•Outline the role of the hormones,
aldosterone and ADH (anti-diuretic
hormone) in the regulation of water and
salt levels in the blood
Water Balance and Blood Pressure
• Water levels in the body are closely
associated with blood pressure.
– Increased water increases blood pressure
– Dehydration decreases blood pressure
– Involves ADH and aldosterone
ADH – anti-diuretic hormone
• Also called vasopressin
• Produced in the brain in the hypothalamus
• Osmoreceptors (detect water levels in the body)
activate neurosecretary cells in the
hypothalamus in response to increased blood
solutes (less water)
• Vasopressin travels to the pituitary gland and is
released into the blood stream.
• ADH acts in the kidneys increasing the
permeability of the distal tubules to water. Water
reabsorption increases.
• Osmoreceptors also make you feel thirsty.
• Increased drinking and increased
reabsorption of water decrease the
concentration of solutes in the blood.
• This acts as negative feedback and stops
the production of ADH (vasopressin)
Aldosterone
• When water levels in the blood decrease, blood
volume and blood pressure decrease. A
decrease in blood pressure changes the
glomerular filtration rate.
• In response to low blood pressure renin is
secreted in the kidneys.
• Renin triggers the adrenal cortex (outside edge
of the adrenal gland) to release aldosterone.
• Aldosterone increases reabsorption of sodium in
the distal tubule which increases reabsorption of
water. Increased water leads to increased blood
pressure.
• Aldosterone and ADH (vasopressin) work
together to effectively maintain water
concentration in the blood and tissues and blood
pressure.
• Patients with Addison’s Disease (inability of the
adrenal gland to secrete sufficient hormone) do
not produce aldosterone. The body is unable to
control the amounts of sodium and potassium.
This can lead to heart failure within a few days.
Hormone injections can be given at
physiological levels. This is called aldosterone
replacement therapy. Drinking a salt solution is
suitable if insufficient aldosterone is produced.