Chapter 2, Homeostasis, Allostasis, & Adaptive Responses to Stressors

Homeostasis

a state of physiological equilibrium or stability maintained by complex, dynamic biological mechanisms that counteract internal or external changes

Allostasis

the process by which the body maintains stability (homeostasis) through physiological or behavioral change. It accounts for how the body adapts to dynamic environmental and internal demands

Allostatic load

the cumulative wear and tear on the body's tissues and organs resulting from prolonged or repeated exposure to chronic stress responses

Stressor

any physical, biological, chemical, or psychological agent, stimulus, or demand that disrupts normal homeostasis and triggers a stress response

Stages of Stress, General Adaptation Syndrome (GAS)

1. Alarm stage

2. Resistance (Adaptation) Stage

3. Exhaustion Stage

Alarm Stage

body initiates an immediate "fight-or-flight" response as the adrenal glands release catecholamines to combat the stressor, pushing physical performance to its peak. During this initial surge, the liver increases glucose production for fast energy, the heart rate rises to boost blood supply and blood pressure, and the bronchioles dilate to increase ventilation, delivering more oxygen to the brain for heightened awareness. Simultaneously, the digestive system suppresses hunger, and the body resists any additional stressors so it can focus entirely on the current threat

Catecholamines

cause body to operate at peak performance

Resistance (Adaptation) Stage

the body activates the HPA axis—where the hypothalamus signals the pituitary gland to prompt the adrenal cortex to produce corticosteroids—to sustain the ongoing resistance response. As this stage continues, the sustained effort causes the body to experience fatigue, irritability, and decreased concentration

Exhaustion Stage

persistent, unchecked stress ultimately depletes the body's energy reserves and compromises the immune system. This prolonged phase exhausts adrenal gland function, leading to a decrease in serum glucose and overall energy availability. Consequently, the body's overall tolerance to stress drops sharply, causing the onset of illness or physical collapse

Contributions of stress

• Relationship between stress + disease

• Disorders by body systems

Relationship between Stress & Disease

• Acute problems following stress response (ex. Stress headache)

• Prolonged vasoconstriction = tissue inflammation and necrosis (stomatitis)

• Can aggravate pre-existing conditions: acute exacerbation of original disease. (ex. Heart disease and BP)

• May be a precipitating factor for a relapse of a chronic condition (ex. Asthma or herpes)

• Following serious life crisis and persistent stress, cancerous process may develop

• Act as causative agent in development of disease (ex. Hypertension, coronary artery disease and diabetes)

Disorders on Body Systems

• Gastrointestinal system

• Nervous system

• Respiratory system

• Musculoskeletal system

• Cardiovascular system

• Skin

• Urinary system

• Other

GI System

peptic ulcer disease, gastric stress ulcers (Curling’s ulcer, Cushing’s ulcer) ulcerative colitis, regional ileitis, nausea, diarrhea, cirrhosis due to alcohol abuse, stomatitis, periodontitis

Nervous System

Multiple sclerosis, seizure disorder, depression, cerebrovascular accident (CVA/stroke)

Respiratory System

Asthma

Musculoskeletal System

Rheumatoid arthritis

Cardiovascular System

Hypertension, angina, heart failure

Skin

Herpes simplex, eczema, acne

Urinary System

Acute renal failure

Other

cancer, opportunistic infection, autoimmune disorders, obesity, post-traumatic stress disorder (PTSD)