Question

The structure and functional unit of the kidney are ________________________.

Answer 1

Kidneys are two bean shaped organs of the human excretory system. Kidneys consist of millions of microscopic structural and functional units called nephrons.

Complete answer:
Each human kidney comprises about one million of nephrons, which is said to be its structural and functional units. The function of nephron is to produce urine during the removal of waste and excess toxic substances from the blood.
Nephron consists of Malpighian corpuscles and renal tubules. The Malpighian or renal corpuscles is made up of tufts of capillaries called glomerulus and a double layered cup shaped structure called Bowman’s capsule. Blood enters the glomerulus through an afferent arteriole and leaves it through an efferent arteriole.
Renal tubule is a long, convoluted tube that emerges from glomerulus and it consists of Proximal Convoluted Tubule (PCT), Loop of Henle and Distal Convoluted Tubule (DCT). PCT is lined by cuboidal epithelial cells that bears a brush border of tall microvilli which increases the surface area. It helps in the reabsorption of salts by active transport. The loop of Henle consists of descending limb and an ascending limb.
The descending limb is permeable to water but impermeable to an electrolyte, while the ascending limb is permeable to electrolytes but impermeable to water. DCT is the last part of the nephron and is lined by the cuboidal cells. It collects and empties the contents into the collecting duct. It also maintains the pH, sodium and potassium level balance in the blood cells.

Note: Depending upon the location, nephrons can be of two types: juxtamedullary and cortical nephrons. Juxtamedullary lies close to the inner matrix of the cortex whereas the cortical nephron lies in the outer cortex.