Excretory System and Kidney Function

Vitamin C (ascorbic acid) is a water-soluble vitamin that is not stored in the body. Excess amounts are excreted through urine in higher vertebrates. Unlike fat-soluble vitamins (A, D, E, K) which can be stored in liver and adipose tissue, Vitamin C requires regular dietary intake as surplus is eliminated renally.

The pungent smell in public urinals is caused by bacterial action. Bacteria (particularly urease-producing bacteria like Proteus mirabilis) convert urea into ammonia through hydrolysis. The ammonia gas produces the characteristic strong odor. Option A is incorrect because uric acid is not the primary source of the smell in this context. Option B is incorrect because the Ornithine cycle (urea cycle) occurs in the liver, not in urinals.

Arginase is the final enzyme in the urea cycle (ornithine cycle) that converts arginine to urea and ornithine in the liver. This is the fifth and final step of urea production. Urease breaks down urea (opposite direction), and uricase acts on uric acid, not urea production.

Micturition is possible only if the muscles of urinary bladder contract and the urethra relaxes.

The proximal convoluted tubule (PCT) is the primary site of glucose reabsorption in the nephron. Nearly 100% of filtered glucose is reabsorbed here via sodium-glucose cotransporters (SGLT2 and SGLT1) and GLUT transporters. The Bowman's capsule is the filtration site, loop of Henle concentrates urine, and distal convoluted tubule handles fine-tuning of electrolyte balance.

Human kidneys develop through three embryological stages: pronephros (transient, non-functional), mesonephros (functional in embryo), and metanephros (permanent, functional adult kidney). Adult humans have metanephric kidneys, which are the most developed and efficient type. Opisthonephros is found in some lower vertebrates like fish and amphibians.

The kidney performs multiple functions including pH regulation (through bicarbonate reabsorption and hydrogen ion secretion), mineral level regulation (sodium, potassium, calcium, phosphate), and urea formation (though urea is primarily produced in liver, kidney regulates its concentration). Erythropoiesis (RBC production) occurs in bone marrow - the kidney secretes erythropoietin that stimulates it, but does not directly perform erythropoiesis.

Glomeruli are the filtration units of the nephron and are located exclusively in the renal cortex. The medulla contains the loops of Henle and collecting ducts, while the pyramidal tissue refers to the renal pyramids in the medulla. The cortex contains the glomeruli, Bowman's capsules, and proximal/distal convoluted tubules.

Blood enters the glomerulus through the afferent arteriole and exits through the efferent arteriole. This unique arrangement (both vessels being arterioles) helps maintain the hydrostatic pressure needed for filtration. The efferent arteriole has smaller diameter than afferent, creating pressure gradient. Renal veins drain blood from the kidney after it passes through peritubular capillaries.

The renal vein carries deoxygenated blood away from the kidney toward the inferior vena cava. The afferent arteriole brings blood TO the glomerulus, and efferent arteriole carries blood away FROM the glomerulus (but still within kidney). Renal portal veins are found in lower vertebrates like birds and reptiles, not mammals. Renal vein is the correct answer for the vessel that 'takes away blood from the kidney.'

Bowman's capsule is the cup-shaped structure that surrounds the glomerulus. It is part of the uriniferous tubule (nephron) and is the site where blood filtration occurs - plasma filters from glomerular capillaries into Bowman's space. Options C and D incorrectly associate it with liver. Option B is incorrect because reabsorption of water and glucose occurs primarily in proximal convoluted tubule, not Bowman's capsule.

The Malpighian corpuscle consists of the glomerulus and Bowman's capsule. It is located in the renal cortex, the outer region of the kidney. The medulla contains the loop of Henle and collecting ducts, while the pelvis is the central funnel-shaped structure.

The ascending limb of loop of Henle is impermeable to water. It actively transports sodium, potassium, and chloride ions from the tubular fluid into the medullary interstitium. Water reabsorption occurs in PCT (proximal convoluted tubule), descending limb (via osmosis), and DCT (distal convoluted tubule, regulated by ADH).

Cockroaches are uricotelic animals, meaning they excrete nitrogenous waste primarily as uric acid. This is an adaptation for water conservation since uric acid is relatively non-toxic and can be excreted as a semi-solid, requiring minimal water. Ammonia is highly toxic and needs dilution, while urea requires some water for excretion.

Marine teleost fish live in a hyperosmotic environment and constantly lose water to their surroundings. They actively excrete excess sodium and chloride ions through specialized cells (chloride cells) in their gills. Kidneys primarily excrete divalent ions like Mg2+ and SO42-, while conserving water by producing small volumes of isotonic urine.