The Adrenals and their Hormones Flashcards
What are the parts of the adrenal gland from the outside to the inside?
Zona Glomerulosa (aldosterone production) Zona Fasciculata (cortisol and sex steroids) Zona Reticularis (cortisol and sex steroids) Adrenal Medulla
What is the direction of blood flow in the adrenals?
From the cortex towards the medulla (most however go through the cells)
What is produced by the adrenal medulla? What are the cells involved called?
Catecholamines by the Chromaffin cells ( catecholamines are NOT associated with chromaffin cells)
What is produced in the adrenal cortex? State the four hormones produced.
- Corticosteroids: Mineralocorticoids - aldosterone + Glucocorticoids - cortisol
- Sex Steroids - androgens and oestrogens
What is androstenedione?
It is a weak androgen that can be converted to testosterone and dihydrotestosterone
How are corticosteroids transported in the blood?
They bind to plasma proteins. There is so much albumin that some corticosteroids will non-specifically bind to albumin. There are more specific plasma proteins - corticosteroid binding globulin
Describe the difference in the blood concentrations of cortisol and aldosterone.
The concentration of cortisol is 1000 times greater than the concentration of aldosterone.
How does cortisol concentration vary?
Cortisol concentration changes with the circadian rhythm. It is a stress hormone so is released more at times of stress.
What are the effects of aldosterone?
Increased potassium and H+ secretion Increase sodium reabsorption
Describe the mechanism of action of aldosterone.
- Passes through membrane and binds to intracellular receptors.
- RHC moves to nucleus and acts as a transcription factor and binds to DNA.
- Proteins produced are enzymes/pumps.
a. proteins may stimulate ATPase on basolateral membrane to pump Na+ into blood
b. Stimulates synthesis if ion channels eg Na+ channels in apical membrane
Describe the arrangement of the juxta-glomerular apparatus in the kidneys.
The juxta-glomerular cells are in contact with the afferent arteriole. The macula densa cells are next to the juxta-glomerular cells and are in the DCT.
What hormone is stimulated by an increase in plasma osmolality?
Vasopressin
What is a consequence of increase extracellular fluid volume?
Hypertension
Describe how the juxtaglomerular apparatus can lead to production of aldosterone.
- Liver produces angiotensinogen
- Renin breaks angiotensinogen to angiotensin I
- ACE ( angiotensin converting enzyme) converts angiotensin I to angiotensin II
- Angiotensin II stimulates zona glomerulosa to produce aldosterone
State three causes of renin release.
- Decreased renal perfusion pressure
- Increased renal sympathetic activity
- Decreased sodium concentration at the top of the loop of Henle
Describe the steps in the production of angiotensin II from the angiotensinogen.
Renin converts angiotensinogen (produced by the liver) to angiotensin I Angiotensin I is converted by ACE (which is found in high concentration in the lung endothelium) to Angiotensin II
What are the effects of cortisol?
- Increased hepatic gluconeogenesis
- Increase glycogenolysis Increased fat metabolism
- Stimulates peripheral protein catabolism
- Enhances effects of glucagon and catecholamines
What are the three effects of large amounts of cortisol?
Anti-inflammatory Immunosuppressive Anti-allergic
Which receptors do a) aldosterone and b) cortisol bind to?
Aldosterone - mineralocorticoid receptors Cortisol - glucocorticoid receptors AND mineralocorticoid receptors
Describe the mechanism of action of cortisol.
Cortisol binds to intracellular receptors, moves to the nucleus and causes a GENOMIC change.
For example, annexin 1 which has an autocrin effect and binds. Annexin 1 receptor on same cell. This stimulates phospholipase which works on phospholipids to increase arachidonic acid. Cortisol blocks the production of arachidonic acid thereby decreasing prostaglandin synthesis.
Describe the control of cortisol.
There is direct negative feedback by ACTH on the hypothalamus Cortisol also have negative feedback effects on the hypothalamus and on the adenohypophysis
What is dehydroepiandrosterone (DHEA)?
This is a very weak androgen that peaks around 20-30 years. It is particularly important in post-menopausal women as a precursor for oestrogen.
As cortisol has a much higher blood concentration than aldosterone, why doesn’t cortisol constantly bind to mineralocorticoid receptors?
The kidneys have an enzyme called 11 beta-hydroxysteroid dehydrogenase 2 that converts cortisol into the inactive CORTISONE.
Where is each of the corticosteroids made?
Aldosterone - Zona glomerulosa Cortisol - Zona fasciculata and reticularis Sex steroids - Zona fasciculata and reticularis
What are all corticosteroids derived from?
cholesterol
What hormones are made in the adrenal medulla?
Adrenaline - 80% Noradrenaline - 20% Dopamine - very small amounts
Whats the precursor for aldosterone?
progesterone
What is the precursor for oestrogens?
androgens
Draw the structure of the adrenal gland
Contrast how Aldoesterone and cortisol are carried in blood
Aldosterone:
- 40% - Free Hormone
- 15% - CBG
- 45% - Albumin
Cortisol:
- 10% - Free Hormone
- 80% - CBG
- 10% - Albumin
