Excretory Products and Their Elimination: questions with answers

The renal pelvis is the broad funnel-shaped space inner to the hilum and receives the calyces. The tough capsule covers the outside, the cortex lies beneath it, and the medulla lies further inward around the collecting region.

A long loop extending deep into the medulla with a developed vasa recta identifies a juxtamedullary nephron. Its renal corpuscle, PCT and DCT nevertheless remain in the cortical region; the loop is the part that dips into the medulla.

The primary function of sweat is to cool the body surface. Sweat also helps eliminate water, sodium chloride and small amounts of urea and lactic acid. This accessory role does not make sweat chiefly a urea-excretion mechanism, nor does it make kidneys the only excretory organs.

Micturition is a neural reflex involving bladder-wall stretch receptors, CNS signalling and voluntary CNS control. Urine release requires contraction of bladder smooth muscle together with relaxation of the urethral sphincter. Normal urine is watery and slightly acidic at about pH 6.0.

Glomerular capillary pressure filters through endothelium, basement membrane and Bowman's-capsule epithelium with filtration slits. Almost all plasma constituents except proteins pass into the lumen; the approximately 125 mL min⁻¹ formed is filtrate, not the much smaller final urine output.

A fall in GFR activates juxtaglomerular cells to release renin. In the chapter's account, renin helps stimulate glomerular blood flow and return GFR toward normal; this feedback is distinct from tubular secretion of ions or ammonia.

The DCT is a conditional rather than invariant site for sodium and water reabsorption; it also helps acid-base and ionic balance. The collecting duct can reclaim large amounts of water, let some urea enter the medullary interstitium, and secrete H+ and K+.

The PCT performs bulk reabsorption, including nearly all essential nutrients and about 70–80% of electrolytes and water. Water leaves the descending limb, whereas electrolytes leave the water-impermeable ascending limb, so descending filtrate concentrates and ascending filtrate dilutes.

Counter current refers to opposite directions in paired limbs of Henle's loop and likewise of the vasa recta. This arrangement helps maintain a corticomedullary gradient rising approximately 300→1200 mOsmol L⁻¹, with NaCl and urea as the principal solutes described.

Vasa-recta exchange limits NaCl washout by returning salt to the medullary interstitium, while urea also recycles through the described tubular route. Retained solute maintains the osmotic gradient, which facilitates water passage from the collecting tubule and supports urine approaching four times initial-filtrate concentration.

A fall in glomerular flow, pressure or GFR activates JG cells to release renin and leads to angiotensin II. Angiotensin II raises pressure and promotes aldosterone-mediated distal sodium-water reabsorption; ANF opposes this response through vasodilation and reduced blood pressure.

Uremia is harmful accumulation of urea in blood. Because nitrogenous wastes are absent outside the tube, they move out of blood across the porous membrane down their concentration gradients. The process clears the blood of wastes; it does not transfer whole blood cells into the fluid.

In the textbook dialysis model, uremia is accumulation of urea in blood when kidney function is impaired. Small waste molecules pass across the dialysis membrane down concentration gradients, while blood cells remain in the blood. The chapter describes heparin before blood enters the unit and an anti-heparin step before it returns. This is the simplified sequence tested here, not a complete clinical dialysis protocol.

mammals are listed as mainly ureotelic. Metabolic ammonia is converted to urea in the liver, released into blood and then filtered and excreted by the kidneys.

Ammonia is the most toxic major nitrogenous waste and needs much water. Many bony fishes generally diffuse it across body or gill surfaces with no significant kidney role, while marine fishes are listed among mainly ureotelic animals.