The Adrenal Glands

ANSC 312

location of adrenal glands

two bilaterally symmetrical endocrine organs located just anterior to the kidneys

what are the two sections of the adrenal gland?

cortex and medulla

what are adrenal hormones important for?

for adaptation to adverse environmental conditions

• stress

• extreme temperatures

• anxiety, fear, excitement

• injury/illness

adrenal gland depicted in textbook

adrenal gland depicted on radiograph

adrenal gland depicted on abdominal ultrasound

function of cortex zone of adrenal gland

• produces steroid hormones

  • corticosteroid hormones

    • cortisol

    • aldosterone

function of medulla zone of adrenal gland

• produces amine hormones

  • norepinephrine

  • epinephrine

what are the 3 adrenal cortex layers?

• zona glomerulosa (outermost)

• zona fasciculata (middle)

• zona reticularis (innermost)

adrenocortical cells have intracellular features characteristic of steroid hormone synthesis. what are these features?

• abundance of lipid droplets (containing cholesterol)

• mitochondria

• smooth ER

the adrenal cortex produces 2 major types of corticosteroid hormones. what are they?

• glucocorticoids

• mineralocorticoids

glucocorticoids are produced by…

• Zona Fasciculata (MOST PRODUCTION)

• Zona Reticularis

function of glucocorticoids

regulation of all aspects of metabolism

major hormone produced by glucocorticoids

cortisol

mineralocorticoids are produced by…

Zona Glomerulosa

function of mineralocorticoids

important role in electrolyte balance and blood pressure

major hormone produced by mineralocorticoids

aldosterone

how are corticosteroid hormones transported in the blood

remember they’re steroid hormones

carried in blood through specific binding globulins called Corticosteroid-Binding Globulins (CBG)

List the ways that the Glucocorticoid hormone, cortisol, is transported in the blood

• Transcortin (75%)

• albumin (15%)

• unbound cortisol (10%)

list the ways that the mineralocorticoid hormone, aldosterone, is transported in the blood

• transcortin (10%)

• albumin (50%)

• unbound aldosterone (40%)

while there are distinct differences between corticosteroids and the effects they have on the body, it’s important to realize that there is some overlap in _________ _______

biological activity

glucocorticoids are important mediators of ___________

metabolism

function of glucocorticoids in relation to metabolism

• stimulates hepatic gluconeogenesis → increases blood glucose

• inhibits glucose uptake and metabolism → increases blood glucose

  • the ability to store excess blood glucose in tissues is inhibited

  • effect is referred to as Anti-Insulin Effect

  • clinical significance = iatrogenic diabetes mellitus

• stimulates lipolysis/fat redistribution to liver and abdomen

• inhibits protein synthesis and stimulates protein catabolism

• stimulates water excretion (diuresis)

regulation of glucocorticoid synthesis follows a negative-feedback system. Thus, glucocorticoids will inhibit the release of hormones. What hormones does it inhibit the release of?

• hypothalamic corticotropin-releasing hormone (CRH)

  • results in decreased ACTH secretion by the pituitary gland

• anterior pituitary ACTH

  • results in decreased cortisol release from adrenal gland

the glucocorticoid response to stress is __________

immediate

(the glucocorticoid response is proportional to the severity of the stress)

clinical symptoms of chronic excess glucocorticoids includes…

• tendency for high blood glucose

  • due to gluconeogenesis and anti-insulin effect

• larger liver and abdomen

  • due to increased fat storage in liver and abdomen

• muscle wasting

  • due to muscle break down and hindered repair

• excessive drinking and urinating

  • due to hindered water retention by kidneys

clinical significance of Glucocorticoids

• suppresses inflammation

  • injuries

  • allergic reactions

  • arthritis

  • itching

  • pain

what are the primary physiologic effects of mineralocorticoids

• electrolyte balance

• blood pressure homeostasis

mineralocorticoids promote electrolyte balance by acting on kidneys and promoting…

• retention of

  • sodium (Na+)

• excretion of

  • potassium (K+)

  • hydrogen (H+)

adrenocorticotropic hormone (ACTH) corticotropin stimulates secretion of glucocorticoids by the _______ __________ and Zona Reticularis is by the tropic hormone

Zona Fasciculata

the regulation of mineralocorticoid secretion is controlled by factors produced in the ______

kidney

(regulation of mineralocorticoids) in response to decreases in blood pressure, cells in the kidney produce and enzyme called ____________

renin

renin acts on _____________, an alpha2 globulin produced by the liver and is already present in the circulation

Angiotensinogen

the combination of renin with angiotensinogen results in…

a substance called Angiotensin I.

Angiotensin I is further hydrolyzed by an enzyme resulting in a substance called _____________

Angiotensin II

Angiotensin II stimulates the ________ _________ to produce mineralocorticoids (such as Aldosterone)

Zona Glomerulosa

Aldosterone acts on Kidneys to stimulate ____________ of Na+ and H2O, and ___________ of K+ and H+

retention; excretion

this results in electrolyte balance and blood pressure regulation

what is the central portion of the adrenal gland?

medulla

what does the adrenal medulla produce?

amine hormones called Catecholamines

what are the 2 types of catecholamines produced by the adrenal medulla?

• norepinephrine

• epinephrine

when are both norepinephrine and epinephrine released?

when nerve fibers to the adrenal medulla are stimulated during times of stress

what is epinephrine commonly referred to as?

adrenaline or “epi”

what is the major catecholamine secreted by the adrenal medulla of most mammals?

epinephrine

(synthesis of catecholamines within chromaffin cells) the synthesis of the catecholamines begins with either one of these amino acids…

Phenylalanine or Tyrosine

most catecholamines are derived from __________

tyrosine

chromaffin cells

the cells of the adrenal medulla which synthesize catecholamines

what is contained within chromaffin cells?

granules which contain the synthesized catecholamines (norepinephrine and epinephrine)

acetylcholine

release from the nerve fibers initiates the synthesis and release of the catecholamines by the medullary cells

the stimulation of release of catecholamines from chromaffin granules, a phenomenon called…

stimulus-secretion coupling

catecholamines are important mediators of

• metabolism

• acute stress response

a major metabolic change from catecholamine release is…

increased blood glucose

what is the primary catecholamine responsible for increased blood glucose?

epinephrine — inhibition of insulin secretion from pancreas

what happens during acute stress response?

• stimulate cardiac function (fast HR)

• relaxation of bronchial smooth muscle

• relaxation of smooth muscle of GI tract

• urine retention

• excitation of the CNS

  • awake and aware

  • sweating

  • piloerection

the main factors that stimulate catecholamine secretion are…

• acute stress response

• hypoglycemia