USMLE physiology 2 Flashcards

Terms Definitions
Stroke volume
Name the hormone—glucagon, insulin, or epinephrine:• Glycogenic, gluconeogenic, lipogenic, proteogenic, glycolytic, and stimulated by hyperglycemia, AAs, fatty acids, ketosis, ACh, GH, and Beta-agonist
Renal glomerular capillary pressure
45-50 mmHg
↓17OH-steroids ↑ACTH, ↑blood pressure, ↓aldosterone, ↑11-deoxycorticosterone, ↑17-ketosteroids
11β-OH deficiency
Increased urinary excretion of what substance is used to detect excess bone demineralization?
What are the primary neurotransmitters at the following sites?
• All motor neurons, postganglionic parasympathetic neurons
Increased urinary excretion of what substance is used to detect excess bone demineralization?
Site of synthesis of CRH
Paraventricular nucleus
Structural protein of the thick filaments, contains cross-bridges that attach to actin. Has ATPase activity to terminate actin-myosin cross-bridges. ATP decreases actin-myosin affinity.
Atrial flutter
Repeated succession of atrial depolarizations. Continuous P waves. Saw-tooth appearance.
What hormone constricts afferent and efferent arterioles (efferent more so) in an effort to preserve glomerular capillary pressure as the renal blood flow decreases?
What form of renal tubular reabsorption is characterized by high back leak, low affinity for substance, and absence of saturation and is surmised to be a constant percentage of a reabsorbed filtered substance?
Gradient-time system
What occurs when the lower esophageal sphincter fails to relax during swallowing due to abnormalities of the enteric nervous plexus?
What type of potential is characterized as graded, decremental, and exhibiting summation?
Subthreshold potential
Fastest conducting cells of the heart
Purkinje cells
Capillary membranes
Are freely permeable to substances dissolved in plasma except proteins. Separate ISF and plasma.
Atrial fibrillation
No discernable P waves, irregular QRS
Primary hypoaldosteronism
Na and water loss, hypotension, hyperkalemic metabolic acidosis, ↑ renin and angiotensin II, no edema
Primary hyperaldosteronism
Na and water retention, hypertension, hypokalemic metabolic alkalosis, ↓ renin and angiotensin, no edema due to pressure diuresis and natriuresis.
What enzyme is essential for the conversion of CO2 to HCO3-?
Carbonic anhydrase
What hormone is characterized by the following renal effects?• Calcium reabsorption, phosphate reabsorption
Vitamin D3
What hormone disorder is characterized by the following abnormalities in sex steroids, LH, and FSH?
• Sex steroids ↑, LH ↓, FSH ↓?
GnRH constant infusion
Name the phase of the ventricular muscle action potential based on the following information:
• Fast channels open, then quickly close, and sodium influx results in depolarization
Phase 0
What enzyme is needed to activate the following reactions?
• Trypsinogen to trypsin
Poiseuille equation
Q = P1 - P2 / R;
Actions of ANP
Atrial stretch or ↑ osmolarity --> ANP secretion --> dilation of afferent, constriction of efferent --> ↑ GFR --> natriuresis; also decreases permeability of collecting ducts to water.
Anterior pituitary hormones
ACTH, TSH, LH, FSH, GH, prolactin
Excessive secretion of ADH in spite of low osmolarity. Concentrated urine is formed.
What is the primary target for the action of glucagon?
Liver (hepatocytes)
What serves as a marker of endogenous insulin secretion?
C-peptide levels
What component of an ECG is associated with the following?
• Conduction delay in the AV node
PR interval
The clearance of what substance is the gold standard of renal plasma flow?
Para-aminohippurate (PAH)
What is the term for the summation of mechanical stimuli due to the skeletal muscle contractile unit becoming saturated with calcium?
Name the Hgb-O2 binding site based on the following information:
• Remains attached under most physiologic conditions
Site 1
What thyroid abnormality has the following?
• TRH decreased, TSH decreased, T4 increased
Secondary hyperthyroidism (Increased TSH results in increased T4 production and increased negative feedback on to hypothalamus and decreased release of TRH.)
PR interval
Due to conduction delay of AV node. 0.12 - 0.2 seconds or 120 to 200 miliseconds
↑ PTH, ↓ Ca, ↓ phosphate
Secondary hyperparathyroidism. Causes: deficiency of vitamin D due to bad diet or fat malabsorption.
Causes of left axis deviations
Left ventricular hypertrophy or dilation, conduction defects of left ventricle, AMI on right side
Initial AMI in ECG
ST segment depression, prominent Q waves, T wave inversion
How is active tension produced?
Calcium binds troponin --> tropomysion exposes actin sites --> myosin cross-bridges bond to actin --> myosin ATPase generates energy to break cross-bridge link --> cycle repeats --> active tension. The more cross-bridges that cycle, the greater the active tension.
Enterohepatic circulation
Bile acids are reabsorbed only in the distal ileum. Resection or malabsoption syndromes lead to steatorrhea and cholesterol gallstones.
Clinical features of hyperthyroidism
↑ metabolic rate with heat intolerance and sweating, ↑ apetite with weight loss, muscle weakness, tremor, irritability, tachycardia, exophthalmos.
What primary acid-base disturbance is caused by a loss in fixed acid forcing the reaction to shift to the right, thereby increasing HCO3- levels?
Metabolic alkalosis (summary: high pH, low H+ and high HCO3-)
What pancreatic islet cell secretes somatostatin?
delta-Cells; somatostatin has an inhibitory effect on alpha- and Beta-islet cells.
What has occurred to the renal arterioles based on the following changes in the GFR, RPF, FF, and glomerular capillary pressure?
• GFR ↑, RPF ↓, FF ↑, capillary pressure ↑
Constriction of efferent arteriole
What is the term for the amount of blood expelled from the ventricle per beat?
Stroke volume
What is the main factor determining GFR?
Glomerular capillary pressure (increased glomerular capillary pressure, increased GFR and vice versa)
Actions of cortisol in stress situations
Mobilizes fat, carbs and proteins
Source of calcium for skeletal muscle contraction
Sarcoplasmic reticulum. No extracellular calcium is involved because it doesn’t have voltage-gated Ca channels.
Isotonic fluid loss diagram
Decreased ECF, no change in ICF. Causes: hemorrhage, isotonic urine, diarrhea, vomiting
Potassium dynamics in acute alkalosis
Hypokalemia, ↑ intracellular K, ↑ renal K excretion, negative K balance
How is free water clearance calculated?
V - (Uosm(V) / Posm)
Characteristics of white muscle
Large mass, high ATPase activity (fast muscle), anaerobic glycolysis, low myoglobin
↓ glucose, ↑ insulin, ↓ C peptide
Factitious hypoglycemia (insulin injection)
↓ resistance, ↑ capillary flow, ↓ capillary pressure
Venous dilation - ↑ metabolism
What type of muscle is characterized by no myoglobin, anaerobic glycolysis, high ATPase activity, and large muscle mass?
White muscle; short term too
How do elevated blood glucose levels decrease GH secretion? (Hint: what inhibitory hypothalamic hormone is stimulated by IGF-1?)
Somatotrophins are stimulated by IGF-1, and they inhibit GH secretion. GHRH stimulates GH secretion.
In the systemic circulation, what blood vessels have the largest pressure drop? Smallest pressure drop?
Arterioles have the largest drop, whereas the vena cava has the smallest pressure drop in systemic circulation.
Which CHO is independently absorbed from the small intestine?
Fructose; both glucose and galactose are actively absorbed via secondary active transport.
Is bone deposition or resorption due to increased interstitial Ca2+concentrations?
Bone deposition increases with increased Ca2+ or PO 4- concentrations, whereas resorption (breakdown) is increased when there are low levels of Ca2+ or PO4-.
True or false? Epinephrine has proteolytic metabolic effects.
False. It has glycogenolytic and lipolytic actions but not proteolytic.
What happens to extracellular volume with a net gain in body fluid?
The ECF compartment always enlarges when there is a net gain in total body water and decreases when there is a loss of total body water. Hydration status is named in terms of the ECF compartment.
Effects of hypothyroidism in juveniles
Cretinism results in ↓ bone growth and ossification --> dwarfism. Due to lack of permissive action on GH.
Clinical features of primary hyperparathyroidism
↑ plasma Ca and ↓ plasma phosphate, phosphaturia, polyuria, calciuria (filtered load of Ca exceeds Tm), ↑ serum alkaline phosphatase, ↑ urinary hydroxyproline, muscle weakness, easy fatigability.
Factors that shift vascular function curve down and to the left
↓ blood volume, ↑ venous compliance
Parallel circuits with greatest resistance
Coronary > cerebral > renal > pulmonary
PO2 in atrial septal defect
↑ Right atrial PO2, ↑ right ventricular PO2, ↑ pulmonary artery PO2, ↑ pulmonary blood flow and pressure
Effect of sympathetic stimulation in the GI tract
↓ motility, ↓ secretions, ↑ contraction of sphincters
Simple diffusion curve in a graph
Linear. Slope increases if diffusion area or concentration increases. Slope decreases if membrane thickness increases
Renal treshold for glucose
180 mg/dl or 1.8 mg/ml. Represents the beginning of splay.
↓ sex steroids, ↓ LH, ↓ FSH
Pituitary hypogonadism or constant GnRH infusion (downregulates GnRH receptors of pituitary.
Fetal circulation: percent O2 saturation in descending and abdominal aorta
Blood from left ventricle (67%) mixes with blood from ductus arteriousus (50%) --> yields 60%
Specialized cells of the distal tubule and collecting duct
Principal cells (aldosterone) and intercalated cells (create HCO3)
Anatomical and alveolar dead spaces together constitute what space?
Physiologic dead space is the total dead space of the respiratory system.
What two pituitary hormones are produced by acidophils?
GH and prolactin are produced by acidophils; all others are by basophils.
What type of resistance system, high or low, is formed when resistors are added in a series?
A high-resistance system is formed when resistors are added in a series.
What hormones, secreted in proportion to the size of the placenta, are an index of fetal well-being?
hCS and serum estriol, which are produced by the fetal liver and placenta, respectively, are used as estimates of fetal well-being.
When a person goes from supine to standing, what happens to the following?
• Cardiac output

Remember, the carotid sinus reflex attempts to compensate by increasing both TPR and heart rate.
Does the oncotic pressure of plasma promote filtration or reabsorption?
The oncotic pressure of plasma promotes reabsorption and is directly proportional to the filtration fraction.
If the radius of a vessel is decreased by half, what happens to the resistance?
The resistance increases 16-fold.
What cell type in the bone is responsible for bone deposition?
Osteoblast (Remember, blasts make, clasts take)
When the ECF osmolarity increases, what happens to cell size?
Increase in ECF osmolarity means a decrease in ICF osmolarity, so cells shrink.
The closure of what valve indicates the beginning of isovolumetric contraction?
Mitral valve closure indicates the termination of the ventricular filling phase and beginning of isovolumetric contraction.
What is the most potent stimulus for glucagon secretion? Inhibition?
Hypoglycemia for secretion and hyperglycemia for inhibition
Amount of plasma volume
1/3 of ECF. 14 L --> 4 L plasma
What does a ventilation/perfussion relationship under and over 0.8 mean?
Under 0.8 (at the bases) lungs are underventilated and less gas exchange takes place, therefore PACO2 and end-capillary PCO2 will be higher and PAO2 and end-capillary PO2 will be lower.
Systemic ciruit Vs. pulmonary system
Cardiac output and heart rate is the same as they're connected in series. The systemic circuit has higher resistance and lower compliance therefore work of the right ventricle is lower.
What triggers phase 0 of the action potential in a ventricular pacemaker cell?
Calcium influx secondary to slow channel opening
What is the amount in liters and percent body weight for the following compartments? • Total body water
42 L, 67% of body weight
What is the effect of T3 on the glucose absorption in the small intestine?
Thyroid hormones increase serum glucose levels by increasing the absorption of glucose from the small intestine.
Why is there a transcellular shift in K+ levels in a diabetic patient who becomes acidotic?
The increased H+ moves intracellularly and is buffered by K+ leaving the cells, resulting in intracellular depletion and serum excess. (Intracellular hypokalemia is the reason you supplement potassium in diabetic ketoacidosis, even though the serum levels are elevated.)
Where does most circulating plasma epinephrine originate?
From the adrenal medulla; NE is mainly derived from the postsynaptic sympathetic neurons.
What four conditions result in secondary hyperaldosteronism?
1. CHF
2. Vena caval obstruction or constriction
3. Hepatic cirrhosis
4. Renal artery stenosis
What two factors result in the apex of the lung being hypoperfused?
Decreased pulmonary arterial pressure (low perfusion) and less-distensible vessels (high resistance) result in decreased blood flow at the apex.
Why is the clearance of creatinine always slightly greater than the clearance of inulin and GFR?
Because creatinine is filtered and a small amount is secreted
When is the surface tension the greatest in the respiratory cycle?
Surface tension, the force to collapse the lung, is greatest at the end of inspiration.
What are the three end products of amylase digestion?
1. Maltose
2. Maltotetrose
3. α-Limit dextrans (α-1, 6 binding)
How is potassium affected by alkalosis?
Low concentration of ECF H --> H diffuses to ECF --> K diffuses to ICF --> hypokalemia
Lung volumes in obstructive disease
↑ TLC, ↑ RV, ↑ FRC, ↓ FEV1, ↓ FVC, ↓ FEV1/FVC
Describe what type of fluid is either gained or lost with the following changes in body hydration for the ECF volume, ICF volume, and body osmolarity, respectively:• ECF, increase; ICF, decrease; body, increase
Gain of hypertonic fluid (mannitol or hypertonic saline)
What are the following changes seen in the luminal fluid by the time it leaves the PCT of the nephron?• Concentration of CHO, AA, ketones, peptides
No CHO, AA, ketones, or peptides are left in the tubular lumen.
True or false? Renin secretion is increased in 21-β-hydroxylase deficiency.
True. Increased renin and AT II levels occur as a result of the decreased production of aldosterone.
What is the rate-limiting step in the production of steroids?
The conversion of CHO to pregnenolone via the enzyme desmolase
Where in the GI tract does the reabsorption of bile salts take place?
Bile salts are actively reabsorbed in the distal ileum.
What is the rate-limiting step in the synthetic pathway of NE at the adrenergic nerve terminal?
The conversion of tyrosine to dopamine in the cytoplasm
What are the two best indices of left ventricular preload?
LVEDV and LVEDP (left ventricular end-diastolic volume and end-diastolic pressure, respectively)
Phase 2 of the ventricular action potential
Slow Ca channels open, ↑ gCa, ↓ gK. Plateau phase is due to slow calcium current and decreased K current
Differences in blood flow between the base and the apex of the lung
Blood vessels of the apex are less distended, have more resistance and receive less blood flow. Blood vessels of the base are more distended, have less resistance and receive more blood flow
True or false? Thyroid size is a measure of its function.
False. Thyroid size is a measure of TSH levels (which are goitrogenic).
Why would a puncture to a vein above the heart have the potential to introduce air into the vascular system?
Venous pressure above the heart is subatmospheric, so a puncture there has the potential to introduce air into the system.
At the base of the lung, what is the baseline intrapleural pressure, and what force does it exert on the alveoli?
Intrapleural pressure at the base is -2.5 cm H2O (more positive than the mean), resulting in a force to collapse the alveoli.
At the base of the lung, what is the baseline intrapleural pressure, and what force does it exert on the alveoli?
Intrapleural pressure at the base is -2.5 cm H2O (more positive than the mean), resulting in a force to collapse the alveoli.
What cell in the heart has the highest rate of automaticity?
SA node; it is the reason it is the primary pacemaker of the heart.
Left atrium pressure
5-10 mmHg
Name the hormone—glucagon, insulin, or epinephrine:
• Glycogenic, gluconeogenic, lipogenic, proteogenic, glycolytic, and stimulated by hyperglycemia, AAs, fatty acids, ketosis, ACh, GH, and Beta-agonist
Ejection fraction
Stroke volume / EDV
Stimulates melanocytes and causes darkening of skin. Synthesized along with ACTH from pro-opiomelanocortin.
True or false? The parasympathetic nervous system has very little effect on arteriolar dilation or constriction.
True or false? Miniature end-plate potentials (MEPPs) generate action potentials.
Site of synthesis of GnRH
Preoptic region
Due to GH insensitivity during prepuberty
↑ permeability of collecting ducts, ↓ urine, ↑ urine osmolarity, ↓ ECF, ↑ osmolarity
What causes pulsus parvus et tardus?
Aortic stenosis
What presynaptic receptor does NE use to terminate further neurotransmitter release?
What happens to the following during skeletal muscle contraction?
• Sarcomere
What hormone is required for 1, 25-dihydroxy-vitamin D (1, 25-diOH-D) to have bone resorbing effects?
What stage of male development is characterized by the following LH and testosterone levels?
• Both LH and testosterone levels drop and remain low.
Electrochemical gradient
Exists when the electrical and/or chemical forces are not balanced. Its what determines difussion of the ion.
Receptor-mediated endocytosis
The ligand binds receptor near clathrin-coated pits. More rapid and specific than constitutive endocytosis.
Electrical synapse
Action potential transmitted from one cell to the next via gap junctions, without synaptic delay and in both directions. Cardiac muscle, smooth muscle.
Composition of bone
Phosphate and calcium precipitate forming hydroxyapatite in osteoid matrix.
Factors that increase slope of vascular function curve
Sarcoplasmic calcium-dependent ATPase
Supplies energy to terminate contraction and pump Ca back into sarcoplasmic reticulum.
Muscle contraction steps
Action potential travels down T-tubules --> activates dihydropiridine voltage sensors --> foot processes are pulled aways from ryanodine calcium release channels of sarcoplasmic reticulum --> calcium is released --> calcium attaches to troponin --> tropomyosin moves exposing actin binding sites for myosin cross-bridges --> myosin binds actin --> myosin ATPase breaks down cross bridges producing active tension and shortening --> contraction terminated by active pumping of Ca into the sarcoplasmic reticulum.
↓ glomerular pressure, ↓ peritulbuar pressure, ↓ RPF
Afferent arteriole constriction
What is the most important factor in determining bone fracture risk in women?
Thin extremities, fat collection on the upper back and abdomen, hypertension, hypokalemic alkalosis, acne, hirsutism, wide purple striae, osteoporosis, hyperlipidemia, hyperglycemia with insulin resistance, and protein depletion are all characteristics o
Hypercortisolism (Cushing syndrome)
What bile pigment is formed by the metabolism of bilirubin by intestinal bacteria, giving stool its brown color?
What endocrine abnormality is characterized by the following changes in PTH, Ca2+, and inorganic phosphate (Pi)?
• PTH decreased, Ca2+ increased, Pi increased
Secondary hypoparathyroidism (vitamin D toxicity)
What hormone is characterized by the following renal effects?
• Calcium reabsorption, phosphate reabsorption
Vitamin D3
What muscle type is characterized by low ATPase activity, aerobic metabolism, myoglobin, association with endurance, and small muscle mass?
Red muscle
What is the name of the regulatory protein that covers the attachment site on actin in resting skeletal muscle?
Conditions that affect capillary hydrostatic pressure
Essential hypertension increases resistance and decreases capillary hydrostatic pressure. Hemorrhage decreases capillary hydrostatic pressure and promotes reabsorption.
Types of protein transport
Facilitated (down a concentration gradient), active (against gradient, requires ATP)
Secondary active transport
Depends indirectly on ATP. E.g. Na/glucose cotransporter in the renal tubule depends on Na/K countertransporter
Neuromuscular transmission
Action potential travels down axon and opens pre-synaptic Ca channels --> calcium influx --> release Ach vesicles --> Ach diffuses and attaches to nicotinic ion channels --> ↑gNa --> end-plate depolarization (local) spreads to areas with voltage-gated Na channels --> depolarization of muscle fiber
Hormones of the GI system
Gastrin, CCK, secretin, GIP
Total ventilation
Total ventilation = Tidal volume X respiratory rate.
Residual volume
Air in the lungs after maximal expiration. 1,200ml
What is brown fat responsible for in newborns?
Heat production
What period is described when a larger-than-normal stimulus is needed to produce an action potential?
Relative refractory period
What is the term for the force the ventricular muscle must generate to expel the blood into the aorta?
Actions of aldosterone
↑Na channels in lumen of principal cells, ↑activity of Na/K ATPase of principal cells --> increases Na reabsorption. Also ↑ secretion of K and H leading to hypokalemic metabolic alkalosis.
Which substances are cleared less than creatinine?
Inulin, glucose, sodium
Metabolic hypothesis of autoregulation
Tissue can produce a vasodilatory metabolite that regulates blood flow. Example adenosine in coronaries.
Chief cells
Located in the deep part of the gastric glands. Secrete pepsinogen which is converted to pepsin by acid medium. Pepsin begins digestion of proteins to peptides
What is the titratable acid form of H+ in the urine?
H2PO4- (dihydrogen phosphate)
Place in order from fastest to slowest the rate of gastric emptying for CHO, fat, liquids, and proteins.
Liquids, CHO, protein, fat
What is secretin's pancreatic action?
Secretin stimulates the pancreas to secrete a HCO3--rich solution to neutralize the acidity of the chyme entering the duodenum.
Name the lung measurement based on the following descriptions:
• Maximal volume that can be expired after maximal inspiration
Vital capacity (VC)
What two compensatory mechanisms occur to reverse hypoxia at high altitudes?
Increase in erythropoietin and increase in 2, 3-BPG, also called 2, 3-diphosphoglycerate (2, 3-P2Gri) (increase in glycolysis)
Stimulus for the zona glomerulosa
Angiotensin II and potassium in hypekalemia stimulate production of aldosterone
Factors that affect hormone binding protein synthesis
Estrogen increases binding proteins; androgens decrease binding proteins. In pregnancy there's increased total hormones with normal levels of free hormone.
Gain of isotonic fluid diagram
Osmolarity stays the same, ECF increases. Causes: isotonic saline infusion.
Third-degree block in ECG
No impulses conducted from atria to ventricles. No correlation between P waves and QRS complexes.
Conditions that affect interstitial oncotic pressure
Increased by lymphatic blockage and increased capillary permeability to proteins (burns)
Highest resistance segment of the systemic circulation
Arterioles. Also responsible for greatest pressure drop.
Do the PO2 peripheral chemoreceptors of the carotid body contribute to the normal drive for ventilation?
Under normal resting conditions no, but they are strongly stimulated when PO2 arterial levels decrease to 50 to 60 mm Hg, resulting in increased ventilatory drive.
True or false? Epinephrine has proteolytic metabolic effects.
False. It has glycogenolytic and lipolytic actions but not proteolytic.
What triggers phase 3 of the action potential in a ventricular pacemaker cell?
Rapid efflux of potassium
In the systemic circulation, what blood vessels have the largest pressure drop? Smallest pressure drop?
Arterioles have the largest drop, whereas the vena cava has the smallest pressure drop in systemic circulation.
What respiratory center in the caudal pons is the center for rhythm promoting prolonged inspirations?
Apneustic center (deep breathing place)
What receptor is in the smooth muscle cells of the small bronchi, is stimulated during inflation, and inhibits inspiration?
Stretch receptors prevent overdistension of the lungs during inspiration.
Actions of glucagon in stress situations
Mobilizes glucose by increasing liver glycogenolysis
Factors that control renal circulation
Small changes in blood pressure invoke autoregulatory responses. Sympathetic may influence blood flow in extreme conditions (hemorrhage, hypotension)
What factors affect capillary exchange?
Exchange is by simple diffusion only. Proteins do not cross the capillary membrane. Factors that affect diffusion rate are: surface area, membrane thickness, concentration gradient, solubility
Tissues independent of insulin for glucose uptake
Brain, kidneys, intestinal mucosa, red blood cells, beta cells of the pancreas.
Phase 4 of the ventricular action potential
Voltage-gated and ungated potassium channels are open, ↑ gK. The delayed rectifiers close but are responsible for the relative refractory period.
Phase 0 of SA nodal cells
Depolarization due to opening of voltage-gated slow Ca channels.
Does the heart rate determine the diastolic or systolic interval?
Heart rate determines the diastolic interval, and contractility determines the systolic interval.
When is the surface tension the greatest in the respiratory cycle?
Surface tension, the force to collapse the lung, is greatest at the end of inspiration.
If the radius of a vessel doubles, what happens to resistance?
The resistance will decrease one-sixteenth of the original resistance.
What is the relationship between preload and the passive tension in a muscle?
They are directly related; the greater the preload, the greater the passive tension in the muscle and the greater the prestretch of a sarcomere.
What happens to free hormone levels when the liver decreases production and release of binding proteins?
Free hormone levels remain constant, and the bound hormone level changes with a decrease in binding hormones.
Does physiologic splitting of the first heart sound occur during inspiration or expiration? Why?
Splitting of the first heart sound occurs during inspiration because of the increased output of the right ventricle, delaying the closure of the pulmonic valve.
What causes a skeletal muscle contraction to terminate?
When calcium is removed from troponin and pumped back into the SR, skeletal muscle contraction stops.
What is the major hormone produced in the following areas of the adrenal cortex?
• Zona glomerulosa

Remember, from the outer cortex to the inner layer, Salt, Sugar, Sex. The adrenal cortex gets sweeter as you go deeper.
What component of the cardiovascular system has the largest blood volume? Second largest blood volume?
The systemic veins have the largest blood volume, and the pulmonary veins have the second largest blood volume in the cardiovascular system. They represent the reservoirs of circulation.
What happens to intraventricular pressure and volume during isovolumetric contraction?
As the name indicates, there is no change in volume but there is an increase in pressure.
What is the most important stimulus for the secretion of insulin?
An increase in serum glucose levels
PO2 in patent ductus arteriosus
No change in right atrial PO2 nor right ventricular PO2, ↑ pulmonary artery PO2, ↑ pulmonary flow and pressure
What is the rate-limiting enzyme for steroid hormone synthesis?
Desmolase - converts cholesterol into pregnenolone
When does the rate of uptake becom diffusion-limited?
When concentration between capillary and tissue are not in equilibrium.
Where does the synthesis of ACh occur?
In the cytoplasm of the presynaptic nerve terminal; it is catalyzed by choline acetyltransferase.
In an adrenergic nerve terminal, where is dopamine converted to NE? By what enzyme?
Dopamine is converted into NE in the vesicle via the enzyme dopamine-Beta-hydroxylase.
What are the five hormones produced by Sertoli cells?
1. Inhibin 2. Estradiol (E2) 3. Androgen-binding protein 4. Meiosis inhibiting factor (in fetal tissue) 5. Antimüullerian hormone
If the pH is low with increased CO2 levels and decreased HCO3- levels, what is the acid-base disturbance?
Combined metabolic and respiratory acidosis
Is CO2 a perfusion-or diffusion-limited O2 gas?
Since CO2 is 24 times as soluble as O2, the rate at which CO2 is brought to the membrane determines its rate of exchange, making it perfusion-limited a gas. For O2 the more time it is in contact with the membrane, the more likely it will diffuse, making it diffusion-limited.
Describe what type of fluid is either gained or lost with the following changes in body hydration for the ECF volume, ICF volume, and body osmolarity, respectively:
• ECF, decrease; ICF, no change; body, no change
Loss of isotonic fluid (diarrhea, vomiting, hemorrhage)
What is the site of action of cholera toxin?
Cholera toxin irreversibly activates the cAMP-dependent chloride pumps of the small and large intestine, producing a large volume of chloride-rich diarrhea.
What happens to total and alveolar ventilation with
• Increased depth of breathing?
With an increased depth of breathing both the total and alveolar ventilation increase.

This concept is always tested on the boards, so remember it.
↑ capillary flow, ↑ capillary pressure, no change in resistance
↑ arterial pressure - ↑ CO, volume expansion
What is the effect of a foreign object occluding a terminal bronchi?
Ventilation decreases, therefore ↓ Va/Q --> ↑ PACO2, ↓ PAO2
What substances are reabsorbed in the proximal tubule and how much?
Na (2/3 of filtered load), glucose (100%), amino acids (100%), HCO3 (indirectly, 80%), H20 (2/3), K (2/3), Cl (2/3)
In a ventricular pacemaker cell, what phase of the action potential is affected by NE?
Phase 4; NE increases the slope of the prepotential, allowing threshold to be reached sooner, and increases the rate of firing.
What term is described as the prestretch on the ventricular muscle at the end of diastole?
Preload (the load on the muscle in the relaxed state)
What are the three characteristics of autoregulation?
1. Flow independent of BP
2. Flow proportional to local metabolism
3. Flow independent of nervous reflexes
What are the three effects of insulin on protein metabolism?
1. Increased amino acid uptake by muscles
2. Decreased protein breakdown
3. Increased protein synthesis
What organ of the body has the smallest AV oxygen difference?
The renal circulation has the smallest AV O2 (high venous PO2) difference in the body because of the overperfusion of the kidneys resulting from filtration.
What percentage of CO2 is carried in the plasma as HCO3- ?
90% as HCO3-, 5% as carbamino compounds, and 5% as dissolved CO2
Effects of sympathetics on pacemaker cells
Slope of phase 4 increases due to ↑ funny current and ↑ gCa. Action via β1 receptors.
What is the ratio of T4:T3 secretion from the thyroid gland?
20:1T4T3. There is an increase in the production of T3 when iodine becomes deficient.
What are the five tissues in which glucose uptake is insulin independent?
1. CNS
2. Renal tubules
3. Beta Islet cells of the pancreas
4. RBCs
5. GI mucosa
Does the left or right vagus nerve innervate the SA node?
Right vagus innervates the SA node and the left vagus innervates the AV node
What is the effect of a thrombus in a pulmonary artery?
Blood flow decreases, therefore ↑ Va/Q --> ↓ PACO2, ↑ PAO2
True or false? Enterokinase is a brush border enzyme.
False. It is an enzyme secreted by the lining of the small intestine.
How is the net transport rate for a substance calculated?
Net transport rate = filtered load - excretion rate = (GFR X Px) - (Ux X V)
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