Session 9 Flashcards
Describe in general terms the structure and functions of adrenaline
Amino acid derivative hormone - small molecules synthesised from amino acids
Hydrophilic - transported in bloodstream dissolved in plasma
Produced in the adrenal medulla (tyrosine –> dopamine –> noradrenaline –> adrenaline)
Secreted in response to stress (flight or fright response) - has effects on cardiovascular system, CNS, carbohydrate and lipid metabolism
Overproduction may be due to a tumour
List the hormones produced by the pituitary and adrenal glands together with their functions
Anterior pituitary - GH, ACTH, LH/FSH, TSH, prolactin
GH - stimulates by GHRH, inhibited by somatostatin, pulsatile release, excess = gigantism/acromegaly
ACTH - caused by stress, pulsatile release (increased in early morning), excess = Cushing’s, deficiency = Addison’s
LH/ FSH - GnRH stimulates pituitary, negative feedback, circadian rhythm
TSH - TRH stimulates pituitary, activates follicular cells on thyroid (T3+T4), negative feedback
Prolactin - (caused by pregnancy, physiological, pharmacological, pituitary, polycystic ovaries) stimulated by oestrogen, pulsatile secretion, initiates and maintains lactation
Posterior pituitary - osmoreceptors, ADH release (diabetes insipidus = ADH deficiency - water not reabsorbed)
Describe in general terms the structure of the steroid hormones
Produced in the adrenal cortex
Mineralocorticoids (C21) by zona glomerulosa e.g. aldosterone
Glucocorticoid (C21) by zona fasciculata, reticularis e.g. cortisol, corticosterone
Androgens by zona reticularis (C19)
Explain how the steroid hormones affect their target tissue
Bind to cytoplasmic receptors –> enters nucleus –> changes rate of transcription of specific genes
Decreased amino acid uptake, protein synthesis
Increased proteolysis, gluconeogenesis, glycogenolysis, lipolysis
Explain how cortisol secretion is controlled by ACTH and CRH
CRH (hypothalamus) –> ACTH (pituitary) –> cortisol (adrenal cortex)
Cortisol has a negative feedback effect on CRH and ACTH
Explain how ACTH can lead to increased pigmentation in certain areas of the body
Biosynthetic precursor of ACTH is POMC
POMC –> ACTH, a-MSH (a-melanocyte stimulating hormone), endorphins
a-MSH - increased pigmentation on exposed areas of body, friction points, buccal mucosa, scars, palmar creases
Describe the main actions of cortisol
Decreased amino acid uptake and protein synthesis
Increased proteolysis, gluconeogenesis, glycogenolysis, lipolysis
Explain the effects of over- and under- secretion of cortisol
Over-secretion (Cushing’s syndrome)
Increased activity of adrenal cortex due to tumour
Disorder of ACTH secretion caused by pituitary adenoma (Cushing’s disease) or ectopic secretion of ACTH
Leads to steroid diabetes, wastage of proximal muscles, fat deposits around abdomen and face, purple striae on abdomen, easy bruising, increased susceptibility to bacterial infections, acne, osteoporosis, hypertension
Under secretion (Addison’s disease)
Autoimmune destruction of adrenal cortex
Disorders in pituitary or hypothalamus
Leads to extreme muscular weakness, increased pigmentation, hypotension, hypoglycaemic episodes
Addisonian crisis must be treated immediately with IV cortisol and fluid replacement (dextrose in saline)
Describe tests of adrenal cortical function
Dexamethasone when given orally would suppress the secretion of ACTH and cortisol (suppression of plasma cortisol by >50% is characteristic of Cushing’s disease - diseased pituitary retains some sensitivity to potent synthetic steroids)
Suppression not in adrenal tumours or ectopic ACTH
Synacthen (synthetic ACTH) given intramuscularly would normally increase plasma cortisol by >200 nmol/L (normal result excludes Addison’s disease)
Explain how cortisol can have weak mineralocorticoid and androgen effects
The steroid proteins have three main regions:
Hydrophobic hormone binding region
DNA binding region rich in cysteine and basic amino acids
Variable region
Cortisol will bind to the mineralocorticoid and androgen receptors with low affinity - binding may be significant with high levels of hormone
