Excretory Products And Their Elimination

Urea is reabsorbed passively by the tubular epithelial cells in various segments of the nephrons. This passive transport mechanism is essential for maintaining osmolarity, as urea moves along with other nitrogenous wastes.

Whenglomerular filtration rate (GFR)is reduced, the kidney activates mechanisms to restore normal filtration pressure and blood volume.Thejuxtaglomerular apparatus (JGA)senses the decrease in perfusion pressure (via the afferent arteriole) and/or reduced sodium chloride delivery to the macula densa. In response, it secretesrenin, which initiates therenin–angiotensin–aldosterone system (RAAS).Here’s what happens next:Reninconverts angiotensinogen (from the liver) intoangiotensin I.Angiotensin-converting enzyme (ACE)converts angiotensin I toangiotensin II.Angiotensin IIcauses vasoconstriction (increasing glomerular pressure) and stimulates secretion ofaldosteronefrom the adrenal cortex.Aldosteroneincreases sodium and water reabsorption, raising blood volume and pressure, which helps restore GFR.So, when GFR decreases:ReninincreasesAngiotensin I and IIincreaseAldosteroneincreases✅Correct answer: Option B“Levels of renin, angiotensin I and II, and aldosterone are increased.”