⚡ Quick Revision: The Concept of Excretion
Excretion is the process of removing toxic metabolic waste products (like urea, uric acid, and excess salts) from the body to maintain internal balance (homeostasis).
Primary Excretory Organs
- 1 Kidneys: The main excretory organs that filter blood to produce urine.
- 2 Skin: Eliminates excess water and salts through sweat glands.
- 3 Lungs: Remove carbon dioxide (CO₂) and water vapor during exhalation.
⚡ Quick Revision: The Human Urinary System
The urinary system consists of organs that produce, store, and eliminate urine. It is the body's primary filtration plant.
Components of the Urinary System
- 1 Kidneys: Two bean-shaped organs located on either side of the backbone. They filter nitrogenous wastes from the blood.
- 2 Ureters: Two narrow tubes that carry urine from the kidneys to the urinary bladder.
- 3 Urinary Bladder: A muscular sac that stores urine temporarily until it is expelled.
- 4 Urethra: A canal through which urine is passed out of the body.
The right kidney is slightly lower than the left kidney because of the space occupied by the liver on the right side.
⚡ Quick Revision: The Nephron & Urine Formation
Each kidney contains millions of microscopic filtering units called Nephrons. They are the functional units of the kidney.
Structure of a Nephron
- A Bowman's Capsule: A cup-shaped structure that encloses a cluster of blood capillaries called the Glomerulus.
- B Renal Tubule: A long, coiled tube where essential substances are reabsorbed back into the blood.
Steps in Urine Formation
1. Ultrafiltration: Blood flows through the glomerulus under high pressure, filtering water and small molecules into the Bowman's capsule.
2. Selective Reabsorption: As the filtrate travels through the tubule, useful substances like glucose, amino acids, and water are taken back by the blood.
3. Secretion & Excretion: The remaining fluid, containing urea and excess salts, becomes Urine and moves to the collecting duct.
⚡ Quick Revision: Disorders and Dialysis
When the kidneys fail to function properly, metabolic wastes build up in the blood, leading to a life-threatening condition called Uremia.
Common Excretory Disorders
- ✔ Kidney Stones: Hard deposits of minerals (like calcium oxalate) that block the flow of urine.
- ✔ Urinary Tract Infection (UTI): Bacterial infection in any part of the urinary system.
- ✔ Kidney Failure: The total or partial inability of kidneys to filter waste from the blood.
Artificial Kidney (Hemodialysis)
Dialysis is a medical procedure used to filter the blood of a patient whose kidneys have failed. It uses a machine to perform the functions of a healthy kidney.
The patient's blood is passed through a machine containing semi-permeable tubes. Waste products move from the blood into a dialyzing fluid by the process of diffusion, and the "clean" blood is pumped back into the body.