As shown in this diagram, increased blood osmolarity stimulates hypothalamic osmoreceptors. What happens next? (What goes in the yellow box?)
Posterior pituitary releases ADH
Adrenal medulla releases aldosterone
Kidneys release erythropoietin
Anterior pituitary releases oxytocin
Adrenal cortex releases norepinephrine
The Correct Answer is A
A. Posterior pituitary releases ADH: Dehydration increases blood osmolarity. This is sensed by hypothalamic osmoreceptors. In response, the hypothalamus signals the posterior pituitary to release antidiuretic hormone (ADH). ADH then acts on the distal convoluted tubules and collecting ducts of the kidney to promote water reabsorption, thereby concentrating the urine and reducing blood osmolarity.
B. Adrenal medulla releases aldosterone: Aldosterone is released from the adrenal cortex, not medulla, and is more responsive to low sodium or high potassium, not directly to osmolarity.
C. Kidneys release erythropoietin: Erythropoietin is released in response to hypoxia, not dehydration or osmolarity.
D. Anterior pituitary releases oxytocin: Oxytocin is released by the posterior pituitary, and it is not involved in osmolarity or water balance.
E. Adrenal cortex releases norepinephrine: Norepinephrine is released by the adrenal medulla, and is involved in fight-or-flight, not osmolarity regulation.
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Related Questions
Correct Answer is A
Explanation
A. Impermeability of the collecting tubule to water: In the absence of ADH, the collecting duct is impermeable to water, allowing dilute urine to be excreted.
B. The presence of ADH: ADH increases water reabsorption, leading to concentrated urine, not dilute.
C. Relative permeability of the distal tubule to water: If the tubule is permeable to water (due to ADH), water is reabsorbed, and urine becomes concentrated.
D. Transport of sodium and chloride ions out of the descending nephron loop: The descending limb is not permeable to salts-only the ascending limb actively reabsorbs Na⁺ and Cl⁻.
Correct Answer is C
Explanation
A. Urine concentration and volume are determined by countercurrent mechanisms: The countercurrent multiplier (nephron loop) and countercurrent exchanger (vasa recta) help establish a medullary osmotic gradient that allows for urine concentration or dilution.
B. The kidneys produce a large volume of dilute urine when overhydrated: In overhydration, ADH secretion is suppressed, leading to reduced water reabsorption and a larger volume of dilute urine.
C. The concentration of urine is lower when urine volume is reduced: This is incorrect. When urine volume is reduced (e.g., dehydration), the urine is more concentrated, not less.
D. The kidneys produce a small volume of concentrated urine when dehydrated: In dehydration, ADH is secreted, causing increased water reabsorption, resulting in concentrated urine with low volume.
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