The Adrenal Gland Flashcards
Around how many grams does each adrenal gland roughly weigh?
- 4g
State the names of the 2 seperate endocrine glands that make up the adrenal gland
- Adrenal medulla
- Adrenal cortex
What is the adrenal medulla derived from?
- Neural crest tissue (ectoderm)
What does the adrenal medulla secrete?
- Catecholamines
(adrenaline, noradrenaline and dopamine)
What is the adrenal cortex derived from?
- Mesoderm
The adrenal cortex is a true endocrine gland that secretes which 3 classes of steroid hormones?
- Mineralocorticoids (e.g. aldosterone: involved in the regulation of Na+and K+) - ESSENTIAL FOR SURVIVAL
- Glucocorticoids (e.g. cortisol: involved in maintaining plasma glucose) - ESSENTIAL FOR SURVIVAL
- Sex steroids (e.g. testosterone)
In the adrenal cortex, the
(a) Zona glomerulosa secretes
(b) Zona fasciculata secretes
(c) Zona reticularis secretes
(a) Aldosterone
(b) Glucocorticoids
(c) Sex hormones
In the adrenal cortex, how are different products produced in the different adrenal zones?
- All steroid hormones are derived from cholesterol, but different enzymes are found in different adrenal zones, resulting in different end products (hormones)
What is the prehormone of testosterone and oestrogen that is secreted by the adrenal cortex?
- DHEA
(dehydroepiandosterone)
Defects in 21-hydroxylase is a common cause of what?
- Congenital adrenal hyperplasia
(resulting in deficiency of aldosterone and cortisol and associated disruption of salt and glucose)
Descibe the control pathway for cortisol secretion
- It is known as the Hypothalamic-Pituitary-Adrenal Pathway
- The hypothalamus secretes the hormone CRH into the hypothalamic-hypophyseal system and transported to the anterior pituitary
- CRH then stimulates the release of ACTH from the anterior pituitary
- There is a short-loop feedback by ACTH on CRH
- ACTH in turn acts on the adrenal cortex to promote synthesis and release of cortisol
- Cortisol then acts as a negative feedback signal, inhibiting ACTH and CRH secretion
Why does a deficit in 21-hydroxylase results in 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.
Cortisol is a _________ hormone. What does this mean?
- Glucocorticoid
- Influences glucose metabolism
After diffusing out of adrenal glands into the plasma, how is most cortisol transported in the blood?
~ 95% of plasma cortisol is bound to a carrier protein, cortisol binding globulin (CBG)
What does cortisol do when it is released out of the blood and goes into taget cells?
- Cortisol is a steroid hormone therefore its receptor is in either the cytoplasm or nucleus
- Cortisol enters the cell and binds to a cytoplasmic/nuclear receptor
- This hormone receptor complex then migrates to the nucleus (if not already in the nucleus) and binds to DNA
- This alters gene expression, translation and transcription
Comparing ACTH to cortisol, which has “bursts” that last longer and why?
- Cortisol
- The half-life of cortisol is much longer
Describe the circadian rhythm of cortisol
- Peak is 6am - 9am
- Lowest level ~ midnight
(Notes: Other fluctutations during the day are due to effects of other stimuli which are related to stress. Diagram shows cortisol bursts > ACTH bursts)
If the adrenal glands are removed from an animal, what are the consequences?
- DEATH (within a few weeks)
- Loss of cortisol means animals cannot deal with stress, particularly in terms of maintaining blood glucose levels.
(the animal dies when exposed to any environmental stress - silverthorn)
Why is cortisol important for the brian?
- Cortisol helps to maintain blood glucose levels and so is crucial in helping to protect the brain from hypoglycaemia
What is more vital for the brain?
Cortisol or glucagon?
Why?
- Cortisol
- Glucagon alone is inadequete in responding to a hypoglycaemic challenge (in the absence of cortisol)
(Cortisol is required for full glucagon activity)
What are the 4 actions of cortisol on glucose metabolism? (glucocorticoid actions)
- Gluconeogenesis
- Decreases insulin sensitivity of muscle and adipose tissue
- Proteolysis (breakdown of skeletal muscle proteins is a substrate for gluconeogenesis)
- Lipolysis (gylcerol is a substrate for gluconeogenesis, free fatty acids is an alternative fuel supply that allows BG to be protected)
Excess cortisol?
- Diabetogenic
(becuase too much glucose will be release into the blood)
State the additonal actions of of cortisol (non- glucocorticoid)
(LATER)
LATER
What are the side effects of glucocorticoid therapy (cortisol)?
- Increased severity and frequency of infection (funciton of the immune system is suppressed)
- Muscle wastage (muscle is broken down - protein catabolism)
- Loss of percutaneous fat stores gives the appearance of thinning skin making it more fragile (lipolysis of adipose tissue)
Aldosterone increase the reabsorption of ___ ions and promotes the excretion of ___ ions
Aldosterone increase the reabsorption of Na+ ions and promotes the excretion of K+ ions
Increased aldosterone causes increased/decreased blood pressure.
- INCREASED
(Aldosterone release causes sodium and water retention, which causes increased blood volume, and a subsequent increase in blood pressure)
Hypersecretion of cortisol causes _________ while hyposecretion of cortisol causes __________
Hypersecretion = Cushing’s Syndrome
Hyposecretion = Addison’s Disease
Pheochromocytoma notes:
Pheochromocytoma is a rare neuroendocrine tumour, found in adrenal medulla which results in excess catecholamines (i.e noradenaline). This leads to:
↑HR → ↑CO → ↑BP
Diabetogenic due to adrenergic effect on glucose metabolism.
Responds well to surgery.
Withdrawing chronic glucocorticoid treatment (LATER)
- LATER
