Adrenal Gland, Stress Response Flashcards
Adrenal Glands
- aka suprarenal glands
- Paired, pyramid-shaped glands on superior surface of each kidney
- Covered externally with connective tissue capsule
Two glands in one
– Adrenal cortex: Outer region that produces corticosteroids
▪ Subdivided into three zones: Zona glomerulosa, zona fasciculata, Zona reticularis
– Adrenal medulla: Inner region that produces catecholamines
Aldosterone (principal mineralocorticoid)
– Secreted by zona glomerulosa of adrenal cortex
– Stimulus: Humoral (Renin-Angiotensin-Aldosterone mechanism)
▪ See next slide
– Stimulus: Hormonal (Adrenocorticotropic hormone from anterior pituitary)
– Target: Kidneys
▪ Action: stimulates Na+ reabsorption and K+ secretion
◦ Na+ reabsorption causes water reabsorption by osmosis
◦ Results in increased blood volume and blood pressure
▪ Action: promotes H+ excretion in urine
◦ Regulates blood pH and prevents acidosis (blood pH below 7.35)
Renin-Angiotensin-Aldosterone System
When your blood pressure falls, your kidneys release the enzyme renin into your bloodstream.
Renin splits angiotensinogen, a protein your liver makes and releases, into pieces. One piece is the hormone angiotensin I.
Angiotensin I, which is inactive (doesn’t cause any effects), flows through your bloodstream and is split into pieces by angiotensin-converting enzyme (ACE) in your lungs and kidneys. One of those pieces is angiotensin II, an active hormone.
Angiotensin II causes the muscular walls of small arteries (arterioles) to constrict (narrow), which increases blood pressure. potassium through your urine.
The increase in sodium in your bloodstream causes water retention. This increases blood volume and blood pressure, thus completing the renin-angiotensin-aldosterone system.
Aldosterone Regulation
Angiotensin II also triggers your adrenal glands to release aldosterone and your pituitary gland to release antidiuretic hormone (ADH, or vasopressin).
Together, aldosterone and ADH cause your kidneys to retain sodium. Aldosterone also causes your kidneys to release (excrete)
Cortisol (principal glucocorticoid), corticosterone, cortisone
– Secreted by zona fasciculata of adrenal cortex
– Stimulus: Hormonal (Adrenocorticotropic Hormone from anterior pituitary)
– Target: Liver, Muscles, Adipose tissue
▪ Action: Increases nutrients for stress
◦ Increases protein breakdown – amino acids can be used for synthesis of new proteins
◦ Increases lipolysis – release of fatty acids
◦ Increases gluconeogenesis – synthesis of new glucose molecules for ATP production
– Target: Blood vessels
▪ Action: Increase sensitivity to other vasoconstrictors
◦ Increases blood pressure
– Target: White blood cells
▪ Action: Anti-inflammatory
◦ Inhibit white blood cells that participate in inflammatory response
◦ Slows wound healing
◦ Useful in treatment of chronic inflammatory disorders (e.g., rheumatoid arthritis)
▪ Action: Depression of immune response
◦ High doses given to organ transplant recipients to retard tissue rejection
cortisol regulation
Your hypothalamus, a small area of your brain involved in hormonal regulation, and your pituitary gland, a tiny gland located below your brain, regulate the production of cortisol in your adrenal glands. When the levels of cortisol in your blood fall, your hypothalamus releases corticotropin-releasing hormone (CRH), which directs your pituitary gland to produce adrenocorticotropic hormone (ACTH). ACTH then stimulates your adrenal glands to produce and release cortisol
Gonadocorticoids
- DHEA (dehydroepiandrosterone) – principal androgen
– Secreted by zona reticularis of adrenal cortex
– Stimulus: Hormonal (Adrenocorticotropic Hormone from anterior pituitary)
▪ Does not affect negative feedback inhibition of ACTH
– Amount produced by adrenals is less than amount from testes
– Converted to estrogen in females
– Target: various body organs
▪ Action: Development of secondary sex characteristics
◦ Promotes libido (sex drive)
◦ Stimulates growth of axillary and pubic hair
◦ Contributes to prepubertal growth spurts
Epinephrine (adrenaline) and norepinephrine (noradrenaline)
– Secreted by adrenal medulla
– Stimulus: Neural (sympathetic stimulation)
– Target: Various body organs
▪ Action: Prolongs effects of sympathetic nervous (fight-or-flight) response
◦ Increases output of heart
◦ Increases blood pressure
◦ Increases blood flow to heart, liver, skeletal muscles, adipose tissue
◦ Dilates airways to lungs
◦ Increases blood levels of glucose and fatty acids
Alarm Reaction (Fight-or-Flight Response)
- Immediate reaction to stress
- Initiated by hypothalamic stimulation of the sympathetic
nervous system
– Adrenal medulla stimulated to secrete epinephrine & norepinephrine
to prolong response - Brings large amounts of oxygen and glucose to organs most
active in warding off danger: brain, heart, skeletal muscles - Inhibits nonessential digestive, urinary, reproductive activities
- Decreased blood flow to kidneys promotes renin secretion
– Stimulates aldosterone secretion for water retention and increased
blood pressure
Resistance Reaction
- Occurs after a few hours as glycogen stores in liver are depleted
- Initiated by hypothalamic secretion of releasing hormones
– Corticotropin Releasing Hormone (hypothalamic-pituitary-adrenal axis)
▪ Cortisol increases gluconeogenesis, lipolysis, protein catabolism
▪ Aldosterone increases Na+ retention (increases blood pressure)
– Growth Hormone Releasing Hormone (hypothalamic-pituitary-somatic axis)
▪ GH & IGF increase lipolysis and glycogenolysis
– Thyrotropin Releasing Hormone (hypothalamic-pituitary-thyroid axis)
▪ Thyroid hormones increases metabolism and ATP production
– Increased nutrients produce more ATP or repair damaged cells - Helps body continue fighting stressor long after fight-or-flight
reaction dissipates
Exhaustion Stage
- Occurs after weeks or months as resources are depleted
- Continued secretion of resistance reaction hormones
– Cortisol secretion continues to increase glucose levels
▪ Body becomes progressively weaker as body cells are broken
down (muscle wasting)
– Cortisol secretion also suppresses immune system
– Aldosterone secretion may cause fluid, electrolyte, & pH imbalances - May lead to organ failure and death
Stress response
see slide
