15 - The Kidneys

Main Functions of the Kidneys

1. Regulation of ECF volume and blood pressure

2. Regulation of osmolarity

3. Maintenance of ion balance

4. Homeostatic regulations of pH

5. Excretion of wastes

6. Production of hormones

1) Regulation of ECF volume and blood pressure

• If ECF volume decreases, blood pressure decreases, and blood flow to brain and organs decreases

• Kidneys work with cardiovascular system to maintain BP and tissue perfusion

2) Regulation of Osmolarity

• Through thirst and drinking

• Reabsorption of water (i.e. producing more concentrated urine)

• Sensors for osmolarity found in hypothalamus and the kidney (macula densa)

3) Maintenance of Ion Balance

Balance dietary intake with urinary loss (Na⁺, Ca²⁺, K⁺, etc.)

4) Homeostatic Regulation

• Kidneys remove H⁺ and conserve HCO₃^- when pH decreases (perform the opposite when pH increases)

• Not as big of a role as the lungs in pH balance

5) Excretion of wastes

Removal of metabolic waste products and foreign substances

Production of Hormones

• Erythropoietin for RBC synthesis

• Renin for Na⁺ balance

• Vitamin D for Ca²⁺ balance