Ch8 Endocrinology Flashcards
Where are corticosteroids made?
Zona fasciulata of the adrenal cortex
How much cortisol does the body secrete per day?
15-25mg/day (basal levels) and 250-300mg/day during stress
What is the half-life of cortisol?
90 mins
What is the HPA control for cortisol?
Hypothalamus (CRH) > Pituitary (ACTH) > Adrenal (Cortisol)
What is Addison’s disease?
Primary adrenal insufficiency
What is a normal physiological corticosteroid replacement?
Hydrocortisone 20mg OM and 10mg ON
Are hydrocortisone and cortisol the same?
Yes
What are the equivalent steroid doses to 20 mg hydrocortisone?
Prednisolone 5 mg; Methylprednisolone 4 mg; Dexamethasone 0.75 mg;
What are the symptoms of adrenal insufficiency?
Fatigue, weakness, arthralgia, anorexia, nausea, hypotension, hypoglycaemia, low Na, high K and addisonian crisis.
How can the basal adrenal function be monitored?
Morning cortisol levels
What are the s/e of steroids?
CVS - hypertension / low K / high Na Endo - HPA suppression, cushingoid features, stunted growth, high BMs GI - Ulcers and pancreatitis Glaucoma / cataracts Poor wound healing AVN, osteoporosis and muscle weakness Haem - immunosuppression and hypercoagulability
What is the best test for hypocortisolism?
8am cortisol
What are the features of Addisonian crisis?
Confusion, lethargy, weakness, postural hypotension, hyperthermia, low glucose, high K and low Na.
What is the treatment of Addisonian crisis?
100mg IV hydrocortisone stat; followed by 50gm QDS IV fluid resuscitation and correction of electrolyte disturbances
When should mineralocorticoids be administered in adrenal insufficiency?
Primary adrenal insufficiency (i.e. when the adrenal gland is destroyed) and not secondary such as with pituitary disease
How can primary and secondary hypothyroidism be distinguished?
In primary there is a high TSH whilst in secondary there is a low TSH
What are the anaesthetic complications related to operating on a patient with hypothyroidism?
Poor wound healing and cardiac complications
What is Schmidt syndrome?
Hypothyroidism associated with immune mediated destruction of the adrenal gland
What is the treatment for hypothyroidism and adrenal insufficiency?
Hydrocortisone 400mg IV over 24 hours before thyroid replacement as this may precipitate an adrenal crisis
What are the features of myxoedema coma?
Unresponsiveness, hypotension, bradycardia and hypothermia
What is the treatment for myxoedema coma?
- Hydrocortisone 400mg IV over 24 hours (this will correct the electrolyte abn)
- Thyroid replacement with 500mcg levothyroxine
- IV glucose
- IV fluids / warming
How does the posterior pituitary gland develop embryologically?
This is an evagination of the ventral diencephalon (infundibulum) - these are neural crest cells = neuroectoderm
How does the anterior pituitary gland develop embryologically?
From the Rathke’s pouch, which is epithelial (ectodermal) tissue from the roof of the mouth. The Rathke’s pouch detachs to form a vesicle which then migrates to form the anterior pituitary
What is the median eminance?
The recess in the floor of the third ventricle due to the infundibulum aka infundibular recess
What is caused by the failure of the separation of the Rathke’s pouch?
Craniopharyngeal duct, which can be the source of recurrent meningitis
What forms from the anterior portion of Rathke’s pouch?
Pars distalis
What forms from the posterior portion of Rathke’s pouch?
Pars intermedius
What is the pars tuberalis of the pituitary gland?
The extension of the anterior pituitary gland that wraps around the base of the pituitary stalk
Where are remnants of Rathke’s pouch (rathke’s cleft) found?
Pars intermedius
What type of circulation does the pituitary gland have?
Portal
Where are hypothalamic hormones released?
From neurones in the tuber cinereum that are conveyed to the median eminence of the pituitary stalk via the tuberohypophysial tract. The hormones are released into capillaries of the hypophyseal portal circulation which are transported to the anterior pituitary
Where are posterior pituitary hormes synthesized?
Magnocellular neuroendocrine neurones in the supraoptic and paraventricular nuceli of the hypothalamus. These pass through the supra-optic hypophyseal tract to the posterior pituitary via the pituitary stalk
What is POMC?
Proopiomelanocortin - precursor to ACTH, MSH, lipotropin, beta-endorphin and met-enkephalin
How is prolactin release from the ant. pituitary controlled?
Under dopaminergic inhibition from the hypothalamus. Release is pulsatile with peak at 6 am. Other inhibitory factors are TRH and VIP (vasoactive intestinal peptide).
What protein is released in response to GH?
IGF-1 (insulin like growth factor 1) is secreted by the liver
What hormone suppresses GH release?
Somatostatin suppresses release only and does not affect synthesis of GH
Where does GH act?
Directly on the epiphyseal endplates to stimulate chondrocyte proliferation
What hormones stimulate GH release?
GHRH and Ghrelin
What hormones control TSH release?
TRH stimulates and Somatostatin inhibits
What controls ADH release?
Increase in Serum Osmolality causes ADH release (which results in water reabsorption from the collecting duct). ADH is also a vasoconstrictor.
