Adrenals Flashcards
What is the embryological connection between the adrenal glands and the gonads?
Both develop in the same place from the adrenogonadal primordium
What is the direction of blood flow in the adrenal gland?
The blood supply is provided from the adrenal artery above the capsule (adrenal cortex) which supplies the layers of the adrenal cortex via the medullary artery and sub scapular plexus) and then forms the medullary plexus which supplies the medulla of the adrenal gland and this then drains into the adrenal veins.
What stimuli cause activation of the adrenal gland?
Stress! From starvation, infection or severe blood volume loss
In which layer of the adrenal cortex are mineralocorticoids such as aldosterone produced?
Zona glomerulosa
In which layer of the adrenal cortex are glucocorticoids such as cortisol produced?
Zona fasciculata
In which layer of the adrenal cortex are androgens such as testosterone produced?
Zona reticularis
What is the action of aldosterone (a mineralocorticoid)
It increases potassium and sodium reabsorption in the kidneys which also increases water reabsorption and therefore increases circulating blood volume
What causes the stimulation of aldosterone production of the zona glomerulosa of the adrenal cortex?
Low potassium levels (hypokalaemia) and low blood pressure
Describe the mechanism of action of aldosterone
- Increases expression and stimulates the basolateral Na+/K+ ATPase in the collecting duct to increase uptake into the blood and create a sodium gradient to encourage reabsorption.
- In addition, aldosterone increases numbers of ENaC channels (sodium channels) so that more sodium enters, as well as water (potassium leaves to remain electro-neutrality).
- Aldosterone also stimulates H+ ATPase in the intercalated cells of the collecting duct to increase H+ excretion
How may hyperaldosteronism lead to metabolic alkalosis?
Aldosterone stimulates the H+ ATPase in the distal nephron which leads to increased H+ excretion, which can eventually lead to deficiency if aldosterone is present in excessive amounts
How may hyperaldosteronism lead to hypokalaemia?
Increased sodium reabsorption (due to increased ENaC presence) will cause potassium to enter the tubular fluid in order to maintain electro-neutrality and therefore this excess excretion of K+ can lead to deficiency
What two molecules can bind to the mineralocorticoid receptor in the kidney?
Cortisol and aldosterone
How can the kidney prevent the binding of cortisol to the mineralocorticoid receptor?
It can facilitate the conversion of active cortisol into inactive cortisone via the action of 11-beta-HSD2 enzyme
What is Conn’s syndrome?
A form of primary hyperaldosteronism
What is primary hyperaldosteronism?
This is also known as Conn’s syndrome and it is characterised by hypertension, suppressed renin activity (negative feedback) and increased aldosterone secretion
What may cause Conn’s syndrome?
This is a form of hyperaldosteronism and therefore can occur as a result of an aldosterone-producing adenoma or due to bilateral adrenal hyperplasia
What is glucocorticoid remediable aldosteronism?
This is a familial form of hyperaldosteronism that is autosomal dominant.
In this condition there is fusion of the cortisol synthase promoter region to the aldosterone synthase coding region and therefore this leads to ACTH-dependent aldosterone secretion in the zona fasciculata rather than the zona glomerulosa
What similarities are there between the enzymes that produce glucocorticoids and mineralocorticoids?
The enzymes are isoenzymes of each other;
Aldosterone synthase is known as CYP11B2 whereas the enzyme responsible for cortisol synthesis is CYP11B1 (11 beta hydroxylase)
How may glucocorticoid remediable aldosteronism be treated?
Through the administration of glucocorticoids in order to reduce ACTH secretion from the pituitary gland by negative feedback.
How can large liquorice consumption affect the mineralocorticoid receptor?
Excess liquorice consumption leads to the direct inactivation of the 11beta-HSD2 enzyme that is involved in the conversion of cortisol to cortisone (inactive form so that it can’t bind to the mineralocorticoid receptor. Therefore, in excess liquorice consumption, high cortisol levels persist.
