Question

How is urine produced in the kidneys?

Answer 1

Nephrons are the functional and structural unit of kidneys which play an important role in the production of urine.

Complete answer:
The kidneys play an important role in the excretion of waste from the body in the form of urine. The urine is formed in our body in three phases:

Glomerular filtration: the first step is ultrafiltration or Glomerular filtration. The blood passes through the network of capillaries called the Glomerulus. The blood is then filtered due to the sieve like the fine membrane of the Bowman’s capsule. All the constituents of the plasmas i.e. water, ions, waste produce (urea), and glucose pass into the nephron. The solution entering the nephron is called the ultrafiltrate. While all other proteins and blood cells that cannot pass the membrane remain in the blood.

Reabsorption: About 99% of the filtrate which contains urea, ions, and glucose is reabsorbed by the nephron so that they can be used by the body. This happens most in the proximal convoluted tubule.
Secretion: The next step is the tubular secretion. Here, tubular cells secrete substances like hydrogen ions, potassium ions, etc into the filtrate. The secreted ions combine with the filtrate and form urine by this process, the iconic, acid-base, and the balance of other body fluids are maintained. The urine then passes out of the nephron tubule into a collecting duct.

Note: The urine contains 95% water and 5% is the wastes like urea, ammonia, creatinine, and ions like sodium, potassium, etc. The kidney maintains the osmotic pressure of the blood during the filtration and processing of urine by the process known as osmoregulation.