Describe the structure and functioning of nephrons.

Explanation

The nephron has a cup-shaped bag at its upper end which is called Bowman's capsule. The lower end of Bowman's capsule is tube-shaped and it is called a tubule. The Bowman's capsule and the tubule taken together make a nephron (Each kidney has about 1 million nephrons). One end of the tubule is connected to

Bowman's capsule and its other end is connected to a urine-collecting duct of the kidney. The Bowman's capsule contains a bundle of capillaries which is called glomerulus. One end of glomerulus is attached to renal artery which brings the dirty blood containing the urea waste in it. The other end of glomerulus comes out of Bowman's capsule as a blood capillary, surrounds the tubule of nephron and finally joins a renal vein (putting urea-free clean blood into it). The function of glomerulus is to filter the blood passing through it.
The dirty blood containing waste like urea (brought by renal artery) enters the glomerulus. The glomerulus filters this blood. During filtration, the substances like glucose, amino acids, salts, water and urea, etc., present in the blood pass into Bowman's capsule and then enter the tubule of nephron. When the filtrate containing useful substances as well as the waste substances through the tubule, then the useful substances like all glucose, all amino acids, most salt, and most water, etc., are reabsorbed into the blood through blood capillaries surrounding the tubule. Only the waste substances urea, some unwanted salts and excess water remain behind in the tubule. The liquid left behind in the tubule of nephron is urine. The nephron carries this urine into the collecting duct of the kidney from where it is carried to ureter. From the ureter, urine passes into urinary bladder. Urine is stored in the bladder for some time ultimately passed out of the body through urethra.