What is the best explanation for the microvilli on the apical surface of the proximal convoluted tubule (PCT)?
Their movements propel the filtrate through the tubules.
They move materials from the filtrate to the blood plasma
They increase the surface area and allow for a greater volume of filtrate components to be reabsorbed.
They hold on to enzymes that cleanse the filtrate before reabsorption.
They increase the amount of surface area that comes in contact with the blood's plasma to help actively excrete toxins.
The Correct Answer is C
A. Their movements propel the filtrate through the tubules. Cilia, not microvilli, possess the microtubule structure required for active propulsion of fluid. Microvilli are non-motile extensions of the plasma membrane designed for absorption rather than mechanical movement. The flow of filtrate through the nephron is primarily driven by hydrostatic pressure gradients.
B. They move materials from the filtrate to the blood plasma. While the proximal convoluted tubule performs significant reabsorption, the microvilli themselves represent a structural adaptation rather than a functional transport mechanism. Transport of solutes across the membrane relies on specific carrier proteins and ion channels. This choice identifies the general function but ignores the primary structural purpose.
C. They increase the surface area and allow for a greater volume of filtrate components to be reabsorbed. The brush border significantly expands the total apical surface area available for transmembrane transport proteins. This allows for the reabsorption of approximately 65 percent of the glomerular filtrate, including glucose and amino acids. Increased surface area is essential for high-capacity obligatory water and solute recovery.
D. They hold on to enzymes that cleanse the filtrate before reabsorption. The primary function of the proximal convoluted tubule is metabolic recovery and secretion rather than enzymatic cleansing of the lumen. While some membrane-bound enzymes exist, they do not define the structural necessity of the brush border. Most processing occurs via endocytosis or specialized transport.
E. They increase the amount of surface area that comes in contact with the blood's plasma to help actively excrete toxins. The apical microvilli face the tubular lumen and the filtrate, not the peritubular capillaries containing blood plasma. Excretion of toxins occurs via secretion from the blood across the basolateral membrane and then through the apical surface. The microvilli facilitate movement into the lumen.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is D
Explanation
A. decrease the production of aldosterone: Angiotensin 2 serves as the primary secretagogue for the zona glomerulosa of the adrenal cortex. It directly stimulates the synthesis and release of aldosterone to enhance sodium retention. Increasing aldosterone is a vital step in the homeostatic response to low blood pressure.
B. decrease water absorption: This effector molecule promotes water retention by stimulating thirst centers in the hypothalamus and increasing the release of antidiuretic hormone. It also enhances sodium reabsorption in the proximal tubule, which creates an osmotic gradient for water. These actions collectively increase total body water volume.
C. decrease arterial blood pressure: Angiotensin 2 is one of the most potent endogenous vasoconstrictors known in human physiology. Its primary systemic effect is to increase peripheral resistance and venous return to elevate blood pressure. Decreasing pressure would contradict the corrective goals of the renin-angiotensin-aldosterone system.
D. constrict arterioles and increase blood pressure: By binding to AT1 receptors on vascular smooth muscle, angiotensin 2 induces rapid systemic vasoconstriction. This increases systemic vascular resistance and immediately raises arterial blood pressure to maintain organ perfusion. It specifically targets the efferent arterioles to maintain glomerular filtration during hypotension.
E. increase the production of ADH: While angiotensin 2 does stimulate the posterior pituitary to release antidiuretic hormone, choice D is the most direct and comprehensive description of its primary cardiovascular function. ADH works synergistically with angiotensin 2 to restore blood volume and pressure. Both are essential for long-term hemodynamic stability.
Correct Answer is B
Explanation
A. is easily broken and replaced often: The epithelial cells of the nephron loop are durable and maintained through normal cellular repair mechanisms. They are not designed to be "broken" or frequently replaced as a standard part of renal function. The structural integrity of the tubule is essential for maintaining the osmotic gradients in the medulla.
B. aids in the passive movement of water out of the tubule: The descending limb of the nephron loop is composed of simple squamous epithelium that is highly permeable to water but relatively impermeable to solutes. As filtrate descends into the hypertonic renal medulla, water moves out of the tubule by osmosis. This process significantly concentrates the tubular fluid.
C. aids in the passive excretion of nitrogenous waste: The primary role of the thin descending limb is water conservation rather than the excretion of wastes like urea or creatinine. Nitrogenous waste excretion occurs primarily through filtration at the glomerulus and secretion in the convoluted tubules. The loop focuses on the concentration and dilution of urine.
D. helps to pack a greater number of nephron loops into a smaller space: The thinness of the segment refers to the height of the epithelial cells (simple squamous) rather than the overall diameter of the tube for packing purposes. This anatomical design is a functional adaptation for rapid osmotic diffusion. It allows for the concentration of urine without requiring active transport in this segment.
Whether you are a student looking to ace your exams or a practicing nurse seeking to enhance your expertise , our nursing education contents will empower you with the confidence and competence to make a difference in the lives of patients and become a respected leader in the healthcare field.
Visit Naxlex, invest in your future and unlock endless possibilities with our unparalleled nursing education contents today
Report Wrong Answer on the Current Question
Do you disagree with the answer? If yes, what is your expected answer? Explain.
Kindly be descriptive with the issue you are facing.