Which renal structure is responsible for producing hypertonic urine by reabsorbing water while allowing metabolic wastes and NaCl to pass through?
Glomerulus
Collecting duct
Nephron loop (loop of Henle)
Proximal convoluted tubule
The Correct Answer is B
A. Glomerulus is involved in filtering blood but not in producing hypertonic urine.
B. Collecting duct reabsorbs water and concentrates urine, making it hypertonic.
C. Nephron loop (loop of Henle) creates a concentration gradient in the medulla that helps in water reabsorption but is not the primary site for final urine concentration. This option is partially correct but less specific than the collecting duct.
D. Proximal convoluted tubule reabsorbs a significant portion of water and solutes but does not produce hypertonic urine.
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Correct Answer is C
Explanation
A. Tubuloglomerular feedback involves the macula densa sensing changes in sodium chloride concentration and adjusting the glomerular filtration rate (GFR) via the juxtaglomerular apparatus.
B. Renal autoregulation includes mechanisms like the myogenic mechanism and tubuloglomerular feedback that maintain stable GFR despite blood pressure changes. This option is too broad and not specific to the mechanism described.
C. The myogenic mechanism refers to the smooth muscle's tendency to contract when stretched, helping to stabilize GFR by adjusting the diameter of the afferent arterioles. This is the correct answer.
D. Sympathetic control influences renal blood flow and GFR through hormonal and nervous system regulation, but it is not the specific mechanism described in the question.
Correct Answer is D
Explanation
A. Ca2+: prevents the entrance of any more sperm- While calcium ions play a role in the slow block to polyspermy, the fast block involves sodium ions.
B. Na+: prevents the entrance of more Na- The fast block to polyspermy involves sodium ions (Na+), but the depolarization of the egg membrane prevents the entrance of more sperm, not just more Na+.
C. Na+: prevents the entrance of Ca2+. The fast block prevents additional sperm from entering, not calcium ions.
D. Na+: prevents the entrance of any more sperm: The fast block to polyspermy involves the opening of sodium ion channels, leading to depolarization of the egg membrane. This depolarization prevents other sperm from binding to and penetrating the egg.