Which structural feature of the glomerular filtration barrier prevents proteins and blood cells from entering Bowman's capsule?
Semipermeable walls of the renal tubule
Absence of blood supply in Bowman's capsule
Active protein pumps
Podocyte processes and capillary endothelial fenestrations
The Correct Answer is D
A. Semipermeable walls of the renal tubule: Reabsorption and secretion occur across the tubular walls, but the initial barrier to protein entry is located within the renal corpuscle. By the time fluid reaches the tubules, it should already be an ultrafiltrate. The tubules do not perform primary filtration.
B. Absence of blood supply in Bowman's capsule: Bowman's capsule is intimately associated with the glomerulus, which is a high-density capillary network. It receives a massive blood supply specifically to facilitate filtration. The absence of blood would mean no filtrate or urine could ever be produced.
C. Active protein pumps: The filtration of blood at the glomerulus is a passive process driven by hydrostatic and oncotic pressures. There are no active metabolic pumps that move proteins against a gradient in the filtration barrier. The exclusion of protein is based on size and charge.
D. Podocyte processes and capillary endothelial fenestrations: The three-layered barrier consists of fenestrated endothelium, the glomerular basement membrane, and podocyte slit diaphragms. These structures provide a mechanical sieve and a negative charge. They prevent the passage of large cells and anionic plasma proteins like albumin.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is A
Explanation
A. Sodium and potassium: These cells represent the primary site for aldosterone-mediated electrolyte regulation in the distal nephron. They utilize apical sodium channels and potassium channels to facilitate sodium reabsorption and potassium secretion. This mechanism is critical for maintaining systemic fluid balance and normokalemia.
B. Glucose and urea: Glucose reabsorption occurs almost exclusively in the proximal convoluted tubule via specialized sodium-glucose cotransporters. While the medullary collecting ducts are permeable to urea under certain conditions, principal cells do not regulate its transport. Their metabolic machinery is specialized for ion and water homeostasis.
C. Bicarbonate and chloride: Acid-base balance and bicarbonate transport are the primary functions of intercalated cells, which are distinct from principal cells. While chloride often follows sodium passively, principal cells do not actively regulate its concentrations. Intercalated cells manage the secretion of hydrogen and bicarbonate ions.
D. Calcium and phosphate: The regulation of these minerals occurs primarily in the proximal tubule and the distal convoluted tubule under parathyroid hormone influence. Principal cells lack the specific receptors and transporters required for significant calcium or phosphate handling. Their role is restricted to water and monovalent cation transport.
Correct Answer is A
Explanation
A. ADH: Arginine vasopressin is released from the posterior pituitary when baroreceptors detect a significant decrease in mean arterial pressure or blood volume. It increases the water permeability of the collecting ducts. This facilitates rapid water recovery to restore systemic hemodynamics.
B. Renin: This enzyme is secreted by the juxtaglomerular cells to initiate the angiotensin cascade. While it eventually leads to water retention via aldosterone, renin itself is a proteolytic enzyme, not a hormone that directly recovers water. It is a catalyst for the system.
C. Aldosterone: This hormone promotes water recovery indirectly by increasing the active reabsorption of sodium. While it is vital for volume expansion, its primary direct target is the sodium ion. ADH remains the primary hormone for direct, regulated water recovery via aquaporins.
D. ANP: Atrial natriuretic peptide is released in response to atrial stretch caused by high blood volume. It functions to increase the excretion of sodium and water to reduce blood pressure. It is an antagonist to the volume-conserving effects of ADH.
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