Urinary System

• 1. Excretion (unwanted substances)
• 2. maintenance of water & electrolytes 
• 3. pH regulation of body fluids
• 4. Production of hormones
• 5. Regulation of RBC's production
• 6. Regulation of blood glucose levels
• 7. Regulation of blood pressure volume & osmolarity

• 1. Angiotensin II
• 2. Aldosterone
• 3. Antidiuretic hormone
• 4. Atrial natriuretic peptide
• 5. Parathyroid hormone

1. Low blood pressure - Kidney cells secrete Renin (angiotensinogenase)

2. Renin converts Angiotensinogen from the liver into Angiotensin I

3. Angiotensin converting enzyme (ACE) secreted by the lungs & kidneys (proximal convoluted tubules) converts Angiotensin I into Angiotensin II - The active form of the hormone

• 4. Angiotensin II (a blood protein):
• Triggers vasoconstriction
• Triggers pituitary gland to release ADH (vasopressin)
• Stimulates adrenal cortex to produce Aldosterone.

• 5. Aldosterone:
• Causes the kidneys to retain sodium (Na) and excrete Potassium (K)

This causes water retention, increasing blood volume and blood pressure.

ANP is released from the heart when there is a large increase in blood volume/pressure.

• 1. It inhibits reabsorption of sodium (Na+) & water in the renal tubules
• 2. It suppresses anti-diuretic hormone & aldosterone.

This results in an increased excretion of sodium (Na) in the urine and increased urine output which decreases blood volume & pressure

• Reduced water concentration in the blood & lowered blood volume (e.g haemorrhage) causes increased osmotic pressure of the blood.
• Osmoreceptors in the hypothalamus stimulate posterior pituitary to secrete ADH
• ADH increases the permeability of the distal convoluted tubules, thus increasing water re-absorption in the kidneys, thereby aiding in rebalancing the osmotic pressure.
• ADH secretion is regulated by a negative feedback mechanism.

LOW blood calcium stimulates the parathyroid glands to release parathyroid hormone:

PTH stimulates the kidneys tubules to reabsorb more calcium and inhibits phosphate reabsorption.