The Adrenal Gland Flashcards
Where are the kidneys located?
Superior pole of kidneys in retroperitoneal space
How does the anatomy of the adrenal veins differ?
Left adrenal vein drains into left renal vein
Right adrenal vein drains directly into IVC
Describe the structure of the adrenal glands
Adrenal medulla (25%) Adrenal cortex (75%)
What does the adrenal medulla secrete?
Catecholamines (adrenaline, noradrenaline and dopamine)
What kind of tissue is the adrenal medulla?
It is a modified sympathetic ganglion derived from neural crest tissue
What kind of tissue is adrenal cortex?
True endocrine tissue derived from mesoderm
What hormones does the adrenal cortex secrete?
Mineralocorticoids
Glucocorticoids
Sex hormones
Give an example of a mineralocorticoid
Aldosterone
What is the role of aldosterone?
Involved in regulation of Na and K
Give an example of a glucocorticoid
Cortisol
What is the role of cortisol?
Involved in maintaining plasma glucose
How is the medulla arranged?
Surrounded by cortex and arranged into 3 concentric zones which produce different hormones
What are the different layers of the medulla and what do they produce?
Zona glomerulosa –> aldosterone
Zona fasciculata –> glucocorticoids
Zona reticularis –> sex hormones
How are all the different hormones in the adrenals made?
All steroid hormones, hence derived from cholesterol but different enzymes for the different end products are in each zone
What are the main products of the adrenal cortex?
Cortisol and aldosterone - these are essential for life
Apart from cortisol and aldosterone what products are made in the adrenals?
DHEA (prehormone of testosterone and oestrogen)
What causes congenital adrenal hyperplasia?
Defects in 21-hydroxylase (an enzyme essential for the synthesis of aldosterone and cortisol)
What are the features of congenital adrenal hyperplasia?
Disruption of salt and glucose balance
Androgen biosynthesis unaffected so accumulating steroid precursors channelled into excessive adrenal androgen production
Why does deficit in 21-hydroxylase causes adrenal hyperplasia?
Lack inhibits cortisol synthesis, this removes negative feedback on ACTH
Increased ACTH leads to enlargement of the adrenals
What is 95% of plasma cortisol bound to in the plasma?
Cortisol binding globulin
Which cells have receptors for glucocorticoids?
All nucleated cells have CYTOPLASMIC glucocorticoid receptors
Hormone receptor complex migrates to nucleus, binding DNA via hormone response element to alter gene expression, transcription + translation
When are cortisol levels at their highest?
6-9am
When are cortisol levels at their lowest?
Midnight
What other things may cause fluctuation of cortisol levels throughout the day?
Other stimuli related to stress
What does loss of cortisol result in?
Inability to cope with stress, esp. in terms of maintaining BG levels
Cortisol is critical in protecting the brain from hypoglycaemia
How does cortisol impact BG?
Has permissive act on glucagon (glucagon alone is inadequate in responding to hypoglycaemic challenge)
What are the actions of cortisol on glucose metabolism?
Gluconeogenesis
Proteolysis
Lipolysis
Decreases insulin sensitivity
How does cortisol aid gluconeogenesis?
Stimulates formation of gluconeogenic enzymes
How does cortisol aid proteolysis?
Stimulates muscle protein breakdown
How does cortisol aid lipolysis?
Stimulates lipolysis in adipose tissue –> increase FFA in plasmsa
Why is excess cortisol diabetogenic?
Cortisol acts to oppose insulin
What are the non-glucocorticoid actions of cortisol?
Negative effect on Ca balance
Impaired cognitive function + depression in hypercortisolaemia
Permissive effects on NE
Suppression of immune system
How does cortisol negatively effect Ca balance?
Decreases absorption from gut, increases excretion at kidney and increases bone resorption –> osteoporosis
Why is Cushing’s disease (hypercortisolaemia) associated with HTN?
In vascular smooth muscle, cortisol has a permissive effect on NE so increases vasoconstriction
True or false:
Low levels of cortisol are associated with HTN
False - low levels of cortisol are associated with hypotension
How does cortisol suppress the immune system?
Reduces lymphocyte count, reduces antibody formation and inhibits inflammatory response
What are the side effects of glucocorticoid therapy?
Immune suppression: increased freq. + severity of infections
Protein catabolism: muscle wasting
Lipolysis: loss of percutaneous fat gives thinning of skin appearance
For unknown reasons fat redistributed to trunk and face (moon face)
What kind of hormone is aldosterone?
Mineralocorticoid
Where does aldosterone act?
Distal tubule of kidney
What is the role of aldosterone?
Increases resorption of Na
Promotes excretion of K
Name the system that controls the secretion of aldosterone
Renin-angiotensin-aldosterone system (RAAS)
What does increased levels of aldosterone lead to?
Increased Na and decreased K –> increased blood volume and increased BP
What does decreased levels of aldosterone lead to?
Na loss and increased plasma K –> diminished blood volume and decreased BP
What is hypersecretion of cortisol known as?
Cushing’s disease/syndrome
What is the most common cause of hypersecretion of cortisol?
Pituitary tumour (cushing’s disease) - due to too much ACTH
What other things can cause Cushing’s syndrome?
Adrenal tumour
Iatrogenic - too much cortisol administered
What is the biggest cause of hyposecretion of cortisol?
Addison’s disease (hyposecretion of ALL adrenal steroid hormones)
What causes Addison’s disease?
Autoimmune destruction of adrenal cortex
How does alcohol affect ACTH/CRH?
It depresses the neurons involved in negative feedback further enhancing stress effect and increasing ACTH and CRH
–> inc. cortisol and immunosupression
Describe the structure of the adrenal medulla
Preganglionic sympathetic fibres terminate on specialised postganglionic cells in the adrenal medulla (these do not have axons and release adrenaline into the blood directly)
What is a phaeochromocytoma?
Tumour of the adrenal medulla which secretes xs catecholamines –> increased HR, increased BP
How will the levels of CRH, ACTH and cortisol be affected by pathology in the hypothalamus?
CRH high
ACTH high
Cortisol high
How will the levels of CRH, ACTH and cortisol be affected by pathology in the pituitary?
Low CRH
High ACTH
High cortisol
How will the levels of CRH, ACTH and cortisol be affected by pathology in the adrenals?
Low CRH
Low ACTH
High cortisol
Why do you have to be careful withdrawing chronic glucocorticoid treatment?
Additional therapeutic cortisol enhances negative feedback on hypothalamus + pituitary reducing release of CRH and ACTH
Loss of trophic action of ACTH on adrenal gland –> adrenal atrophy
Risk of adrenal insufficiency if withdrawal too fast
