Physiology of the Adrenal Gland Flashcards
what is the adrenal gland?
small triangular glands located craniomedially to each kidney
retroperitoneal?
situated or occurring behind the peritoneum
the adrenal gland is like the kidney in what respect?
it is retroperitoneal
only their ventral surface is in contact with parietal peritoneum
why are they called adrenal glands?
ADrenal because of proximity to kidneys
what are the two parts of the adrenal gland?
outer cortex - steroid hormones such as cortisol and aldosterone
inner medulla - catecholamines such as adrenaline (epinephrine) and noradrenaline (norepinephine)
cortex development origins of the adrenal gland?
cortex develops from mesodermal tissue and secretes steroid hormones, primarily under control of the anterior pituitary gland
medulla development of the adrenal gland?
medulla develops from neuronal tissue and is functionally part of the sympathetic nervous system
it releases the catecholamine hormones adrenaline (epinephrine) and noradrenaline (norepinephrine)
the adrenal cortex can be further divided into three zones - what are these?
Zona glomerulosa - synthesis mineralocorticoids
Zona fasciculata - synthesises glucocorticoids
Zona reticularis - synthesises androgens
what are the hormones of the adrenal cortex called?
adrenocortical hormones
all steroid hormones are derived from?
from cholesterol
what is the end product hormone of each region of the cortex?
Zona glomerulosa - aldosterone
Zona fasciculata - cortisol
Zona reticularis - androstenedione and testosterone
structure of the hormones of the adrenal cortex?
all have the basic steroid carbon skeleton
what is the starting point of the structure of the hormones of the adrenal cortex?
cholesterol is the starting point - derived from cholesterol
first step of synthesis of the hormones of the adrenal cortex?
first step is removal of the cholesterol side chain (C22-C27)
hormones of the adrenal cortex are…
lipid soluble
hormones of th eadrenal cortex having cholesterol side chain forms?
pregnenolon
wherwe does th eformation of pregnenolon occur?
in the mitochondria of adrenocortical cells
what is the first step regulated by for the fomration of pregnenolone?
by the pituitary hormone 0 adrenocorticotropic hormones (ACTH) in the inner zones
Angiotensin Ii in outermost xone
ACTH is part of what axis?
hypothalamic-pituitary-adrenal axis
includes hypothalamus pituitary and adrenal glands
what si the primary stimulua of hypothalamic - pituitary-adrenal axis?
stress
rejun?
produced and released by the juxtaglomerular cells
what is rejun?
enzyme that converts the precursor angiotensinogen to angiotensin I
mineralocorticoids have crucial effects on what?
on the homeostasis of important inorganic ions (Na+ K+ Cl-)
aldesterone?
the most active hormone that is produced by the zona glomerulosa
what is ACTH necessary for?
for aldosterone secretion. howeber it has minor importance for the regulation of the rate of secretion
regulation of aldosterone secretion is mainly under control of what?
of the renin-angiotensin system (angiotensin II) and the extracellular conc of K+
aldosterone is produced and secrteed where?
from the zona glomerulosa of the adrenal gland
why is aldosterone produced?
in response to activation of the renin-angiotensin-aldosterone system
what does angiotensin II stimulate?
stimulates the release of aldosterone from the adrenal cortex
action of aldosterone stimulated by?
by systemic hypotension or high K+ intake
what membrane does aldosterone cross?
basolateral membrane of renal tubule cells
and binds to mineralocorticoid nuclear receptor
activation of aldosterone activates the transcription and synthesis of?
of new Na+ channels
New K+ channels
New Na+/K+ pumps
why does aldosterone act?
to increase reabsorption of Na+ and secretion of K+
Glucocorticoids?
the most important glucocorticoid in most domestic mammals in cortisol
(corticosterone in birds and rodents)
how is glucocorticoids transported?
it is tightly bound to cortisol-binding-globulin (CBG) so lasts longer - longer half-life
what is the release of glucocorticoids related to?
to circadian rhythms, particularly in humans - less so in domestic species
what is the main stimulus for release of glucocoticoids?
stress
what are the actions of glucocorticoids?
all nucleated cells in the body have cortisol receptors
describe cortisol molecules?
these are lipid soluble which can diffuse across the cell membrane and bind to cortisol receptors
what does the cortisol-receptor complex do?
it then binds to DNA and stimulates or inhibits the transcription of different genes
cortisol is an important stress hormone - explain why?
plasma levels increase greatly when sustained/high levels of stress affecting digestion, BP, and body’s energy resources
it also has a permissive action for catecholamines to induce vasoconstriction
immunomodulatory effects of glucocorticoids?
high levels of cortisol can reduced/reverse inflammatory and allergic responses (immunosuppression)
