Describe the process of urine formation in kidneys.

Explanation

Urine is formed in the kidneys in the nephron , i.e., the structural and functional unit of kidney. Blood at high pressure travels into these tubules by the tuft of blood capillaries called glomerulus.
The following steps are involved in the process
(i) Filtration Blood enters the glomerulus through the afferent arterioles, it passes under pressure that results in filtration of blood . Water and small molecules are forced out of glomerular capillary walls and Bowman's capsule. Large molecules remain in the blood of the glomerulus.
(ii) Selective reabsorption Some molecules are selectively reabsorbed into the blood. The glomerular filtrate flows through the proximal convoluted tubule, the U- shaped Henle's loop and distal convoluted tubule.
The useful substances present such as glucose , amino acids and salts are reabsorbed by a process , which requires energy . The filtrate now contains urea, some salts and The water is then resbsorbed into blood by osmosis (osmoregulation).
(iii) Tubular secretion Some nitrogenous waste products like creatinine and some other substances like `K^(+)` are removed from blood by DCT (Distal convulated tubule), and are added to urine. The urine formed is collection in the urinary bladder.