Kidneys and nephron function, excretion, osmoregulation

1. Introduction to the Excretory System

1. The excretory system is responsible for the removal of metabolic wastes from the body.
2. Major excretory products include urea, uric acid, ammonia, carbon dioxide, and excess salts.
3. The main organs involved in excretion are the kidneys, lungs, liver, and skin.

2. Structure of the Human Kidney

1. Humans have a pair of bean-shaped kidneys, located in the abdominal cavity.
2. Each kidney is covered by a protective layer called the renal capsule.
3. The kidney consists of three major parts:
   • Cortex: Outer part containing nephrons.
   • Medulla: Inner part containing renal pyramids.
   • Pelvis: Central cavity where urine collects before moving to the ureter.

3. Nephron: The Functional Unit of the Kidney

1. A nephron is the basic structural and functional unit of the kidney.
2. Each kidney contains approximately 1.2 million nephrons.
3. Nephron consists of:
   • Bowman’s Capsule: A cup-shaped structure surrounding the glomerulus.
   • Glomerulus: A network of capillaries where filtration occurs.
   • Proximal Convoluted Tubule (PCT): Reabsorbs nutrients, water, and ions.
   • Loop of Henle: Helps in concentrating urine by reabsorbing water and salts.
   • Distal Convoluted Tubule (DCT): Further regulates ion balance and pH.
   • Collecting Duct: Collects urine and transports it to the renal pelvis.

4. Function of the Nephron

1. The nephron plays a key role in the process of urine formation.
2. Filtration: Blood is filtered in the glomerulus; large molecules like proteins remain in the blood.
3. Reabsorption: Useful substances like glucose, amino acids, and water are reabsorbed in the tubules.
4. Secretion: Additional waste products like hydrogen ions and potassium ions are secreted into the tubules.
5. Excretion: The final urine is collected and passed to the ureter.

5. Urine Formation

1. Urine formation occurs in three steps:
   • Glomerular Filtration: Blood pressure forces small molecules into the Bowman’s capsule.
   • Tubular Reabsorption: Essential substances are reabsorbed into the blood.
   • Tubular Secretion: Additional waste materials are actively secreted into the nephron.
2. The average urine output per day is about 1.5 liters.
3. The primary component of urine is water (95%), with urea, salts, and other waste materials.

6. Role of the Kidneys in Osmoregulation

1. Osmoregulation is the regulation of water and ion balance in the body.
2. The kidneys regulate blood pressure, blood volume, and pH levels.
3. Antidiuretic Hormone (ADH) controls the amount of water reabsorbed in the collecting duct.
4. When water levels are low, ADH increases, causing more water reabsorption and concentrated urine.
5. When water levels are high, ADH decreases, causing less water reabsorption and diluted urine.
6. Aldosterone regulates sodium and potassium levels, affecting water retention.

7. Excretory Organs Other than Kidneys

1. Lungs: Expel carbon dioxide and water vapor.
2. Liver: Converts ammonia into urea (urea cycle).
3. Skin: Removes excess salts and water through sweat.
4. Intestines: Excrete undigested food and metabolic waste.

8. Disorders of the Excretory System

1. Kidney Stones: Hard mineral deposits in the kidney causing severe pain.
2. Urinary Tract Infection (UTI): Bacterial infection in the urinary system.
3. Renal Failure: Loss of kidney function, requiring dialysis or transplant.
4. Gout: Excess uric acid leading to joint inflammation.

9. Dialysis: Artificial Kidney

1. Dialysis is a process that removes waste products from the blood when the kidneys fail.
2. There are two types:
   • Hemodialysis: Blood is filtered through an external machine.
   • Peritoneal Dialysis: Uses the lining of the abdominal cavity to filter blood.
3. Kidney transplant is a permanent solution for kidney failure.

10. Summary of the Excretory System

11. Conclusion

1. The excretory system plays a vital role in maintaining body balance.
2. Kidneys and nephrons ensure proper filtration and excretion.
3. Osmoregulation helps maintain water and ion balance in the body.
4. A healthy lifestyle helps prevent kidney diseases.