HSP): binds to hydrophobic portions of proteins when they are exposed to surface and they protect protein from further unfolding or aggregating. In the resting state of receptor, HSPs are bound to the ligand binding domains. §༊ Once hormone binds, the HSP dissociates from ligand binding domain and the receptor undergoes conformational change. §༊ In addition, the ligand- binding domain will unmask a nuclear translocation signal, leading to activation of transactivation domain. • - The ligand- receptor complex will then be transported into the nucleus, where they may either dimerize or have hormone response elements (HREs) bind to the DNA- binding domain. This will then alter gene expression. §༊ On the DNA- binding domain are also zinc fingers, which allow for the binding of DNA segments. §༊ Because it goes through this complicated process, the steroid hormone effects have a slower onset and lasts longer. o Nuclear Receptors – thyroid hormones, estrogen, vitamin D, prostaglandins §༊ Nuclear receptors do not have transactivation domain because they don’t need it (they’re already in the nucleus) Regulation of receptors: - If a receptor remains activated for a long period of time, there is an enzyme, called arrestin receptor kinase, which will help regulate. o First found in β- adrenergic receptors, called βARK (β adrenergic receptor kinase). βARK phosphorylates the ser/thr residue on the β- adrenergic receptor. This will then promote binding of arrestin o Arrestin binds to activated receptor à༎ G protein no longer able to bind to receptor à༎ inactivates receptor o How is this process reversed? Use phosphatase. Phosphatase removes the phosphate group, and decreases affinity of arrestin to receptor. - Down- regulation of receptors – occurs by endocytosis à༎ receptor removed from membrane - Decrease synthesis of receptors. Lecture 2 – 8/4/11 Eicosanoids Hypothalamus + Pituitary Hypothalamic tropic hormones: GHRH, somatostatin, TRH, GnRH, dopamine, CRH Anterior pituitary (adenohypophysis): GH, TSH, ACTH, PRL, FSH/LH Posterior pituitary (neurohypophisis): ADH, oxytocin Eicosanoids - Diagram of synthesis: §༊ - - Precursor: arachidonic acid à༎ derived from fatty acid o PLA2 (phospholipase A2) cleaves phospholipids, releasing fatty acid and arachidonic acid o Arachidonic acid can also be formed through cleaving of DAG by lipase. Arachidonic acid can react with different enzymes and get converted to different products: 5- lipoxygenase à༎ makes leukotrienes §༊ They are inflammatory agents and cause bronchodilation o Cyclooxygenase (COX) à༎ makes PGG2 (a prostaglandin precursor) §༊ PGG2 can then be converted to PGH2 via peroxidase. PGH2 can then become prostaglandin E2, prostacyclin, or thromboxane §༊ Effects of prostaglandin (E2): ↑ inflammation, ↑ pain, smooth muscle contraction (e.g. in uterus à༎ menstrual cramps), ↑ set point (increases fever) §༊ There are 3 groups of COX: COX 1, COX 2, and COX 3. NSAIDs (non- steroidal anti- inflammatory drugs) o Main example: aspirin §༊ Aspirin is a potent irreversible inhibitor of all 3 COXs. By doing so, it will decrease the production of prostaglandins, and reduces fever as a result. §༊ However, because aspirin is an acid, and it inhibits COX 3 (which produces a group of prostaglandins responsible for mucus secretion), overdosing on aspirin can produce symptoms such as gastritis or peptic ulcer. §༊ Recently, studies have shown that by taking aspirin at low dose (81mg daily, which is 1/3 of its normal dosage) have been correlated with a decreased mortality rate from heart attacks. How does it work? • Inhibit COX à༎ ↓ prostaglandin H2 à༎ ↓ thromboxane (this is the agent that activates platelets to trigger blood coagulation) o - Hypothalamus - Some functions of the hypothalamus: o Detect and regulate osmolarity o Respond to change in blood pressure and volume o Appetite regulation o Circadian rhythms o Thermoregulation o Aggression and rage responses o Sex drive and gonad regulation o Adrenal cortex regulation o Thyroid regulation Pineal Gland - Secretes melatonin o Melatonin is derived from tryptophan, and is secreted in the nighttime because it favors sleep. Melatonin secretion is inhibited in presence of light, but in dark, the inhibition is removed and this hormone is released. This is how the circadian rhythm works. Hypothalamus- Pituitary- Portal System (aka hypothalamic- hypophyseal portal system) - Normal circulatory sequence: aorta à༎ arteries à༎ arteriole à༎ capillary bed à༎ venule à༎ vein à༎ vena cava - Portal circulatory sequence: aorta à༎ arteries à༎ arteriole à༎ 1st capillary bed à༎ venule à༎ vein à༎ venule à༎ 2nd capillary bed à༎ venule à༎ vein à༎ vena cava - The hypothalamic- hypophyseal portal system is one of the two portal systems of the human body (the other being the hepatic portal system) - What’s the point of the portal system? o Hepatic portal system à༎ ensures that the liver gets first shot at whatever was absorbed in the small intestines and stomach (both nutrients and toxins) o Similarly, the hypophyseal portal system, the anterior pituitary receives first shot of hypothalamic hormones as well. This directs signal better for hormones and also prevents hormones from getting diluted. - The brain is protected by the blood- brain barrier to prevent diffusion of large polar molecules from blood into the CSF. However, there is no BBB in the hypophyseal portal system, and therefore allows large polar peptide hormones to freely diffuse into the anterior pituitary. Pituitary - Bulb shaped structure below hypothalamus. Has two parts: anterior and posterior. o Posterior pituitary – contains neurons from hypothalamus where it receives hormones. o Anterior pituitary – contains 5 types of cells: §༊ Somatotrophs – secretes GH §༊ Lactotrophs – secretes prolactin §༊ Thyrotrophs – secretes TSH §༊ Gonandotrophs – secretes FSH/LH §༊ Corticotrophs – secretes ACTH - In the front of the pituitary, there is the optic chiasm where optic nerves come in. It also contains nerve fibers for peripheral vision. Therefore, one of the indicators of pituitary tumor is a decreased peripheral vision. Hypothalamic Tropic Hormones: - GHRH o Target: somatotrophs o Effect: ↑ GH secretion - Somatostatin o Target: somatotrophs o Effects: ↓ GH secretion - Ghrelin o Target 1: somatotrophs §༊ Effect: ↑ GH secretion o Target 2: hypothalamus §༊ Effect: ↑ appetite - Dopamine o Target: lactotrophs o Effect: ↓ PRL secretion - TRH o Target 1: thyrotrophs §༊ Effect: ↑ TSH o Target 2: lactotrophs §༊ Effect: ↑ PRL secretion - CRH o Target: corticotrophs o Effect: ↑ ACTH o ↑ CRH secretion can be stimulated through trauma, pain, starvation, stress, hypoglycemia, etc. - GnRH o Target: gonandotrophs o Effect: ↑ FSH/LH Anterior Pituitary Hormones - Growth Hormone (aka somatotropin) – bind to cytokine receptors o Target: liver o Effect: ↑ IGF- 1 o ↑ GH secretion: §༊ ↑ Food (especially arginine) §༊ Hypoglycemia – why? GH stimulates protein synthesis, which can help spare body protein from catabolism. o Other effects of GH: §༊ ↑ Insulin resistance à༎ ↓ carbohydrate metabolism (because you need glucose) §༊ ↑ Fat metabolism in adipocytes (because you need acetyl CoA for electron transport and ketogenesis) §༊ ↑ Amino acid uptake (because you want to increase protein synthesis) Stimulates growth in bones and other cells. Before puberty, there are growth cartilages at the ends of each bone. Abnormal conditions: §༊ Deficiency of growth hormone during growing stage (the years before end of adolescence when the long bone cartilages are sealed, around 18 years old) à༎ dwarfism (will have short arms and legs but normal shaped heads) §༊ Defective GH receptors à༎ Laron dwarfism (they may have normal levels of GH, but because the receptors are non- functional, IGF- 1 are not produced in sufficient amounts) §༊ Elevated amounts of GH during growing stage à༎ gigantism §༊ Elevated amounts of GH after growing years (usually from tumor in anterior pituitary): bones won’t grow longer but will thicken à༎ acromegaly (large extremities, thick skin, broad faces) • Other diagnostic methods: o Measure GH in blood o Inject insulin to induce hypoglycemia, and see if body will produce GH. If not, then there may be a problem. Secretion of GHRH occurs in pulses and the degree of GH secretion is genetically regulated. §༊ o - o PRL o o o o o - Target: breast Effect: milk production Prolactin is produced during early pregnancy, but only a limited amount of milk is produced. Why? The sex hormones estrogen and progesterone are elevated during pregnancy. These two hormones prevent the production of milk. §༊ However, right after delivery, the levels of estrogen and progesterone decrease. This increases milk production for the mother to feed the newborn. §༊ In addition, baby suckling will activate mechanoreceptors in hypothalamus. This will decrease dopamine secretion and stimulate PRL, which increases milk production. Other effects: §༊ ↓ Sensitivity to GnRH (lasts for an average of 10 months after delivery, but duration also depends on the nutritional state of the woman. Better nourishment à༎ shorter duration, and the woman will start ovulation earlier) • This contraceptive effect is important because getting pregnant again soon after delivering a baby would be a tremendous burden. Prolactinoma – tumor of the lactotrophs, resulting in ↑ prolactin secretion. Can occur in both males and females §༊ In both males and females, prolactinoma can induce galactorrhea, which is the letdown of milk §༊ Furthermore, because prolactin desensitizes GnRH, this will decrease the concentration of FSH/LH, and the person will have a higher probability of infertility. §༊ Treatment options: • Surgery or radiation. Problem: may hit places you don’t want to hit • Bromocriptine – dopamine agonist. Can also be used to treat Parkinson’s disease. ACTH o Target: adrenal cortex o Effect: ↑ cortisol o ACTH is derived from pro- opiomelanocortin (POMC). Other things that derive from POMC: γ lipotropin, β endorphin, γ- MSH o ACTH can also be used to make α- MSH, which has the following effects: melanin synthesis (↑ skin pigmentation), ↓ immune response, ↓ appetite o Primary adrenal insufficiency: ↓ cortisol à༎ no negative feedback à༎ ↑ CRH à༎ ↑ ACTH à༎ ↑ α- MSH à༎ ↑ melanin à༎ ↑ skin pigmentation (one of the visible signs) o Abnormal conditions: §༊ Cushing’s syndrome – general hypercorticism. Can be either primary (problem with the adrenal cortex), secondary (problem with anterior pituitary), or tertiary (problem with hypothalamus) • • - - Symptoms include central obesity, moon face, stretch marks, hypertension, etc. (You’ll learn more once we talk about the adrenal cortex) Note: because the elevated cortisol levels can be due to different set of reasons, the condition is given the syndrome label. On the other hand, Cushing’s disease specifically refers to elevated ACTH levels due to a problem with the anterior pituitary (i.e. it would be secondary hypercorticism) TSH o Target: thyroid o Effect: ↑ T4/T3 FSH/LH o Target: gonads (testes & ovaries) o Effect: ↑ sex hormones (estrogen + progesterone for females and testosterone + DHT for males) Diagram of Hypothalamic & Anterior Pituitary Hormones Posterior Pituitary Hormones - Antidiuretic Hormone (ADH or vasopressin) o Stimuli for release: §༊ ↑ Osmolarity (primary stimulus) - §༊ ↓ Blood volume (secondary stimulus) §༊ ↓ Blood pressure (also secondary stimulus) o Effects: §༊ ↑ H2O reabsorption, which will lead to: ↓ osmolarity, ↑ blood volume, ↑ blood pressure • Mechanism: there are vesicle- bound proteins called aquaporins in the kidneys. In the collecting duct, it is normally impermeable to water. ADH induces the exocytosis of aquaporin vesicles, and causes them to be implanted in the walls of collecting duct, and water is reabsorbed via the osmotic pressure gradient generated by the Loop of Henle. §༊ ↑ Sympathetic tone §༊ ↑ Vasoconstriction à༎ ↑ blood pressure §༊ ↑ Thirst o Alcohol and caffeine both inhibit ADH secretion, which is why you want to urinate more. o Dehydration also causes lower blood pressure (due to low blood volume). This stimulates ADH secretion and cause vasoconstriction (hence the name vasopressin) o Abnormal conditions: §༊ Diabetes mellitus – large amounts of urine excreted due to high osmolarity as a result of high glucose levels. §༊ Diabetes insipidus – caused by deficiency of ADH à༎ large volumes of dilute urine excreted à༎ chronic thirst, and may lead to death by dehydration. • However, because this large volume of urine is not due to hyperglycemia, the urine did not have the sweet taste. This is why it has been given “insipidus” (meaning bland or boring) Oxytocin o Stimuli for release: §༊ Mechanoreceptors – found in both cervix and nipples o Functions §༊ Milk letdown: suckling à༎ signal to hypothalamus à༎ increase oxytocin à༎ contraction à༎ milk ejection §༊ Also secreted during orgasms (love hormone) §༊ Positive feedback of uterine contraction: cervical stretch à༎ signal to hypothalamus à༎ ↑ oxytocin à༎ ↑ uterine contraction à༎ push fetus forward à༎ further cervical stretch à༎ etc.. §༊ Once fetus is delivered, oxytocin causes uterus to contract to prevent excess bleeding. Crying baby à༎ even more oxytocin secretion à༎ further contraction of uterus Lecture 3 – 8/9/11 Thyroid Hormones: T4 + T3 Regulation of Secretion Synthesis + Secretion Actions Hypothyroidism: myxedema, Hashimoto’s thyroiditis, etc. Hyperthyroidism: Graves’ disease, iatrogenic, tumors, etc. Thyroid Hormones Thyroid Gland Anatomy - Contains 2 types of cells: follicular and C cells. - Follicular cells surround colloid globules. T3/T4 are synthesized in these globules. - C cells secrete calcitonin. Calcitonin decreases plasma [Ca2+] levels, an important component of calcium homeostasis (more on this later) Secretion - Hypothalamus releases TRH (tripeptide hormone) à༎ targets thyrotrophs of anterior pituitary to release TSH, and lactotrophs to release prolactin. - TSH à༎ targets thyroids to increase uptake of iodide, which is used to synthesize T3/T4 Regulation of Secretion - T3/T4 inhibits release of TRH and TSH through negative feedback. - T3 is the more potent of the two hormones, and is the main inhibitor Synthesis - Diagram: - - - - - - Thyroid hormones are synthesized through iodination of tyrosine at carbons 3 and 5: o 2 tyrosine + 4 I- à༎ thyroxine (T4) aka 3,5,3’,5’- tetraiodothyronine o 2 tyrosine + 3 I- à༎ 3,5,3’- triiodothyronine (T3) Majority of secretion is T4 (95%) T4 can be converted to T3 through deiodination of C5 of the hydroxyphenyl group on the left Reverse T3: result of deiodination of C5 on the tyrosine à༎ inactive Iodide absorption: o 1. TSH binds to receptor on follicular cell. This results in the following effects: §༊ ↑ Growth of cells and blood vessels §༊ ↑ NIS channel §༊ ↑ Thyroglobulin (TGB) §༊ ↑ Thyroid peroxidase (TPO) §༊ ↑ Endocytosis of iodinated TGB o 2. Iodine is absorbed in the GI tract, and is usually converted to iodide. o 3. Thyroid follicular cells have iodide channels to allow passage of I- into cells. Once inside, I- are concentrated ~10x. o 4. The process of iodide entry is coupled with the entry of 2 Na+ ions (the channel is called NIS, or sodium- iodide synport) o 5. 3 Na+ is then pumped out of cell against its concentration gradient in exchange for 2 K+ pumped in through a Na+/K+ ATPase. o 6. Iodide proceeds to diffuse across cell into the colloid side through an I- channel called Pendrin. Thyroglobulin: o It is synthesized in the rough ER of the thyroid follicular cells. o Once it is further processed in the Golgi apparatus, it is exocytosed to the colloid side. o Thyroglobulin contains about 140 tyrosine residues, but only 4 are iodinated because of sterics. - Thyroid Peroxidase o This enzyme catalyzes the reaction: TGB- tyr + I- + H2O2 à༎ TGB- tyr- I (monoiodotyrosine, or MIT) o MIT can be iodinated to form diiodotyrosine (DIT) o MIT + DIT à༎ T3 o DIT + DIT à༎ T4 o Propylthiouracil (PTU) – a drug that inhibits TPO, which can be used to treat some forms of hyperthyroidism. - Results: o TGB can be made into either TGB- T3 or TGB- T4. These are still in the colloid. In order to be secreted, they are endocytosed across thyroid follicular cells and released to the extracellular fluid o During the process of endocytosis, lysosomes cleave T3/T4 off of TGB. o Overall path of TGB: §༊ TGB in rough ER à༎ processed in Golgi à༎ secreted into colloid à༎ iodinated in colloid à༎ TGB- T3/T4 gets endocytosed back to follicular cell à༎ TGB- T3/T4 cleaved by lysosome, releasing T3/T4 à༎ T3/T4 are release back to blood. §༊ In blood, T3/T4 is transported by binding to the following proteins with different binding strengths: 70% thyroid binding globulin, 20% transthyretin, and 10% albumin. • Functions of these transport proteins: 1. To maintain solubility 2. To prevent excretion of these hormones (because they’re not filtered in the kidneys. This is why thyroid hormones have such long half- lives. • Too little binding proteins à༎ causes elevated levels of free T3/T4 à༎ can produce some symptoms of hyperthyroidism • To much binding proteins à༎ not enough free T3/T4 to bind to receptors (because they’re bound to these proteins already) Thyroid Imaging - 123I – radioactive iodide that can be used for imaging to see if the thyroid gland is functioning properly. Can be used to detect nodules that may be taking up much more iodide than necessary (“hotspots”), or nodules that do not take in iodide (“coldspots”). Hotspots are usually benign, but coldspots can be malignant. - High dose of 123I limits iodide uptake and can also be a poison for the thyroid gland. T3/T4 Actions - Receptors: o Nuclear receptors – contain zinc fingers §༊ T3/T4 bind à༎ increases TREs (thyroid hormone response element) à༎ receptor- TRE complex binds to DNA à༎ alter transcription o Not associated with heat shock proteins - Functions: o ↑ Growth and development o ↑ Myelination in brain §༊ Deficiency of thyroid hormones during development à༎ brain impairment à༎ mental retardation (this condition is called cretinism, AKA congenital hypothyroidism). Cretinism is irreversible. Other signs of cretinism: • Dwarfism • Impaired bone development • Lethargy, depression §༊ Because of the ↑ conduction velocity, this also results in ↑ reflexes. o ↑ Bone formation o ↑ O2 consumption (basal metabolic rate) o ↑ Na+/K+ ATPase and Ca2+- ATPase o ↑ Myosin o o o o ↑ Synthesis of β- adrenergic receptors §༊ β- 1 receptors à༎ found in myocardial cells. Activation à༎ increase heart rate (positive chronotropic effect) and contractility (similar to effect of epinephrine) • Thyroid hormone deficiency à༎ fewer β1 receptors à༎ slower heart rate • Excess thyroid hormone à༎ tachycardia/increased cardiac output. §༊ β- 2 receptors à༎ found in bronchioles. Activation à༎ bronchodilation §༊ β- 3 receptors à༎ found in adipocytes. Activation à༎ ↑ Lipolysis and thermogenesis ↑ Uncoupling of oxidative phosphorylation à༎ ↓ efficiency à༎ ↑ non- shivering thermogenesis §༊ Too little T3/T4 à༎ cold intolerance §༊ Too much T3/T4 à༎ heat intolerance ↑ G.I. motility §༊ ↓ T3/T4 à༎ constipation §༊ ↑ T3/T4 à༎ vomiting or diarrhea Stimulates respiratory centers in the medulla oblongata §༊ ↓ T3/T4 à༎ can get hypoventilation Abnormal Conditions - Nomenclature/convention: o Primary = problem with thyroid gland o Secondary = problem with anterior pituitary o Tertiary = problem with hypothalamus - Hypothyroidism – deficiency in T3/T4 o Categories §༊ Primary hypothyroidism: ↓ T4/T3, ↑ TRH, ↑ TSH §༊ Secondary Hypothyroidism: ↓ T4/T3, ↑ TRH, ↓ TSH §༊ Tertiary hypothyroidism: ↓ T4/T3, ↓ TRH, ↓ TSH o Signs/Symptoms §༊ ↓ Basal metabolic rate à༎ weight gain §༊ ↓ GI motility à༎ constipation §༊ ↓ Heat generation à༎ cold intolerance §༊ Lethargy, apathy, slow reflexes §༊ ↓ Heart rate à༎ blood can back up into heart, stretching it and causes enlargement (cardiomegaly) §༊ Myxedema – due to increased synthesis of mucopolysaccharides (extracellular proteins) à༎ ↑ osmotic pressure, which draws water to subcutaneous regions. The water accumulates beneath the skin, and gives a puffy look. §༊ Hypoventilation §༊ ↓ Response to catecholamines o Associated Diseases/Causes §༊ Hashimoto’s thyroiditis – primary hypothyroidism: ↓ T4/T3, ↑ TRH, ↑ TSH • Autoimmune condition • Antibodies attack thyroid à༎ causes ↓ T3/T4 secretion • Drug treatment: Levothyroxine (it’s basically thyroxine that rotates plane polarized light to the left, i.e. levorotary) – one of the most prescribed drugs in the U.S. o Thyroxine can be absorbed through the intestines and can be stored. o Exogenous thyroxine also exhibits negative feedback to TRH and TSH. - Hyperthyroidism – excess T3/T4 (AKA thyrotoxicosis) o Categories §༊ Primary - ↑ T3/T4, ↓ TRH, ↓ TSH §༊ Secondary - ↑ T3/T4, ↓ TRH, ↑ TSH §༊ Tertiary - ↑ T3/T4, ↑ TRH, ↑ TSH o Signs/Symptoms o - §༊ Tachycardia §༊ Diarrhea (due to ↑ GI motility) §༊ Nausea/vomiting §༊ Nervousness, hyperexcitability, sweating §༊ Weight loss (due to ↑ metabolism) §༊ Heat intolerance (due to ↑ heat generation) Associated Diseases/Causes §༊ Graves’ disease – primary hyperthyroidism caused by antibodies activating TSH receptors (autoimmune condition) à༎ ↑ T3/T4, ↓ TRH, ↓ TSH • Symptoms: o Exophthalmos – bulging eyes §༊ This symptom is characteristic of Graves’ disease, but is not present in other forms of hyperthyroidism. §༊ Caused by antibodies reacting with antigens behind the eyes, generating an inflammatory reaction that bulges out the eyes. • The degree of disparity in bulging can cause double vision because the eyes cannot focus on a certain object in the same way. o Nervousness o Tibial myxedema (dermopathy near the shin region) o Slight goiter – diffused growth rather than nodules • Treatments: o PTU – inhibits TPO o 123I – decreases number of functional cells in thyroid Goiter o Can be caused by either hyper- or hypothyroidism o Example: iodine deficiency à༎ hypothyroidism §༊ Because of this, the thyroid will try to compensate by enlarging in size. This results in the characteristic bulge found on some people’s necks. §༊ However, trace amounts of iodine are enough to prevent this condition, which led to the manufacturing of iodized salt. Lecture 4 – 8/11/11 Male Reproduction: Anatomy + Histology Hypothalamic- Pituitary- Testes Axis Hormonal Regulation Sex Steroids, Androgens, Estradiol, Progesterone Effects of Testosterone + Dihydrotestosterone (DHT) Sexual Development + Puberty Male Reproduction Male Gross Anatomy - Male Accessory Structures – developed from Wolffian duct under influence of testosterone o Epididymis – where sperm is stored o Seminal vesicle – adds the fructose to semen o Vas deferens - Male external genitalia – developed through effect of DHT o Penis o Scrotum o Prostate – even though this is technically on the “inside”, it is still categorized as “external” because development is influenced by DHT. - Sperm Movement: o Seminiferous tubules à༎ epididymis à༎ vas deferens à༎ urethra (there is a valve that prevents semen from going into the urinary bladder, and also prevents urine from entering vas deferens) à༎ seminal vesicle (provides fructose) à༎ prostate (provides mucus and buffers) à༎ bulbourethral gland (provides additional mucus) à༎ penis - With age, the prostate can enlarge. This presses against the urethra, which can make it difficult to urinate for aging men. - Scrotum – a layer of skin that surrounds the testes. This allows the testes to be in an environment that is a few degrees cooler, which is important for proper sperm development. - The penis contains erectile tissues (similar to those in the clitoris of females) - Cross section of the penis (coronal view): o Corpora cavernosa (erectile tissue) – central arteries pass through this section. §༊ During erection, arteries dilate à༎ ↑ blood flow à༎ compresses veins (↑ input, and ↑ resistance for output) à༎ enlarges in size o Corpora spongiosum – located in the inferior portion of the penis. The urethra passes through this section. - Mechanism of erection in detail: o Acetylcholine targets endothelial cells à༎ bind to mACh receptors à༎ ↑ [Ca2+] à༎ activate Ca2+ dependent enzyme nitric oxide synthase (NOS) à༎ ↑ NO à༎ stimulate guanylyl cyclase à༎ ↑ cGMP à༎ relaxation of smooth muscles à༎ vasodilation à༎ erection o How to turn off erection? §༊ 1. Hydrolyze ACh via acetylcholinesterase §༊ 2. Hydrolyze cGMP into GMP via cGMP phosphodiesterase o Sildenafil (Viagra) – originally intended to reduce blood pressure, but now used to treat erectile dysfunction §༊ Mechanism: inhibits cGMP phosphodiesterase à༎ ↑ cGMP action Male Microscopic Anatomy - Two types of cells in the testes: o Leydig cells §༊ These cells have receptors for LH §༊ Upon activation, Leydig cells secrete testosterone §༊ In peripheral tissues, the enzyme 5- α- reductase converts testosterone to the more potent version: dihydrotestosterone (DHT). DHT is responsible for the development of male external genitalia (more on this later) §༊ Testosterone can also be converted to estradiol via aromatase. Estradiol is a type of estrogen. o Sertoli cells §༊ These cells have receptors for FSH §༊ Upon activation, Sertoli cells secrete: • Androgen binding protein (ABP) –binds testosterone or DHT and maintains a high level of these hormones in the seminiferous tubule to allow proper functioning of sertoli cells and production of mature sperm. • Inhibin B – serves as negative feedback (only inhibits FSH, not LH) - Spermatogenesis: o Embryonic state/Pre- puberty §༊ Spermatogonium (diploid) undergoes mitotic division to make more spermatogonia o Puberty and onward: §༊ Spermatogonia continue to undergo mitosis §༊ Some of the spermatogonia will have DNA duplication and crossing- over of sister chromatids to make primary spermatocytes (diploid + duplicated) §༊ These primary spermatocytes then undergo the first meiotic division, which results in secondary spermatocytes (haploid + duplicated) Secondary spermatocytes then undergo second meiotic division, which results in spermatids (haploid) §༊ Each spermatid then mature into haploid sperms Summary: 1 diploid spermatogonium results in 4 haploid sperms. §༊ o Hypothalamus- Pituitary- Testes Axis - Hypothalamus releases GnRH in pulses (30- 120 min intervals. The reason for pulse secretion is because continuous stimulation will cause downregulation of receptors on gonandotrophs, and eventually they will no longer respond to GnRH.) à༎ pituitary gonandotrophs secrete: o FSH à༎ sertoli cells à༎ ↑ ABP + ↑ inhibin o LH à༎ leydig cells à༎ secrete steroids: testosterone, DHT, estradiol, androstenedione, progesterone Hormonal Regulation - Inhibin o Negative feedback inhibitor on FSH only (NOT LH!) - Steroids (especially testosterone) o Negative feedback inhibitor for both hypothalamus and anterior pituitary Male Hormones - Synthesis Pathways: Precursor for sex hormones: cholesterol. Cholesterol is transported into the mitochondrial matrix via a transporter called StAR (steroidogenic acute regulatory protein). o Once in the matrix, cholesterol is converted to pregnenolone, which can be converted into any androgen, depending on the pathway - DHEA – weak androgen that is also synthesized in the adrenal glands by both males and females o Oxidation and/or hydroxylation of this hormone results in synthesis of androstenedione, which is the precursor of testosterone. - Testosterone – consists of 95% of hormones secreted by testes o Dihydrotestosterone (DHT) – converted from testosterone via enzyme 5- α- reductase. It is the more potent version of testosterone. §༊ This hormone is responsible for the development of primary sexual characteristics (e.g. external genitalia) o Estradiol – converted from testosterone via enzyme aromatase (occurs mainly in ovaries). §༊ However, this conversion is also present in males by the peripheral tissues §༊ Aromatase is known to be correlated with breast cancer (estrogen- dependent breast cancer). o Functions of androgens (mainly testosterone): §༊ Anabolism à༎ ↑ protein synthesis §༊ ↑ Muscle mass §༊ ↑ Hematocrit (red blood cell count), ↑ hemoglobin synthesis • Males have higher hematocrit compared to females §༊ ↑ Growth cartilage à༎ growth spurt • Ossification – when the osteoblasts secreted over time become bone tissue à༎ growth stops §༊ ↑ Growth of larynx/vocal cord à༎ lower voice §༊ ↓ HDL §༊ Development of pubic hair, axillary hair, body hair (beard, mustache, chest hair, back hair, etc.) §༊ Stimulation of sebaceous glands à༎ ↑ acne §༊ Stimulation of sweat glands à༎ ↑ body odor §༊ ↑ Sex drive (libido) §༊ Male pattern baldness (stimulated by DHT) • Some treatment for baldness include 5- α- reductase inhibitor §༊ Broadened shoulders - Sometimes people abuse anabolic steroids to build muscle mass. This could lead to a variety of negative consequences: o ↑ Acne o Breast development (gynecomastia) – due to increased concentration of estrogen that was converted from the excess androgens. o Liver toxicity o Infertility – how? ↑ Androgens à༎ ↓ FSH/LH à༎ ↓ maturation of sperms Male Sexual Development - Early embryos are in the bipotential stage, meaning they can become either male or female. The embryo contains a cortex and a medulla. Sex is determined by presence or absence of the SRY gene found in the sex- determining region of the Y chromosome. - Presence of SRY gene will allow the embryonic medulla to develop into testes. - The leydig cells secrete testosterone, which is responsible for the development of Wolffian duct into accessory structures (vas deferens, seminal vesicle, and epididymis). - In addition, testosterone is converted to DHT via 5- α- reductase. DHT is responsible for the development of male external genitalia (penis, prostate, scrotum) - Sertoli cells secrete anti- Mullerian hormone (AMH), which degrades the Mullerian duct. o Mullerian duct develops into female accessory structures What would happen if a XY embryo were missing 5- α- reductase? - No 5- α- reductase à༎ no DHT à༎ born with female external genitalia but has testes instead of ovaries. o - Furthermore, because testosterone can still exhibit its effect, the baby will still have the male accessory structures. What would happen if a XY embryo had nonfunctional androgen receptors? - No effect from BOTH testosterone and DHT à༎ degradation of Wolffian duct, and no male external genitalia will develop. In addition, sertoli cells continue to secrete AMH, which degrades the Mullerian duct. o As a result, the baby will have testes + female external genitalia, and no accessory structures at all. **End of Midterm Material** Lecture 5 – 8/16/11 Female Reproduction: Hormonal Regulation: Hypothalamus (GnRH) à༎ pituitary (FSH/LH) à༎ ovaries (estrogens, androgens, progesterone, inhibins) Anatomy, Histology, Follicular development Menstrual cycle: Ovarian: follicular phase (early, mid, late) Uterine: luteal, menstrual Birth Control Pregnancy Midterm: Thursday 8/18/11 from 3:30pm- 4:50pm • Material covers up to last Thursday’s lecture (end of male reproduction). Today’s lecture (female reproduction) will NOT be covered Female Reproduction Anatomy • External genitalia (developed with the ABSENCE of DHT): o Clitoris – contains erectile tissue o Labia majora o Labia minora o Urethra o Lower vagina • Accessory structures (developed with the ABSENCE of AMH): o Fallopian tube o Upper part of vagina o Uterus – 2 layers §༊ Outer layer = myometrium • Proliferates under influence of androgens, and will breakdown during menstrual flow §༊ Inner layer = endometrium • Contains cells necessary for outer layer proliferation Development • Once again, around the 6th week, the embryonic gonads are in the “bipotential stage” • No SRY gene à༎ gonad develops into ovaries • No anti- Mullerian hormone à༎ Wolffian duct degrades and the Mullerian duct develops into the female accessory structures • No dihydrotestosterone à༎ female external genitalia develops • As you can see, female development is the “default” pathway. As long as there is an absence of the signals preventing female development (i.e. DHT and AMH), then the embryo will automatically turn into a female. • Why do males require additional signals (testosterone/DHT) but females do not? o Pregnant mothers already have elevated levels of estrogen and progesterone, so if the fetus were to require ADDITIONAL female androgens, it would pretty much be swimming in these hormones à༎ doesn’t make sense to have this. Hormonal Regulation: • Hypothalamus releases GnRH à༎ targets gonandotrophs on anterior pituitary to release FSH and LH à༎ FSH/LH will target specialized cells on ovaries (more on this later) • Depending on where the woman is during her menstrual cycle, androgens can either negatively OR positively feedback to hypothalamus/pituitary (more on this later) Menstrual Cycle – lasts about 28 days, has several phases: • • Menstrual flow – this marks the start of a menstrual cycle Follicular phase o Follicular maturation: • 400,000 – 500,000 primordial follicles are generated in the baby during 6th to 8th month of pregnancy in mom. Each follicle contains a single oocyte (primary oocyte), which has duplicated DNA but is arrested in prophase (i.e. no meiotic division) until ovulation (and this may last as long as 50 years!) o The primary oocyte is surrounded by a layer of granulosa cells (equivalent to sertoli cells in the testes) o From puberty until menopause there will be a small number of follicles that undergo maturation every month: primordial follicle à༎ primary follicle à༎ secondary à༎ tertiary (aka antral follicle) à༎ Graafian. The maturation process consists of a gonandotropin- independent and –dependent stage: §༊ Hormone independent stages (i.e. not under influence of FSH/LH): • Primordial à༎ primary follicle (lasts about 5 months) • Primary à༎ secondary (lasts about 4 months) • Secondary à༎ tertiary (aka antral) §༊ Hormone dependent stages • When granulosa cells surrounding follicle begin secreting antral fluid. During this stage (called antral stage), the follicles (aka antral follicles or tertiary follicles) have grown to a diameter of 0.5 cm. • The follicle will continue to grow in size, and the accumulation of fluid causes the follicle to forma “blister” in the ovaries. Can grow up to 2 cm (the size of mature Graffian follicle) • The tertiary follicle also contains two types of specialized cells: granulosa (equivalent to sertoli cells in males) and theca (equivalent to leydig) o Theca cells respond to LH, and will secrete androgens and progesterone. o Granulosa cells contain the enzyme aromatase, which converts the androgens into estradiol and other estrogens. o Granulosa cells also secrete inhibin, which inhibits FSH release. This serves as a “follicle selection” process (i.e. only the selected follicle will have sufficient FSH receptors and will be able to mature into the dominant follicle, the rest will die off) o Hormonal effects (after the dominant follicle has been selected) §༊ Under influence of LH à༎ theca cells secrete androgens, which will then be converted to different estrogens §༊ Under influence of the estrogens, the endometrium layer proliferates and thickens. • In addition, estrogen levels will continue to increase, initially inhibiting FSH/LH release through negative feedback. • However, after the estrogen levels reach a high enough level, the negative feedback suddenly switches to positive feedback, where it will actually stimulate GnRH release. • This then triggers a tremendous surge in LH, which is what signals ovulation. §༊ Highest levels of estrogen = late follicular phase, right before ovulation Ovulation o Due to the LH spike (which lasts about 48- 50 hours) o First meiotic division occurs, which results in the secondary oocyte and first polar body. The secondary oocyte is released once the mature follicle ruptures. o After ovulation, the remnants of follicle form the corpus luteum, which begins secreting progesterone. o In addition, FSH/LH and estrogen levels all decrease o The basal body temperature will also increase by about 1oC Luteal phase o Occurs once corpus luteum (yellow body) is developed from ruptured follicle. Corpus luteum continues to secrete estrogens, progesterone, and inhibin. o The high levels of progesterone will negatively feedback on GnRH and FSH/LH, and help maintain the endometrium lining of uterus (to prepare for gestation) o Now, two things can happen: §༊ If no fertilization occurs à༎ • • • Corpus luteum will eventually degrade to corpus albicans (white body). This causes a drop in progesterone, which will then cause the outer layer of uterus to break down and initiate the menstrual flow (i.e. the period). o In order for the uterine lining to break down, necrosis must be triggered. This happens through the synthesis of two types of prostaglandins: PGF2α (a vasoconstrictor) and PGE2 (a vasodilator) §༊ PGF2α limits the blood flow to the uterine layer. After a period of time, this layer becomes ischemic and deprived of oxygen. Then, PGE2 will cause vasodilation, which will increase blood flow through the process called reperfusion injury. The sudden increased perfusion to an already oxygen- deprived tissue will cause inflammation, and this is what maintains necrosis/break down of the uterine layer. §༊ FYI: menstrual cramps are caused by increased synthesis of PGF2α. Therefore, NSAIDs are often taken by women to help treat this condition. • In addition, the inhibition on hypothalamus will be lifted. It will now start secreting GnRH again, and thus starting the menstrual cycle over again. If fertilization DOES occur à༎ • A new hormone, the human chorionic gonandotropin (hCG) is released. • hCG is analogous to LH (which will sustain the corpus luteum) but is not subject to the negative feedback effects from estrogen/progesterone. o Because the corpus luteum is now sustained, it will continue secreting estrogens and progesterone. This will now prevent the break down of lining à༎ no period • Well, you get pregnant… • §༊ Pregnancy o How the egg is fertilized: o Tip of sperm head contains vacuole of protein that enables the sperm to pass zona pellucida of the egg o During point of fusion, the Ca2+ channels open and causes ↑ [Ca2+] in the oocyte. This will trigger exocytosis of vesicles near the membrane of oocyte to block off all possibilities of fusion from additional sperms (called polyspermy block) o Upon fertilization, the second meiotic division occurs, producing the zygote and 2nd polar body. o Figure 26- 18 o Day 1: fertilization occurs in fallopian tube o Day 2- 4: cell division takes place o Day 4- 5: blastocyte travels through fallopian tube and reaches uterus §༊ The blastocyte consists of inner wall mass, which develops into placenta, and outer wall mass for implantation o Day 5- 9: blastocyte implants on uterine wall o What can go wrong during implantation? §༊ Since egg gets fertilized in the fallopian tube, it is possible for it to get implanted there instead of the uterus (called tubule pregnancy). This is an emergency situation because if the tube ruptures, the woman can die. Surgical procedure to remove the fallopian tube is required. o Some signs of early stage pregnancy: o Fatigue o Nausea/vomiting (morning sickness) due to elevated levels of estrogen o Breast tenderness o Some galactorrhea o Missed period – because the uterine lining is maintained o Increased urination Contraception/Birth Control o Barrier method: condoms, diaphragm o o o o Chemical method: spermicides Mechanical devices: IUD (intrauterine device) – inserted in uterus to prevent implantation of fertilized egg. Problem: high risk of pelvic infection. Synthetic steroid hormones (birth control pills): progestins (progesterone analog), estrogen analog. These pills work by utilizing the negative feedback functions of these androgens: o Progesterone inhibits GnRH, FSH, and LH à༎ prevents maturation of oocyte à༎ prevents ovulation o Disadvantage: estrogen induces blood clotting and is associated with estrogen- dependent cancers. What happens if there is an unwanted pregnancy? o Mifepristone (RU- 486) – synthetic progesterone antagonist. §༊ It binds to ligand binding domain of progesterone receptor and does not activate or release heat shock protein. This prevents progesterone from binding, and prevents implantation of embryo. However, in order for this work, this drug must be taken within 1 week of intercourse §༊ This is controversial, because it induces “medical abortion”. Lecture 6 – 8/23/11 Endocrinology of Pregnancy: hCG, hPL, relaxin, estrogen progesterone, prolactin + others à༎ all increase Labor + delivery: CRH, oxytocin Estrogen effects: puberty à༎ menopause - - - o- - - - Pancreatic Hormones: insulin + glucagon Glucagon: fasting state + hypoglycemia Stimuli + effects Insulin: fed state Stimuli, secretion mechanism, effect Diabetes mellitus Endocrinology of Pregnancy Placental Hormones: • Human chorionic gonandotropin (hCG) – homologous to LH o Secreted within 10 days of fertilization (or within 24 hours of implantation). Usually used to detect pregnancy. o Because it is like LH, it will sustain the corpus luteum, and not subject to negative feedback from estrogens and progesterone. As a result, because the corpus luteum is sustained, it will continue synthesizing and releasing estrogen and progesterone. • Human placental lactogen (hPL) – homologous to GH o Known as the “growth hormone of pregnancy” o Effects: §༊ ↓ Glucose utilization §༊ ↑ Insulin resistance à༎ can sometimes cause gestational diabetes because it increases the level of circulating glucose §༊ ↑ Lipolysis à༎ ↑ fatty acids §༊ ↑ Amino acids • Relaxin o Effects: §༊ Causes the relaxation of the ligaments in the bones at the pelvic region à༎ this allows the pelvis to stretch, which aids in the delivery of the baby §༊ ↓ Excitability of uterine smooth muscle à༎ ↓ action potentials à༎ inhibits contractility §༊ ↓ Number of oxytocin receptors §༊ Causes “ripening” of cervix (becomes softer) Other hormones: • Progesterone o Decreases excitability and contractility of the myometrium o During the 2nd trimester, another form of progesterone (17- hydroxy- progesterone) is released. This form also decreases excitability/contractility of uterine smooth muscle. • Estrogens o Synthesis: §༊ DHEA à༎ androstenedione à༎ testosterone à༎ estradiol o Effects on uterus: §༊ ↑ Growth of myometrium §༊ ↑ Excitability of myometrium §༊ ↑ Number of oxytocin receptors §༊ These effects start kicking in after oxytocin has been released o Effects on the breast: §༊ ↑ Breast growth §༊ ↓ Milk production o Other effects – §༊ Secondary sexual characteristics • ↑ Breast growth o Which is why men who take too much anabolic steroids start developing boobs, because the steroids were converted to estrogens via aromatase. • ↑ Hip, and hip width • ↑ Glutei • ↑ Pubic hair o Pattern is more triangular compared to that of males • ↑ Auxiliary hairs (armpit hair) • ↑ Sebaceous glands à༎ secretes sebum, which may cause acne development • ↑ Libido o This effect is also shared by androgens §༊ ↑ Thickness of uterus §༊ ↑ Elasticity of mucus (“ferning”) §༊ ↑ Growth spurt – sealing of epiphyses §༊ ↑ Pigmentation of areolae (around the nipples) + genitalia §༊ ↑ HDL, ↓ LDL §༊ ↑ Mineralization of bone (↓ bone resorption) • This is why post- menopausal women (↓↓ estrogen) have a much higher risk for developing osteoporosis (i.e. the rate of bone resorption exceeds the rate of bone formation) §༊ ↑ Blood clotting • Which is why hormone replacement treatment for post- menopausal osteoporosis is not such a good idea anymore, because ↑ blood clotting also increases the risk of stroke or myocardial infarction. §༊ ↑ Temperature §༊ The drop in estrogen after menopause is also theorized to attribute to post- menopausal depression. §༊ High estrogen levels have also been correlated with certain types of breast cancer Pregnancy stages: separated into 3 trimesters spanning 270 days (~40 weeks) • Hormonal level changes: o Prolactin – continually increase throughout pregnancy o FSH/LH – relatively constant o hPL – continually increase throughout pregnancy (acts as growth hormone for the mom) CRH – increases slightly throughout entire duration of pregnancy, but shoots up within the last 10 days of pregnancy o Estrogens – all of which increase throughout pregnancy §༊ Could be responsible for morning sickness o Progesterone – constantly increase throughout pregnancy o DHEA – decrease because most are converted to estrogens o Insulin – increases o Glucocorticoids increase à༎ ↑ glucose, ↑ fatty acid, ↑ amino acid Mid to Late- stage Pregnancy o Amniotic sac – test can be done on the amniocentesis to see sex of baby, possible genetic disorders, etc. o What signals delivery? §༊ Increase CRH à༎ ↑ corticoids à༎ ↑ changes in contraction §༊ When contractions under rhythmic intervals (labor), delivery is imminent within 24 hours §༊ Current theory: the fetus is what signals the contractions, generating a positive feedback on the contraction - - - - - - - - - - - - - - o- - - - - - - - - - - - - - o • Hormones & Metabolism *Might be a good idea to review metabolic pathways (BIBC 102 stuff) Anatomy of Pancreas • Islet of Langerhans (2% by mass) – contain several types of cells o α- islet cells: secrete glucagon o β- islet cells: secrete insulin o δ- islet cells: secrete somatostatin • Exocrine cells (98% by mass) – secrete bicarbonate juice and various digestive enzymes Glucagon • Hormone of the “fasted” state because it stimulates catabolic pathways (such as glycogenolysis, gluconeogenesis, β- oxidation of fatty acids, etc.) • Stimuli of secretion: o ↓ Blood glucose levels o Activation of sympathetic nervous system o Activation of parasympathetic (to a lesser extent) §༊ However, the parasympathetic is usually inhibited when one is fasting • Inhibition of secretion: o Insulin o Somatostatin o ↑ Blood glucose levels • Effects o ↑ Glycogenolysis via: §༊ Gαs à༎ ↑ AC à༎↑ cAMP à༎ ↑ PKA à༎ phosphorylates glycogen phosphorylase kinase at the ser/thr residues à༎ ↑ glycogen phosphorylase à༎ catalyzes reaction: Glycogen(n) + Pi à༎ Glycogen(n- 1) + G1P • G1P is converted to G6P, which will then be dephosphorylated via G6P phosphatase (note: this enzyme is ONLY found in the liver!) to make glucose. Skeletal muscles do NOT have this enzyme, and therefore they can only USE glucose, but cannot MAKE glucose. o ↑ Release of hormone- sensitive lipase (from adipocytes). o These enzymes catalyze the oxidation of fats. o ↑ Gluconeogenesis à༎ ↑ Blood glucose levels Insulin • Hormone of the “fed” state: because it activates biosynthetic pathways (fatty acid biosynthesis, glycogen synthesis, etc.) o Therefore, it is the hormone that makes you fat • Insulin structure/synthesis: o The c- peptide (connecting peptide) is cleaved out, and the remaining peptides (A and B) are connected by disulfide bridges. This connected peptide chain makes up the hormone • Stimuli of secretion: o ↑ Blood glucose §༊ Mechanism of insulin secretion – why does glucose stimulate insulin secretion? β- cell require glucose to make ATP. Low glucose à༎ little ATP production à༎ no insulin secreted. • K+ normally leaks out of cell through ATP- K+ channels due to a Na+/K+ antiport, making a negative potential inside cell and positive outside. With increased [ATP], the ATP- K+ is blocked à༎ don’t lose as much K+ à༎ cell becomes depolarized • Depolarization of β- cell causes voltage gated Ca2+ channels to open, which allows influx of Ca2+ into cell à༎ this triggers exocytosis of insulin vesicles. • Overall process: glucose cross GLUT 2 on β- cell à༎ ↑ ATP à༎ block K+ channel à༎ cell depolarize à༎ voltage- gated Ca2+ channels open à༎ influx of Ca2+ à༎ exocytosis of insulin o Certain drugs (sulfonylureas) block K+ channels, which will induce the secretion of insulin. This can help treat type II diabetes (useless for type I, because they already have non- functional β- cells) ↑ GLP- 1 (glucagon- like peptide 1) and ↑ GIP (glucose insulinotropic peptide) §༊ Both of these peptides belong to a group of molecules called incretins. §༊ Both bind to different GPCRs on β- cells to induce insulin secretion. §༊ Incretin analogs have also been used to treat type II diabetes, because it induces secretion ↑ Glucagon – why? §༊ Even if you have ↑ glucose due to glucagon, you won’t be able to utilize them unless you have insulin to exocytose GLUT4 and help transport to muscle cells. ↑ Parasympathetic activity via vagus nerve (uses ACh and mACh receptors) à༎ “rest and digest” • o o o Glucose Transporters • GLUT 1 – general glucose transporter found in most cells, including RBC. Not found in intestines, proximal tubules, liver, muscles, and adipocytes. GLUT 1 has medium affinity for glucose. • GLUT 2 – found in kidneys, intestinal cells, β- cells, and liver cells. GLUT 2 has low affinity for glucose. • GLUT 3 – found in neurons. GLUT 3 has highest affinity for glucose. When blood glucose levels fall, most organs cannot utilize glucose except for neurons. This is because the brain can only use glucose as source of energy • GLUT 4 – found in intracellular vesicles of skeletal muscles and adipocytes that become part of the membrane when exocytosed under signal by insulin. Exercise will trigger exocytosis of vesicles and decrease the muscle requirement of insulin (makes insulin release easier). Blood glucose levels: • Normal fasting level: 70- 110mg/dL • Hypoglycemia: if fasting level < 70mg/dL • Hyperglycemia: if fasting level > 110mg/dL Lecture 7 – 8/25/11 Insulin: Transduction Pathways MItogenic + Growth effects Metabolic effects: ↑ glucose uptake: skeletal muscle, adipocytes, liver; ↑ glycolysis, ↑ aa uptake, ↑ protein synthesis, ↑ lipogenesis Glucose tolerance test Diabetes mellitus type I & type II Metabolic syndrome Insulin Transduction Pathways • Insulin binds to growth factor receptors. Upon binding, receptors will dimerize, and receptor tyrosine kinase will autophosphorylate receptors. Then, IRS (insulin response substrates) such as SH2 or SH3 bind to phosphorylated receptors. Once IRS is activated, there are 2 pathways: o Mitogenic à༎ growth and cell division. Involves responses with different proteins. §༊ In addition, insulin also promotes the uptake of amino acids, and increases protein synthesis. o Metabolic à༎ §༊ Activation of: • 1. Glycogen synthase à༎ ↑ glycogen synthesis • 2. Glucokinase (aka hexokinase): first step of glycolysis where it converts glucose into G6P • 3. Lipoprotein lipase: found in adipose tissue. Lipoproteins are the means by which lipids travel in blood o Lipoprotein lipase cleaves triglycerides into glycerol + 3 fatty acids. Glycerol can be diffused into cells. The free fatty acids can either undergo β- oxidation for energy or synthesized back to triglyceride for storage via lipid synthase. §༊ Inhibition of: • 1. Glycogen phosphorylase à༎ ↓ glycogenolysis • 2. Hormone sensitive lipase (in adipocytes) à༎ ↓ breakdown of lipids/lipocytes • Other effects of insulin: o ↑ Glucose uptake in skeletal muscles and adipocyte through exocytosis of GLUT 4. §༊ Exercise will also trigger exocytosis of vesicles and decreases the muscle requirement of insulin (i.e. causes release of insulin easier). If diabetics are under certain insulin routine and start exercising, their normal dose of insulin at rest may turn into overdose and therefore may result in hypoglycemia. o ↑ Glycolysis o ↑ Fatty acid biosynthesis Glucose Tolerance Test • Administer 75g of glucose in 300mL water to patient after 8 hour period of fasting and measure the blood glucose level. Baseline fasting [glucose]plasma levels: o 70- 110 mg/dL à༎ normal fasting state §༊ After drinking 75g of glucose, the glucose level raises up to around 130- 140 mg/dL within 30 minutes. However, after 1- 2 hours, the glucose will drop down to the normal fasting level. o >126 mg/dL à༎ diabetic (only diagnostic, but doesn’t specify which type) o >200 mg/dL 2 hours after meal à༎ diabetic (also diagnostic) §༊ The elevated levels of glucose remain that way for a much longer period of time compared to that of normal subjects. o <70 mg/dL à༎ hypoglycemia • If plasma [glucose] ≥ 300 mg/dL, all GLUT are working at maximum rate but the concentration has already exceed renal threshold à༎ glucose will be excreted in urine (condition called glucosuria) o This is what gave rise to the name diabetes “mellitus” (“honey bee”) – because the urine tasted sweet (gross…) • Metabolic syndrome (or Syndrome X) – “pre- diabetes”. Will eventually develop type II diabetes and/or other cardiovascular diseases. o Caused by impaired response to insulin o Signs/Symptoms: §༊ Obesity §༊ Hypertension §༊ Dyslipidemia – abnormal levels of lipids • How would insulin secretion with oral administration of glucose compare to that of intravenous administration? o It was found that taking oral glucose is a greater stimulus for insulin secretion than IV glucose. §༊ Why? Because incretins (GIP & GLP- 1) are released from the intestines. Presence of simple carbohydrates (e.g. glucose, fructose, sucrose) in the GI tract will allow incretins to be secreted. The incretins will then stimulate insulin secretion. Metabolic Disorders • Diabetes Mellitus Type I o Cause: §༊ Autoimmune condition à༎ antibodies attack and destroy β- cells of the pancreas o No insulin à༎ no glucose uptake in liver, adipocytes, and muscles (because GLUT 4 can’t be utilized) o Signs/Symptoms: §༊ Glucosuria – glucose found in urine • Due to [glucose] exceeding renal threshold §༊ Polyuria – high urine output • Due to presence of glucose in urine à༎ ↑ osmolarity of filtrate à༎ ↑ water excreted in urine • This can lead to dehydration, ↓ blood volume, and ↓ blood pressure o Hypotension and/or ↓ blood volume à༎ can lead to circulatory shock, which may result in coma/death • In addition, ↑ blood glucose levels will also damage blood vessels in the retina, which can result in blurred vision. §༊ Polydipsia – constantly thirsty • ↑ Water excreted à༎ ↑ ADH à༎ ↑ thirst §༊ Ketoacidosis (which leads to a whole bunch of other bad consequences) • Caused by accumulation of ketone bodies (acetoacetic acid and β- hydroxybutyric acid). Why ketogenesis? This is because the muscles/adipocytes are unable to take up glucose (no GLUT 4, remember?). As a result, the body interprets this as no glucose and will activate β- oxidation to generate the only alternative source of energy for the brain o This is why diabetes is called a “tantalizing” disease, because there’s an abundant source of glucose, and yet the cells are unable to take up for use. o Analogy: you’re stuck on an island and you’re dying of thirst. There’s water all around you, but you can’t drink it because it’s seawater. • Normal pH range: 7.35- 7.45 (very narrow range – because protein structures are very sensitive to pH). Ketoacidosis à༎ pH < 7.35 • ↓ pH à༎ hypoexcitability of neurons à༎ can lead to coma • ↑ Ketone bodies à༎ acetone breath • Atkins diet (all fat + protein, no carbs) à༎ ketogenic diet, and can lead to ketoacidosis o Ketogenic diets have been given to epileptic (hyperexcitability of neurons) children. Results have shown that they no longer needed anti- epileptic drugs. • ↓ pH à༎ stimulates chemoreceptors in medulla oblongata à༎ can stimulate hyperventilation §༊ Polyphagia – increased hunger • Because your brain interprets the “low” glucose levels as hunger • Neurons require insulin to take up glucose in the satiety center. o No insulin à༎ no satiety à༎ ↑ hunger Other medical complications that may result from diabetes mellitus (not limited to type I): §༊ Damage to kidneys à༎ diabetic nephropathy §༊ Damage to nerves à༎ diabetic neuropathy §༊ Damage to retina à༎ diabetic retinopathy §༊ Skin à༎ infections, lesions, dermopathy, etc. §༊ Increased risk for: atherosclerosis, myocardial infarction, stroke, and other cardiovascular diseases. So, how can you tell if a diabetic is in a coma due to hyperglycemia or hypoglycemia? (Your decision on treatment can result in life or death!) §༊ Hyperglycemia à༎ ketoacidosis à༎ hyperventilation and acetone breath §༊ Hypoglycemia à༎ no signs of hyperventilation or acetone breath. Instead, there will be sympathetic activation, which results in: paleness, sweating, ↑ heart rate, etc. Glucose can react with amines to form glycated protein: §༊ One example is glycated hemoglobin A1C (HbA1C). Measuring the level of glycosylation can be diagnostic for diabetes. • Normal levels: HbA1C ≤ 5- 6%. Measuring this gives an idea of the average glucose concentration over a period of 3 months. ↑ Glucose à༎ ↑ % of HbA1C Treatment: §༊ Insulin administration • However, the levels of insulin need to be constantly adjusted. • Furthermore, if one continually oscillates between hyper- and hypoglycemia, it can be a very dangerous situation too. This is one of the challenges for treating type I diabetics: to administer the right amount of insulin at any given point of time §༊ Pancreatic β- cell implants – possible, but one would require immunosuppressants to prevent further autoimmune reactions. • o o o o Hypoglycemia • Symptoms/Signs: o Sympathetic activation: §༊ ↑ Heart rate §༊ Vasoconstriction §༊ ↑ Blood pressure §༊ Aggression o Not enough ATP to maintain Na+/K+ pump à༎ neurons rapidly depolarize, which can cause: §༊ Confusion §༊ Loss of consciousness §༊ Seizures §༊ Coma Metabolic Disorders cont. • Diabetes Mellitus Type II o In this case, β- cells are completely functional, and insulin can still be released. In fact, type II diabetics often have a higher level of insulin secretion, but they do not get enough effects from insulin. o Type II is more like a “syndrome” than a “disease” due to the variety of possible causes o Possible causes: §༊ Genetic factors • “Thrifty genes” o Pima Indians usually lived in a poor environment, where food is scarce. Thus, they have developed these “thrifty” genes, where it allows greater efficiency in metabolism. They eat little food to satisfy the caloric needs. However, if one has the thrifty genes and eat more than necessary, all the extra calories will be transformed into fat storage. This is exactly what happened to some of the Pima Indians once they moved to the U.S. o After moving to the U.S. and becoming rich, they began eating much more than what they have in the past (and much less healthier too…cheeseburgers, milk shakes, french fries, etc.) As a result, 99% of these Pima Indians who moved to the U.S. became obese, and developed type II diabetes. §༊ Two groups of people that may get type II: • Obese o 2/3 of the US population today is overweight or obese à༎ this caused a tremendous increase in the number of type II cases. o Type II is now also observed in children, all of which are obese o Correlation with the manufacturing of high- fructose corn syrup. • Non- obese o Adipocyte hormones (adipokines): §༊ Leptin • Secreted by adipocytes when fat storage increases • Effects: ↓ appetite, ↑ metabolism §༊ Adiponectin - ↑ insulin sensitivity, metabolism §༊ Resistin – discovered in rodents via isolation of mRNA • Found that this hormone increased insulin resistance in rats • In humans, resistin is secreted by adipocytes in visceral and abdominal fats (i.e. not all adipocytes in the human body have the same properties) o Peroxisome proliferator activator receptor gamma (PPAR- γ) – in charge of adiponectin and resistin secretion. §༊ Activation à༎ ↑ adiponectin, ↓ resistin à༎ ↑ insulin sensitivity. o Treatment options – both general and pharmacological §༊ General: Complex carbohydrate meals (e.g. pasta, rice, bread, or anything rich in starch) à༎ don’t spike as much in glucose levels • ↑ Exercise Glitazones – PPAR- γ agonists. Market names: Avandia or Actos. • Mechanism: activate PPAR- γ receptor à༎ ↑ sensitivity to insulin • However, Avandia have been known to increase risk of sudden death from myocardial infarction. Mechanism is unknown, but Avandia is no longer used. Sulfonylureas – induce insulin secretion by blocking K+ channels in β- cell of pancreas • ↑ Insulin à༎ ↑ the amount of response by insulin Incretin analogs (GIP/GLP- 1) – stimulate insulin secretion. They also inhibit appetite. Incretins are broken down by dipeptidases (DPP4) Dipeptidase inhibitors – prolong the effects of incretins • Dipeptidase inhibitors, incretin analogs, and sulfonylureas all functions to increase insulin release. However, they may also increase risk of hypoglycemia. Biguanides – “double ureas”. Example: Metformin. • Metformin activates protein kinase in liver that phosphorylates enzymes, which will ↓ gluconeogenesis. • One of the potential side effects of metformin is lactic acidosis. α- Glycosidase inhibitors – prevent the breakdown of sugars in intestines. These drugs are not very effective because ↑ sugar will cause ↑ bacteria, causing many other side effects. They DON’T increase insulin, only decrease the breakdown of sugars. • §༊ §༊ §༊ §༊ §༊ §༊ Lecture 8 – 8/30/11 Calcium Homeostasis: Regulation of Plasma + ECF [Ca2+] Parathyroid hormone + calcitriol Stimuli for secretion + actions Hyper- and hypocalcemia Bone formation and resorption - - - - o- - - - Adrenal cortex: Functional anatomy + secretions Glucocorticoids: cortisol, cortisone Calcium Homeostasis Extracellular [Ca2+] levels are maintained at a very narrow range (1.1- 1.3mM, which is only about a 10- 15% change) • At rest, the cytoplasmic [Ca2+] is about 0.1µM (10- 7- M). The extracellular free [Ca2+] is about 1.2mM. This generates a concentration gradient of nearly 10,000 fold. o Voltage- gated channels have a voltage sensor in the membrane. The voltage sensor has positively charged lysine residues at middle and negatively charged carboxyl groups near the extracellular side of membrane. At resting state, extracellular side of membrane is positively charged while intracellular side is negatively charged. Activity of voltage sensor depends on the amount of extracellular charges present. §༊ Example: If extracellular space contains an abundant amount of positive charges (either due to ↑ ions such as Ca2+, or ↑ H+ due to acidosis), then the voltage sensor will be pushed towards the “inner” side of the membrane. This acts as a depressant, because now the voltage sensor will be less sensitive, and the channels will be less likely to open. §༊ Conversely, if extracellular space contains an abundant amount of negative charges (e.g. ↑ pH due to alkalosis), now the voltage sensor will be pulled towards the “outer” side of membrane. Now, the sensor is more sensitive, and channels are more likely to open, causing an increase in excitability. Plasma [Ca2+] levels (i.e. the total amount of calcium) are usually 2.5mM. This concentration includes calcium that is bound to various factors, such as albumin, phosphate, or citrate. The protein- bound calcium is not directly relevant to biological activity, that is the function of “free” Ca2+. • What keeps the concentration low? o Ca2+- ATPase: found in ER and plasma membrane o Mitochondria take up Ca2+ o Ca2+ transporters: §༊ Ex: Na+/Ca2+ antiport – remove calcium from heart à༎ allow relaxation 2+ Functions of Ca : • Blood clotting o Act as cofactor for several vitamin K- dependent coagulation factors 2+ • Ca signaling o Ex: Gq pathway • Muscle contraction o Ex: L- type Ca2+ channels in heart • Exocytosis of hormones or neurotransmitters stored in vesicles o Ex: exocytosis of insulin Hormones: • Parathyroid hormone (PTH) – serves to ↑ [Ca2+] in plasma o In bones, PTH promote resorption of bones by dissolving Ca10(PO4)6(OH)2 (hydroxyapatite) to release free Ca2+ and phosphate. §༊ Hydroxyapatite favors alkaline pH o In kidneys, PTH will target the distal tubule to ↑ Ca2+ reabsorption, ↑ phosphate excretion, and ↑ synthesis of calcitriol o In the intestines, PTH increases response to calcitriol. Essentially, PTH indirectly increases Ca2+ absorption in intestines (see next section for details) o How does it the parathyroid gland detect Ca2+ levels and know when to release PTH? §༊ It contains Ca2+ sensing receptor, which is coupled to Gq pathway • ↑ [Ca2+] activates receptor à༎ ↑ PLC- β à༎ PIP2 converted to: o IP3 à༎ IP3 induces Ca2+ release in the cytoplasm o DAG à༎ ↑ PKC à༎ opens channels, allowing Ca2+ to enter cell. The ↑ intracellular [Ca2+] inhibits PTH. (Wait a minute, influx of Ca2+ INHIBITS the exocytosis of the hormone? à༎ it’s been found that exocytosis of PTH is actually triggered by magnesium) • Conversely, ↓ [Ca2+] will stimulate PTH secretion • 1,25- (OH)- Vitamin D3 (1,25 dihydroxy vitamin D3, aka calcitriol) – derivative of vitamin D o Synthesis: derived from 7- dehydrocholesterol (found in skin). After absorbing UV light, 7- dehydrocholesterol is converted to cholecalciferol (vitamin D3). The liver hydroxylates cholecalciferol into 25- OH- cholecalciferol (aka calcidiol). Then, in the kidneys, it is hydroxylated again, and converted to calcitriol. §༊ The hydroxylation process in kidneys is stimulated by PTH o Receptor used: nuclear. Activation à༎ alters gene expression o In the intestines: §༊ ↑ Synthesis of calbindin, which binds absorbed calcium that enters cell, and can diffuse across cell §༊ ↑ Ca2+ transporters in the apical (luminal) side of intestinal cells, will aids in absorption §༊ ↑ Ca2+- ATPase in the basolateral membrane, which pumps Ca2+ through to increase calcium uptake. • Bones • Bones contain about 99% of the calcium in a typical person. It plays a critical role in calcium homeostasis. • Types of bones: o Cortical (compact) bone – very dense (make up 80% of bone mass) Consists of the outer layer of bone o Trebacular (spongy) bone – softer (20% by mass). Consists of the interior region of bone. Allows for some elasticity and flexibility §༊ Because it is softer, the turnover rate of trebacular bones is much faster than that of cortical bones, and is the bone that is most affected by osteoporosis. • Bone metabolism is very dynamic. Bones constantly undergo remodeling, which is the process of alternating between bone formation and bone resorption (breakdown) • Bones have two main types of cells. The interaction between these two cells pretty complex, but here is an image that will hopefully help simplify some concepts: o o Osteoblasts – stimulates bone formation §༊ Osteoblasts contain receptors for both PTH and calcitriol: • Under influence of PTH and calcitriol, they secrete extracellular proteins such as collagen that forms an osteoid (in which hydroxyapatite will be made). Once mineralized, it develops into new bone tissue. §༊ Osteoblasts also express a membrane protein called RANK- L (RANK ligand). This protein binds to RANK receptors on osteoclasts, and will stimulate osteoclast activities. RANK- L is influenced by both PTH and calcitriol §༊ Osteoblasts also secrete a protein called osteoprotegerin (OPG). OPG binds to RANK- L, and therefore prevents RANK- L from binding to RANK receptors on osteoclasts. In other words, OPG inhibits the activation of osteoclasts Osteoclasts – directly responsible for bone resorption. Contains 3 types of receptors: M- CSF, calcitonin, and RANK §༊ Macrophage colony stimulating factor (M- CSF), which is released by osteoblasts, will bind to M- CSF receptor and cause monocytes to differentiate into osteoclasts §༊ How they break down bone: • “Ruffled” membrane of osteoclasts attach to bone surface • In the membrane, there are H+/K+ ATPase (same proton pumps responsible for HCl secretion in stomach), which decreases the pH in the area between osteoclast membrane and bone surface significantly (down to 4). • The acidic environment dissolves the hydroxyapatite on surface to calcium, phosphate, and water. This will then increase the extracellular free calcium concentration In addition, osteoclasts also collagenases, which will further breakdown collagen, and bone. • Because of this, osteoclasts are also known as “external lysosomes”. §༊ Upon binding to calcitonin receptors, it activates a Gi pathway, which will ↓ cAMP, and consequently decrease osteoclast activity • Interestingly, calcitonin actually has no physiological role (i.e. if you remove the thyroid C cells, and remove calcitonin completely, there is no effect on bone metabolism) • However, adding calcitonin does slow down bone resorption, and has been a treatment option for osteoporosis. §༊ Osteoclasts also have RANK receptors. These receptors bind to RANK- L that is released from osteoblasts. Upon activation, osteoclasts will be activated §༊ Furthermore, osteoclasts are also stimulated by interleukin- 6 (IL- 6). IL- 6 is secreted by osteoblasts. Estrogens inhibit IL- 6 secretion, and therefore inhibit bone resorption (which is why androgen replacement therapy for post- menopausal women would have been a good treatment for osteoporosis if it didn’t cause a whole bunch of other problems). • However, it was also found that the receptors for estrogens in bones are different than those found in breasts and uterus. • A drug called Raloxifene selectively activates estrogen receptors in bone, but block estrogen receptors in breast and uterus. Summary: anything that increases the expression of RANK- L (and thus, anything that increases activity of RANK receptors) will stimulate osteoclasts to break down bone. • o Abnormal Conditions: • Osteoporosis – results when osteoblasts cannot keep up with osteoclasts • Occurs with age, especially with post- menopausal women. • Osteoporosis causes a significant decrease in bone density • Effects of estrogens on bone: o ↓ Activity of IL- 6 §༊ IL- 6 causes ↓ OPG, ↑ RANK- L à༎ ↑ osteoclast activity à༎ ↑ Bone resorption o For post- menopausal women, there are very low concentrations of estrogens. With a decreased inhibition on IL- 6, they are more prone to bone fracture • Some treatment options: o ↑ Calcium and vitamin D in diet o Bisphosphonates – bind to hydroxyapatite and accumulate on bone surfaces. This inhibits the ability of osteoclasts to resorb bone. §༊ Complication: while this prevents bone loss, it also inhibits repair in general. Essentially, the quantity of bone may be preserved, but is accomplished at the expense of the quality o Hormone replacement therapy §༊ Raloxifene (see above) • Hypercalcemia (high [Ca2+]) o Too much calcium à༎ ↑ number of positive charges in extracellular space à༎ voltage sensor will lean towards inner membrane à༎ harder to open channels à༎ ↓ excitability o Symptoms: §༊ Stones à༎ due to increased mineralization §༊ Bones à༎ ↑ density §༊ Groans à༎ ↑ intestinal motility §༊ Moans à༎ ↓ nervous system activation • Hypocalcemia (low [Ca2+]) • ↓ Number of positive charges in the extracellular space à༎ voltage sensor will lean towards the outer membrane à༎ easier to open channels à༎ ↑ excitability • In the heart, hypocalcemia will cause o ↓ Contractility • o ↓ Repolarization period (i.e. long Q- T interval) In neurons and muscles: o ↑ Excitability o ↑ Reflex o ↑ Seizures o ↑ Tetany - - - - - - - - - - - - - - - - - o- - - - - - - - - - - - - - - - - Adrenal Cortex Anatomy • The adrenal gland is located on top of the kidneys in the shape of a hat. It consists of the cortex and medulla. • Outer layer of the adrenal gland is the cortex. In the middle of the gland are sympathetic neurons with no axons, which make up the adrenal medulla. • Regions of the adrenal cortex o Zona glomerulosa – outermost layer of the cortex. §༊ This area lacks an important enzyme: 17- α- hydroxylase • 17- α- hydroxylase hydroxylates C17 on pregnelonone and converts to 17- OH- pregnelnone, which is the precursor to androgens and glucocorticoids. • Without this enzyme, these compounds cannot be synthesized §༊ Therefore, the only possible products from steroid synthesis are mineralocorticoids (e.g. aldosterone and corticosterone) §༊ This area also lacks ACTH receptors, and therefore is not affected by elevated levels of ACTH o Zona fasciculate (middle layer) and zona reticularis (inner layer) §༊ Both layers contain 17- α- hydroxylase and ACTH receptors §༊ Secretes glucocorticoids (e.g. cortisol) and androgens (e.g. DHEA and androstenedione) §༊ Too much ACTH will cause this layer to hypertrophy. Glucocorticoids (e.g. Cortisol) • Functions: o ↑ Blood glucose via: §༊ ↑ Gluconeogenesis in the liver §༊ ↓ Insulin responses §༊ ↑ Adrenergic responses (mainly through β- adrenergic receptors) à༎ ↑ glycogenolysis o ↑ Lipolysis in adipocytes o ↑ Proteolysis in muscles à༎ ↑ gluconeogenesis Lecture 9 – 9/1/11 Adrenal Cortex, cont. Effects of cortisol Cushing’s symptom/disease, Addison’s disease Mineralocorticoids: aldosterone, RAAS Hypo- + hyperaldosterism - - - o- - - Adrenal Medulla Catecholamine synthesis Adrenergic receptors: α1, α2, β1, β2, β3 Pheochromocytoma Adrenal Cortex Hormonal secretion • Stress (physical, psychological, emotional) – all will stimulate release of CRH from hypothalamus • CRH targets corticotrophs to release ACTH • ACTH targets adrenal cortex to release cortisol • Cortisol then exhibits negative feedback to both anterior pituitary and hypothalamus Naming/Convention (again) • Primary = problem with the gland itself o Ex: primary adrenal insufficiency = adrenal cortex not secreting enough cortisol. Hormone level changes: ↓ cortisol, ↑ CRH, ↑ ACTH • Secondary = problem with anterior pituitary o Ex: secondary adrenal insufficiency = not enough ACTH secreted either due to lesion or nonfunctional corticotrophs. Hormone level changes: ↓ ACTH, ↓ cortisol, ↑ CRH • Tertiary = problem with the hypothalamus o Ex: tertiary adrenal insufficiency = not enough CRH secreted. Hormone level changes: ↓ CRH, ↓ ACTH, ↓ cortisol • Iatrogenic = problem caused by a treatment (e.g. can be a side effect of a drug treatment) Effects of cortisol: • Immune system: suppresses function o This is achieved through: §༊ ↓ Number of immune cells §༊ ↓ Cellular responses §༊ ↓ Antibody synthesis §༊ ↓ PLA- 2 activity à༎ ↓ prostaglandins/leukotrienes à༎ ↓ inflammation, ↓ pain, etc. §༊ ↓ COX activities à༎ ↓ inflammation • However, one subtype of COX (COX 1) is responsible for mucous producing prostaglandins. Inhibiting COX 1 led to higher incidences of peptic ulcers. o Which is why corticosteroids are used to treat various autoimmune or inflammatory diseases • Liver: ↑ gluconeogenesis • Muscle: ↑ proteolysis • Adipose tissue: ↑ lipolysis • Pancreas: ↓ insulin secretion • Connective tissues: causes ↓ fibroblasts and ↓ collage, which decreases wound healing and skin thickness o This is why you can see striae on people with hypercorticism (Cushing’s), because their skin becomes so thin that you start seeing the stretch marks. • ↑ Adrenergic receptor responses (mainly at heart, blood vessels, and GI tract) o This is why glucocorticoids are essential for life. Lack of glucocorticoids à༎ lack of sympathetic responses à༎ results in death On the other hand, too much cortisol will also cause overactivity of receptors, which can cause symptoms such as hypertension. Cortisol binds to both glucocorticoid and mineralocorticoid receptors. o In the kidneys, the enzyme 11- β- hydroxysteroid dehydrogenase type 2 oxidizes cortisol into cortisone. Cortisone cannot bind to mineralocorticoid receptors, so the kidneys will avoid generating these responses. o In the periphery, the enzyme 11- β- hydroxysteroid dehydrogenase type 1 reduces cortisone back into cortisol. Brain: o Euphoria o Anxiety o ↓ Memory o ↑ Appetite Kidney: ↓ Ca2+ reabsorption Intestines:↓ Ca2+ and Mg2+ reabsorption Bones: ↑ Osteoclast activity à༎ ↑ bone resorption o • • • • • Abnormal Conditions: • Cushing’s Syndrome/Cushing’s disease o Cushing’s disease is specifically caused by a tumor of anterior pituitary, leading to elevated levels of ACTH secretion o Cushing’s syndrome is a more generalized hypercorticism; the source of problem can be iatrogenic, primary, secondary, or tertiary. §༊ Iatrogenic – found in people who used corticoids for treatment §༊ Primary – overactivity of adrenal cortex §༊ Secondary – pituitary tumor or something else overproducing ACTH §༊ Tertiary (rare) – hypothalamus secreting too much CRH o Symptoms/Signs: §༊ Central obesity (fat accumulating in abdominal and visceral regions) §༊ Moon face – very round face §༊ Striae (stretch marks) §༊ Hypertension due to: • ↑ Mineralocorticoids or cortisol • ↑ Adrenergic responses • ↑ Epinephrine synthesis §༊ Diabetic manifestations (hyperglycemia, insulin resistance, etc.) • Addison’s disease o Can be primary (most common), secondary, or tertiary o Tuberculosis was the main cause of primary hypocorticism. Now, with proper vaccinations for TB, the most common cause of Addison’s disease is autoimmunity. o Signs/Symptoms: §༊ Weight loss §༊ Anorexia §༊ Fatigue §༊ Depression, lethargy §༊ Hypotension due to lack of sympathetic responses §༊ Hyperpigmentation due to ↑ α- MSH from elevated levels of ACTH (only observed in primary adrenal insufficiency) Mineralocorticoids (e.g. aldosterone) • Functions of aldosterone o ↑ Expression of Na+/K+ pumps o o o ↑ Number of sodium channels ↑ Number of luminal/apical potassium channels (potassium here is excreted) Overall, results in: §༊ ↑ Na+ and H2O reabsorption (fluid retention) §༊ ↑ Extracellular volume (blood volume), leading to increased blood pressure §༊ ↑ K+ excretion (which may lead to hypokalemia) §༊ ↑ H+ excretion (which may lead to metabolic alkalosis) Renin- Angiotensin- Aldosterone System (RAAS) Diagram: • • • • • • • In the kidney, there’s a group of cells called the juxtaglomerular apparatus. These cells are secretory and respond to variety of signals such as: o ↓ Cl- in kidney filtrate o ↑ Adrenergic stimulation (β- 1 receptors) o Hypoxia à༎ ↓ blood pressure These cells contain pressure receptors from the afferent arteriole. If the pressure decreases, these cells secrete the enzyme renin. The liver secretes an inactive peptide called angiotensinogen. Renin cleaves angiotensinogen, resulting in angiotensin I. Endothelial cells in blood vessels create another enzyme called angiotensin converting enzyme (ACE), which cleaves angiotensin I into its active form, angiotensin II. Angiotensin II has several functions: o Vasoconstriction à༎ ↑ Blood pressure o In hypothalamus, it increases thirst o In the zona glomerulosa layer of adrenal cortex, it increases secretion of aldosterone §༊ Stimuli of secretion here: ↑ extracellular [K+], ↓ blood pressure, ↓ blood volume Methods to treat hypertension by tweaking the RAAS: o ACE- inhibitors (e.g. Captopril) – inhibit the formation of angiotensin II o o Loop diuretics/thiazides – promote fluid excretion by blocking different ion channels K+ sparing diuretics (e.g. aldosterone receptor antagonists): decrease sodium reabsorption à༎ ↓ water reabsorption à༎ ↑ urine output à༎ ↓ blood volume/pressure §༊ This helps avoid the major side effect (hypokalemia) observed in other types of diuretics Adrenal Medulla Catecholamine Synthesis: • • • • • • • All are derived from the amino acid tyrosine Tyrosine undergoes hydroxylation to make L- DOPA. This reaction is catalyzed by tyrosine hydroxylase L- DOPA is decarboxylated to form dopamine. This reaction is catalyzed by DOPA decarboxylase Dopamine is then hydroxylated again by dopamine hydroxylase to make norepinephrine The 4th enzyme, phenylethanolamine- N- methyltransferase (PNMT) is only found in a single type of cell: chromaffin cells. During 8th of pregnancy, these are the cells that will develop into the adrenal medulla. They are similar to adrenal sympathetic ganglia, but do not have axons. PMNT catalyzes the methylation of norepinephrine to make epinephrine. Path of synthesis: tyrosine à༎ L- Dopa à༎ Dopamine à༎ Norepinephrine à༎ Epinephrine Majority of the products synthesized from the adrenal medulla is epinephrine Adrenergic Receptors • α- Adrenergic receptors. Norepinephrine has a higher affinity for these than epinephrine. o α- 1: Gq coupled: DAG + IP3 à༎ ↑ intracellular Ca2+ à༎ smooth muscle contraction §༊ Smooth muscle contraction can be found in blood vessels (vasoconstriction), eyes (pupil dilation), skin (piloerection), or prostate §༊ Drugs that block α- 1 can be used to treat hypertension or prostate hyperplasia. However, one of the side effect of α- 1 is orthostatic hypotension. o α- 2: Gi coupled: ↓ cAMP à༎ inhibitory à༎ ↓ synaptic transmission, ↓ intestinal motility • β- Adrenergic receptors. Epinephrine has a higher affinity than NE for these receptors. All are Gs coupled o β- 1: §༊ In heart à༎ ↑ heart rate, ↑ contractility à༎ ↑ cardiac output • β- 1 blockers (remember Atenolol from your midterm? J༄ ) à༎ can be used to treat cardiac arrhythmia §༊ In kidney à༎ ↑ renin secretion o β- 2: binds almost exclusively to epinephrine. Causes smooth muscle relaxation §༊ In blood vessels à༎ vasodilation • During exercise, sympathetic activation dilates the arteries in skeletal muscles to increase the rate of perfusion. §༊ In bronchioles à༎ bronchodilation Giving a general β- blocker (i.e. blocks all β receptors) to a patient for heart disease (e.g. propranolol) à༎ may produce an aversive side effect of asthma attack because it caused bronchoconstriction through blocking β2 receptors. This can be an emergency situation because, depending on the degree of bronchoconstriction, the person may die from asphyxia in a matter of minutes. o “Epi- pens” have been developed because of this. It is basically an epinephrine injection. When someone is in an asthmatic attack, injecting epinephrine will activate β- 2, and will open up the airways. o β- 3: only found in adipocytes. Activation will stimulate lipolysis. Abnormal Conditions: • Pheochromocytoma – tumor of the adrenal medulla o Can have tonic excess secretions of epinephrine or norepinephrine. o People with pheochromocytoma will exhibit symptoms of elevated sympathetic activation: tachycardia, hypertension, nervousness, anxiety (due to fight or flight response) o The excessive secretion of E/NE occurs not only in constant fashion, but also in unpredictable surges. • ...
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