Adrenal gland Flashcards
Where is the adrenal gland
Located above the kidney at the back of the abdomen and is protected by ribs
Blood supply to the adrenal glands
57 arteries by only one vein which supplies the adrenal gland
Left adrenal gland blood supply
Left adrenal vein drains into renal vein . Many arteries
Right adrenal gland
Right adrenal vein drains into IVC. Many arteries but only one vein
3 parts of the adrenal cortex
Zona glomerulosa
Zona Fasiculata
Zona reticularis
What does the adrenal cortex secrete
Corticosteroids ( cortisol)
What does the adrenal medulla secrete
Catecholamines ( adrenaline )
Catecholamines
Adrenaline / epinephrine ( 80%)
Noradrenaline / norepinephrine (20%)
[Dopamine]
Corticosteroids
Mineralocorticoids ( aldosterone) Glucocorticoids ( Cortisol) Sex steroids ( Androgen, Oestrogens)
Where do set steroids come from
Most come from ovaries and testes but a bit comes from the adrenal gland ( e.g. in children before puberty)
Where is aldosterone released
Zona glomerulosa
What does aldosterone do
Controls sodium and potassium ion channels ( controls blood pressure )
Where is cortisol and a bit of the sex steroids ( androgens and oestrogen) produced
Zona fasciculata and zona reticularis
Which is produced in the adrenal gland / is present in the blood stream more , aldosterone or cortisol
Aldosterone - measured in picomol
Cortisol - measured in nanomol
What is a steroid
A hormone that is based on a cholesterol molecule - so the adrenal cortex secretions precursor is cholesterol
What is an enzyme
Proteins that catalyse a specific reaction
Various enzymes are present in cells
Specific enzymes catalyse the synthesis of particular alterations to the molecule
How is aldosterone ( a mineralocorticoid ) produced in the zona glomerulosa
Cholesterol - pregnenolone ( side chain cleavage ) - progesterone( 3 beta Hydroxylase steroid dehydrogenase) - 11 deoxycorticosterone ( catalysed by 21 Hydroxylase) - Corticosterone ( catalysed by 11 Hydroxylase) - aldosterone ( catalysed by 18 Hydroxylase )
How is glucocorticoid/ cortisol made in zona fasicularis
Cholesterol (side chain cleavage)- pregnenolone - progesterone ( 3 beta Hydroxy steroid dehydrogenase ) - 17 Hydroxy progesterone ( catalysed by 17 Hydroxylase) - 11 deoxy-cortisol ( catalysed by 21 Hydroxylase) - cortisol ( catalysed by 11 deoxyhydroxylase)
What does aldosterone do
Stimulates Na+ reabsorrption in distal convoluted tubule and cortical collecting duct in kidney ( and in sweat glands, gastric glands , colon)
Stimulates K+ and H+ secretion, also in distal convoluted tubule and the cortical collecting duct
Increased sodium reabsorption water reabsorption , raises blood volume
SO WORKS ON K+/Na+ ION CHANNEL TO KEEP BLOOD PRESSURE
How is aldosterone regulated
When blood pressure falls, Renin is released,
Decreased renal perfusion pressure is normally associated with decreased arterial BP .
Increased renal sympathetic activity ( direct to Juxtaglomerular apparatus)
Decreased Na+ load to top of the loop of Henle ( macula dense cells)
Renin and aldosterone release
Cells of macula densa sense the sodium load delivered to the distal tubule and regulate levels of circulating renin according to the body’s sodium requirements
If the sodium concentration in the tubular fluid is low, the juxtoglomerular cells increase secretions of renin
Renin acts on protein angiotensin ( secreted by liver) to convert it to angiotensin 1
ACE catalyses conversion of angiotensin 1 to angiotensin 2
Angiotensin 2 regulates aldosterone release and so now increased sodium reabsorption by distal tubule
What other hormone can regulate aldosterone
ACTH but to a lesser extent that angiotensin 2
Effects of angiotensin 2 on adrenals
Activation of the following enzymes Side chain cleavage 3 hydroxysteroid dehydrogenase 21 Hydroxylase 11 Hydroxylase 18 hydroxylase
Summary of action of aldosterone
Controls blood pressure, sodium and lowers potassium
How is cortisol secretion regulated
ACTH
Physiological effects of cortisol
Normal stress response
Metabolic effects ; peripheral protein catabolism, hepatic gluconeogenesis, increased blood glucose concentration , fat metabolism ( lipolysis in adipose tissue) , enhanced effects of glucagon and catecholamines
Weak mineralocorticoid effects - may maintain BP and has an effect on heart
Renal and cardiovascular effects ; excretion of water load , increased vascular permeability
Effects of ACTH on the adrenal gland
Activation of the following enzymes Side chain cleavage 3 hydroxysteroid dehydrogenase 21 Hydroxylase 11 Hydroxylase 17 Hydroxylase
What rhythm does cortisol have
Diurnal - peaks in the morning and then decreases during the night- cortisol is released in pulses
Cortisol and circadian rhythm
ACTH simulates cortisol and so the ACTH cycle is slightly ahead of the cortisol cycle
Addison’s disease
Primary adrenal failure
Autoimmune disease where the immune system decides to destroy the adrenal cortex
Tuberculosis of the adrenal glands ( commonest cause worldwide - TB bacteria destroy adrenal gland)
Pituitary starts secreting lots of ACTH and hence MSH and so become tanned
Addison’s disease
Adrenal glands do not produce sufficient steroid hormone
Adrenal crisis; fever, syncope, convulsion , hypoglycaemia, hyponatremia, severe vomiting and diarrhoea
Hyperpigmentation of skin Low bp Weakness Weight loss Gastric problems Vitiligo
Why do patients with Addison’s disease have a good tan
POMC is a large precursor protein that is cleaved to form a number of smaller peptides , including ACTH , MSH and endorphins
So people who have pathologically high levels of ACTH may become tanned
Summary of Addison’s disease
Cortisol deficiency Aldosterone deficiency Salt loss Low bp Eventual death
Urgent treatment of Addisonian crisis
Rehydrate with normal saline
Give dextrose to prevent hypoglycaemia which could lead to the glucocorticoid deficiency
Give hydrocortisone or another glucocorticoid or cortisol or give pregnenolone ( analogue of cortisol)
What happens if you have too much cortisol
Metabolism changes and you put on weight
What can cause too much cortisol
A tumour of the adrenal - excess cortisol
Tumour of pituitary - excess ACTH
Symptoms of Cushing’s syndrome
Mental changes ( depression) Red cheeks Fat pads Moon face Easy brusining Red stretch marks Poor wound healing Thin skin Impaired glucose tolerance High blood pressure Proximal myopathy - muscle weakness . Diabetes , hypertension and osteoporosis Immunosuppression
Catecholamines
Medulla derived from ectoderm album neural crest
Precursor for ADR and NA synthesis = tyrosine
Catecholamines stored in cytoplasmic granules and released in response to ACh from preganglionic sympathetic neurones
Role of catecholamines
Fight or flight response
Tachycardia, sweating , increased blood glucose , alertness, vasoconstriction
NA and ADR circulate bound to albumin
Degraded by two hepatic enzymes ; monoamine oxidase and catecholamines-O-methyl transferase
What controls aldosterone release
Angiotensin 2
What 4 things can cause an increase in cortisol and so possible Cushings Syndrome
prolonged steroid use - can often be be used to treat autoimmune conditions as glucocorticoids can suppress immune system
pituitary adenoma
ectopic ACTH (lung cancer)
adrenal ademona or carcinoma
difference between cushings disease and syndrome
cushings disease= excess cortisol as a result of a pituitary tumour. cushings syndrome = anyone who has excess cortisol
