MDS PREP
What is the effect of muscarinic stimulation on the pupil of the eye?
1) Dilation (mydriasis)
2) Constriction (miosis)
3) No effect on pupil size
4) Paralysis of the pupil
The pupillary light reflex is under the control of the parasympathetic nervous system, which stimulates muscarinic receptors in the iris sphincter muscle. This leads to pupil constriction (miosis) in response to light, as part of the body's attempt to regulate the amount of light entering the eye.
What is the threshold for phosphate excretion in the urine?
1) 0.10 mM
2) 0.50 mM
3) 1.00 mM
4) 2.00 mM
Physiology
Answer: 2
The threshold for phosphate excretion is when the plasma phosphate concentration reaches approximately 0.50 mM, causing some to be filtered into the urine.
What is the role of calmodulin in the contraction of smooth muscle cells?
1) It binds to calcium and initiates muscle contraction directly
2) It activates the sarcoplasmic reticulum to release calcium
3) It inhibits the release of calcium from the sarcoplasmic reticulum
4) It activates myosin kinase (MLCK) in the presence of calcium
Answer: 4) It activates myosin kinase (MLCK) in the presence of calciumExplanation: Calcium binds to calmodulin, forming a calcium-calmodulin complex. This complex then activates myosin kinase, which phosphorylates the myosin light chain, leading to the formation of cross-bridges between actin and myosin and initiating muscle contraction in smooth muscles.
The rate of gastric emptying is influenced by:
1) The quantity and type of food ingested
2) Distension of the duodenum
3) Gastric hormones like gastrin
4) All of the above
The rate of gastric emptying is influenced by the presence of food in the stomach, the type of food (carbohydrates, proteins, and fats), the distension of the duodenum, and the hormone gastrin, which can increase the rate of emptying.
Which of the following is NOT an action of bile salts?
1) Emulsification of fat
2) Facilitation of fat absorption
3) Neutralization of stomach acid
4) Conjugation of bile acids
Physiology
Answer: 3
Bile salts are involved in the emulsification and absorption of fat, not in neutralizing stomach acid.
What is the typical osmolality of intestinal chyme?
1) Isotonic with blood (~300 mOsm/L)
2) Hypotonic (<300 mOsm/L)
3) Hypertonic (>300 mOsm/L)
4) Varies greatly depending on the composition of ingested food
E) Is not relevant for nutrient absorption
The osmolality of intestinal chyme can vary widely depending on the type and quantity of food consumed. It can range from isotonic to hypertonic or hypotonic relative to blood. The intestinal mucosa plays a critical role in adjusting water and ion transport to maintain the osmolality of the blood and facilitate the absorption of nutrients.
An increase of the pressure within one of the carotid sinuses would result in an increase in
1) Mean arterial pressure
2) Cardiac output
3) The activity of the pressor center
4) The activity of cardiac vagal fibers
Physiology
Answer: 4
An increase of the pressure within one of the carotid sinuses would result in an increase in The activity of cardiac vagal fibers
Which of the following statements about the sensory neurons and their pathways in the spinal cord is correct?
1) All sensory neurons synapse with motor neurons in the ventral horn to form spinal reflex arcs
2) Only pain and temperature sensations ascend to the brainstem for conscious perception
3) The axons of sensory neurons from the dorsal root ganglion may directly synapse with motor neurons or ascend to the brain
4) Sensory neurons only project to the reticular formation and thalamus for nonspecific arousal
The axons of sensory neurons from the dorsal root ganglion can follow three routes: forming spinal reflexes by synapsing with motor neurons, ascending to the brainstem for conscious perception, or relaying through the reticular formation and thalamus for general arousal.