18. The Adrenal Glands Flashcards
What are the layers of the adrenal gland?
Capsule
Cortex - zona glomerulosa (mineralocorticoids), zona fasiculata (glucocorticoids), zona reticularis (glucocorticoids and androgens)
Medulla - chromatin cells
What do corticosteroids do?
Affect gene transcription
What are the types of corticosteroids?
Mineralocorticoids
Glucocorticoids
Androgens
Give an example of a mineralocorticoid
Aldosterone
Give examples of glucocorticoids
Cortisol
Corticosterone
Cortisone
Give examples of androgens
Dehyrdroepiandrosterone
Androstenedione - testosterone and oestrogens
Describe steroid hormones
Synthesised from cholesterol in adrenal glands and gonads
Lipid soluble hormones
Bind to receptors of the nuclear receptor family to modulate gene transcription
How do corticosteroids work?
Readily diffuse across plasma membrane
Bind to glucocorticoid receptors
Binding causes dissociation of chaperone proteins
Receptor ligand complex trans locates to nucleus
Dimerisation with other receptors can occur
Receptors bind to glucocorticoid response elements (GREs) or other transcription factors
Where is aldosterone synthesised and released from?
Zona glomerulosa of adrenal cortex
What is the carrier protein of aldosterone?
Mainly serum albumin and to a lesser extent transcortin
How does aldosterone work?
Aldosterone receptor is intracellular and exerts its actions by regulating gene transcription
What is the role of aldosterone?
Regulation of plasma Na+, K+ and arterial blood pressure
Main actions in distal tubules and collecting ducts where it promotes expression of Na+/K+ pump promoting reabsorption of Na+ and excretion of K+
What is primary hyperaldosteronism?
Too much aldosterone produced
Defect in adrenal cortex
Can be due to either bilateral idiopathic adrenal hyperplasia or aldosterone secreting adrenal adenoma (Conn’s syndrome)
Low renting levels
What is secondary hyperaldosteronism?
Too much aldosterone produced
Due to overactivity of renin-angiotensin-aldosterone system (RAAS)
Can be due to renin producing tumour or renal artery stenosis
High renin
What are the signs if hyperaldosteronism?
High BP Left ventricular hypertrophy Stroke Hypernatraemia Hypokalaemia
What is the treatment for hyperaldosteronism?
Depends on type
Aldosterone producing adenomas removed by surgery
Spironolactone (mineralocorticoid receptor antagonist)
Where is cortisol synthesised and released from?
Zonal fasiculata in response to ACTH
Negative feedback o hypothalamus inhibits CRH and ACTH release
What is the carrier protein of cortisol?
Transcortin
How does the cortisol receptor exert its actions?
By regulating gene transcription
What are the actions of cortisol?
Increased protein breakdown in muscles Increased lipolysis in fat Increased gluconeogenesis in liver Resistance to stress Anti-inflammatory effects Depression of immune system
What are the net effects of glucocorticoid on metabolism?
Increased glucose production
Breakdown of protein
Redistribution of fat
What are the external causes of Cushing’s syndrome?
Prescribed glucocorticoids
What are the endogenous causes of Cushing’s syndrome?
Benign pituitary adenoma secreting ACTH (Cushing’s disease)
Excess cortisol produced by adrenal tumour (Adrenal Cushing’s)
Non pituitary-adrenal tumours producing ACTH or CRH e.g. in small cell lung cancer
What are the signs and symptoms of Cushing’s syndrome?
Plethoric moon-shaped face Buffalo hump Abdominal obesity Purple striae Acute weight gain Hyperglycaemia Hypertension
What are the signs and symptoms of Addison’s disease?
Postural hypotension Lethargy Weight loss Anorexia Increased skin pigmentation Hypoglycaemia
What is Addison’s disease?
Chronic adrenal insufficiency
Most common cause is destructive atrophy from autoimmune response
Why does hyperpigmentation occur in Addison’s disease?
Decreased cortisol Negative feedback on anterior pituitary reduced More POMC required to syntheses ACTH Increased POMC leads to increased MSH MSH promotes melanin synthesis
What is Addisonian crisis?
Life threatening emergency due to adrenal insufficiency
What is addisonian crisis precipitated by?
Sever stress Salt deprivation Infection Trauma Cold exposure Over exertion Abrupt steroid drug withdrawal
What are the symptoms of addisonian crisis?
Nausea Vomiting Pyrexia Hypotension Vascular collapse
What is the treatment for addisonian crisis?
Fluid replacement
Cortisol
What is male dehydroepiandrosterone (DHEA) converted to?
Testosterone in testes
After puberty this is insignificant since testes release for more testosterone themselves
What do adrenal androgens do in females?
Promote libido and are converted to oestrogens by other tissues
After menopause this is only source of oestrogens
What is phaeochromocytoma?
Chromatin cell tumour
Rare, catecholamine-secreting tumour
What are the characteristics of phaeochromocytoma?
Severe hypertension Headaches Palpitations Diaphoresis Anxiety Weight loss Elevated blood glucose
