Question

1. What happens to the GFR if systemic blood pressure decreases, if BP increases?

2.  Describe hormonal influence on the volume and concentration of urine.

Answer 1

1.answer) GFR (glomerular filtration rate) increases if systemic blood pressure increases.

GFR decreases if systemic blood pressure decreases.

Hydrostatic pressure in the glomerular capillaries is directly proportional to the systemic blood pressure.

Hydrostatic pressure favours filtration.

If systemic blood pressure increases,hydrostatic pressure of glomerular capillaries increases. So more the filtration occurs causing increase in GFR.

If systemic blood pressure decreases, hydrostatic pressure of glomerular capillaries decreases leading to decrease in GFR.

2. answer) The main hormone influence on the volume and concentration of urine is ANTIDIURETIC HORMONE.

Antidiuretic hormone is released when there is increase in plasma osmolality and decrease in blood volume (hypovolemia).

Increase in plasma osmolality and decrease in effective circulating blood volume stimulate osmoreceptors located in the anterior pituitary gland and hypothalamus then antidiuretic hormone secreted from anterior pituitary.

Increase in antidiuretic hormone increases the permeability of distal convoluted tubule and collecting tubules to water, which causes increase in water reabsorption and decrease in water excretion.

Decrease in water excretion from kidneys causes decreased amount of water in urine.

So, volume of urine decreases.

As less amount of water is urine, the urine becomes more concentrated causing increased concentration of urine.

Another hormone which also influence the volume and concentration of urine - ALDOSTERONE

Aldosterone hormone is secreted from adrenal cortex when there is decreased GFR.

Aldosterone causes reabsorption of sodium ions and water from the distal convoluted tubule and collecting duct.

So, volume of urine decreases and concentration of urine increases.