Revision: Class 11 >> Excretory Products and Their Elimination NEET (UG) Excretory Products and Their Elimination

During different metabolic activities taking place in our body, the body produces many substances, of which some are useful and some are useless.
The process of removing useless and harmful metabolic waste substances is called excretion.

The process of removal of chemical wastes (Mainly Nitrogenous) from the body is known as ''excretion''. It plays an important role in maintaining the homeostatic (steady-state) condition of the body.

Kidneys are the primary excretory organs, eliminating nitrogenous wastes (chiefly urea) from the blood and throwing it out in the form of urine.

During different metabolic activities taking place in our body, the body produces many substances of which some are useful and some are useless.
If retained in the body the unwanted substances may become poisonous and cause much harm and in severe cases, even death. The organs which remove these unwanted and toxic substances from the body are called excretory organs.

The blood flows through the glomerulus under great pressure which causes the liquid part of the blood to filter out from the glomerulus into the renal tubule. This filtration under high force is called Ultrafiltration.

Glomerular filtration rate is the amount of glomerular filtrate formed in all the nephrons of both kidneys per minute. In a healthy individual, it is about 125 ml/minute.

The artificial process which cleans and filters the blood in a person where one or both the kidney may stop working properly is called dialysis.

Inside the kidney, there are millions of microscopic tubes called renal tubules or nephrons. It is the structural and functional unit of the kidney.

Ultrafiltration is the process in which blood is filtered under high pressure in the glomerulus, allowing water and small solutes to pass into the Bowman’s capsule.

Glomerular filtrate is the fluid formed after ultrafiltration that enters the renal tubule and contains water, urea, salts, glucose, and other small molecules.

Selective absorption is the process by which only useful substances like glucose, some salts, and water are absorbed from the renal tubule back into the blood, without disturbing its normal concentration.

Tubular secretion is the active transfer of certain substances, such as ions and drugs, from the blood into the renal tubule during urine formation.

• The human excretory system consists of a pair of kidneys, two ureters, a urinary bladder and a urethra.
• Kidneys are dark red, bean-shaped, retroperitoneal structures located from the 12th thoracic to the 3rd lumbar vertebra. Size: 10-12 cm × 5-7 cm × 2-3 cm; weight: 150 g (males), 135 g (females).
• Ureters are narrow tubular structures made of transitional epithelium that carry urine from the kidneys to the urinary bladder.
• The urinary bladder is a pear-shaped, hollow, muscular organ in the pelvic cavity, lined by transitional epithelium, and acts as a reservoir of urine.
• Two sphincters exist between the bladder and the urethra: the internal sphincter (involuntary, detrusor muscles) and the external sphincter (voluntary, striated muscles).
• The urethra is a canal-like structure that opens to the exterior via the urethral orifice, much longer in males than in females.
• The aorta supplies oxygenated blood to the kidneys; the inferior vena cava carries deoxygenated blood away from the kidneys.

• Besides kidneys, organs like skin and lungs also help in the excretion of waste products.
• Sweat glands in the skin excrete water, salts (NaCl), urea, and lactic acid, and also help in thermoregulation.
• Sebaceous glands secrete sebum, which lubricates and protects the skin from infection and damage.
• Lungs excrete carbon dioxide (CO₂) and water vapour produced during cellular respiration.
• Thus, skin and lungs assist in the removal of wastes and help maintain the internal balance of the body.