Human Excretion and Kidney Physiology

The phenomenon of compensatory hypertrophy is seen in regeneration of human kidney and liver.

Calcium oxalate is the primary component of most kidney stones. It precipitates when calcium and oxalate ion concentrations exceed solubility product in urine. These crystals form hard, stony deposits that can obstruct urinary flow. The other compounds are not typical kidney stone constituents.

Epinephrine (adrenaline) is a catecholamine hormone produced by the adrenal medulla. It is not a kidney structure (glomeruli), embryonic tissue (mesoderm), or nephridial part. Options A, B, and D describe anatomical structures incorrectly. Option C correctly identifies epinephrine as an adrenal hormone.

Glucocorticoids like cortisol stimulate gluconeogenesis (formation of glucose from non-carbohydrate sources) in the liver, which enhances overall glucose formation. They also promote protein catabolism to provide amino acid substrates for this process. Options C and D describe mineralocorticoid (aldosterone) effects on sodium balance, not glucocorticoid effects.

Vasopressin (antidiuretic hormone) is produced by the hypothalamus and released by the pituitary. It acts on the kidneys to increase water reabsorption, thereby concentrating urine and conserving body water.

The cells lining the proximal convoluted tubule are well adapted for reabsorption of materials from the filtrate. They have abundant mitochondria and bear numerous microvilli on the free side thus giving brush border appearance.

Angiotensinogen is an a-globulin protein produced by liver. Renin serves as an enzyme in the conversion of the plasma protein angiotensinogen into angiotensin. This protein stimulates the adrenal cortex to produce aldosterone which acts on the cells of the ascending limb of the loop of Henle and increases the rate of reabsorption of Na+.

The renal cortex is the outer portion of the kidney between the renal capsule and the renal medulla. It is the part of the kidney where ultrafiltration occurs. Erythropoietin is produced in the renal cortex.

Intercalated cells come in α and β varieties and participate in acid-base homeostasis.

The kidneys are covered by the peritoneum in the front and on the side and they rest against the abdominal muscles. Their position is slightly asymmetrical, the left kidney being a little higher than the right.

These are pea-sized structures located on the sides of the urethra. These glands produces transparent, slippery fluid which serves to lubricate the urethra and to neutralize the acidity being present due to the drops of urine in the urethra.

A uriniferous tubule/nephron is a long tubule differentiated into four regions: Bowman's capsule, proximal convoluted tubule, loop of Henle and distal convoluted tubule. Collecting ducts are the larger tubes, each receiving the collecting tubules of several nephrons. Collecting duct does not form a part of the uriniferous tubule.

The excretory system in man is formed of one pair of kidneys, a pair of ureters, a urinary bladder and a urethra. The gall bladder is a pear-shaped, hollow structure located under the liver and on the right side of the abdomen.

Elimination of uric acid as the main nitrogenous waste material is called uricotelism. Animals showing uricotelism are called uricotelic animals. It is a common method seen in birds, land reptiles, insects, land snails and some land crustaceans.