The Adrenal gland Flashcards
(29 cards)
How much does an adrenal gland weigh?
4g
Describe the venous drainage of the adrenal veins
Left adrenal vein - left renal vein
Right adrenal vein - inferior vena cava
What does the adrenal medulla produce?
Catecholamines e.g. norepinephrine and epinephrine
What are the 3 layers of the adrenal cortex (outermost to innermost) and what do they each produce?
Zona glomerulosa - mineralocorticoids e.g. aldosterone
Zona fasciculata - glucocorticoids e.g. cortisol
Zone reticularis - androgens e.g. sex hormones
What are the main products of the cortex?
Aldosterone and cortisol
What type of hormones are produced in the adrenal gland, and what are they derived from?
Steroid hormones, all derived from cholesterol
What is the pre-hormone of the sex hormones which declines with age?
DHEA
What is a common cause of congenital adrenal hyperplasia?
Defects in 21-hydroxylase
What are some feedback loops in the hypothalamic-pituitary-adrenal pathway?
Cortisol inhibits corticotrophin releasing hormone (CRH) via long loop feedback
Also short-loop feedback by ACTH on CRH.
How much of cortisol is protein bound in plasma, and what to?
~95% of plasma cortisol is bound to a carrier protein, cortisol binding globulin (CBG).
What cells express cortisol receptors?
ALL nucleated cells
What are the functions of glucocorticoids?
Glucocorticoids, such as cortisol, respond to signs of stress and play a role in the regulation of glucose metabolism and turn off pro-inflammatory genes to act as a feedback mechanism for the immune system e.g. COX enzymes, NO etc
When is there typically high levels of cortisol in the blood?
Highest peak in the morning when we wake up
Why is cortisol important for survival?
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.
Removal of adrenal glands also renders animals incapable of maintaining their extracellular fluid volume, an effect mediated by aldosterone
Describe 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 to maintain brain supply while also creating a substrate (glycerol) for gluconeogenesis.
Decreases insulin sensitivity of muscles and adipose tissue.
What are the non-glucocorticoid actions of cortisol?
Negative effect on Ca2+ balance: decrease absorption from gut, increases excretion at kidney resulting in net Ca2+ loss. Also increase bone resorption → osteoporosis e.g. following long term glucocorticoid therapy
Impairment of mood and cognition: depression and impaired cognitive function are strongly associated with hypercortisolaemia.
Permissive effects on norepinephrine: particularly in vascular smooth muscle (α-receptor effect = vasoconstrictive). Cushing’s 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. use of glucocorticoids for asthma/organ transplant patients, avoid LT though!
What are the side effects of glucocorticoid therapy?
Frequent infections with increased severity
Muscle wasting
Thinned skin
What is the function of aldosterone?
Aldosterone increases the reabsorption of Na+ ions and promotes the secretion of K+ ions.
What is the result of increased aldosterone?
Increased aldosterone release stimulates Na+ (and H2O) retention and K+ depletion, resulting increased blood volume and increased blood pressure.
What is the result of decreased aldosterone?
Decreased aldosterone leads to Na+ (and H2O) loss and ↑[K+]plasma, resulting in diminished blood volume and decreased blood pressure.
What stimulates aldosterone production by the adrenal glands?
Production of aldosterone (in adult humans, about 20–200 micrograms per day) in the zona glomerulosa of the adrenal cortex is regulated by the renin-angiotensin system. Renin is secreted from the kidneys in response to variations in blood pressure and volume and plasma sodium and potassium levels.
What can cause hypersecretion of cortisol?
Cushing’s syndrome/disease: Hypersecretion is most commonly due to a tumour either in:
• Adrenal cortex (1o hypercortisolism = Cushings’s syndrome)
• Pituitary gland (2o hypercortisolism = Cushing’s disease) Most common. Excess ACTH due to pituitary tumour
Iatrogenic - Too much cortisol administered therapeutically (prednisone)
What can cause hyposecretion of cortisol?
Addison’s disease - Hyposecretion of all adrenal steroid hormones due to AI destruction of adrenal cortex
What are some signs of Cushings?
Red moon face
Thin arms - muscle and fat wastage
Abdominal fat gain
