Lecture 5 - Stress and Pregnancy

Question 1

Homeostasis and Stress and Allostasis Model

Answer 1

• See-saw model
• Homeostasis: Bodies optimal range for functioning
  
  • Mechanisms can alter the equilibrium in response to situations (like fever)
• Stressor: distrupts homeostasis (pushing down the stupid see-saw thing)
  
  • Other things that promote homestasis can counteract against the stressor
  • Includes pain
  • Stress can also be prolonged and not immediate
  • Prolonged stress releases glucocorticoids
• Allostasis: internal changes that are needed to restore homestasis can itself cause stress
  
  • Pain perception is reduced during immediate stress response

Question 2

Glucocoritcoids

(Process and evidence)

Answer 2

• In mammals. reptiles and birds
• Help the organism deal with longer term stressors thatn cholamines
  
  • Tradeoff in energy allocation: supresses growth, reproduction, immunity
• Process: Sympathetic nervous system sends signal to:
  
  • Hypothalamus - releases coritcotropin releasing hormone CRH to ->
  • Adrenal glands
    
    • Releases catecholamines (energy mobilization, alertness, blood flow, respiration)
    • Glucocorticoids also released, and sent back to the CNS (negative feedback loop)
• Evidence: Time since stressor glucocorticoid release peaks after then returns to baseline
  
  • Some conditions have glucorticoids stay high and never return to baseline (like depression)

Question 3

Sapolsky

(crazy beard)

Answer 3

• Stress response is adaptive, but chronic mobilization of stress response can be pathogenic

Question 4

3 Effects Glucocorticoids on the brain

Answer 4

• Atrophy of dendrites
• Death or neurons (through necrosis and apoptosis)
• Inhibition of neurogenesis
  
  • Decrease in hippocampal volume for every day of untreated depression

Question 5

Pregnancy

(adaptations for prolonged/chronic stress management)

Answer 5

• During pregnancy, cortisol secretion is dampened
  
  • Thought to be because its bad for the baby
  • But CRH is produced by the placenta and is 100x higher in mom than fetus
    
    • Placenta is constructed from dads genes and are not expressed by mom (imprinting)
  • Thought to be because it serves as a clock for important pregnancy events
    
    • “Placental clock hypothesis” - Problem: CRH supresses contractions
    • Suggests Maternal-Fetal conflict

Question 6

Maternal-fetal conflicts

Answer 6

• Mom and fetus only share 50% of genes
• Opportunity for conflicts over amount of resources mom gives fetus
  
  • Fetus can prodcues chemicals that force mom to provide more resources
  • Opposite for mom
• Co-evolutionary arms race
  
  • Disorders like gestational diabetes (mom develops IR - more glucose to fetus), and preclampsia (high BP in mom - more delivery of nutrients)
    
    • Fetus getting the upper-hand on mom

Question 7

Evidence for pregnancy idea

Answer 7

• CRH as an adaptation of the fetus to increase maternal provisioning
• CRH increases placental uptake of glucose
• Placental CRH increases during maternal fasting
  
  • Tries to take more resources from already limited amount
• CRH doesn’t harm the fetus (turns it to inactive form)

Question 8

Alternative Views

Answer 8

• Body did not evolve to handle this kind of chronic stress
• Chronically high stress responses have negative effects because:
  
  • Body DID evolve to handle chronic stress and the negative effects are best understood as tradeoffs