Adrenal glands Flashcards
What are the 2 regions of the adrenal glands?
Cortex
Zona medulla
What are mineralocorticoids?
A corticosteroid which is involved with maintaining the salt balance in the body, such as aldosterone.
In plasma, aldosterone binds weakly to proteins, this stimulates transcription of specific genes coding for proteins that stimulate the Na+/K+ pump, or facilitate Na+ entry (sodium channels) into the tubular renal cells.
Increased Na+ reabsorption causes a simultaneous water reabsorption which stimulates potassium excretion.
What is secretion of aldosterone stimulated by?
An increase in the concentration of K+ in the interstitial fluid (strong effect).
A decrease in Na+ concentration (weak effect).
ACTH (weak effect).
Renin-angiotensin-aldosterone pathway (strong effect).
What is hyperaldosteronism?
Hyperaldosteronism is a disorder in which the adrenal gland releases too much of the hormone aldosterone into the blood.
Hyperaldosteronism can be primary or secondary.
What do adrenal androgens do?
Androgens help people enter puberty and mature physically.
Females with high androgen levels may develop acne, facial hair and other issues.
Males with too little androgen may have low sex drives and develop breasts (gynecomastia).
Mainly dehydroepiandrosterone (DHEA) and Androstendione.
Release is stimulated by Adrenocorticotropic hormone (ACTH).
Excessive secretion may lead to a tumour of the adrenal gland.
What are glucocorticoids?
Glucocorticoids are corticosteroids that bind to the glucocorticoid receptor that is present in almost every vertebrate animal cell.
They maintain blood pressure and cardiovascular function.
They are essential for regulation of carbohydrate and protein metabolism.
They stimulate:
Synthesis of glycogen in the liver.
Breakdown of proteins.
Breakdown of lipids.
Conversion of protein and fat products into carbohydrates.
They reduce the immune system’s inflammatory response.
Why is cortisol important?
What is the effect cortisol has on metabolism?
Cortisol is crucial for maintaining normal metabolism.
During stress situation plasmatic cortisol can raise dramatically.
Cortisol will promote glucose and glycogen synthesis giving the organism enough energy to face the stressful situation.
Catabolism of amino acids and fatty acids into glucose precursors.
More glucose available.
Glycogen synthesis.
What is Cushing’s syndrome?
Occurs when the body’s tissues are exposed to excessive levels of cortisol for long periods of time.
Due to:
Prolonged intake of corticoids to treat an inflammatory disease like asthma, rheumatoid (iatrogenic cause).
Overproduction of endogenous cortisol (pituitary tumors, lung tumors).
Symptoms:
Moon face (round, red and full).
Buffalo hump.
Muscle weakness, spindly arms and legs.
Weight gain (redistribution of fat, with central obesity).
Skin blushing and flushing.
Poor wound healing.
Hyperglycaemia.
Can be:
ACTH dependent (pituitary tumour or ectopic tumour). ACTH levels extremely high.
Non-ACTH dependent (iatrogenic cause, adrenal tumour).
ACTH level extremely low.
What is Addison’s disease?
Addison’s disease develops when the outer layer of your adrenal glands (adrenal cortex) is damaged, reducing the levels of hormones it produces.
Classical Addison’s disease:
Total or near total destruction of both adrenal glands (primary insufficiency; cause: autoimmune disease,
can be also be related to tuberculosis).
Secondary adrenal insufficiency:
Pituitary alteration of secretion of ACTH, aldosterone secretion may remain adequate.
Symptoms:
Fatigue, loss of appetite, nausea weight loss.
Low blood pressure, Muscle weakness.
Craving for salty foods.
Inappropriate tan, hyperpigmentation (ACTH/MSH oversecreted).
What does the adrenal medulla consist of?
The adrenal medulla, which is composed of chromaphin cells, forms the gray core of the adrenal gland.
These cells synthesize and store the catecholamines norepinephrine, epinephrine, and dopamine.
The adrenal medulla is considered a specialized postganglionic sympathetic neuron devoid of an axon.
Synthesis:
Hydroxylation of tyrosine (tyrosine hydroxylase).
Decarboxylation of DOPA to dopamine.
Hydroxylation to Norepinephrine (in dense granules).
Methylation of Norepinephrine to Epinephrine .
How does release following sympathetic activation work?
Preganglion fibre releases Ach.
This leads to Ach nicotinic receptor activation
Depolarization/Ca2+ entry, this releases adrenaline and NA.
Cholinergic preganglion neurone binds to nicotine receptor.
Nicotine Ach receptor stimulation which promotes adrenaline release.
Sympathetic stimulation can be induced by stress.
What are catecholamines?
The body releases catecholamines in response to emotional or physical stress.
Catecholamines are responsible for the body’s “fight-or-flight” response.
Dopamine, adrenaline, and noradrenaline are all catecholamines.
What do epinephrine and norepinephrine target?
Epinephrine and Norepinephrine target adrenoceptors, released from the adrenal medulla under sympathetic stimulation.
The absence of the adrenal medulla is not critical.
Oversecretion: Phaechromocytoma (rare, mainly caused by tumour of adrenal medulla).
What role does stress play on the adrenal glands?
Stress activates nervous and endocrine responses that prepare the body for physical activity.
Increased CRH release from the hypothalamus and increased sympathetic stimulation of the adrenal medulla.
CRH stimulates ACTH secretion from the anterior pituitary, which in turn stimulates cortisol from the adrenal cortex.
Increased sympathetic stimulation of the adrenal medulla increases epinephrine secretion
Increased sympathetic stimulation increases norepinephrine secretion from sympathetic (postganglionic) nerve endings.
Catecholamines and cortisol increase blood glucose levels and the release of fatty acids from adipose tissue and the liver.
Sympathetic innervation of the pancreas decreases insulin secretion.
Glucose becomes more available to the nervous system; and fatty acids (in addition to glucose) can be used by skeletal muscle, cardiac muscle, and other tissues.
Epinephrine and sympathetic stimulation also increase cardiac output, blood pressure, and act on the CNS to increase alertness and aggressiveness.
Cortisol decreases the initial inflammatory response.
