Question 82: Describe the process of urine formation in kidneys.
Answer:
Nephron is composed of two parts renal cortex and renal medulla. Renal cortex is composed of Bowman’s capsule, Proximal convoluted tubule and Distal convoluted tubule and on the other hand, renal medulla is composed of Loop of Henle.
Urine formation occurs in kidneys and involves three processes:- Glomerular filtration, tubular reabsorption and tubular secretion.
1. Glomerular filtration:- Bowman’s capsule is a double walled cup present at the starting of the nephron structure and lies in the renal cortex. Capsule encloses a cluster of blood vessels known as glomerulus. The Bowman’s capsule and the glomerulus (group of almost 50 capillaries) together form the Renal corpuscle or also known as Malpighian body. The inner wall of the Bowman’s capsule has wide gaps called slit pores. So, the basement membrane of the capillary walls is present in between the blood in the glomerulus capillaries, helping in the ultrafiltration.
2. Tubular reabsorption:- From the Bowman’s capsule, the glomerular filtrate passes into the tubules and flows through it to the collecting ducts. Selective reabsorption of nutrients like glucose, amino acids, salts and an excessive amount of water process occurs when urine flows along the tube. It contains distal convoluted tubule in which When the amount of water or any fluid get increased above the normal amount, then ultra-filtration process will be increase due to
increase in blood pressure of the glomerulus. Then this sends the signal to the brain or the hypothalamus to stop the release of the hormone vasopressin or antidiuretic hormone (ADH) which automatically helps in the regulation of the amount of the urine. ADH hormone deficiency slows down the permeability of the cells of the distal convoluted tubule and collects duct that decrease re-absorption of water.
3. Tubular secretion:- In this the waste, foreign substances or hydrogen ions and ammonia are actively secreted into the filtrate in the proximal convoluted tubule. These substances combine with the remaining filtrate and form urine. Then the urine flows out from nephron tubules to the collecting ducts and passes out of the kidneys through the renal pelvis then into the ureter and down to the urethra.
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