Week 9 + 10 Flashcards
What are the main steroid hormone types in the adrenal cortex
Glucocorticoids- cortisol
Mineralocorticoids- aldosterone
Adrenal androgens- adrenal androgen precursors
Synthesis, actions, regulation of each (effects of ACTH)
What is produced by the adrenal medulla
Catecholamines- adrenaline and noradrenaline
What is the histological zonation of adrenal
Outer capsule
Cortex:
Zona glomerulosa- mineralocorticoids (aldosterone) ‘salt’
Zona fasciculata (largest zone)- glucocorticoids (cortisol) ‘sugar’
Zona reticularis- androgens (DHEA) ‘sex’
Medulla:
Catecholamines
Steroidogenesis
Cholesterol is the common precursor for all steroid hormones
Metabolised in the adrenal gland
Each step is mediated by an enzyme
Enzymes expressed differentially in various zones of adrenal cortex
Adrenal insufficiency
Too little:
Glucocorticoid deficiency
Mineralocorticoid deficiency
Adrenal androgen deficiency
What causes Cushing’s syndrome
Glucocorticoid excess, excess of cortisol
What causes Conn’s syndrome
Mineralocorticoid excess- excess aldosterone
What causes phaeochromocytoma (tumour of adrenal medulla)
Catecholamine excess
What are corticosteroids
Lipid soluble- can pass through biological membranes without need of receptor
Bind to specific intracellular receptors
Exact action depends on structure, ability to bind specific receptors
Alter gene transcription directly or indirectly
How do glucocorticoids work
Cortisol diffuses across cell membrane into the cell
Cortisol binds to glucocorticoid receptor
Glucocorticoid receptor becomes active and binds to glucocorticoid response element on DNA sequence in nucleus
Coactivators bind to receptor
Gene transcription occurs
Actions of glucocorticoids
Important in homeostasis
Have actions on most tissues
Many actions ‘permissive’ (do not directly initiate but allow to occur in presence of other factors) e.g. the effects of catecholamines on vascular tone
‘Permissive’ actions only apparent with deficiency
Effects of glucocorticoids
Brain/CNS: depression, psychosis
Eye: glaucoma
Pituitary: decrease LH, FSH release, decrease TSH release
GI tract: peptic ulcerations
Carbohydrate/ lipid metabolism: promote glycogen breakdown and glucose release from liver and muscle,
Increase insulin resistance, type 2 diabetes,
Promotes breakdown of fat in adipose tissue, increasing amount of circulating lipids, promotes visceral central obesity
Cardiovascular/renal: salt and water retention, hypertension
Breakdown protein/ collagen, skin thinning, muscular atrophy
Decrease in bone formation, decrease in bone mass and osteoporosis
Decrease in linear growth
Immune system: anti-inflammatory action, immunosuppression
What are the Actions of glucocorticoids
Increase glucose mobilisation:
Augment gluconeogenesis, amino acid generation, increased lipolysis
Maintenance of circulation: vascular tone, salt and water balance
Immunomodulation: dampen immune response
Transport of glucocorticoids
Hydrophobic so not able to circulate freely
In the circulation glucocorticoids are heavily bound to proteins- when bound its inactive decreases affects of glucocorticoids
90% bound to corticosteroid-binding globulin (CBG)
5% bound to albumin
5% free cortisol- active part can cross plasma membrane, bioavailable so can exert a biological function
When CBG decreases free cortisol increases vice versa
In clinical practice total not free measured
CBG levels decrease with inflammation/stress so increase free cortisol
Regulation of glucocorticoid synthesis
The hypothalamic-pituitary-adrenal (HPA) axis regulates glucocorticoid synthesis
System is sensitive to stimuli such as circadian rhythm, stressors: physical, emotional, fever, hypoglycaemia, hypotension
CRH (corticotrophin-releasing hormone) released by hypothalamus
ACTH (adreno-corticotropic hormone or corticotropin) released by anterior pituitary
Negative feedback occurs
Effect of ACTH on adrenal size
ACTH deficiency- atrophy of adrenal gland, decrease in size, can be seen in patients who take glucocorticoids such as for drugs
ACTH excess- hypertrophy of adrenal cortex
Circadian rhythm for cortisol
Very low levels of circulating cortisol when sleeping
Peak when we wake up as need more energy
As day progresses cortisol levels decrease
Cortisol regulated by ACTH so follow same pattern
Stress
The sum of the bodies responses to adverse stimuli
Infection
Trauma
Haemorrhage
Medical illness
Psychological
Exercise/exhaustion
HPA axis function during acute illness
‘Stress’ cytokines
Lower levels of CBG, decrease in synthesis, more bio available cortisol increase impact
Cytokines, local steroid activation
Less negative feedback