7 - adrenal glands

what are the adrenal glands composed of

adrenal cortex and adrenal medulla

what does the adrenal medulla secrete

catecholamines (epinephrine and norepinephrine)

what is the adrenal medulla

modified sympathetic ganglion i.e. neuroendocrine gland

how is the adrenal cortex split up

3 sections

- zona glomerulosa

- zona fasciculata

- zona reticularis

what does the zona glomerulosa secrete

mineralocorticoids (aldosterone)

- involved in Na+ and K+ balance

what does the zona fasciulata secrete

glucocorticoids (cortisol)

- maintain plasma glucose

what does the zona reticularis secrete

sex hormones (testosterone and oestrogen)

what are steroid hormones derived from

cholesterol

what is 21-hydroxylase

enzyme needed for steroid hormone formation

What are the consequences of a defect in 21-hydroxylase?

Adrenal hyperplasia leading to aldosterone and cortisol deficiency, disrupting salt and glucose balance.

In a 21-hydroxylase defect, what happens to androgen biosynthesis?

Androgen biosynthesis remains unaffected, leading to excessive adrenal androgen production due to accumulating steroid precursors.

describe the hypothalamic-pituitary-adrenal pathway

hypothalamus secretes corticotropin releasing hormone

detected by anterior pituitary and this releases ACTH (adrenocorticotropic hormone)

detected by adrenal cortex

cortisol release

sent to target tissues for a response

why does a 21-hydroxylase deficiency cause adrenal hyperplasia

inhibits synthesis of cortisol

removes negative feedback on ACTH and CRH release

increased ACTH secretion - responsible for enlargement of adrenal glands

what type of hormone is cortisol

glucocorticoid

what is the main purpose of cortisol

gluconeogenesis - glucose metabolism

what is the effect of cortisol binding to receptors

migration to nucleus

bind to DNA via hormone-receptor response element

altered gene expression, transcription and translation

when is cortisol at peak levels

6am-9am

when is cortisol at its lowest levels

midnight

why does cortisol level fluctuate throughout the day

stress

if the adrenal glands are removed, what happens in terms of cortisol

loss of cortisol

- cannot deal with stress

- cannot maintain BG

- cannot protect brain from hypoglycaemia

- cannot maintain ECF levels

- death within weeks

what are the glucocorticoid actions of cortisol

gluconeogenesis

- cortisol stimulates formation of gluconeogenic enzymes in liver

proteolysis

- stimulates breakdown of muscle protein to provide gluconeogenic substrate for liver

lipolysis

- allows protection of BG while creating gluconeogenic substrate

decreased insulin sensitivity of muscles and adipose tissue

excess cortisol can cause what disease

diabetes

what are the non-glucocorticoid actions of cortisol

negative effect on Ca2+ balance - decreased absorption and increased kidney excretion

increased bone resorption = osteoporosis

impaired mood and cognition - depression is strongly associated with hypercortisolaemia

permissive effects on norepinephrine - particularly in vascular smooth muscle

suppression of immune system by reducing circulating lymphocytes

what can happen if chronic glucocorticoid treatment is stopped too fast

exogenous cortisol suppresses CRH/ACTH through negative feedback, causing the adrenal gland to atrophy - risk of adrenal insufficiency

what type of hormone is aldosterone

mineralcorticoid

how does aldosterone work

increased reabsorption of Na+ and promotes excretion of K+

how is aldosterone secretion controlled

RAAS - renin-angiotensin-aldosterone system

what happens if aldosterone increases

release of aldosterone stimulates Na+ and H2O retention and K+ depletion

results in increased blood volume and BP

what happens if aldosterone decreases

leads to Na+ and H2O loss and increased K+ plasma

decreased blood volume and BP

what disease is associated with hypersecretion of cortisol

Cushing's disease

what is cushings disease

hypersecretion of cortisol usually due to a tumour on pituitary gland (excess ACTH)

secondary hypercortisolism

most common

features: Extremity wasting, "moon face," trunk fat redistribution, and hypertension 

if there is an adrenal cortex tumour causing hypersecretion of cortisol what is this called

cushings SYNDROME

- primary hypercortisolism

what is Addisons disease

adrenal insuffiencency

- Autoimmune destruction of the adrenal cortex leading to low levels of all adrenal steroids. 

features : Hyperpigmentation, hypotension

what are the main symptoms of Addison's disease

Hyperpigmentation

Orthostatic hypotension

hyponatremia

hyperkalemia

Decreased sex hormones in WOMEN: lack of libido, amenorrhea, decreased pubic/axillary hair

why does hyperpigmentation occur in Addisons

due to excess MSH stimulation of melanocytes

why do ACTH levels also increase in Addisons

MSH is produced from same precursor as ACTH - increased MSH = increased ACTH

why is hypotension present in addisons

due to loss of permissive effects of cortisol on adrenoreceptors and loss of ability to retain Na+ leading to hypovolaemia

what is the main complication of Addisons and what are the symptoms

Addisonian crisis

- hypotension

- hypoglycaemia

stress increases the vulnerability to infection via action on hypothalamo-pituitary-adrenal axis (HPA), why does this happen

CRH and ACTH release due to stress

alcohol, caffeine, lack of sleep all disinhibit HPA depressing neurones involved in negative feedback increasing CRH and ACTH

elevation of cortisol decreases immune system

what is the adrenal medulla similar to in terms of function

posterior pituitary

What is a phaeochromocytoma?

 A rare neuroendocrine tumour of the adrenal medulla causing excessive catecholamine release, which can be diabetogenic 

what does phaeochromocytoma result in

excess catecholamines - increases HR, CO and BP

consequences on plasma hormone levels : tertiary hypersecretion due to hypothalamic problem

CRH - high

ACTH - high

Cortisol - hgih

consequences on plasma hormone levels: secondary hypersecretion due to pituitary problem

CRH - low

ACTH - high

cortisol - high

consequences on plasma hormone levels; Primary hypersecretion due to problem with adrenal cortex

CRH - low

ACTH - low

cortisol - high