Adrenal disorders Flashcards
Is the adrenal medulla necessary for life?
- no, the nervous system can kick in to produce E and NE
How long can you live without adrenal function?
- 4-14 days
GFR
Glomerulosa:mineralocorticoids
Fasciculata: cortisol
reticularis: sex hormones (androgens)
What are adrenocorticoids?
steroid hormones secreted by adrenal cortex and classified by biological activity
- glucocorticoids, mineralocorticoids, and androgens
(acetate and cholesterol basis to all of these hormones)
What controls the secretion of the glucocorticoids?
- ACTH which is secreted by anterior pituitary gland
- aldosterone is controlled by renin which is secreted by the kidneys
What are glucocorticoids?
general classification of adrenal cortical steroid hormones that are primarily active in protecting against stress and in affecting protein and carbohydrate metabolism (cortisol)
hypothalamus control over the adrenocroticoids?
- regulated by negative feedback by HPA system
- hypothalamus releases: CRH -> anterior pituitary -> releases ACTH -> adrenal glands -> cortisol and androgens
When does coritol peak?
- in the morning, declines as the day progresses due to CNS and rhythmic cycle
What are mineralocorticoids?
- steroid hormone regulating the retention and excretion of fluids and electrolytes (especially Na and K) by the kidneys (aldosterone)
What are 2 different meanings of corticosteroids?
- can refer to any of the steroid hormones secreted by the adrenal cortex or steroid hormones manufactured synthetically for use as a drug
What is the purpose of the adrenal sex hormones?
- exert little effect on sexual function
- DHEA (dehydroepiandrosterone)
- pubertal growth of body hair
What is made in the adrenal medulla?
- epi and NE
What are the 3 parts of the adrenal cortex?
- zona glomerulosa: mineralocorticoid- aldosterone
- zona fasciculata: glucocorticoids- cortisol, corticosterone
- zona reticularis: androgens- DHEA, androstendione
Adrenal medulla physiology?
core of the adrenal gland
- made of chromaffin cells (named because of their brown staining with chromic acid salts) -main source of catecholamines, epi, and NE)- hormones underlying the fight or flight response
- receives input from SNS through preganglionic fibers originating in the thoracic spinal segments 5-11.
- cortisol produced in the adrenal cortex reaches the medulla in high levels causing up regulation increasing production of epi
NE and E have longer or shorter effects when released from adrenals compared to nervous system?
- 5x longer effects when released from adrenals
- just short term response from SNS: won’t last as long, pupils will dilate
Main functions of the SNS?
- “fight or flight”
- mobilize energy stores of the body
- increase blood flow to skeletal muscles and heart while diverting flow from skin and internal organs
- dilation of bronchioles
- dilation of pupils
Where are Epi and NE released from?
- from adrenal medulla
- interact with both alpha and beta receptors
What are the actions of Epi and NE?
- cardiovascular: strengthens teh contractility of myocardium (beta 1 action, inotropic action)
increases rate of contraction (beta 1 action, chronotropic action)
constricts arterioles in the skin (alpha 1 action)
dilates vessels to liver and skeletal muscle (Beta 2 action) - respiratory: powerful bronchodilation: by acting directly on bronchial smooth muscle (beta 2 action) this is impt to understand because it relieves all known allergic or histamine induced bronchoconstriction and can be life saving in the case of anaphylactic shock
- hyperglycemia: increased release of glucagon, increased glycogenolysis (conversion of glycogen to glucose)
- lipolysis
What is a pheochromocytoma?
- a tumor derived from neural crest cells of the SNS that is responsible for about 0.1-2% of all cases of hypertension
- the tumor relesases catecholamines, which cause episodic or sustained signs and sxs, such as palpitations, sweating, HAs, fainting spells, and hypertensive emergenices.
- this is a surgically correctable form of HTN
What are the 2 main catecholamines?
- NE and E
what is the relationship b/t adrenal medulla and ANS?
receives input from SNS through preganglionic fibers originating in the thoracic spinal cord segments 5-11 SNS -> fight or flight
How can we specifically explain sxs in a pt who has pheochromocytoma?
- increased HR, pounding heart, cold hands and feet
What meds can be used to help lower BP in pt with pheochromocytoma?
Phenoxybenzamine (alpha blocker)
Where do the great majorit of pheochromocytomas present?
- in adrenal medulla
Sxs of pheochromocytoma?
can be described by the effects that epi and NE have on the various organ systems:
- heart: catecholamines have 2 major effects, each mediated by Beta1 receptor
- blood vessels: vasoconstriction of cutaneous blood vessels via alpha 1 receptor
vasodilation of skeletal muscle blood vessels via Beta 2 receptor
-
If a pt had bad asthma, what would happen with their asthma sxs during an attack from the pheochromocytoma?
- the asthma sxs would improve because of the increased release of epi and NE
What is the 90% tumor rule for pheochromocytoma?
- 90% of time they arise from the adrenal medulla (with other 10% they can arise anywhere but the majority occur in the mediastinum or abdomen)
- 90% of the time adrenal pheochromocytoma will be unilateral (otherwise it is bilateral and is likely to be a genetic syndrome)
- 90% of time it isn’t malignant
- 90% of time it occurs in adults
What are some keys to pheochromocytoma?
Hx is very impt: pt usually has episodes of HTN, HA, palpitation, and sweating
- dx is made by demonstrating elevated urinary exretion of catecholamines or their metabolites (metanephrines and vanillylmandelic acid) during a period of HTN (24 hr urine test)
- once a dx is made: have to hunt for a source: CT of abdomen with focus on adrenal gland or MRI
What is the function of aldosterone and where is it made?
- made in the zona glomerulosa and is a mineralocorticoid
- it increases Na and water reabsorption by the kidneys and increases the secretion of K, thereby indirectly regulating blood volume and blood pressure
- this is the most impt sodium retaining hormone
- it regulates water and salt balance
What controls aldosterone secretion?
- secretion dictated minimally by adrenocorticotropic hormone by pituitary
- *** secretion dictated to a much greater degree in association with changes in blood pressure
If more aldosterone is released via low blood pressure, then wahat do you think it helps to do?
Helps to retain volume, so increased Na reabsorption means increased water absorption and this will increase BP
What is the system that responds to lowering of the blood pressure?
- the renin-angiotensin-aldosterone system controls blood pressure
- lowering of blood pressure is sensed by the distal tubules of the kidneys and the system releases aldosterone
What can block the renin-angiotensin-aldosterone system?
diuretics -> flush out Na and water
Kidneys control of BP?
The kidneys provide a hormonal mechanism -> regulation of BP by managing blood volume - renin-angiotensin -aldosterone system of the kidneys regulates blood volume
- decreasing blood pressure -> juxtaglomerular cells secrete renin and renin converts the plasma protein angiotensin II by the lungs
- Angiotensin II activates 2 mechanisms that raise blood pressure. Angiotensin II constricts blood vessels throughout the body -> raising blood pressure. Constricted blood vessels reduce the amount of blood delivered to the kidneys, decreasing excretion of water (raising blood pressure by increasing blood volume)
- angiotensin II stimulates the adrenal cortex to secrete aldosterone, reducing urine output by increasing retention of water by the kidneys (increasing bp by increasing blood volume)
What happens in the presence of increased aldosterone?
- increased blood volume and blood pressure
- increased K excretion in the urine meaning the pt will be hypokalemic
What is hyperaldosterone associated with?
- HTN, hypokalemia, and hypernatremia
Cause of hyperaldosterone?
- 1 or both of adrenals are hyperactive
- adrenals are being overstimulated (secondary hyperaldosterone)
What happens with with decreased aldoseterone?
- decreased blood volume and blood pressure
- decreased K excretion in the urine meaning hyperkalemia
What is the cause of primary aldosteronism?
- occasionally a small tumor of the zona glomerulosa cells occurs and secretes large amounts of aldosterone
(aldosterone causes an exchange transport of Na and K) so with primary aldosteronism we have Na conservation and K excretion
hypernatremia -> increased volume -> hypertension
hypokalemia -> if severe enough can cause muscle paralysis
Tx of primary aldosteronism?
- usually surgical removal of adrenal tumor