The fluid in glomerular capsule is similar to plasma except that it does NOT contain a significant amount of
hormones
plasma protein
glucose
electrolytes
The Correct Answer is B
A. hormones: Most small hormones, particularly steroid and peptide hormones not bound to large carrier proteins, are small enough to pass through the filtration membrane. They are often found in the initial filtrate in the capsular space. Their presence does not distinguish filtrate from plasma significantly.
B. plasma protein: The basement membrane and filtration slits are negatively charged and sized to repel large proteins like albumin. Consequently, the filtrate is essentially protein-free under normal conditions. The absence of these macromolecules is the primary chemical difference between plasma and glomerular filtrate.
C. glucose: Glucose is a small, uncharged molecule that moves freely across the filtration membrane into the capsular space. The concentration of glucose in the initial filtrate is identical to its concentration in the plasma. It is later reabsorbed entirely by the proximal convoluted tubules.
D. electrolytes: Ions such as sodium, potassium, and chloride are small enough to pass through the fenestrated capillaries and filtration slits without restriction. The electrolyte composition of the glomerular filtrate initially mirrors that of the blood plasma. Their balance is adjusted later during tubular processing.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is D
Explanation
A. is not reabsorbed by the tubule cells: While some substances like mannitol act as osmotic diuretics because they remain in the tubule lumen, alcohol follows a different physiological pathway. Alcohol is a lipid-soluble molecule that can diffuse across membranes rather than relying on tubular transport inhibition. Its diuretic effect is neuroendocrine in origin rather than purely osmotic.
B. increases the rate of glomerular filtration: Although alcohol can cause minor changes in systemic blood pressure, it does not significantly increase the glomerular filtration rate as its primary mode of action. A slight increase in flow would not account for the profound volume of dilute urine produced. The primary diuretic effect occurs later in the distal segments of the nephron.
C. increases secretion of ADH: Increased secretion of antidiuretic hormone would result in the insertion of aquaporins and the retention of water, leading to concentrated urine. This is the opposite of the clinical effect observed with alcohol consumption. Stimulating ADH would prevent diuresis rather than promote it, leading to fluid volume expansion.
D. inhibits the release of ADH: Ethanol directly suppresses the hypothalamic-hypophyseal tract, reducing the secretion of antidiuretic hormone from the posterior pituitary. Without ADH, the collecting ducts remain impermeable to water, preventing reabsorption and resulting in the excretion of large volumes of dilute urine. This inhibition is the primary cause of alcohol-induced dehydration.
Correct Answer is D
Explanation
A. antidiuretic hormone: This hormone acts primarily on the principal cells of the collecting ducts to increase water permeability via aquaporin insertion. It does not directly stimulate the macula densa cells. The macula densa is part of the feedback loop that regulates the filtration rate.
B. changes in pressure in the tubule: Pressure changes are primarily sensed by the granular cells of the afferent arteriole, which act as baroreceptors. The macula densa cells are specialized chemoreceptors rather than mechanoreceptors. They monitor the chemical composition of the fluid rather than its physical pressure.
C. aldosterone: This steroid hormone acts on the distal tubules and collecting ducts to increase sodium reabsorption and potassium secretion. It is a downstream product of the renin-angiotensin-aldosterone system. It does not serve as a primary stimulus for the macula densa chemoreceptors.
D. changes in Na+ content of the filtrate: Macula densa cells are located in the distal ascending limb and monitor the concentration of sodium chloride in the filtrate. High salt levels indicate a high filtration rate, triggering tubuloglomerular feedback. This causes afferent arteriole vasoconstriction to reduce the glomerular filtration rate.
E. renin concentration: Renin is an enzyme secreted by the granular cells in response to signals from the macula densa. Therefore, renin is an output of the juxtaglomerular apparatus rather than the stimulus for the macula densa. These cells initiate the cascade that leads to renin release.
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