Human Excretion and Kidney Physiology

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.

The kidneys filter blood to produce urine, which travels through ureters to the bladder for storage and exits via the urethra. These organs collectively form the urinary/excretory system, removing metabolic waste from the body.

Dialysis is a medical procedure that artificially removes waste products and excess fluid from blood when kidneys can no longer perform these functions. It acts as an artificial kidney, filtering blood to maintain the body's chemical balance when renal failure occurs.

Jaundice is caused by liver dysfunction when the liver cannot process bilirubin properly, leading to its accumulation. This causes yellowing of skin and eyes (sclera). While jaundice affects eyes and skin visibly, it originates from liver disease or bile duct obstruction. Urine may darken but jaundice is not a disease of urine.

Of the nephron segments listed, the distal convoluted tubule (DCT) has the minimum reabsorption. The proximal convoluted tubule (PCT) reabsorbs about 65% of filtrate, Henle's loop reabsorbs significant water and solutes, while the DCT only fine-tunes electrolyte balance. The collecting duct can reabsorb large amounts of water under ADH influence.

The function of the stomach is to digest food and that of kidney is to excrete waste products.