Question

Part I: You are drifting at sea and are so thirsty that you decide to drink about 8 oz of salt water. Your MAP is normal. Will ADH be elevated in your blood? Explain your answer.

Part II: Will aldosterone be elevated in your blood?

Part III:Name both a STEROID and NON-steroid hormone that is produced at the end of the RAAS pathway:

Answer 1

Part I: The secretion of antidiuretic hormone (ADH) depends on changes in plasma osmolarity. Although reduced blood pressure and blood volume via stimulation of stretch receptors on atria /carotid arteries/aorta also induces ADH production, the increased osmolarity will have more drastic effect by increasing ADH secretion.

The imbibition of salt water by the individual will cause increased sodium and chloride levels in blood. This will increase the electrolyte concentration of plasma. The 8oz volume may not increase blood volume and hence there may not be any change in MAP. Increased plasma osmolarity will stimulate the receptors on the hypothalamus. This signaling will increase production of ADH. ADH will increase the water reabsorption in the collecting ducts of kidneys to increase water levels in blood in order to dilute the salt. Thus, ADH should be elevated in this individual.

Part II: The juxtamedullary cells of the afferent arteriole in kidneys sense decreased blood pressure. Renin is secreted by these cells, which then acts on angiotensinogen in blood to form angiotensin I. Angiotensin I is converted to angiotensin II by angiotensin converting enzyme (ACE). This occurs in the lungs. Angiotensin II then stimulates the secretion of aldosterone in the adrenal glands. Aldosterone stimulates reabsorption of sodium in the distal nephron of kidneys.

The MAP is not elevated in the individual. Thus is there is no change in blood pressure. This will not induce renin secretion. Hence, aldosterone should not be elevated in the individual.

Part III: Aldosterone is the steroid hormone released by the cortex of the adrenal gland in response to angiotensin II production. It is produced by the zona glomerulosa of the adrenal cortex. It is a steroid hormone derived from corticosterone that is produced from cholesterol.

Renin is the non-steroid hormone secreted by the juxtamedullary cell of the afferent arterioles in kidneys. It is a peptide hormone of 37 kDa and contains 340 amino acids. It is secreted due to decreased stretch sensed by the afferent arterioles when renal blood flow decreases.