Physiology: Physiology of the Adrenal Gland Flashcards
What is the HPA axis?
Cortisol and androgen production are regulated by hormones produced by hypothalamus and anterior pituitary gland
Describe the metabolic effects of cortisol
Carbohydrate: ↑ blood sugar
Lipid: ↑ lipolysis, central redistribution
Protein: ↑ proteolysis
What is the RAAS?
Activated in response to decreased blood pressure
Leads to production of angiotensinogen II which causes direct (vasoconstriction) and indirect (aldosterone) methods of BP elevation
Describe the effect of cortisol on the CNS
Mood lability
Euphoria/psychosis (in excess)
↓ libido
Describe the synthesis of catecholamines in the adrenal medulla
Adrenaline and noradrenaline are dopamine derived, which in turn is derived from tyrosine
Describe the effect of cortisol on the circulatory/renal system
↑ cardiac output
↑ blood pressure
↑ renal blood flow and GFT
Which region of the adrenal gland synthesises cortisol?
Zona fasciculata
What are the actions of aldosterone?
Sodium/potassium balance
BP regulation
Regulation of extracellular volume
What is the rate-limiting step in the biosynthesis of corticosteroids in the adrenal cortex?
Cholesterol → pregnelolone via P-450ssc
Describe the mechanism of action of aldosterone
Effects via mineralocorticoid receptor - expressed primarily in the kidneys but also in the salivary glands, gut and sweat glands
Describe the mechanism of action of corticosteroids
Bind to intracellular receptors (primarily nuclear)
Receptor/ligand complex binds DNA to affect transcription
Which region of the adrenal gland synthesises DHEA and androstendione?
Zona reticularis
Which region of the adrenal gland synthesises aldosterone?
Zona glomerulosa
Describe the effect of cortisol on bone/connective tissue
Accelerates osteoporosis
↓ serum calcium
↓ collagen forming
↓ wound healing
Name the enzyme which converts DHEA and androstendione into testosterone and dihydrotestosterone in the peripheral tissues
5⍺ reductase
