The Adrenal Gland Flashcards
where are adrenal glands situated?
superior pole of the kidney in the retroperitoneal space, each weighing ~4g in adults.
what is the adrenal medulla?
modified sympathetic ganglion derived from neural crest tissue. Secretes catecholamines, mainly epinephrine (adrenaline), also norepinephrine and dopamine
what is the adrenal cortex?
is a true endocrine gland derived from mesoderm and secretes 3 classes of steroid hormones
what are 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
what are the 3 concentric zones that surround the medulla? and what hormones do they produce?
Zona glomerulosa aldosterone
Zona fasciculata glucocorticoids
Zona reticularis sex hormones
what are all steroid hormones derived from?
cholesterol, but different enzymes are found in different adrenal zones, resulting in different end products
what is a common cause of congenital adrenal hyperplasia?
deficiency of aldosterone and cortisol and associated disruption of salt and glucose balance.
why does a deficit in 21-hydroxylase cause adrenal hyperplasia?
Lack of 21-hydroxylase inhibits synthesis of cortisol.
This removes the negative feedback on ACTH and CRH release.
Increased ACTH secretion is responsible for enlargement of adrenal glands.
Negative feedback of ACTH on CRH synthesis remains.
Babies become very ill within a few days of birth
what kind of hormone is cortisol?
glucocorticoid hormone
how much of plasma cortisol is bound to a carrier protein?
95%
what percentage of nucleated cells have cytoplasmis glucocorticoid receptors?
all 100%
why is cortisol so important?
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 vitals as glucagon alone is inadequate in responding to a hypoglycaemic challenge.
what are the actions of cortisol on glucose metabolism?
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: similarly, cortisol 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.
what are additional actions of cortisol (non-glucocorticoid)
Negative effect on Ca2+ balance: decrease absorption from gut, increases excretion at kidney resulting in net Ca2+ loss. Also increase bone resorption osteoporosis
Impairment of mood and cognition: depression and impaired cognitive function are strongly associated with hypercortisolaemia.
Permissive effects on norepinephrine: particularly in vascular smooth muscle (-receptor effect = vasoconstrictive). Cushings Disease (hypercortisolaemia) is strongly associated with hypertension. Likewise, low levels of cortisol are associated with hypotension.
Suppression of the Immune System: Cortisol reduces the circulating lymphocyte count, reduces antibody formation and inhibits the inflammatory response. Latter effect can be useful clinically e.g. asthma/ulcerative colitis/organ transplant.
what is aldosterone?
Aldosterone is 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.
