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 A
Explanation
A. Kidney perfusion will increase. When systemic mean arterial pressure drops below 80 mmHg, the resulting activation of the renin-angiotensin-aldosterone system leads to potent vasoconstriction. Angiotensin 2 constricts renal arterioles to divert blood to the brain and heart, which actually decreases total renal blood flow and perfusion. Increased perfusion would only occur if systemic pressure were restored or resistance lowered.
B. Blood plasma and extracellular fluids volume will increase. Renin initiates the cascade producing aldosterone and antidiuretic hormone, which promote the retention of sodium and water in the collecting ducts. This physiological response is designed to expand the intravascular and interstitial fluid compartments to compensate for hypotension. The ultimate goal is to restore circulating volume and systemic blood pressure.
C. Glomerular filtration rate (GFR) will decrease. A significant drop in mean arterial pressure reduces the hydrostatic pressure within the glomerular capillaries. Despite local autoregulatory efforts, such as efferent arteriole constriction, the net filtration pressure falls, leading to a diminished volume of filtrate. This reduction in the filtration rate is a protective measure to conserve body fluids.
D. Net filtration pressure (NFP) will decrease. Net filtration pressure is the sum of forces promoting filtration minus those opposing it. Since the glomerular hydrostatic pressure is the primary driver and is directly dependent on systemic blood pressure, a drop in mean arterial pressure reduces this outward force. Consequently, the overall pressure gradient driving fluid into the capsular space is weakened.
Correct Answer is E
Explanation
A. urethra: This terminal duct of the male reproductive system serves a dual purpose by transporting both urine and semen. It is divided into prostatic, membranous, and spongy segments. As the final conduit for ejaculation, it is an essential component of the male reproductive ductal network.
B. ductus deferens: Also known as the vas deferens, this muscular tube propels sperm from the epididymis toward the ejaculatory duct during sexual arousal. It travels within the spermatic cord and enters the pelvic cavity via the inguinal canal. It represents a major segment of the internal duct system.
C. seminiferous tubules: These tightly coiled structures within the testicular lobules are the site of spermatogenesis. While they are the initial location where sperm are formed, they function as the beginning of the ductal pathway. They lead directly into the tubuli recti and the rete testis.
D. epididymis: This comma-shaped organ stores immature sperm and provides the environment for them to acquire motility and fertility. It consists of a highly coiled duct that connects the efferent ductules to the ductus deferens. It is a vital intermediary in the male reproductive tract.
E. corpus spongiosum: This is a column of erectile tissue that surrounds the spongy urethra within the penis. Its primary function is to prevent the compression of the urethra during an erection, ensuring a patent pathway for ejaculation. It is an anatomical erectile body rather than a duct.
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