Chapter 11: Stress

Stress

any significant disturbance of homeostasis, as by extreme temperatures or psychological factors

Stressor

A condition, agent, or other stimulus that causes stress to an organism

Stress response

A suite of physiological and behavioral responses that help to reestablish homeostasis

Allostasis

the physiological/behavioral process of getting back to homeostasis

Allostasic load

The total cost of the allostasis process

Fight-or-Flight response

the automatic and endocrine responses that prepare an individual to battle or flee from real or perceived attack, harm, or threats to survival

During Fight-or-Flight

E and NE increase blood oxygen, blood glucose, and altertness
E acts first and doubles from resting values

Epinephrine

A hormone that increases blood glucose, oxygen, and alertness during the fight-or-flight response

Norepinephrine

A hormone that must increase fivefold to have the same effect as a doubling of epinephrine

After Fight-or-Flight

Glucocorticoids released minutes after and increase blood glucode levels

Glucocorticoids

Hormones that increase blood glucose levels and are released minutes after a fight-or-flight response

Corticosterone

The primary glucocorticoid in most rodents, birds, reptiles, and fish

Cortisol

The primary glucocorticoid in most primates, large mammals, and carnivores

Walter B Cannon

Pioneer in Stress Research and established the concept of homeostasis

HPA Axis

A complex and interactive system that comprises three endocrine glands: the hypothalamus, pituitary gland, and adrenal gland that constitute a major neuroendocrine system that regulates stress responses

HPA: Stress stimulates ____

release of E from adrenal medulla
release NE from sympathetic nervous system

HPA: E and NE stimulate _______

hypothalamus to release CRH

HPA: CRH stimulates _______

anterior pituitary to release ACTH and Beta-endorphis

HPA: ACTH stimulates _______

adrenal cortex to release glucocorticoids

HPA: Glucocorticoids signal ______

Hypothalamus and Pituitary to decrease CRH and ACTH release (negative feedback cycle)

General adaptation syndrome (GAS)

A three-stage reaction to stress proposed by Hans Selye, including the alarm, adaptation (resistance), and exhaustion stages

Hans Selye

Father of modern stress research

Alarm reaction

The first stage of GAS where there is decreased resistance to stress and physiological systems may suffer

Resistance

The second stage of GAS, where there is resistance to stress via increased adrenal function

Exhaustion

The third stage of GAS, believed to be the termination of the stress response, but actually the result of prolonged exposure to stress hormones

If stress prolonged or resistance fails

Exhaustion: with physiological and behavioral coping mechanisms failing and survival compromised

Adaptive features of acute stress response

Include immediate availability of energy, increase in oxygen uptake, decrease in blood flow in non-essential areas, inhibition of digestion, growth, immune function, reproductive function, pain perception, and enhancement of memory and perception.

Chronic stress impact on neurogenesis

impair neurogenesis and reduce learning and memory performance.

Pathological features of chronic stress

Include fatigue, myopathy, cardiovascular disease, gastric ulcers, psychosocial dwarfism, impotence, anovulation, compromised immune function, and potentially accelerated neural degeneration during aging.

Acute stress response

Adaptive in nature, but chronic stress response can be harmful.

Status and stress relationship

Varies across species; high-ranked individuals may show pronounced stress responses in some species, while low-ranked individuals may show it in others.

Physiological indicators of stress in social hierarchy

Tend to be state-dependent rather than trait-dependent, reflecting an animal's current position in a social hierarchy.

Wild Dogs and Mongooses

Elevated Corticosterone, with alpha individuals showing higher values than subordinate animals.

Alpha pair of African wild dogs

Only the alpha pair breeds, while other adult members assist in breeding efforts.

Effects of stressed pregnant rats

Result in offspring with permanently altered brain morphology and behavior.

Stressed human mothers

With elevated glucocorticoids, had children with reduced birth weights, developmental delays, and social deficits.

Post-natal exposure to mild stressors

Decreases the negative impact of stress in adult rodents.

Moderate or high stressors

Increase the negative impact of stress in adult rodents, leading to long-term decreases in food intake.

Contact comfort

Can serve as a powerful buffer against stress in nonhuman primate infants.

In an Orphanage ____

cortisol concentrations increase as a function of time

Cortisol levels in children from Romanian orphanages

higher cortisol levels than Canadian-born children
the longer the children remained institutionalized, the higher their cortisol concentrations were 6 or more years later.

Psychosocial dwarfism

A grouping of disorders of retarded growth caused by neglect and abuse; this syndrome is also termed failure to thrive.

Characteristics of psychosocial dwarfism

a lack of growth despite adequate nutrition, disruption of sleep cycles and GH secretion, and absence of tissue responsiveness to exogenous GH.

Hypopituitary Dwarfism

GH treatment restores normal growth, but this therapy doesn’t work with Psychosocial Dwarfism

Reversibility of psychosocial dwarfism _____

after termination of the stressors.

Case study of psychosocial dwarfism

A girl was drinking from puddles and eating from garbage cans before admission to the hospital at age 15.3 years; her height was in the normal range for 9-year-old children.

Abnormal GH release, LH and FSH undetectable

Psychosocial Dwarfism Case Study: Growth after hospitalization

After 1 month in the hospital, the girl grew 2.5 cm and began to undergo puberty.

Stress and male sexual behavior

Stress impairs male sexual behavior (both motivation and performance) by suppressing testosterone.

Glucocorticoids effect on GnRH (Gonadotropin Releasing Hormone)

Glucocorticoids can inhibit GnRH, and thus lower LH and FSH release, and thus lower testosterone release and spermatogenesis.

Cortisol's effect on testosterone

Cortisol inhibits testosterone secretion in men by impairing testicular LH receptors.

In female long distance runners, LH pulses are ______

less frequent, which may be related to the high reported incidence of amenorrhea among such women.

Stress effects on female sexual behavior

interrupts timing of neuroendocrine events necessary for ovulation and sexual behavior
interrupts pregnancy and lactation if severe enough

Rodent Crowding effects

When rodents are confined to a cage, the population increases quickly and significantly, later crashing, due to excessive glucocorticoid concentrations

Pathological Factors that Moderate Stress Response

Control, Predictability, Coping, Habituation

Control

Fewer stress-related pathologies emerge if conditions can be controlled.

Predictability

Stress that is predictable influences the stress response.

ex. rats that received a signal before a shock had less lengths of gastric ulcerations than unsignaled

Coping

Therapeutic thoughts and perspectives, mental breaks, appropriate behaviors, etc. can lower the effects of stress.

Habituation

Learning that a stressor is not as bad as it seems, such as squirrels learning that people are a source of food.