• Important organs involved in homeostasis are kidney and heart
• Functions of kidney:
  • Control the composition of water and salts in the body (osmotic pressure) 
  • Controls blood pH
  • Remove and excrete waste by the formation of urine
• Each kidney consists of millions of nephrons
  • Nephron consists of:
    • Bowman's capsule
    • Loop of Henle
    • Proximal convoluted tubule
    • Glomerulus
    • Distal convoluted tubule
    • Inside the Bowman's capsule, there is a tangled capillary network called glomerulus

Ultrafiltration:

• Afferent arteriole has a larger diameter than the efferent arteriole
• Thus, it results in high pressure on the blood flow in the glomerulus
• This causes certain blood components to filter out into the Bowman's capsule
• The glomerulus filtrate inside the Bowman's capsule is the same as the blood plasma, except it does not contain plasma protein, red blood cells, and platelets

Reabsorption:

• Components in the glomerulus filtrate are water, urea, glucose, amino acids and salt
• Reabsorption occurs when the substances re-enter the blood capillaries along the renal tubule

Secretion:

• Secretion occurs when waste substances are secreted out from the blood capillaries and into the renal tubule (distal convoluted tubule)

Osmoregulation: A process that regulates water and salt balance in the body in order to maintain a normal blood osmotic pressure

• When the water content is more, the salt content is low (low blood osmotic pressure)
• When the salt content is more, water content is low (high blood osmotic pressure)