MDS PREP
The average time required for spermatogenesis in humans is:
1) 30 days
2) 42 days
3) 74 days
4) 120 days
Spermatogenesis, the process of producing mature sperm cells from spermatogonia, takes approximately 74 days in humans. This includes the development of spermatids and their subsequent transformation into spermatozoa.
Which of the following is the primary active transport mechanism for calcium absorption in the intestine?
1) Vitamin D dependent calcium binding protein (calbindin)
2) Sodium-calcium exchanger (NCX)
3) Calcium-dependent ATPase
4) All of the above
Physiology
Answer: 4
Calcium is absorbed mainly in the duodenum and jejunum by an active transport mechanism regulated by 1,25 (OH)2 D3 (calcitriol). It is transported across the brush border of intestinal epithelial cells via TRPV6 channels and binds to calbindin. The absorbed calcium is then delivered to the basolateral membrane by calbindin, and from there it is transported into the bloodstream by either the sodium-calcium exchanger (NCX) or calcium-dependent ATPase.
What is the primary mechanism of the fight-or-flight response in the regulation of glycogenolysis?
1) Activation of glycogen phosphorylase by epinephrine
2) Inhibition of glycogen synthase by cortisol
3) Stimulation of glucose-6-phosphatase by thyroid hormones
4) Activation of hexokinase by norepinephrine
Answer: 1) Activation of glycogen phosphorylase by epinephrineExplanation: Epinephrine acts on the beta-adrenergic receptors of liver and muscle cells, which activate protein kinase. This kinase then phosphorylates and activates glycogen phosphorylase, an enzyme that breaks down glycogen into glucose-1-phosphate, which is rapidly converted to glucose-6-phosphate for use in glycolysis or for release into the bloodstream to maintain glucose levels during stress.
What is the primary function of the C-peptide after it is cleaved from proinsulin during the synthesis of insulin?
1) It has no significant role
2) It acts as a regulator of insulin secretion
3) It serves as a precursor for other pancreatic hormones
4) It is involved in the maintenance of islet cell structure
The C-peptide is removed during the conversion of proinsulin to insulin and does not have a known biological function. Its primary purpose is to hold the A and B chains of proinsulin together during synthesis.
What is the primary function of the parasympathetic nervous system?
1) Control of sympathetic nervous system
2) Control of visceral functions during rest and digestion
3) Control of musculoskeletal system during rest
4) Control of sensory systems during stress
The parasympathetic nervous system is primarily responsible for the "rest and digest" functions, which include the regulation of the gastrointestinal system, cardiovascular system, and other visceral activities that are not directly involved in movement or emergency response.
What is the primary mechanism by which acid secretion is regulated in the stomach?
1) By the pH of the stomach content
2) By the amount of food present
3) By the time of day
4) By the type of food consumed
Physiology
Answer: 1
The primary mechanism by which gastric acid secretion is regulated is through the feedback loop involving the pH of the stomach content. Low pH inhibits further acid secretion by decreasing the release of gastrin and the responsiveness of parietal cells to gastrin.
What is the primary effect of parathyroid hormone on serum calcium levels during pregnancy?
1) Decreases serum calcium levels
2) Increases serum calcium levels by mobilizing calcium from maternal bones
3) Has no effect on serum calcium levels
4) Increases serum calcium levels by enhancing calcium absorption in the gut
Answer: 2) The primary effect of parathyroid hormone during pregnancy is to increase serum calcium levels by mobilizing calcium from maternal bones for fetal use.
What is the primary mechanism of action of the Na+/I+ symporter in thyroid cells?
1) Primary active transport
2) Facilitated diffusion
3) Secondary active transport
4) Osmosis
The Na+/I+ symporter (NIS) in thyroid cells uses the energy from the electrochemical gradient of sodium to actively transport iodide into the cells, which is an example of secondary active transport.