homeostasis, stress, and adaptation

what is homeostasis?

a dynamic, steady state in which all body systems are balanced at an ideal “set point”

homeostasis is a continuous regulation of what vital functions?

temperature

blood glucose

heart rate

oxygen and acid-base balance

what is allostasis?

the process by which the body responds to stressors in order to regain homeostasis

the body’s active work of adapting

what is stress?

a real or perceived threat to homeostasis

triggers allostatic (compensatory) mechanisms

how can stress look like?

can be physical, chemical, or emotional

what is a stressor?

any factor (real or perceived) that produces tension or strain on the body or mind can act as a stressor

parts of the CNS stress cascade

hypothalamus

anterior pituitary

hypothalamus function

secretes corticotropin-releasing hormone

anterior pituitary function

responds by secreting adrenocorticotropic hormone (ACTH)

what is the purpose of the CNS stress response?

to provide good circulation/perfusion with oxygenated blood

stages of the stress response

1. alarm

2. resistance

3. exhaustion

what happens during the alarm stage?

sympathetic-adenal-medullary (SAM) activation → fight or flight

norepinephrine and epinephrine are released

what does norepinephrine do?

constricts vessels

raises BP

dilates pupiles

inhibits insulin

what does epinephrine do?

INC heart contractility and cardiac output

bronchodilation

INC blood glucose

what is the purpose of norepi/epi?

demand for resources INC so you need more oxygen

what happens during the resistance stage?

HPA (hypothalamic-pituitary-adrenal) axis drives adaptation

presence of cortisol, aldosterone, endorphins

what does cortisol do?

affects protein metabolism, promotes apetite, anti-inflammatory

what does aldosterone do?

reabsorbs Na+/water

raises BP

what do endorphins do?

raise pain threshold

immune cytokines rise

what happens during the exhaustion stage?

body can no longer return to homeostasis

using all our resources and the stressor is not going away

allostatic overload

what is allostatic overload?

cumulative “wear and tear" on organs and tissues → damage is occurring now

what causes the exhaustion stage? what can it progress to?

result of an excessive or poorly regulated stress response

can progress toward disease or death

how does chronic stress effect the body?

other systems are rationed for resources