MDS PREP
Which type of receptors are involved in the contraction of the detrusor muscle during micturition?
1) Muscarinic receptors
2) Adrenergic receptors
3) Dopaminergic receptors
4) Serotonergic receptors
The contraction of the detrusor muscle during micturition is mediated by the activation of muscarinic receptors (specifically M3 receptors) on the smooth muscle cells of the detrusor. This leads to increased muscle tone and the expulsion of urine from the bladder.
What is the function of the pineal gland in regulating circadian rhythms?
1) It produces melatonin in response to light exposure
2) It produces cortisol to maintain wakefulness
3) It regulates body temperature
4) It is not involved in circadian rhythms
The pineal gland produces melatonin in response to light exposure, helping to regulate circadian rhythms and sleep-wake cycles.
What is the primary site of vitamin B12 absorption in the intestine?
1) Stomach
2) Duodenum
3) Jejunum
4) Ileum
Physiology
Answer: 4
The ileum is the primary site of vitamin B12 absorption, facilitated by intrinsic factor binding to specific receptors.
The glomerular filtration barrier consists of:
1) Endothelial cells
2) Basement membrane
3) Podocytes
4) All of the above
The glomerular filtration barrier is a three-layered structure composed of endothelial cells of the glomerular capillaries, the basement membrane, and the podocytes (visceral epithelial cells of Bowman's capsule). These layers work together to filter blood, allowing small molecules to pass into the nephron while retaining larger ones.
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 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.
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.
What is the role of the acrosome in sperm penetration of the egg during fertilization?
1) It produces energy for the sperm's movement
2) It contains enzymes that help dissolve the egg's outer layers
3) It transfers genetic material to the egg
4) It has no role in the penetration process
Physiology
Answer: 2
The acrosome contains enzymes such as hyaluronidase and acrosin that are essential for breaking down the zona pellucida, the egg's outermost layer, allowing the sperm to penetrate and fertilize the egg.