Renin hydrolyzes angiotensinogen, which is released from the _______ to form angiotensin I.
Lungs
Kidneys
Liver
Heart
spleen
The Correct Answer is C
A. Lungs: The lungs are the primary site for the activity of Angiotensin-Converting Enzyme, which transforms angiotensin I into angiotensin II. While they are central to the RAAS pathway, they do not synthesize the precursor protein angiotensinogen. Their role is enzymatic conversion rather than substrate production.
B. Kidneys: The juxtaglomerular cells of the kidneys secrete the enzyme renin in response to low blood pressure. While the kidneys initiate the cascade, they are the source of the enzyme, not the protein substrate angiotensinogen. The kidneys react to the substrate produced by a different organ.
C. Liver: This organ constitutively synthesizes and releases the alpha-2 globulin known as angiotensinogen into the systemic circulation. This protein serves as the essential substrate upon which renin acts to produce angiotensin I. It is the primary biosynthetic source of this precursor molecule.
D. Heart: The heart produces atrial natriuretic peptide in response to atrial stretch, which generally opposes the effects of the RAAS pathway. It does not produce the angiotensinogen required for the initiation of angiotensin I formation. Cardiac tissue is a target rather than a source for this substrate.
E. spleen: The spleen serves primarily as a lymphoid organ and a site for erythrocyte recycling. It does not possess the secretory capacity or the metabolic machinery to produce systemic hormonal precursors like angiotensinogen. It is not a component of the renin-angiotensin-aldosterone system.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is E
Explanation
A. Pyruvate: This 3-carbon carboxylate is the end-product of cytosolic glycolysis. In aerobic conditions, it undergoes oxidative decarboxylation to form acetyl-CoA for entry into the Krebs cycle. It represents a metabolic intermediate rather than the terminal molecular output of respiration.
B. Lactate: Cells produce this conjugate base during anaerobic fermentation when oxygen availability is insufficient. Pyruvate is reduced to lactate to regenerate NAD+ for continued glycolytic flux. It is a marker of anaerobic metabolism and not produced during complete aerobic oxidation.
C. Glucose: This monosaccharide serves as the primary hexose substrate or reactant for the respiratory pathway. It is consumed during the initial stages of phosphorylation to initiate energy extraction. Metabolism focuses on the catabolism of glucose rather than its synthesis as a product.
D. Oxygen: Molecular oxygen acts as the final electron acceptor at complex 4 of the electron transport chain. It is consumed to form water during the reduction process in the inner mitochondrial membrane. As a reactant, its concentration decreases as aerobic respiration proceeds.
E. Carbon dioxide: Aerobic respiration is the process by which cells break down glucose in the presence of oxygen to produce usable energy. The complete chemical reaction is summarized as: 
C6H12O6+6O2→6CO2+6H2O+Energy (ATP). The final products of this reaction are carbon dioxide, water, and ATP. Carbon dioxide is released as a waste product primarily during the Krebs cycle and pyruvate oxidation.
Correct Answer is A
Explanation
A. Kidneys: Antidiuretic hormone primarily targets the principal cells of the collecting ducts and distal convoluted tubules in the nephron. It triggers the insertion of aquaporin-2 water channels into the apical membrane, significantly increasing water reabsorption. This mechanism conserves body water and concentrates the urine to maintain osmolarity.
B. adrenal gland: While the adrenal gland is involved in fluid balance via aldosterone, it is not the primary target of ADH. ADH and aldosterone work through different mechanisms in different regions of the kidney. ADH does not stimulate the secretion of hormones from the adrenal cortex or medulla.
C. anterior pituitary: The anterior pituitary is part of the endocrine signaling cascade but does not serve as an effector organ for ADH. ADH is released from the posterior pituitary and bypasses the anterior lobe to reach its systemic targets. There are no significant ADH receptors located within the adenohypophysis.
D. hypothalamus: The hypothalamus serves as the site of ADH synthesis and contains the osmoreceptors that trigger its release. It acts as the control center rather than the downstream target organ. ADH is secreted into the blood to exert its physiological effects on distant peripheral tissues.
E. pancreas: The pancreas is responsible for regulating blood glucose through the secretion of insulin and glucagon. It does not play a direct role in the homeostatic regulation of water reabsorption or plasma osmolarity managed by ADH. There are no established physiological targets for ADH within the pancreatic tissue.
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