33 - Mineralcorticoid Receptors

Question 1

What is the conversion of cholesterol to aldosterone regulated by?

Answer 1

The conversion of cholesterol to aldosterone is regulated by a number of mechanisms in the body
- includes the adrenal cortex and low sodium levels

Question 2

Describe the regulation of the conversion of cholesterol by the adrenal cortex and the sodium and potassium levels

Answer 2

o Firstly, by the adrenal cortex which can sense the amount of sodium and potassium in the plasma
- If we have low sodium and high potassium, aldosterone production is triggered as it is involved in regulating sodium levels
o Low sodium levels also trigger the renin angiotensin system
- A conversion pathway leading to the conversion of a protein hormone called angiotensinogen into angiotensin 1, which is further converted into angiotensin 2
- It is a proteolytic process

Question 3

What is mineralocorticoid production regulated by?

Answer 3

Mineralocorticoid production is regulated through the renin-angiotensin system
o it is designed to maintain a “safe” plasma Na+ level
- too high Na+ leads to hypertension
- too low Na+ leads to hypotension

Question 4

Aldosterone

Answer 4

o In the zona glomerulosa cholesterol is converted into progesterone, then there is a series of hydroxylations on different positions of the progesterone ring, leading to aldosterone production

Question 5

Mineralocorticoid receptors

Answer 5

o Mineralocorticoid receptors are found in the distal tubule cells of the kidney filtration apparatus
o Once activated these produce a pump which actively recovers Na+ from the bladder back into the blood plasma
o K+ is pumped in the opposite direction
o Angiotensin-2 is also directly involved in regulating blood pressure levels

Question 6

What does aldosterone stimulate?

Answer 6

o Aldosterone stimulates transcription of the gene encoding the sodium potassium ATPase
o This leads to increased numbers of sodium pumps in the basolateral membranes of tubular epithelial cells
o Aldosterone also stimulates expression of a sodium channel that facilitates uptake of sodium from the tubular lumen

Question 7

Aldosterone mechanism

Answer 7

1. Aldosterone interacs with the receptor
2. The enter the nucleus to trigger increased gene transcription
   a. One of these genes codes for a sodium potassium ATPase
3. As sodium levels increase in the blood stream, blood pressure levels also increase because water is transported