Human Excretory System

• Organisms carry out biochemical reactions to produce energy.
• These biochemical reactions taking place in the body may produce toxic wastes, which if accumulated may harm the organism.
• Thus, the process of removal of toxic wastes from the body is important. This removal is called Excretion .

The biological process by which the harmful wastes containing nitrogen are removed from the body is called excretion .

Major waste products produced in the Human body: 

(1) Carbon Dioxide: 

Produced as a waste by the oxidation of food during respiration.

It is removed by lungs .

(2) Urea:

It is produced as a waste by the decomposition of unused proteins in the liver . 

It is removed by the kidneys .

Removal of these wastes is important because their accumulation in the body is poisonous and can harm us. 

Parts of human excretory system :

• Kidneys: 

These are bean-shaped filtration organs , which remove urea, other waste salts and excess water from the blood in the form of urine (yellow liquid waste). 

• Humans have 2 kidneys.
• Each kidney is made up of a large number of excretory units called nephrons .
• Nephrons have a cup shaped bowman's capsule at the upper end. The lower end of the nephron is a tubule.

            Thus, 

Nephron = Bowman's capsule + Tubule

• One end of the tubule is connected to the bowman’s capsule and the other to the urine collecting duct of the kidney.
• Bowman's capsule has a number of small blood capillaries called glomerulus .
• The glomerulus comes from the renal artery bringing blood containing waste and the other connects to the renal vein through the nephron tubule . 
• The renal vein carries clean blood .

• Ureters: 

These are two tubes which carry urine from each kidney , and open into the urinary bladder.

• Urinary bladder: 

A stretchable bag which stores urine until the brain signals to release it.

• Urethra: 

Urine is passed out from the body through the urethra .

Process of Excretion in Humans :

• The function of glomerulus is to filter the blood passing through it.
• It lets substances like glucose, amino acids, salts, water and urea pass into the bowman's capsule and from there into the tubule .
• In the tubule, all useful substances get reabsorbed whereas harmful substances (urea, unwanted salts, excess water ) remain in the tubule.
• The tubule of the nephron then carries these wastes as urine into the collecting ducts of the kidney from where it is taken into the bladder via the ureters.
• This waste is finally removed through the urethra .