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Adrenal Gland

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Question	Answer
Stress	A change that disturbs or threatens to disturb homeostasis Physical - trauma, infection, intense heat or cold, starvation, surgery, severe blood loss, pain, dehydration Psychological - anxiety, depression
Arterial supply	Adrenal arteries branch from the aorta, renal , inferior phrenic arteries Same on both sides Superior suprarenal arteries etc High blood supply ensures hormones are readily perfused into systemic circulation
Venous drainage	Left adrenal vein drains to left renal vein Right adrenal vein drains to IVC
Adrenal gland capillaries	Arteriole supply - widely networked capillaries Moves out to inside Enters via the capsule Branch into capillaries Move through cortex into medulla where enter central adrenal vein
Development of the adrenal glands	Medulla - neural crest cells Cortex - mesoderm Fetal adrenal cortex has two zones = Fetal zone which regresses after birth and definitive zone that forms the adult cortex Shows importance of adrenal in development
Adrenal medulla	Preparation for emergency activity Fight or flight Via adrenaline and noradrenaline
Stimulation of adrenal medulla	Anything that activates the SNS like pain, low BP etc Increases stimulation of medulla oblongata Sympathetic presynaptic neuron releases ACh onto medulla Medulla acts as postsynaptic nerve to release adrenaline and noradrenaline
Action of adrenaline	Fight or flight response Rapid release - seconds Short half life - 10 secs Rapid action - secs Depletes only a small fraction of stored catecholamine so adequate stores remain to respond to subsequent stress
Adrenaline synthesis	Tyrosine - L-dopa by tyrosine hydroxylase to Dopamine by dopa decarboxylase Transported into vesicle and forms noradrenaline by dopamine hydroxylase Transported out of vesicles to form adrenaline by phenyl N methyl transferase
Action of the adrenal medulla	Preparation for emergency activity Increased adrenaline secretion from the adrenal medulla causes changes which increase circulation, increase the availability of energy substrates and decreases non-essential activities
Sympathetic activity in stress via adrenergic receptors	Increases lipolysis Increased glycogenolysis Increased skeletal muscle twitch Dilates arteries in muscle Constricts arteries elsewhere Constricts veins Increases rate and force of heart contraction Dilates bronchi
Phaeochromocytoma	Tumour arising from chromaffin cells Uncontrolled secretion of adrenaline and noradrenaline symptoms - hypertension, tachycardia, hyperstimulation of CNS
Adrenal cortex	Maintenance of essential processes in chronic stress Capsule - protection Zona glomerulosa - aldosterone Zona fasciculata - cortisol Zona reticularis - androgens All steroid hormones, lipid soluble and derived from cholesterol
Synthesis of steroid hormones	Made rapidly from cholesterol via enzymes in mitochondria and SER in response to stress NOT STORED Lots of hydroxylases 3 main pathways - one for each
Plasma transport of adrenal steroids	Plasma albumin binds all steroids with low affinity Cortisol - cortisol binding globulin Aldosterone - no high affinity binding protein Adrenal androgens - sex steroid binding globulins
Breakdown of steroids	Liver converts steroids to hydrophilic metabolites Liver damage e.g. cirrhosis leads to increased plasma steroids
The Hypothalamo-pituitary adrenal axis	Stress detected by hypothalamus - releases CRH Acts on pituitary which releases ACTH Acts on adrenal cortex which releases cortisol All controlled by a negative feedback system to prevent the system becoming harmful
Cortisol secretion in response to the stress of an operation	Minor surgery - smaller release and resolved within a day Major surgery - larger release and levels remain elevated
Glucocorticoids	Preserve glucose for the brain Accelerate gluconeogenesis and lipid/protein catabolism CNS activity e.g. increase appetite Increased RBC production Maintenance of circulation Reduce inflammation and immune response
Mechanism of steroid action	Via activation of intracellular receptors that control transcription Receptor hormone complex enters nucleus HPA axis cortisol is switched on immediately in stress but acts slowly Genomic action - 10% of genes regulated Epigenetic changes
Clinical uses of glucocorticoids	Inflammatory disorders Arthritis Asthma Eczema Inhibit transplant rejection Chemo Antenatal to mature the lungs in fetus threatening preterm labour
Lipid messengers in inflammation	Inflammation usually caused by prostaglandins Cortisol inhibits phospholipase A2 and cyclooxygenase to reduce synthesis of prostaglandins
Causes of excess glucocorticoid secretion	Pituitary tumour secreting ACTH-High ACTH and cortisol in Cushings disease Excess glucocorticoids for other reasons - cushings disease Adrenal cortex tumour excreting excess cortisol Ectopic secretion of ACTH by neoplasma e.g. small cell lung carcinoma
Side effects of glucocorticoids	Buffalo hump fat pads Thin skin Hypertension Thin arms and legs Osteoporosis Infertility Poor wound healing Trunkal obesity Bruising Moon face
Chronic stress in utero	Stress of undernourishment or poor oxygen results in low birth weight Highly correlated with hypertension, diabetes, lower life expectancy, mental health disorders Maladaptation to stress
Chronic stress in childhood	Chronic stress leads to retarded growth
Chronic stress in adulthood	Continuing psychological stress is a major factor in mental health, obesity, CVD and T2 diabetes E.g. due to modern day work styles like shift work
Aldosterone	Class of steroids that regulate salt and water balance Stimulates reabsorption of Na in the distal nephron Acts via nuclear mineralocorticoid receptors to increase transcription of ENaC and Na/K ATPase Stimulates reabsorption of NA in the kidney
Stimulation of renin-angiotensin system	Decreased blood pressure detected by kidney Secretes renin Breaks down angiotensinogen into angiotensin 1 Converted into angiotensin 2 in lungs Stimulates adrenal cortex to release aldosterone Increases water reabsorption and decreased urine volume
Hypoaldosteronism	Sodium loss Low blood volume Low blood pressure
Hyperaldosteronism	Excess sodium retention Water retention Increased blood pressure
Spironolactone	A MR antagonist is a diuretic drug used an an anti hypertensive
Adrenal androgens	Minor component of adrenal secretion in adults Weak androgen DHEA Stimulates pubertal hair growth and secondary sexual characteristic development Large amounts produced in fetus - converted by mother into oestrogen needed for pregnancy maintenance
Congenital adrenal hyperplasia	Inherited defect of steroid synthesis in the adrenals Excessive secretion of adrenal androgens Results in masculinisation of females, precocious puberty in males Mutation in 21-hydroxylase - not used in androgen synthesis so all cholesterol sent here
Addisons disease	Lack of cortisol results in loss of negative feedback so high ACTH and MSH High circulating levels cause hyperpigmentation of skin-stimulates MC1 melanocortin receptors Short synacthen test-no increase from baseline cortisol Treated with hydrocortisone