The Adrenal gland Flashcards
Where are the adrenal (suprarenal) glands situated?
Adrenal glands are situated on the superior pole of the kidney in the retroperitoneal space
What are the 2 separate endocrine glands within the adrenal gland?
Adrenal medulla
Adrenal cortex
What is the adrenal medulla and what does it secrete?
a modified sympathetic ganglion derived from neural crest tissue (makes up 25%)
Secretes catecholamines, mainly epinephrine (adrenaline), also norepinephrine and dopamine.
What is the adrenal cortex and what does it secrete
a true endocrine gland derived from mesoderm
secretes 3 classes of steroid hormones
What are the names of the 3 classes of steroid hormones that the adrenal cortex secretes
Mineralocorticoids e.g. aldosterone: involved in the regulation of Na+ and K+
Glucocorticoids e.g. cortisol: involved in maintaining plasma glucose
Sex steroids e.g. testosterone
Which 2 steroid hormones are essential for survival
cortisol and aldosterone
What are the 3 zones of the adrenal cortex
Zona glomerulosa
Zona fasciculata
Zona reticularis
Which hormone is secreted from the Zona glomerulosa
aldosterone
enzymes needed to make aldosterone are found only in the zona glomerulosa
Which hormone is secreted from the Zona fasciculata
glucocorticoids
Which hormone is secreted from the zona reticularis
sex hormones
What are all steroid hormones derived from
cholesterol
What is a common cause of congenital adrenal hyperplasia? and what is the effect of this
defects in the 21-hydroxylase enzyme
results in deficiency of aldosterone and cortisol associated disruption of salt and glucose balance
androgen biosynthesis is unaffected - accumulating steroid precursors are channeled into excessive adrenal androgen production
babies become very ill within a few days of birth
What % of plasma cortisol is bound to a carrier protein called cortisol binding globulin (CBG)?
95%
What is ACTH
Adrenocorticotropic hormone (ACTH) regulates levels of cortisol
Describe cortisol release
Marked circadian rhythm (same daily)
preceded by a similar pattern of release of ACTH. Cortisol burst persists longer than ACTH due to longer half-life
Peak is ~ 6-9am, nadir (lowest level) is ~ midnight.
Other fluctuations during the day are due to effects of other stimuli which are related to stress.
Why is cortisol so essential for life?
Loss of cortisol means animals cannot deal with stress, particularly in terms of maintaining blood glucose levels.
Cortisol as a glucocorticoid is crucial in helping to protect the brain from hypoglycaemia. It has a permissive action on glucagon, which is vital as glucagon alone is inadequate in responding to a hypoglycaemic challenge.
Actions of cortisol on glucose metabolism (4)
Gluconeogenesis: Cortisol stimulates formation of gluconeogenic enzymes in the liver thus enhancing gluconeogenesis and glucose production.
This is aided by cortisol’s action on muscle:
Proteolysis: cortisol stimulates the breakdown of muscle protein to provide gluconeogenic substrates for the liver.
Lipolysis: stimulates lipolysis in adipose tissue which increases [FFA] plasma creating an alternative fuel supply that allows [BG] to be protected while also creating a substrate (glycerol) for gluconeogenesis.
Decreases insulin sensitivity of muscles and adipose tissue.
How is excess cortisol diabetogenic?
Cortisol acts to oppose insulin
What other actions does cortisol have that are non-glucocorticoid
Negative effect on Ca2+ balance
impairment of mood and cognition - depression + impaired cognitive functioning links with hypercortisolaemia
permissive effects on norepinephrine
suppression of the immune system
How does cortisol suppress the immune system
Cortisol reduces the circulating lymphocyte count, reduces antibody formation and inhibits the inflammatory response.
Side effects of glucocorticoid therapy
Increases severity and frequency of infection (immune suppression
muscle wastage
loss of percutaneous fat stores gives appearance of ‘thinning skin’ making it more fragile
What is Aldosterone and what is it’s function
Aldosterone is a mineralocorticoid, which acts on the distal tubule of the kidney to determine the levels of minerals reabsorbed/excreted.
Aldosterone increases the reabsorption of Na+ ions and promotes the excretion of K+ ions.
What controls the release of aldosterone by the adrenal cortex
a complex reflex pathway originating in the kidney - the RAAS system
What is the end effect of aldosterone
Mainly on CVS
Increased aldosterone release stimulates Na+ (and H2O) retention and K+ depletion, resulting in increased blood volume and increased blood pressure.
Decreased aldosterone leads to Na+ (and H2O) loss and [K+]plasma, resulting in diminished blood volume and decreased blood pressure.
Which disease is associated with hypersecretion of cortisol
Cushing’s syndrome
Hypersecretion is most commonly due to a tumour in either the adrenal cortex or the pituitary gland
Which disease is associated with hyposecretion of cortisol
Addison’s disease
Hyposecretion of all adrenal steroid hormones
Due to autoimmune destruction of adrenal cortex
What is cushing’s disease characterised by?
wasting of the extremities (due to catabolic action of cortisol) but for unknown reasons fat is redistributed to the face (“moon face”) and trunk.
What things disinhibit the hypothalamo-pituitary-adrenal axis?
alcohol
caffeine
lack of sleep
Adrenal medulla
Modified sympathetic ganglion, not true endocrine tissue.
Similar to posterior pituitary in having neuroendocrine role.
Preganglionic sympathetic fibres terminate on specialised postganglionic cells in the adrenal medulla. These postganglionic fibres do not have axons – instead they release their neurohormones (adrenaline) directly into the blood.
What is Pheochromocytoma
A rare neuroendocrine tumour, found in adrenal medulla which results in excess catecholamines: increased HR => increased CO => big increase in BP
Diabetogenic due to adrenergic effect on glucose metabolism.
Responds well to surgery.
Name 3 sites of pathology in hypothalamic-pituitary-adrenal axis
In the hypothalamus
In the anterior pituitary
In the adrenal cortex
Why is care required when withdrawing glucocorticoid treatment
Due to enhanced negative feedback effects of exogenous cortisol
Additional, therapeutic cortisol enhances the negative feedback on hypothalamus and pituitary reducing release of CRH and ACTH.
Loss of trophic action of ACTH on adrenal gland cause atrophy of gland.
Risk of adrenal insufficiency if withdrawal is too fast.
