The Adrenal Gland Flashcards
What kind of hormone is cortisol?
Glucocorticoid hormone
What does a glucocorticoid hormone do?
Influences glucose metabolism
Binding of plasma cortisol
95% is bound to carrier protein - cortisol binding globulin (CBG)
What cells have cytoplasmic glucocorticoid receptors?
All nucleated cells
What kind of hormone is aldosterone?
Mineralcorticoid
Function of increased aldosterone
Increases reabsorption of Na+ ions and therefore H20 retention
Promotes the secretion of K+
Resulting in increased blood volume and increased BP
Function of a mineralocorticoid hormone
Acts on distal tubule of the kidney to determine the levels of minerals reabsorbed/excreted
Where is aldosterone secreted from?
Adrenal cortex
What is the secretion of aldosterone from the adrenal cortex primarily controlled by?
Renin-angiotensin-aldosterone (RAAS) system
Function of decreased aldosterone
Leads to Na+ (and H20) loss and increased [K+] plasma
Resulting in diminished blood volume and decreased BP
Where are the adrenal glands found?
Superior pole of the kidney
Retroperitoneal space
Where does the left adrenal vein drain into?
Left renal vein
Where does the right adrenal vein drain into?
IVC
What is found on the outside and the inside of the adrenal gland?
Outside - cortex
Inside - Medulla
How much of the adrenal gland is the medulla?
25%
How much of the adrenal gland is the cortex?
75%
Tissue of adrenal medulla
Modified sympathetic ganglion derived from neural crest tissue
Tissue of adrenal cortex
True endocrine derived from mesoderm
What type of hormones does the adrenal medulla secrete?
Catecholamines
What are the main catecholamines that the adrenal medulla secretes?
Epinephrine / Adrenaline
Norepinephrine
Dopamine
What 3 classes of steroid hormones does the adrenal cortex secrete and give an example of each?
Mineralcorticoids e.g. aldosterone
Glucocorticoids e.g. cortisol
Sex steroids e.g. testosterone
What two hormones produced by the adrenal gland are ESSENTIAL for survival?
Aldosterone
Cortisol
3 zones of the cortex
Zona reticularis
Zona fasciculata
Zona glomerulosa
What does the zona reticularis secrete?
Sex hormones
What does the zona fasciulata secrete?
Glucocorticoids
What does the zona glomerulosa secrete?
Aldosterone
Is the adrenal medulla true endocrine tissue?
No
Features of post ganglionic fibres in the adrenal medulla
Do not have axons
Instead release their neurohormones (Adrenaline) directly into the blood
How are different steroid hormones found in different zones of the adrenal cortex?
Different enzymes are found in different adrenal zones
What is the pre-hormone of testosterone and oestrogen called?
DHEA
What does DHEA decline with?
Age
What does ACTH stand for?
Adrenocorticotrophic hormone
What stimulates ACTH to be released from the anterior pituitary?
Corticotrophin releasing hormone (CRH)
What is used for negative feedback in the hypothalamic pituitary adrenal pathway?
ACTH on CRH
What is found in the pattern of cortisol release?
A marked circadian rhythm
What is the circadian rhythm of release of cortisol preceded by?
A similar pattern of release of ACTH
Half life in cortisol vs ACTH
Cortisol burst persists longer but half life is much longer
Peak of cortisol release is when?
approx. 6-9am
Nadir of cortisol release is when?
Midnight
What does nadir mean?
Lowest level
Other fluctuations of cortisol during the day are due to what?
Effects of other stimuli which are related to stress
What does cortisol have a permissive action to?
Glucagon
Actions of cortisol on glucose metabolism
Gluconeogenesis
Proteolysis in muscle
Lipolysis in adipose tissue
Decreases insulin sensitivity of muscles and adipose tissue
Why would lipolysis be an glucocorticoid action of cortisol?
Because lipolysis in adipose tissue increases [FFA] in the plasma creating an alternative fuel supply that allows [BG] to be protected while also creating a substrate (glycerol) for gluconeogenesis
Actions of cortisol which are non-glucocorticoid
Negative effect on Ca2+ balance (decrease absorption from gut, increases excretion at kidneys, increase bone resorption)
Impairment of mood (depression) and cognition
Permissive effects of norepinephrine (vasoconstrictive)
Suppression of immune system
How does cortisol suppress the immune system?
Reduces the circulating lymphocyte count
Reduces antibody formation
Inhibits the inflammatory response
Side effects of glucorticoid therapy
Increased severity and frequency of infection
Muscle wastage
What is a pheochromocytoma?
Rare neuroendocrine tumour found in the adrenal medulla
Pathology of pheochromocytoma
Results in excess catecholamines leading to increased HR -> increased CO and very increased BP
Diabetogenic
Pathology of cushings disease/syndrome
Hypersecretion of cortisol
Causes of cushings syndrome and what does this result in?
Tumour in the adrenal cortex
PRIMARY hypercortisolism
Causes of cushings disease and what does this result in?
Tumour in the pituitary gland
SECONDARY hypercortisolism
What is there an excess of in cushings disease?
ACTH
What is Addison’s disease?
Hyposecretion of all adrenal steroid hormones due to the autoimmune destruction of the adrenal cortex
What are CRH and ACTH release promoted by?
Stress
What are CRH and ACTH aggravated by and what does this do to the hypothalamo-pituitary axis (HPA)?
Alcohol
Caffeine
Lack of sleep
“Disinhibits” the HPA
Why is care required when withdrawing glucorticoid treatment?
Due to enhanced negative feedback effects of exogenous control
Therapeutic cortisol effects on negative feedback
Enhances negative feedback on hypothalamus and pituitary, reducing release of CRH and ACTH
What does loss of trophic action of ACTH on the adrenal gland cause?
Atrophy of the gland
What type of hormone is aldosterone?
Mineralocorticoids
What is another name for sex steroids?
Androgens
What is noradrenaline also produced by?
Sympathetic chain
