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The Excretory System

Excretion and its importance


They eliminate nitrogenous wastes from the body and are helpful in maintaining the water balance of the body by removing excess fluids.

The various nitrogenous wastes such as urea, uric acid etc. are supplied from the blood to the kidneys (this is similar to the removal of CO2 from the blood to the lungs). Thus, the basic filtration unit of the excretory system lies in the kidneys.

Structure of kidneys:

Kidneys are reddish brown bean shaped structures which are found in pairs. Each kidney is divided into two parts - an outer dark region called cortex and inner lighter region called medulla. Each kidney has several microscopic tubular structures called nephrons.

The kidneys consist of a cluster of very thin-walled capillaries. Each cluster is associated with a cup-shaped end of a tube, in which filtered urine is collected. These basic filtering units of the kidneys are called nephrons. Each kidney possesses a large number of nephrons (approximately 1- 1.5 million).

Structure of a nephron

The main components of a nephron are the glomerulus, Bowman’s capsule, and a long renal tube. The blood enters the kidneys through the renal artery, which branches into many capillaries associated with the glomerulus. Water and solutes are transferred to the nephron at the Bowman’s capsule.

In the proximal tubule, some substances such as amino acids, glucose, and salts are selectively reabsorbed and unwanted molecules are added in the urine. The filtrate then moves down into the loop of Henle, in which more water is reabsorbed. From here, the filtrate moves upwards into the distal tubule, and final…

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