Adrenal
These are the glands that sit on top of each kidney. They get their blood supply from the renal arteries, and the abdominal aorta. Like the kidneys, the adrenals have a cortex and medulla. The cortex is the important bit.
Cortex
In the cortex is produced three groups of steroid hormones from cholesterol – the andrenocorticocoids:
- Glucocorticoids
- Mineralocorticoids
- Sex hormones (androgens)
Glucocorticoids
The main one is cortisol (hydro-cortisone). There are others, with similar names like corticosterone and cortisone, and similar actions.
ACTH (Adrenocorticotrophic Hormone) is released from the anterior pituitary, stimulating release of glucocorticoids. They do a lot:
- Gluconeogenesis – raising blood sugar level.
- Lipolysis – energy production.
- Breakdown of proteins - making aminos that can be used to make other proteins, or ATP.
- Promoting absorption of Na+ and water from renal tubules
They are varied highly by circadian rhythm, with hypothalamus control releasing CRH (corticotrophin releasing hormone).
Mineralocorticoids
The main one is aldosterone. Its functions are involved in water and electrolyte levels. Check out the renin-angiotensin-aldosterone page for more, but basically, stimulated by angiotensin 2, and also by high blood potassium, the cortex releases aldosterone, which works in the kidney tubules to:
- Increase sodium reabsorbtion
- Increase potassium excretion
With sodium retention, water stays as well, meaning that high aldosterone levels increase blood pressure. In turn, high blood pressure inhibits the renin-angiotensin-aldosterone pathway.
Sex hormones
A small amount of androgens are made in the cortex, but pretty insignificantly compared with the testes and ovaries. Thought to contribute to puberty. Probably.
Medulla
In the adrenal medulla, noradrenaline and adrenaline is produced. Both are catecholamines – released in times of shock, where they provide an acute response.
Catacholamines
Noradrenaline works more on the blood vessels. Adrenaline works more on the heart and metabolism.
Effects:
- Increasing heart rate
- Increasing blood pressure
- Dilation of vessels in important organs, heart, brain, muscles.
- Constriction of vessels in unimportant organs, skin.
- Increased metabolic rate
- Dilated pupils.
Clinical Conditions
Cushing's Syndrome
This is hypersecretion of glucocorticoids. There are several potential causes:
- pituitary tumour causing excess ACTH secretion (Cushing's Disease)
- non-pituitary tumour releasing ACTH
- iatrogenic causes - overdose of ACTH or glucocorticoids
Presenting symptoms:
- Weight gain - especially of the face and central trunk
- Hyperglycaemia
- Hypertension
- Peptic ulceration
Addison's Disease
Hyposecretion of mineralo and glucocorticoids - if left untreated, it can lead to death
- Rapid weight loss
- GI problems
- Skin pigmentation
- Tiredness, confusion
- Chronic dehydration
Visit the Addison's disease page for more.