Hypoadrenal Disorders Flashcards
How many carbon atoms does cholesterol have?
27
What determines which steroids the different parts of the adrenal gland produce?
The combination of enzymes present in the different parts of the adrenal gland – hydroxylation in different positions of the cholesterol molecule gives different products.
Which enzyme converts cholesterol to pregnenolone?
Cytochrome P450 (short chain cleavage)
Which sets of enzymes are switched on by ACTH?
Cortisol synthesis enzymes
Sex steroid synthesis enzymes
The pituitary gland produces ACTH in response to what?
Stress
Which enzyme converts corticosterone to aldosterone?
Aldosterone synthase (includes 18-hydroxylase)
State three causes of adrenocortical failure.
Tuberculous Addison’s Disesae – most common cause worldwide
Autoimmune Addison’s Disease – most common cause in the UK
Congenital Adrenal Hyperplasia
State some consequences of adrenocortical failure.
Hypotension (due to lack of aldosterone)
Hyperkalaemia
Loss of salt (sodium) in urine
Fall in blood glucose (due to lack of cortisol)
High ACTH –> pigmentation
Vitiligo
Eventual death due to severe hypotension
Why do Addison’s patients get vitiligo?
Vitiligo is an autoimmune disease where you have antibodies against melanin
Autoimmune diseases tend to go hand-in-hand
Why does Addison’s cause skin pigmentation?
The lack of cortisol stimulates the production of huge amounts of ACTH.
ACTH is formed from the cleavage of POMC (pro-opiomelanocortin) to ACTH and alpha-MSH High ACTH also means high alpha-MSH –> skin pigmentation
State some tests for Addison’s disease.
9 am cortisol (this should be high in a normal person)
You could measure ACTH and this should be high in Addison’s Inject synthetic ACTH (synacthen) and if they have functioning adrenals, they should start to produce cortisol
NOTE: 250 mg IM synacthem
What is the most common cause of congenital adrenal hyperplasia (CAH)?
21-hydroxylase deficiency
What are the two degrees of CAH?
Partial or Complete (absence of the enzyme)
Why are foetuses with CAH normally fine in utero?
In utero, the foetus’ will have maternal cortisol and aldosterone so don’t need to rely on their own endogenous production.
Which hormones are absent in complete 21-hydroxylase deficiency?
Cortisol and Aldosterone