Homeostasis, Allostasis, & Adaptive Responses to Stressors Flashcards
Who was first credited with describing the basic premise of “homeostasis”?
Claude Bernard, a 19th-century French physiologist
What concept about homeostasis did Walter B. Cannon create in his 1932 book “The Wisdom of the Body”?
According to Cannon, homeostasis was a process where the body’s biochemical or physiologic variable were maintained within a narrow set-point range.
Who first introduced the concept of allostasis?
Sterling and Eyer in 1988
What is allostasis?
A dynamic process that supports and helps the body to achieve a steady-state.
What does a homeostatic response refer to?
Systems whose purpose is specifically to normalize selected physiologic variables.
Selye coined a process describing the components of adaptation to stressors. What are the 3 components of the general adaption syndrome?
- alarm reaction
- stage of resistance
- stage of exhaustion
What are “stressors”?
Anything that throws the body out of allostatic balance.
What is a “stress response”?
The body’s effort to try and restore balance.
What is another name for the “alarm stage”?
“fight-or-flight” response
What part of the brain activates the GAS in response to a stressor or imbalance in homeostasis?
The hypothalamus
How does the hypothalamus activate the GAS?
The hypothalamus secretes corticotropin-releasing hormone (CRH) which activates the SNS (sympathetic nervous system)
What happens after SNS activation by CRH?
The adrenal medulla (inner portion of the adrenal gland) releases catecholamines (norepinephrine and epinephrine).
What else in the hypothalamus secretes CRH and what does it stimulate?
The paraventricular nucleus (PVN) in the hypothalamus also secretes CRH which stimulates adrenocorticotropic hormone (ACTH) release from the anterior pituitary gland.
What happens after ACTH is releases during the “alarm stage”?
ACTH causes the adrenal cortex to release substantial amounts of glucocorticoids, specifically cortisol.
What is the name of the following pathway?
PVN (hypothalamus) - CRH secretion - anterior pituitary gland secretes ACTH - adrenal cortex releases glucocorticoids (mostly cortisol)
hypothalamic-pituitary-adrenal (HPA) axis
What is the name of the following pathway?
hypothalamus - CRH - adrenal medulla - catecholamine release (epi and norepi)
sympathetic- adrenal- medullary system
During the resistance (or adaptive) stage, what is the purpose of the SNS and adrenal medulla mobilizing the release of glucose, free fatty acids, and amino acids?
These resources act as fuel for metabolically active organs, the brain and heart, during stress.
The amino acids act as building blocks for later growth and repair after stress-state ends.
Why does “exhaustion” happen?
Because the stress response and all of it’s biological mediators can be harmful when repeatedly activated.
What is allostatic load?
The wear and tear on the body due to body systems being chronically over- or under-activated in order to support allostasis.
What is “toxic stress” and how does it occur?
“Toxic stress” has been used to describe stressors that cause allostatic imbalance in a situation where the person lacks sufficient resources and control to manage the situation.
In what population would you expect a prominent and more often dysregulatory glucocorticoid response?
Populations with depression and PTSD
In what population might you expect the SNS to be particularly active?
Populations with anxiety and vigilant states.
Are men or women more likely to experience allostatic overload, generally?
Women
From where does the hypothalamus receive information regarding stressors and whether response should be initiated?
From the cerebral cortex and limbic system (hippocampus and amygdala)
Release of catecholamines is prompted by the hypothalamus, but the hypothalamus doesn’t decide to release hormones. Where does the hypothalamus receive it’s information from?
The cerebral cortex and limbic system (including the hippocampus and amygdala) receive information, determine if stressors are harmful, and relay that information to the hypothalamus.
How does the body respond to stressors if the patient in unconscious or comatose (autonomic nervous system)?
Norepinephrine is directly released from the locus ceruleus and epinephrine from the adrenal medulla. Both are activated by the hypothalamus.
Preganglionic fibers synapse at the adrenal medulla as well, releasing epinephrine and some norepinephrine. These catecholamines are released into the bloodstream.
Which catecholamine is the primary constrictor of smooth muscle in blood vessels?
Norepinephrine
Which catecholamine acts as a bronchial smooth muscle dilator, enabling improved oxygenation?
Epinephrine
How does epinephrine elevate blood glucose levels?
By increasing glycogenolysis, releasing glucose from the liver while also inhibiting insulin secretion.
Are glucocorticoids lipid-soluble or non-lipid-soluble?
Lipid-soluble
How do catecholamines affect the heart?
Increased HR
Increased speed of conduction
Increased contractility
How do catecholamines affect the respiratory tract?
Relaxes bronchial smooth muscles to dilate airways
What do catecholamines constrict that reduce perfusion?
Vascular smooth muscle
Skin
Mesenteric bed
Kidneys
What do catecholamines dilate that cause increased perfusion?
Skeletal muscles, lungs, and heart
How do catecholamines increase a patient’s BP?
They vasoconstrict peripheral vasculature
How do catecholamines affect the GI tract?
Decreases peristalsis
Contracts sphincters
Decreases gastric acid secretion
How do catecholamines affect the eyes?
They contract radial muscles to dilate the iris and pupil
How do catecholamines affect the liver?
Gycogenolysis and gluconeogenesis increase glucose levels available
How to do catecholamines affect the CNS?
They promote arousal, attention, and vigilance
In what way do glucocorticoids affect metabolism?
Catabolize muscle, fat, lymphoid tissue, skin, and bone
Live gluconeogenesis
Opposes insulin in transport of glucose into cells
Increases appetite
How do glucocorticoids affect fluid balance?
With sodium and water retention
How do glucocorticoids affect inflammation and infection?
Suppress the inflammatory response
Increase neutrophil release
Decrease new antibody release
Decrease T-lymphocyte production and function
Decrease production of eosinphils, basophils, and monocytes
How do glucocorticoids support catecholamines?
By increasing epinephrine synthesis and enhancing vasoconstriction
