Which hormone is released by the kidneys in response to low blood pressure, ultimately leading to angiotensin II production?
ADH
Cortisol
Renin
Aldosterone
The Correct Answer is C
A. ADH: Antidiuretic hormone is synthesized in the hypothalamus and released by the posterior pituitary gland. Its primary role is to increase water reabsorption in the renal collecting ducts. It does not participate in the biochemical cascade that generates angiotensin II.
B. Cortisol: This glucocorticoid is produced by the adrenal cortex in response to stress and adrenocorticotropic hormone. While it influences glucose metabolism and possesses minor mineralocorticoid activity, it is not a kidney-derived enzyme. It does not initiate the proteolytic cleavage of angiotensinogen.
C. Renin: The juxtaglomerular cells of the kidney secrete this enzyme when they detect decreased perfusion or low sodium delivery. Renin cleaves plasma angiotensinogen into angiotensin I, which is the rate-limiting step of the RAAS. This pathway is essential for systemic blood pressure elevation.
D. Aldosterone: This mineralocorticoid is the end product of the RAAS, secreted by the adrenal cortex under the influence of angiotensin II. It acts on the distal tubules to promote sodium retention. While it helps raise blood pressure, it is not the initiating renal hormone.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is B
Explanation
A. It measures the volume of blood plasma only: Osmolality refers to the concentration of particles per kilogram of solvent rather than the total volume of the compartment. Volume is a quantitative measure of space, while osmolality is a qualitative measure of solute density. These are distinct hemodynamic parameters.
B. It is influenced by the balance of solutes and water in the blood: The ratio of dissolved particles, primarily sodium, glucose, and urea, to the volume of water determines the osmotic pressure. High water intake decreases osmolality through dilution. Conversely, water loss through perspiration or diuresis increases the concentration of these solutes.
C. It has no relationship to hydration status: Plasma osmolality is the primary physiological indicator used by the hypothalamus to monitor hydration. Rising osmolality triggers the thirst mechanism and the release of antidiuretic hormone to conserve water. It is the most sensitive marker for systemic water balance.
D. It varies greatly in healthy individuals: Homeostatic mechanisms maintain plasma osmolality within a very narrow range, typically 280 to 295 mOsm/kg. Tight regulation ensures that cells do not experience osmotic shock or volume shifts. Significant variations usually indicate underlying pathological states or severe dehydration.
Correct Answer is A
Explanation
A. PTH, calcitriol, and calcitonin: Parathyroid hormone raises serum calcium, while calcitriol (active Vitamin D) increases intestinal absorption. Calcitonin serves as a minor antagonist to PTH by promoting bone deposition. Together, they regulate the flux of ions between bone, gut, and kidneys.
B. Thyroxine, epinephrine, and norepinephrine: These hormones regulate basal metabolic rate and the sympathetic "fight or flight" response. While they influence overall physiology, they do not possess specific receptors or mechanisms for mineral homeostasis. They do not directly control calcium or phosphate concentrations.
C. Estrogen, testosterone, and aldosterone: Sex steroids influence bone density over time, but they do not provide the acute regulation of mineral balance. Aldosterone is strictly a regulator of sodium and potassium. They lack the rapid feedback loops required to maintain ionized calcium levels.
D. Insulin, glucagon, and cortisol: These hormones are primarily involved in the regulation of carbohydrate, lipid, and protein metabolism. Cortisol can lead to bone loss in chronic excess, but it is not a primary homeostatic regulator. They do not manage the day-to-day phosphate balance.
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