MDS PREP
What is the primary mechanism of vibration detection in the musculoskeletal system?
1) Meissner's corpuscles
2) Pacinian corpuscles
3) Merkel's discs
4) Ruffini's endings
Pacinian corpuscles are rapidly adapting mechanoreceptors that are highly sensitive to high-frequency vibrations and are responsible for detecting rapid changes in pressure.
What is the role of the post-prandial alkaline tide in the regulation of gastric pH?
1) It increases gastric acidity
2) It decreases gastric acidity
3) It has no effect on gastric acidity
4) It neutralizes gastric acid
E) It promotes the secretion of bicarbonate into the gastric lumen
The post-prandial alkaline tide refers to the increase in blood bicarbonate levels that occurs after a meal due to the secretion of bicarbonate by the pancreas and duodenal mucosa to neutralize the acidic chyme entering the small intestine. This temporary rise in blood pH reduces the secretion of gastrin and therefore decreases gastric acidity.
What is the transport maximum for glucose reabsorption in the kidneys?
1) 125 mg/min
2) 250 mg/min
3) 375 mg/min
4) 500 mg/min
The transport maximum for glucose reabsorption in the kidneys is about 375 mg/min, which indicates the maximum amount of glucose that can be reabsorbed before it appears in the urine.
Which area of the brain is associated with the comprehension of speech?
1) Wernicke’s area
2) Broca’s area
3) Primary auditory cortex
4) Angular gyrus
E. Occipital lobe
Wernicke's area, located in the posterior part of the superior temporal gyrus, is involved in language comprehension. It receives input from the secondary somatic, auditory, and visual association areas and is critical for understanding spoken and written language.
What is the primary effect of norepinephrine on the pupillary dilator muscle?
1) Contraction
2) Relaxation
3) No effect
4) It depends on the presence of other neurotransmitters
Answer: 1) ContractionExplanation: Norepinephrine acts on alpha-adrenergic receptors on the pupillary dilator muscle, causing its contraction and pupil dilatation (mydriasis). This is part of the sympathetic nervous system's response to stress and increased alertness during the fight-or-flight response.
The release of which hormone is triggered by the macula densa cells during tubulo-glomerular feedback?
1) Renin
2) Angiotensin II
3) Atrial Natriuretic Peptide (ANP)
4) Aldosterone
The macula densa cells respond to decreases in sodium chloride concentration in the tubular fluid by releasing renin, which initiates the renin-angiotensin-aldosterone system (RAAS). This leads to increased sodium reabsorption and water retention, thereby restoring the sodium chloride balance and blood volume.
Which of the following is a characteristic of the absolute refractory period during an action potential?
1) The membrane is fully depolarized.
2) The membrane is fully repolarized.
3) The membrane is inexcitable regardless of the strength of the stimulus.
4) The membrane is hyperpolarized.
E. The membrane is depolarized.
The absolute refractory period occurs during the initial phase of repolarization after an action potential. During this period, the membrane is inactivated and cannot be depolarized to generate another action potential, regardless of the stimulus strength. This ensures that action potentials are unidirectional and do not propagate backward along the axon.
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
The threshold for phosphate excretion in the urine is approximately 0.50 mM, above which phosphate begins to appear in the urine.