Adrenal Gland Disorders Flashcards
Describe the structure of the adrenal gland
- zona glomerulosa (outer cortex)
- zona fasciculata (middle cortex)
- zona reticularis (inner cortex)
- adrenal medulla (centre of gland)
What hormone is produced by the zona glomerulosa ?
mineralocorticoid (aldosterone)
What is the structure of the Zona glomerulosa ?
- cells arranged in clumps
What is the structure of the Zona fasciculata ?
cells arranged in cords alongside the blood sinusoids
What is the structure of the Zona reticularis ?
network of smaller cells
What is the structure of the adrenal medulla ?
loose network of neurosecretory cells surrounded by blood vessels
Function of the adrenal cortex
secretes 3 classes of steroid hormones
- glucocorticoids
- mineralocorticoids
- androgens
function of the adrenal medulla
- part of the sympathetic nervous system
- produces catecholamines (adrenaline and noradrenaline
What makes us the adrenal cortex ?
- Zona glomerulosa
- zona fasciculata
- zona reticularis
What hormone is produced by the zona fasciculata ?
glucocorticoid (cortisol)
What hormone is produced by the zona reticularis ?
glucocorticoids & androgens
What are external stimuli that affect the control of glucocorticoid secretion
- hypoxia
- hypoglycaemia
- stress
What internal stimuli is involved in the control of glucocorticoid secretion ?
diurnal rhythms
Define Diurnal Rhythms
- 24 hr cycle of physiological events that are synchronised with environmental cues such as the light-dark cycle
How is the secretion of glucocorticoid stimulated ?
- stimuli affects the hypothalamus
- hypothalamus releases corticotrophin-releasing hormone
- CRH acts on the pituitary gland
- pituitary releases ACTH
- ACTH acts on the adrenal cortex & triggers the release of glucocorticoids
What effect does cortisol have on the immune system ?
immune suppression
What effect does cortisol have on the liver ?
gluco-neogenesis
What effect does cortisol have on muscle ?
protein catabolism
What is another name for primary adrenal cortical hypofunction ?
Addison’s disease –> acute adrenal insufficiency
What effect does cortisol have on adipose tissue ?
lipolysis
What are some clinical features of Addison’s disease ?
lethargy, weakness, weight loss, anorexia, hypotension, hyperpigmentation
What causes Addison’s disease?
- 90% of cases are autoimmune
- remaining 10% can result from ; TB, tumour metastasis, amyloidosis, post adrenalectomy
- withdrawal of glucocorticoids
What is the name of adrenal cortex hyper function the results in excess cortisol?
Cushing’s syndrome
What is the name of adrenal hyperfunciton with results in excess mineralocorticoid ?
Conn’s Syndrome
What causes Conn’s Syndrome?
- adrenal adenoma = 75%
- bilateral hyperplasia of zona glomerulosa
- adrenal carcinoma
What are some clinical features of Conn’s syndrome?
hypertension, muscle weakness, tetany, paresthesia
Define tetany
muscle spasms
Define Paresthesia
abnormal sensation –> tingling or prickling
What are some clinical features of Cushing’s syndrome ?
- moon face
- proximal muscle wasting
- purple striae
- slow healing wounds
What can cause Cushing’s disease?
- antieror pituitary tumour creating excess ATCH –> Excess glucocorticoid released
- Adrenal carcinoma or adenoma
- ectopic ACTH - usually produced by a tumour located elsewhere
- iatrogenic cushings = too much glucocorticoids being taken (medication)
What are Catecholamines?
adrenaline and noradrenaline
What do catecholamines influence ?
- BP
- cardiac output
- fuel metabolism
- sweating
- pupil size
What are the metabolic effects of adrenaline?
- increase glycogen breakdown
- gluconeogenesis
- lipolysis
- increase release of amino acids, lactate & pyruvate
What is Pheochromocytoma ?
- adrenal medulla hyperfunction
- catecholamine secreting tumour
What are some clinical features of pheochromocytoma ?
- hypertension
- vasomotor signs
What are vasomotor signs ?
anxiety, sweating, palpitations, tremors and abdominal pain
How is Cushing’s syndrome Diagnosed ?
- screening tests
- establish cause
What are the 3 screening tests for Cushing’s?
- 24h urine free cortisol
- overnight dexamethasone suppression test
- 48h low dose dexamethasone suppression test
Describe the overnight dexamethasone suppression test
- 1mg of Dexamethasone @ 11pm
- 9am cortisol –> normal response = <50nmol/L
- failure of suppression - Cushing’s syndrome (also pseudocushings & stress?)
What is dexamethasone ?
- a synthetic glucocorticoid
What is the function of Dexamethasone ?
- suppresses pituitary ACTH
- dexamethasone leads to suppression of cortisol
Describe the 48hr low dose dexamethasone suppression test
- 0.5 mg dexamethasone every 6hrs for 2 days
- 9am cortisol day 2
- normal response - <50nmol/L
- fewer false positives than overnight test
What are the functions of Glucocorticoids?
- increase hepatic glujconeogeneis & hepatic glycogen storage
- increase breakdown of plasma & muscle protein to AA’s
- anti-inflammatory
Describe what might affect measuring Cortisol
- diurnal variation - levels high in morning & low/undetectable at night
- part of stress response
- some anti-inflammatory drugs may interfere in measurement
How do you measure Aldosterone ?
- measure after patient has been supine overnight & then upright
- varies greatly with posture
- usual to measure with renin
What are some biochemical signs of Adrenal Hypofunction?
- hyponatraemia
- hyperkalaemia
- hyperuricaemia
- hypoglycaemia
What’s the diagnostic approach for adrenal hypofucntion ?
- 9am cortisol
- usually have to perform short synacthen test
- then you need to establish primary or secondary - measure ACTH
- ACTH High = primary
- ACTH Low = secondary
Describe a Synacthen test
- measure baseline cortisol
- give synacthen
- measure cortisol
- cortisol should increase to a value >550 nmol/L after 30 minutes
What are some biochemical signs of Conn’s Syndrome?
- hypokalaemia
- urinary potassium innaproriately high
- high aldosterone & low renin
Describe Congenital Adrenal Hyperplasia
- inherited metabolic disorder of adrenal hormone secretion
- autosomal recessive
- 21-hydroxylase deficiency - can be partial or incomplete
- 21-hydorxylase deficiency = increase in 17-hydroxyprogesterone
What are some clinical signs of classical Congential Adrenal Hyperplasia ?
Lack of cortisol & aldosterone
–> adrenal crisis
-dehydration
-shock
-death
Describe Non-Classical Congential Adrenal Hyperplasia
- milder non-life threatening
- partial enzyme deficiency
- low cortisol, normal aldosterone & androgens
- premature pubic hair, menstrual irregularities, acne & fertility problems later
Describe diagnostic testing for Congenital Adrenal Hyperplasia
- Hormone measurement - 17-OHP
- clinical evaluation
What are some treatments for CAH ?
- glucocorticosteroid
- mineralocorticoid (classical form)
What is a possible treatment for a Pheochromocytoma ?
- surgical resection
- beta-blocker to control BP
What does a positive result in a Synacthen test indicate ?
- adequate adrenal response
- cortisol should increase to a value >550 nmol/L after 30 minutes with an increase of roughly 200nmol/L between baseline & 30 minute measure
