USMLE World physiology 3 Flashcards

Terms Definitions
What hypothalamic hormone is synthesized in the preoptic nucleus?
QT interval
Indicates ventricular refractorieness. Normal between 0.35 - 0.44 seconds.
Multiple action potentials increase release of calcium thus increasing contraction. Muscle cells have a short refractory period.
What hormone, produced by Sertoli cells, if absent would result in the formation of internal female structures?
Insulin-induced hypoglycemia is the most reliable (by far not the safest) test for what hormone deficiency?
GH deficiency
What are the 17-ketosteroids?
DHEA and androstenidione
Normal capillary hydrostatic pressure of the glomerulus
45 mmHg
↓cortisol, ↑CRH, ↓ACTH, no hyperpigmentation
Secondary hypocortisolism
What type of potential is characterized as being an all-or-none response, propagated and not summated?
Action potential
What stage of male development is characterized by the following LH and testosterone levels?• LH secretion drives testosterone production, with both levels paralleling each other.
What lecithin: sphingomyelin ratio indicates lung maturity?
2.0 or greater
What stage of male development is characterized by the following LH and testosterone levels?
• LH pulsatile amplitude and levels increase, with increased testosterone production.
With a decrease in arterial diastolic pressure, what happens to
• Heart rate?
Lung mechanics during expiration
Diaphragm relaxes, intrapleural pressure increases, lung recoil collpases the lung. Alveoli compress the air and alveolar pressure becomes positive and air flows out of the lungs until alveolar pressure is back to zero. Lung recoil and intrapleural pressure become equal but opposite.
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 is the physiologically active form of Ca2+?
Free ionized Ca2+
Name the valve abnormality based on the following criteria:
• Diastolic murmur; increased preload, stroke volume, and aortic pulse pressure; decreased coronary blood flow; no incisura; and peripheral vasodilation
Aortic insufficiency
Name the phase of the ventricular muscle action potential based on the following information:
• Slow channels close, voltage-gated potassium channels reopen with a large influx of potassium, and the cell quickly repolarizes
Phase 3
What cells of the kidney are extravascular chemoreceptors for decreased Na+, Cl-, and NaCl?
Macula densa
↑ECF, ↓osmolarity, ↑ICF
Gain of hypotonic fluid or hyponatremic hypervolemia. Causes: hypotonic saline, SIADH, tap water.
Actions of somatomedin C
Increases cartilage synthesis at epiphyseal plates (↑ bone length). Also ↑ lean body mass. Protein-bound and long half-life correlates to GH secretion. Also called IGF-1.
Intrapleural pressure
Normally -5 cmH2O. Force that expands the lung. The more negative, the more lung expansion.
Central chemoreceptors
Sense [H+] which is proportional to PCO2 and H2CO3 of the CSF (not systemic)
Baroreceptor reflex
Baroreceptors in the aortic arch send afferents via vagus nerve; baroreceptors in the carotid sinus via glosopharyngeal; baroreceptor center is in the medulla. ↑ firing of baroreceptors is sensed as ↑ blood pressure --> ↑ parasympathetic, ↓ sympathetic
Changes in respiratory alkalosis
Hyperventilation --> ↓ PaCO2 --> ↓ H and HCO3 --> ↑ pH
Indices of contractility
dp/dt (change in pressure/change in time); ejection fraction (stroke volume/EDV)
In what area of the GI tract are water-soluble vitamins absorbed?
What form of diabetes insipidus is due to an insufficient amount of ADH for the renal collecting ducts?
Central/neurogenic diabetes insipidus; in the nephrogenic form there is sufficient ADH available, but the renal collecting ducts are impermeable to its actions.
True or false? There are no central O2 receptors.
What adrenal enzyme deficiency results in hypertension, hypernatremia, and virilization?
11-Beta-Hydroxylase deficiency results in excess production of 11-deoxycorticosterone, a weak mineralocorticoid. It increases BP, Na+, and ECF volume along with production of adrenal androgens.
What phase of the female cycle occurs during days 1 to 15?
Follicular phase
Tidal volume
Volume of air that enters and leaves the lung in a single cycle. 500ml
Characteristics of sub-treshold potentials
Proportional to stimulus stregth, not propagated, decremental with distance, summation
What prevents downregulation of pituitary receptors?
Pulsatile release of hypothalamic hormones.
Characteristics of protein-mediated transport
More rapid than diffusion, transport can be saturated (Tm), is chemically specific, substances compete for transporter
Relative refractory period
A large stimulus can depolarize the cell
Central diabetes insipidus
Not enough ADH secreted. Dilute urine is formed in spite of water deprivation. Responds to injected ADH.
Causes of right axis deviations
Right ventricular hypertrophy or dilation, conduction defect of right ventricle, AMI on left side
What neurotransmitter is essential for maintaining a normal BP when an individual is standing?
NE, via its vasoconstrictive action on blood vessels
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 ↓
Dilation of efferent arteriole
What is the term for the load a muscle is trying to move during stimulation?
What is the respiratory compensation mechanism for metabolic alkalosis?
Hypoventilation, which increases CO2, shifting the reaction to the right and increasing H+
What peripheral chemoreceptor receives the most blood per gram of weight in the body?
The carotid body, which monitors arterial blood directly
Characteristics of smooth muscle
Actin and myosin not organized in sarcomeres, gap junctions, electrical syncytium, calmodulin binds calcium, low ATPase activity, lacks T-tubules, voltage-gated calcium channels.
Enzyme deficiencies that produce congenital adrenal hyperplasia and low cortisol levels
21β-OH, 11β-OH and 17α-OH all result in low cortisol levels.
How is potassium balance in acute alkalosis?
Negative (potassium is excreted)
What are the different contractions of the intestines?
Segmentation contractions (mixing), peristaltic movements (propulsive).
Main drive for ventilation
H+ ions from dissociated H2CO3 which stimulate central chemoreceptors. H2CO3 is proportional to PCO2 of CSF
Indices of left ventricular preload
LVEDV, LVEDP, left atrial pressure, pulmonary venous pressure, pulmonary wedge pressure (swan-ganz)
Characteristics of parallel circuits
The reciprocal of the total resistance is the sum of the reciprocal of the individual resistances. Connecting a resistance in parallel lowers resistance, total resistance is always less than individual resistances.
Factors that influence ADH secretion
↑ osmolarity --> ↑ ADH secretion; ↓ blood volume --> baroreceptors --> medulla --> ↑ ADH secretion
What is the term for the negative resting membrane potential moving toward threshold?
Depolarization (i.e., Na+ influx)
If the radius of a vessel is decreased by half, what happens to the resistance?
The resistance increases 16-fold.
What type of muscle is characterized by no myoglobin, anaerobic glycolysis, high ATPase activity, and large muscle mass?
White muscle; short term too
What is the term for the negative resting membrane potential moving toward threshold?
Depolarization (i.e., Na+ influx)
Does subatmospheric pressure act to expand or collapse the lung?
Subatmospheric pressure acts to expand the lung; positive pressure acts to collapse the lung.
Name the lung measurement based on the following descriptions:
• Amount of air in the lungs after maximal inspiration
Total lung capacity (TLC)
What adrenal enzyme deficiency can be summed up as a mineralocorticoid deficiency, glucocorticoid deficiency, and an excess of adrenal androgens?
21-β-Hydroxylase deficiency leads to hypotension, hyponatremia, and virilization.
What hormone has the following effects: chondrogenic in the epiphyseal end plates of bones; increases AA transport for protein synthesis; increases hydroxyproline (collagen); and increases chondroitin sulfate synthesis?
GH, especially IGF-1. GH also increases the incorporation of thymidine in DNA synthesis and uridine in RNA synthesis.
If free water clearance (CH2O) is positive, what type of urine is formed? And if it is negative?
If positive, hypotonic urine (osmolarity <300 mOsm/L); if negative, hypertonic urine (osmolarity > 300 mOsm/L)>>
What is the term for days 1 to 7 of the female cycle?
Activation and degradation of thyroid hormones
5' monodeiodinase activates T4 into T3. 5-monodeiodinase inactivates T4 into reverse T3.
Acute reflex changes if baroreceptor afferents are cut
↓ afferent baroreceptors --> ↓ parasympathetic, ↑ sympathetic, ↑ blood pressure, ↑ heart rate
Acute reflex changes in orthostatic hypotension or fluid loss
↓ afferent baroreceptors --> ↓ parasympathetic, ↑ sympathetic, ↑ blood pressure, ↑ heart rate
Why can't the heart be tetanized?
A long absolute refractory period extends through most of the contraction. Short relative refractory period.
Volume of distribution formula
Vd = Amount given or dose / Concentration
Characteristics of inulin clearance
A constant amount of inulin is cleared regardless of plasma concentration (parallel line to x axis). Inulin clearance is equal to GFR because it's not secreted nor reabsorbed. If GFR increases, clearance increases (line shifts upward), and vice versa.
What is a diffusion-limited defect?
There's a lung problem where A-a gradient is below normal, therefore diffusion isn't normal
↓ECF, ↑osmolarity, ↓ICF, lots of diluted urine
Loss of hypotonic fluid or hypernatremic hypovolemia. Cause: diabetes insipidus
Loss of hypotonic fluid diagram (hypovolemia)
Decreases ECF and ICF, increases osmolarity. Causes: dehydration, sweating, diabetes insipidus.
Differences in ventilation between the base and the apex of the lung
Base intrapleural pressure is -2.5, alveoli are compliant and small with a small volume of air but receive a large amount of ventilation; Apex pressure is -10, alveoli are large and stiff and contain a large volume of air but receive small amount of ventilation.
Source of calcium for heart and smooth muscle contraction
Sarcoplasmic reticulum and extracellular. Cardiac and smooth muscle have voltage-gated calcium channels.
What is the difference in potassium dynamics between acute and chronic alkalosis?
Acute alkalosis --> ↑ intracellular K; Chronic alkalosis --> ↓ intrecellular K
What four factors shift the Hgb-O2 dissociation curve to the right? What is the consequence of this shift?
Increased CO2, H+, temperature, and 2, 3-BPG levels all shift the curve to the right, thereby making the O2 easier to remove (decreased affinity) from the Hgb molecule.
What are the four characteristics of all protein-mediated transportation?
1. Competition for carrier with similar chemical substances 2. Chemical specificity needed for transportation 3. Zero-order saturation kinetics (Transportation is maximal when all transporters are saturated.) 4. Rate of transportation faster than if by simple diffusion
What are the three functions of surfactant?
1. Increase compliance
2. Decrease surface tension
3. Decrease probability of pulmonary edema formation
Anatomical and alveolar dead spaces together constitute what space?
Physiologic dead space is the total dead space of the respiratory system.
What phase of the menstrual cycle is dominated by estrogen? Progesterone?
Follicular phase is estrogen-dependent with increased FSH levels, while the luteal phase is progesterone-dependent.
What is the signal to open the voltage-gated transmembrane potassium channels?
Membrane depolarization is the stimulus to open these slow channels, and if they are prevented from opening, it will slow down the repolarization phase.
In regards to solute concentration, how does water flow?
Water flows from a low-solute to high-solute concentrations.
Is filtration greater than or less than excretion for net reabsorption to occur?
Filtration is greater than excretion for net reabsorption to occur.
How does sympathetic stimulation to the skin result in decreased blood flow and decreased blood volume? (Hint: what vessels are stimulated, and how?)
A decrease in cutaneous blood flow results from constriction of the arterioles, and decreased cutaneous blood volume results from constriction of the venous plexus.
Effect of sympathetic stimulation in the nephron
↓ GFR, ↑ FF, ↑ peritubular reabsoption
Pathophysiology of iodine deficiency
Thyroid makes less T4 and more T3 so actions of T3 may be normal but low levels of T4 stimulate TSH secretion with development of goiter. Thus euthyroid with goiter.
y wave of the venous pulse
Opening of tricuspid valve and atrial emptying
Fastest and slowest velocities in the systemic circuit
Velocity is inversely proportional to cross-sectional area. Aorta has fastest velocity; capillaries have slowest velocity.
Acute reflex changes with a carotid massage
↑ afferent baroreceptors --> ↑ parasympathetic, ↓ sympathetic, ↓ blood pressure, ↓ heart rate
Normal filtration fraction value
FF = GFR/RPF = 120mi/min / 600ml/min = 0.20
What cells of the parathyroid gland are simulated in response to hypocalcemia?
The chief cells of the parathyroid gland release PTH in response to hypocalcemia.
What thyroid enzyme is needed for oxidation of I– to I'?
Peroxidase, which is also needed for iodination and coupling inside the follicular cell
Why is there an increase in prolactin if the hypothalamic-pituitary axis was severed?
Because the chronic inhibition of dopamine (PIF) on the release of prolactin from the anterior pituitary gland is removed, thereby increasing the secretion of prolactin.
What is the term for the total volume of air moved in and out of the respiratory system per minute?
Total ventilation (minute ventilation or minute volume)
What is the amount in liters and percent body weight for the following compartments? • ECF
14 L, 33% of body weight
Where does the synthesis of ACh occur?
In the cytoplasm of the presynaptic nerve terminal; it is catalyzed by choline acetyltransferase.
What is the central chemoreceptor's main drive for ventilation?
CSF H+ levels, with acidosis being the main central drive, resulting in hyperventilation (the opposite being true with alkalosis)
What is the amount in liters and percent body weight for the following compartments?
• Vascular fluid
4.7 L, 5% of body weight
Factors that decrease slope of cardiac function curve
↓ inotropy, ↓ heart rate, ↑ afterload
Transport of thyroid hormones
99% is bound to TBG, 1% is free. T4 has greater affinity for TBG and a half-life of 6 days. T3 has greater affinity for nuclear receptor and is the active form with a 1 day half-life. 50:1 T4/T3 ratio in periphery.
How many ATPs are hydrolyzed every time a skeletal muscle cross-bridge completes a single cycle?
One, and it provides the energy for mechanical contraction.
What are the two best indices of left ventricular preload?
LVEDV and LVEDP (left ventricular end-diastolic volume and end-diastolic pressure, respectively)
What happens to O2 affinity with a decrease in p50?
O2 affinity increases with a decrease in the p50, making O2 more difficult to remove from the Hgb molecule.
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)
Amount of dissolved oxygen in the blood
0.3 volumes %; 0.3ml per 100ml of blood. Determines PO2 which acts to keep oxygen bound to Hb
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.
Why is the apex of the lung hypoventilated when a person is standing upright?
The alveoli at the apex are almost completely inflated prior to inflation, and although they are large, they receive low levels of alveolar ventilation.
What are the following changes seen in the luminal fluid by the time it leaves the PCT of the nephron?• Percentage of Na+, Cl-, K+ left in the lumen
At the end of the PCT 25% of Na+, Cl-, K+ is left
Why is the base of the lung hyperventilated when a person is standing upright?
The alveoli at the base are small and very compliant, so there is a large change in their size and volume and therefore a high level of alveolar ventilation.
What is the term for the load on a muscle in the relaxed state?
Preload. It is the load on a muscle Prior to contraction.
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