Question

Describe in brief how urine is produced in human body.

Answer 1

Excretory system:

1. Kidney: It is the main excretory organ in the human body. The kidney is made up of nephron or kidney tubules. Nephron is the structural and functional unit of the kidney. The nephron filters the blood and forms urine.
2. The parts of the nephron are glomerulus, Bowman’s capsule, PCT (proximal convoluted tubule), Loop of Henle, DCT (distal convoluted tubule), and collecting duct.
3. The mechanism of urine formation involves the following steps:
4. Glomerular Filteration:-
5. Glomerular filtration occurs in the glomerulus where blood is filtered. This process occurs across the three layers- epithelium of Bowman’s capsule, endothelium of glomerular blood vessels, and a membrane between these two layers.
6. Each nephron has a glomerulus, the site of blood filtration.
7. The glomerulus is a network of capillaries surrounded by a cup like structure, the Bowman’s capsule.
8. As blood flows through the glomerulus, blood pressure pushes water and solutes from the capillaries into the capsule through a filtration membrane. This glomerular filtration begins the urine formation process.
9. The nephrons of the kidneys process blood and create urine through a process of filtration, reabsorption, and secretion. Urine is about 95% water and 5% waste products.
10. Nitrogenous wastes excreted in urine include urea, creatinine, ammonia, and uric acid. Ions such as sodium, potassium, hydrogen, and calcium are also excreted.
11. Urine produced in the kidneys travels down the ureters into the urinary bladder. The bladder expands like an elastic sac to hold more urine.
12. As it reaches capacity, the process of micturition, or urination, begins. Involuntary muscle movements send signals to the nervous system, putting the decision to urinate under conscious control.
13. The internal urethral sphincter and the external urethral sphincter both provide muscle control for the flow of urine.
15. Reabsorption:-Around 99 percent of the filtrate obtained is reabsorbed by the renal tubules. This is known as reabsorption. This is achieved by active and passive transport.
16. Secretion:- The next step in urine formation is tubular secretion. Here, tubular cells secrete substances like hydrogen ions, potassium ions, etc into the filtrate. Through this process, the ionic, acid-base, and the balance of other body fluids are maintained. The secreted ions combine with the filtrate and form urine. The urine passes out of the nephron tubule into a collecting duct.