Adrenal Glands

three layers of the adrenal cortex

zona glomerulosa, zona fasciculata, zona reticularis

zona glomerulosa

outer most layer of the adrenal cortex

secretes mineralcorticoids (aldosterone)

aldosterone

regulates [Na+], [K+] and blood volume (since water follows salt)

specifically Na reabsorption, K secretion

zona fasciculata

middle layer of adrenal cortex

secretes glucocorticoids/glucosteroids (cortisol)

zona reticularis

innermost layer of the adrenal cortex

secretes mostly sex steroids (androgens)

DHEA

androgen

contributes to pubertal growth spurt in both sexes and important in inducing secondary sex characteristics in females

steroid hormone synthesis

the production of a specific adrenal steroid hormone in each zone is determined by which enzymes are present in each zone (which alter the chemical structure of cholesterol)

production of cortisol from cholesterol

cholesterol --> prenenolone --> 17-hydroxyprogesterone--> cortisol

cortisol is considered

the main stress hormone

3 hormone cascade for cortisol

neural inputs cause hypothalamus to secrete CRH

CRH causes anterior pituitary to release ACTH

ACTH causes adrenal cortex to release cortisol

cortisol causes target cells to produce response

CRH

produced by the hypothalamus

corticotropin releasing hormone

tropic hormone

ACTH

released by the anterior pituitary gland (corticotropes)

Adrenocorticotropic hormone

tropic hormone

what cells in the anterior pituitary release ACTH

corticotropes

what part of the 3 hormone cascade for cortisol results in a negative feedback

increased plasma levels of cortisol negatively feedback on the hypothalamus and the anterior pituitary

stimuli that can enhance cortisol secretion

anxiety

pain

trauma

hypovolemia (low blood volume)

hypoglycemia (low blood sugar)

hypothermia (low body temp)

what other hormones are enhanced by the same stimuli as cortisol

catecholamines (epinephrine and norepinephrine)

epinephrine is released from

adrenal medulla (hormone)

Norepinephrine is released from

sympathetic neurons (neurotransmitter)

functions of basal or nonstress levels of cortisol

1. metabolic effects

2. permissive

3. anti-inflammatory/anti-immune

4. fetal/neonatal development

functions of basal or nonstress levels of cortisol: metabolic effects

liver glucose production between meals

provides substrates and maintain enzymes involved in metabolic homeostasis to keep plasma glucose concentrations regular

functions of basal or nonstress levels of cortisol: permissiveness

cortisol is permissive to adrenergic receptors of the cardiovascular system (# of alpha and beta-1 receptors increases to maintain adequate BP)

functions of basal or nonstress levels of cortisol: anti-inflammatory/ anti-immune

prevent hyper-response

functions of basal or nonstress levels of cortisol: fetal/neonatal development

fetal development of brain, intestines, lungs, glands

turns on surfactant late in gestation to help inflate lungs

functions of cortisol in stress

1. metabolic effects

2. bone resorption

3. support sympathetic

4. stimulates erythropoietin

5. anti-inflammatory/ immunosuppression

6. inhibition of non-essential functions

functions of cortisol in stress: metabolic effects

catabolizes body stores of nutrients thereby mobilizing glucose, fatty acids, amino acids for energy and tissue repair

can cause tissue wasting, muscle loss, elevated blood glucose

functions of cortisol in stress: bone resorption

Ca+2 mobilization for possible bone repair

results in osteoporosis with prolonged exposure

functions of cortisol in stress: support sympathetic

supports sympathetic responses related to vasoconstriction

high BP with prolonged exposure

functions of cortisol in stress: stimulates erythropoietin

replaces RBC's if bleeding out

polycythemia with prolonged exposure (too many cells, blood becomes thick)

functions of cortisol in stress: anti-inflammatory/immunosuppression

helps in treatment and prevent rejection of transplanted organs

increased susceptibility for infection with prolonged exposure

functions of cortisol in stress: inhibition of non essential functions

reproduction and growth

adrenal insufficiency results in

cortisol hypo-secretion

primary adrenal insufficiency

Addison's disease

primary adrenal insufficiency is caused by

-destructive tumors

-infection

-autoimmune destruction (most common)

to the adrenal cortex

primary adrenal insufficiency results in

hypotension

low blood glucose

high plasma ACTH and CRH (no negative feedback)

secondary adrenal insufficiency is caused by

anterior pituitary dysfunction = loss of ACTH

secondary adrenal insufficiency results in

similar symptoms as primary adrenal insufficiency, but with low ACTH

hypotension

low blood glucose

high CRH

cortisol hypersecretion

cushing's syndrome/disease

Cushing's syndrome

hypercortisolism and all of its effects, regardless of original cause

when cortisol is HIGH (any scenario)

Cushing's disease

a case of Cushing's syndrome when the cause is identified as an ACTH-secreting tumor (anterior pituitary affected)

cortisol hypersecretion is caused by

hyper-secreting tumors (on adrenal gland or anterior pituitary)

glucocorticoid therapy for other conditions

hypersecretion of cortisol results in

osteoporosis

thin skin

muscle weakness

immunosuppression

high blood glucose

hypertension

decreased fertility

stunted growth

redistribution of fat

redistribution of fat when cortisol levels are high

obesity in trunk and face yet wasting of arms and legs with unusual deposition of fat on back/shoulders

what are other hormones released during stress

aldosterone

vasopressin

growth hormone

glucagon

beta-endorphin

epinephrine

aldosterone

increases Na+ retention and BP

vasopressin

increases water retention and BP

growth hormone

breaks down fat, mobilizes blood glucose

glucagon

mobilizes glucose from liver stores

beta-endorphin

pain relief and mood elevator

stress can decrease the levels of

insulin

insulin

storage hormone

with less insulin during stress, levels of glucose, fatty acids, and amino acids in the plasma increase