Question

2 hours after significant blood loss, you would expect

Select one or more:

a. Low aldosterone

b. High aldosterone

c. Low ADH

d. High ADH

e. Low GFR

f. High GFR

Answer 1

2. 2 hours after significant blood loss, you would expect

b) high aldosterone

d) high ADH

e) low GFR

Explanation:

b) After a significant blood loss, there is severe decrease in the blood volume (hypovolemia). The body activates it's compensatory mechanism to deal with this hypovolemia as prolonged hypovolemic state can damage the vital organs can can be fatal if not corrected immediately.

The body tries to increase the blood volume and decrease the blood loss as well as correct the electrolyte imbalance by retaining water and solutes as much as it can and decreasing their excretion.

Aldosterone is a hormone secreted by the adrenal cortex in response to low sodium levels in the blood under the influence of another hormone called renin. Renin is produced by the JG cells (juxtaglomerular cells) of the kidneys in response to low blood supply to the kidneys.  

After severe blood loss, there is hypovolemia and decreased plamsa level of sodium which stimulates kidneys to secrete renin which in turn stimulates the adrenal cortex to secrete aldosterone. This aldosterone causes increased reabsorption of sodium and water from the nephrons of the kidneys thereby helping in restoring the blood volume and sodium levels.

d) ADH (Antidiuretic hormone) is a peptide hormone synthesized by the hypothalamus and stored and released into the blood stream from neurohypophysis (posterior pituitary) in response to increased osmolarity of blood.

After a significant blood loss, there is increased osmolarity of blood as the body is in dehydrated state due to severe loss of blood. The brain senses this increased osmolarity of blood and releases large amount of ADH from the posterior pituitary into the blood stream. This ADH acts on the distal convoluted tubules and collecting ducts of the nephrons of the kidneys and causes increased reabsorption of water from them, thus helping to restore the osmolarity of blood and blood volume.

e) Renin is secreted by the JG cells of the kidneys in response to decreased blood flow through the kidneys. This renin converts angiotensinogen to angiotensin I which is then converted to angiotensin II by angiotensin converting enzyme (ACE). This angiotensin II causes aldosterone secretion which increases sodium and water reabsorption as well as vascular smooth muscle contraction.

This contraction of the vascular smooth muscle causes constriction of afferent arterioles supplying blood to the nephrons thereby decreasing the GFR ( glomerular filtration rate ) which prevents water loss through the kidneys thus helping in the maintenance of blood volume. GFR is the volume of blood filtered by the glomerulus and bowman's capsule of the kidneys per unit time. It is normally around 125 ml/minute.