The Role of Kidneys in the Body

Main Functions of the Kidneys

• Filtration of Blood:
  • Removes waste products from the blood, primarily urea.
  • Urea is produced in the liver via deamination, where excess amino acids are converted to fats and carbohydrates.
• Regulation of Ions and Water:
  • Maintains balance of ions such as sodium and potassium, which are essential for bodily functions.
  • Ion levels if imbalanced can cause cell damage.
  • Natural ion loss occurs through sweating, but primary regulation is by the kidneys.

Water Regulation

• Sources of water:
  • Consumed through food and drink.
  • Lost through skin (sweating), lungs (breathing), and primarily through kidneys (urine).
• Importance of water balance:
  • Cells can burst or shrink due to osmotic water movement.

Structure and Function of Nephrons

• Nephrons:
  • Each kidney contains about a million nephrons.
  • Tubules:
    • Filtration: Absorbs small molecules like water, glucose, amino acids, and urea.
    • Larger molecules like proteins and cells are not absorbed.
  • Selective Reabsorption:
    • Glucose is reabsorbed completely due to its usefulness.
    • Only some water is reabsorbed; urea is not reabsorbed.
    • Analogy: Like cleaning a house – discard everything outside first and then selectively bring back useful items.

Regulation of Water Levels

• Hypothalamus and Pituitary Gland:
  • Hypothalamus detects blood water concentration.
  • If water is low (dehydration), it signals the pituitary gland to release ADH (Antidiuretic Hormone).
  • ADH prompts kidneys to reabsorb more water, producing less urine.
• ADH Regulation:
  • If water levels are too high, hypothalamus stops signaling the pituitary, reducing ADH release.
  • Less ADH means tubules reabsorb less water, increasing urine production.

Negative Feedback Loop

• Homeostasis:
  • Body constantly monitors and adjusts water levels.
  • Ensures balance: When water levels are high, the body reduces them, and vice versa.

Conclusion

• The kidneys play a crucial role in maintaining the balance of waste products, ions, and water in the body through complex mechanisms.