Weekly Year 2: Physiology Exam - May 29, 2026 (Section A: MC

Question 1

The following neurotransmitter is used by the substantia nigra neurons that project to the caudate and putamen:

Accepted Answer

Dopamine — The substantia nigra pars compacta uses dopamine as its neurotransmitter, and its dopaminergic neurons project to the striatum (caudate and putamen), playing a crucial role in motor control.

Question 2

Which of the following items correctly describes the relationship of cerebrospinal fluid pressure to the venous pressure in the superior sagittal sinus?

Accepted Answer

CSF pressure is normally slightly higher than superior sagittal sinus pressure. — Cerebrospinal fluid (CSF) is absorbed into the venous system, primarily through arachnoid villi that project into the superior sagittal sinus. For absorption to occur, the CSF pressure must be higher than the venous pressure in the sinus.

Question 3

Output signals from Golgi tendon organs are transmitted to which of the following higher centers?

Accepted Answer

Cerebellar cortex and spinal cord interneurons — Golgi tendon organs are sensory receptors that detect muscle tension. Their afferent signals are transmitted to the spinal cord, where they can inhibit motor neurons (autogenic inhibition) and excite antagonist motor neurons. They also project to the cerebellum and, to a lesser extent, the brainstem (e.g., vestibular nuclei) for motor coordination and reflex modulation.

Question 4

Which type of cholinergic receptor is found at synapses between preganglionic and postganglionic neurons of the sympathetic system?

Accepted Answer

Nicotinic receptor — The neurotransmitter at the synapse between preganglionic and postganglionic neurons in both the sympathetic and parasympathetic nervous systems is acetylcholine (ACh). This ACh acts on nicotinic receptors on the postganglionic neuron.

Question 5

The term limbic cortex includes the orbitofrontal cortex, subcallosal gyrus, cingulate gyrus, and which one of the following areas?

Accepted Answer

Hippocampus — The limbic cortex is a collection of cortical areas involved in emotion, motivation, and memory. The hippocampus, although not strictly cortical in the same way as the others, is considered a major component of the limbic system and is often functionally grouped with the limbic cortex.

Question 6

Occlusion of which of the following structures would lead to communicating hydrocephalus?

Accepted Answer

Arachnoid villi — Communicating hydrocephalus occurs when there is impaired absorption of CSF into the venous system, often due to obstruction of the arachnoid villi or increased resistance to flow within the subarachnoid space. Obstruction of the cerebral aqueduct or ventricular foramina leads to non-communicating (obstructive) hydrocephalus.

Question 7

The withdrawal reflex is initiated by stimulation delivered to which of the following receptors?

Accepted Answer

Nociceptors — The withdrawal reflex, a protective reflex, is typically triggered by noxious stimuli that activate nociceptors (pain receptors). This leads to the rapid withdrawal of the stimulated body part from the harmful stimulus.

Question 8

Which substance activates adrenergic alpha and beta receptors equally well?

Accepted Answer

Epinephrine — Epinephrine (adrenaline) has a high affinity for both alpha and beta adrenergic receptors and activates them relatively equally. Norepinephrine primarily stimulates alpha receptors and has less effect on beta-2 receptors. Dopamine has distinct receptor affinities, and isoproterenol is a potent beta-adrenergic agonist.

Question 9

The posterior and lateral hypothalamus, in combination with the preoptic area, are involved in the control of which of the following functions?

Accepted Answer

Thermoregulation — The hypothalamus, including the preoptic area, posterior, and lateral regions, plays a critical role in maintaining homeostasis, with significant involvement in thermoregulation (both heat loss and heat conservation mechanisms). While other functions listed are also hypothalamic functions, thermoregulation is a primary role for this specific combination of areas.

Question 10

Which statement concerning the reticulospinal system is correct?

Accepted Answer

It influences muscle tone and posture. — The reticulospinal tracts are descending motor pathways that originate in the reticular formation of the brainstem. They play a significant role in modulating muscle tone, posture, and balance, as well as influencing spinal reflexes. Fine motor control is more associated with the corticospinal tract.

Question 11

The neurons located in the locus ceruleus release which of the following neurotransmitters at their synaptic terminals?

Accepted Answer

Norepinephrine — The locus ceruleus, a nucleus in the pons, is the principal site for brain synthesis of norepinephrine. Its neurons project widely throughout the brain and spinal cord, influencing arousal, attention, and mood.

Question 12

Which of the following items represents the structural basis of the blood-cerebrospinal fluid barrier?

Accepted Answer

Capillaries of the choroid plexus — The blood-cerebrospinal fluid (CSF) barrier is formed by the specialized structure of the capillaries within the choroid plexus. These capillaries are fenestrated but are covered by a layer of epithelial cells (choroid plexus epithelium) that form tight junctions, controlling the passage of substances from the blood into the CSF.

Question 13

Which of the following is a component of the renal response to metabolic acidosis?

Accepted Answer

Increased reabsorption of bicarbonate — In metabolic acidosis, the kidneys attempt to correct the imbalance by increasing the reabsorption of filtered bicarbonate and by increasing the excretion of hydrogen ions. The generation of new bicarbonate also occurs through the excretion of titratable acids and the production of ammonia.

Question 14

Which of the following will not lead to a diuresis?

Accepted Answer

Increased plasma osmolality — Increased plasma osmolality (e.g., due to dehydration) leads to increased ADH secretion, which promotes water reabsorption in the kidneys, thus reducing urine output, not causing diuresis. Loop diuretics, drinking a large volume of water, and decreased ADH secretion all lead to increased urine output (diuresis).

Question 15

Which of the following contributes directly to the generation of a hypertonic medullary interstitium in the kidney?

Accepted Answer

Active transport of NaCl out of the thick ascending limb — The active transport of NaCl out of the thick ascending limb of the loop of Henle into the medullary interstitium is a key step in establishing and maintaining the corticomedullary osmotic gradient, which is essential for concentrating urine. Urea recycling also contributes, but the active salt transport is a primary driver.

Question 16

An increase in renin is caused by

Accepted Answer

Increased sodium delivery to the macula densa — Decreased renal perfusion pressure (e.g., due to hypotension or decreased circulating volume) is a potent stimulus for renin release from the juxtaglomerular apparatus. Increased sodium delivery to the macula densa and increased blood volume inhibit renin release. Beta-1 adrenergic receptor activation stimulates renin release.

Question 17

What happens at plasma concentrations of glucose higher than transport maximum (TM)?

Accepted Answer

Glucose appears in the urine (glucosuria). — The transport maximum (TM) for glucose reabsorption in the proximal tubule represents the maximum rate at which glucose can be actively transported from the tubular fluid back into the blood. When plasma glucose concentrations exceed the TM, the reabsorptive capacity is saturated, and the excess filtered glucose is excreted in the urine, leading to glucosuria.

Question 18

Which of the following would produce an increase in the reabsorption of isosmotic fluid in the proximal tubule?

Accepted Answer

Increased plasma bicarbonate concentration — An increased plasma bicarbonate concentration leads to increased filtered bicarbonate. To reabsorb this filtered bicarbonate, the proximal tubule also reabsorbs a proportional amount of sodium and water, resulting in an increase in isosmotic fluid reabsorption. Decreased peritubular oncotic pressure and increased hydrostatic pressure would decrease proximal tubule reabsorption.

Question 19

Which of the following would cause an increase in both glomerular filtration rate (GFR) and renal plasma flow (RPF)?

Accepted Answer

Constriction of the efferent arteriole — Dilation of the afferent arteriole increases glomerular capillary hydrostatic pressure, which directly increases GFR. It also increases blood flow into the glomerulus, thus increasing RPF. Constriction of the efferent arteriole would increase GFR but decrease RPF. Constriction of the afferent arteriole would decrease both GFR and RPF.

Question 20

Which of the following is true about reabsorption of filtered HCO3-?

Accepted Answer

It occurs primarily in the proximal tubule. — The vast majority (about 85-90%) of filtered bicarbonate is reabsorbed in the proximal tubule. This reabsorption is coupled to the secretion of H+ into the lumen, where it combines with filtered HCO3- to form H2CO3, which then dissociates into CO2 and H2O, which readily diffuse into the tubule cells. Reabsorption of HCO3- is stimulated by acidosis and inhibited by alkalosis.

Question 21

Kipchoge runs a marathon in 90°F weather and replaces all volume lost in sweat by drinking distilled water. After the marathon, she will have

Accepted Answer

Hyponatremia and increased ADH levels — Sweat is hypotonic, meaning it has a lower sodium concentration than plasma. Drinking large amounts of distilled water (which is pure water with no electrolytes) will further dilute the plasma. This leads to hyponatremia (low plasma sodium) and a decrease in plasma osmolality. A decrease in plasma osmolality inhibits ADH secretion, but the severe dilution and resulting hyponatremia will lead to increased ADH release attempting to conserve water and increase blood volume. However, the primary initial effect is dilution and hyponatremia.

Question 22

Which of the following is a cause of metabolic alkalosis?

Accepted Answer

Severe vomiting — Severe vomiting leads to loss of gastric acid (HCl), which causes metabolic alkalosis. Diarrhea typically causes metabolic acidosis due to loss of bicarbonate-rich intestinal fluid. Diabetic ketoacidosis is a cause of metabolic acidosis. Renal failure can lead to either acidosis or alkalosis depending on the specific dysfunction.

Question 23

The decision to delay extraction of the oocyte until 7 hours after a rise in LH levels is because the midcycle LH surge causes

Accepted Answer

Meiotic maturation of the oocyte — The LH surge triggers the completion of meiosis I and the progression to metaphase II (meiotic maturation) in the oocyte. This process takes approximately 24-36 hours. Ovulation occurs about 30-36 hours after the LH surge. Luteinization and progesterone synthesis begin shortly after the surge but become more prominent later. Therefore, delayed extraction allows for the oocyte to undergo maturation.

Question 24

Loss-of-function mutations of which enzyme would be responsible for the presence of labia in an XY subject at birth?

Accepted Answer

5α-reductase — 5α-reductase is essential for converting testosterone to dihydrotestosterone (DHT). DHT is a more potent androgen that plays a crucial role in the masculinization of the external genitalia during fetal development. In an XY individual with a loss-of-function mutation in 5α-reductase, the external genitalia will appear feminized (e.g., labia) because testosterone is not effectively converted to DHT. 17α-hydroxylase is involved in steroidogenesis; aromatase converts androgens to estrogens; 17β-hydroxysteroid dehydrogenase converts androstenedione to testosterone.

Question 25