Adrenal gland & Steroid hormones

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  • Created by: Becca
  • Created on: 24-12-13 22:41
How are steroid hormones synthesised?
Derived from cholesterol by sequential, enzymatically-mediated modification of the structure - some from cell stories (synthesised from acetyl-CoA), mainly derived from plasma LDL
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What is the rate-limiting step in steroidogenesis?
The transport of cholesterol from the outer to inner mitochondrial membrane. First enzymes in steroidogenesis is located in inner mitochondrial membrane (initial side-chain cleavage of cholesterol)
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What happens in zone-specific steroidogenesis?
Differential expression of biosynthetic enzymes in the different zones of adrenal cortex: colesterol -> pregnenolone -> aldosterone (zone glomerulosa)/cortisol (zona fasciculata)/androgens (zona reticularis)
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What type of hormone is aldosterone? Where & what does it do?
Mineralocorticoid. Acts on DCT/collecting ducts, promotes sodium retention (+ H20 retention) & K+ elimination during urine formation. Secretion stimulated by increased plasma K conc & renin-angiotensin system (largely independent of ACTH)
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What are the different types of androgens? What are they regulated by?
DHEA & androstenedione, 50% in women (axillary/pubic hair growth, libido), negligible contribution in men. Regulated by ACTH but no feedback on CRH/ACTH
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What type of hormone is cortisol? What does it act in response to?
Glucocorticoid (glucose regulation) & mineralocorticoid activity. Stress hormone: emotional (fear, anxiety), physiological (pain, fever, injury, surgery etc) - increase CRH -> increase ACTH -> increase cortisol
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How is cortisol transported? How does it act?
Transported in plasma bound to transcortin & albumin. Acts via glucocorticoid receptor (intracellular receptor), regulates gene expression in tissue
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What are the actions of cortisol?
Metabolic effect (catabolic in muscle/adipose, stimulates gluconeogenesis & glycogen storage in liver -> elevates plasma glucose levels), anti-inflammatory/immunosuppressive (production of lipocortin 1, decrease T-cell activity & cytokine production)
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What happens to cortisol levels in response to stress? (stress = state of threatened homeostasis or dysharmony)
SNS/adrenaline: increases cardiac output, divert blood flow to muscles & heart, mobilisation of glyogen/fat stores & CHR-ACTH-cortisol: permissive action, shift from protein/fat in favour of expanded glycogen stores & plasma glucose availability
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How does cortisol modify thyroid hormones in response to stress?
Decreases thyroid hormones RAS/ADH/GH. Cortisol protects body against damage from potential over-activation of immune defence mechanisms
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What can prolonged elevated cortisol levels lead to?
Muscle wasting, hyperglycaemia, GI ulcers (inreased susceptibility) & impaired immune response
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What is the embryology of the adrenal gland?
Outer cortex developed from coelomi mesothelium, produce steroid hormones, controlled by ant pituitary. Inner medulla derived from neural crest , secrete catecholamines (chromaffin cells), under nervous control
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Which hormones are involved in the foetal adrenal gland?
Adrenals is mostly fetal cortex. Lacks some enzymes but is responsive to ACTH. Adrenal hormones are involved in lung maturation. Passive immunity gives fetus IgG causing gut 'closure' (under corticosteroid influence)
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What is the blood supply to the adrenal gland?
3 arteries: 2 from abdominal aorta & 1 from renal artery. 1 vein: left drains -> renal vein, right drains -> IVC
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What does the capsular artery divide into? What do these supply?
Medullary arteriole: bypass cortical arteriole system, through capsule to feed directly into blood bathing medulla cells, can pick up hormones to influence secretion. Cortical arteriole: expanding capillaries between columns of cells called sinusoids
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What are the different zones of the adrenal cortex? What is the epithelia & hormone secreted associated with each zone?
Zona glomerulosa: columnnar or ovoid/cluster cells, secretes aldosterone. Zone fasiculata: columns of cells (sinusoids between columns), secretes cortisol. Zona reticularis: cords of cells separated by sinusoids, secretes androgens
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What is the innervation of the adrenal gland?
Cells derived from neural crest, pre-ganglionic fibres go straights through ganglion and synapse on medullary cells which contain neurotransmitters. These are released into capillaries to act similarly to sympathetic outflow
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Card 2

Front

What is the rate-limiting step in steroidogenesis?

Back

The transport of cholesterol from the outer to inner mitochondrial membrane. First enzymes in steroidogenesis is located in inner mitochondrial membrane (initial side-chain cleavage of cholesterol)

Card 3

Front

What happens in zone-specific steroidogenesis?

Back

Preview of the front of card 3

Card 4

Front

What type of hormone is aldosterone? Where & what does it do?

Back

Preview of the front of card 4

Card 5

Front

What are the different types of androgens? What are they regulated by?

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