8 - The Adrenals and their hormones Flashcards
How many adrenal glands are there?
2 - left and right
Where do the left and right adrenal glands drain into?
Left - Renal vein
Right - IVC
What is the structure of the adrenal gland?
Draw it.
Middle = medulla Cortex = Zona reticularis Zona faciculata Zona glomerulosa
What does the adrenal cortex produce?
Corticosteroids
-Mineralocorticoids (aldosterone
-Glucocorticoids (cortisol)
Sex steroids – mainly androgens, some oestrogen)
What does the adrenal medulla produce?
Catecholamines
- Adrenaline (epinephrine; 80%)
- Noradrenaline (norepinephrine; 20%)
- Dopamine
Where is aldosterone produced?
Zona glomerulosa (outer part of cortex)
What type of hormones are produced by the adrenal glands?
Steroid hormones
How is cortisol transported in the blood?
CORTISOL
75% bound to corticosteroid binding globulin (CBG, also known as transcortin)
15% bound to albumin
10% free (unbound) -> bioactive
How is aldosterone transported in the blood?
ALDOSTERONE
60% bound to CBG
40% free (unbound) -> bioactive
How are the adrenal glands supplied with blood?
Lots of arteries around the edge.
1 central vein that leaves from the middle of the medulla.
Where in the adrenal cortex is cortisol (and some androgens & oestrogens) produced?
Zona reticular and zona glomerulosa.
Why are different hormones produced in different zones of the adrenal cortex?
Different enzymes are present in different zones so synthesis will follow a different pathway.
Why are steroid hormones found in the blood and not in cells?
They are very lipid soluble so can diffuse out of cells into blood easily.
When is cortisol at its highest and lowest concentrations in the blood?
Highest = morning 140-690 nmol/L Lowest = evening 80-330 nmol/L
What is the aldosterone level of the blood?
140-560 pool/L (1000 times less than cortisol)
What receptors can cortisol bind to?
Glucocorticoid Receptors (GR) AND Aldosterone Receptors (MR - mineralocorticoid receptor)
What receptors can aldosterone bind to?
ONLY Aldosterone Receptors (MR - mineralocorticoid receptor)
What is the name of the enzyme that breaks down cortisol making it inactive? What is the point of this and where is it found?
11b-hydroxysteroid dehydrogenase 2. (11b-HSD2).
It means aldosterone has to be used instead of cortisol.
Found in the kidneys and placenta.
Where is renin produced?
Granular cells that line the afferent artery in the kidney.
What 3 things cause renin to be produced?
- Renal Perfusion Pressure DECREASE
(BP in afferent arteriole) - Renal sympathetic nerves ACTIVATED
- Macular dense cells in distal convoluted tubule detect LOW sodium concentration in the fluid in DCT.
What does renin do?
- Increases sodium and water reabsorption in the kidney.
- Preserves blood pressure.
Explain the renin-angiotensin-aldosterone system.
- Renin (enzyme) released from kidney
- Renin acts on angiotensinogen (protein from liver) making angiotensin I.
- ACE (angiotensin converting enzyme) acts on angiotensin I making angiotensin II.
- Angiotensin II stimulates aldosterone production in the zona glomerulosa.
What 2 other things can stimulate aldosterone production?
- Low blood sodium
- High blood potassium
How is cortisol produced?
- CRH (corticotrophin releasing hormone) released from hypothalamus to anterior pituitary.
- Corticotrophs in the anterior pituitary produce ACTH (adrenocorticotrophin) which goes to the adrenal cortex.
- Cortisol is produced from the zona fasciculate and reticular in the adrenal cortex.
Negative feedback.
