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
What is produced by the adrenal medulla? What are the cells involved called?
Catecholamines by the 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.
Aldosterone binds to intracellular receptors and translocates to the nucleus and causes changes in transcription leading to the synthesis of ion channels and pumps.
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
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.
Macula densa detects a decrease in tubular sodium concentration and stimulates the release of renin from the juxta-glomerular cells. Renin stimulates the production of angiotensin II, which upregulates aldosterone release.
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.
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.
