Homeostasis and Stress Response

Homeostasis

• Maintaining balance between the body's internal and external environments
• Requires feedback systems to regulate bodily functions
• Internal cellular waste is excreted into the external environment

Stress Response

• Control system is responsible for physical, emotional, and behavioral reactions to stressors
• Negative feedback system opposes the stressor
  • Sensor detects change
  • Integrator processes information
  • Effector returns the change to normal
• Positive feedback systems cause instability rather than stability

General Adaptation Syndrome (GAS)

• Three-step process describing the body's reaction to stress
• Describes how the body responds to stressors

Local Adaptation Syndrome (LAS)

• Localized version of GAS
• Body's attempt to minimize the reaction/damage from stress in a smaller area of the body

Alarm Stage (GAS)

• Sympathetic nervous system and the HPA axis are stimulated leading to the release of catecholamines and cortisol
• Body prepares to confront or escape a threat
• Fight or flight response: part of the alarm stage
• Endocrine system and sympathetic system work together
• Parasympathetic system is suppressed

Response Symptoms and Signs (Alarm stage)

• Immune system: repressed/inhibited
• Heart: hypertension, faster heart rate, blood diverted to muscles
• Lungs: tachypnea (faster breathing), increased oxygen consumption, increased carbon dioxide expulsion
• Endocrine System: release of adrenaline and noradrenaline, cortisol

Resistance Stage (GAS)

• Body selects the most effective defense mechanism
• Body recovers from the threat, cortisol levels decrease

Exhaustion Stage (GAS)

• Prolonged stress overwhelms the body's ability to recover and defend itself
• Body becomes depleted of its resources
• Coping is unsuccessful

Cortisol

• Glucocorticoid hormone released by the adrenal cortex
• Increases the actions of epinephrine and glucagon
• Inhibits release and actions of reproductive hormones and Thyroid Stimulating Hormone (TSH)
• Decreases immune cells and inflammatory cells

Skin

• Increased sweating

Pancreas

• Hyperglycemia
• Reduced insulin production

Adrenal Medulla

• Releases epinephrine (adrenaline) and norepinephrine (noradrenaline)

Sympathomimetics

• Drugs that mimic the functions of the sympathetic nervous system

Endorphins

• Body's natural painkillers
• Released during times of stress and exercise from the hypothalamus and pituitary gland

Immunity

• The body's ability to defend itself against pathogens and foreign substances

Lines of Defense

• Primary (innate): non-specific, physical and chemical defenses (skin, mucous membranes, stomach acid, lysozyme)
• Expulsion (coughing, sneezing, vomiting, diarrhea)
• Secondary (innate): macrophages, neutrophils, eosinophils, basophils, monocytes

Adaptive Immunity (Specific/Acquired)

• 3rd line of defense; response developed after antigen exposure
• Cellular: T lymphocytes (mature in the thymus gland) that kill infected cells directly
• Humoral: B lymphocytes (mature in the bone marrow) produce antibodies targeting foreign substances

Complement System

• Group of proteins that fight off infection, viruses, bacteria, and promote tissue healing

Antigen-Presenting Cells

• Help bridge innate and adaptive immunity
• Also known as dendritic cells, responsible for activating T lymphocytes

Antibody-mediated Response (Primary Phase)

• IgM marks the primary response
• Host cell is exposed to antigen, and proliferation of Igs neutralizes the invader

Antibody-mediated Response (Secondary/Amnestic Phase)

• IgG marks the secondary response
• A second exposure to the same antigen leads to a stronger response with higher IgG levels

Immunoglobulins

• Antibodies/protein molecules
• IgG: most abundant, antiviral, antibacterial, and antitoxin properties. Can cross the placenta.
• IgA: found in secretions (tears, saliva, breast milk)
• IgM: first antibody produced, responsible for primary immune response
• IgE: involved in allergic reactions

Hypersensitivity

• Type 1: immediate hypersensitivity (e.g., allergic reactions, anaphylaxis)
• Type 2: cytotoxic (e.g., blood transfusions, autoimmune diseases like myasthenia gravis)
• Type 3: immune complex deposition (e.g., systemic lupus, rheumatoid arthritis)
• Type 4: delayed hypersensitivity (e.g., contact dermatitis, poison ivy rash)

Immunization

• Active: long-term immunity (e.g., contracting a disease or receiving a vaccine)
• Passive: short-term immunity (e.g., receiving preformed antibodies via breast milk, injection)

HIV/AIDS

• Attacks CD4 cells and macrophages, slowly debilitating T cells/B cell immunity.
• Transmission routes: blood, sexual activity, saliva, breast milk, transplants, transplacenta
• Diagnosis: measuring HIV antibodies, viral loads, and CD4 cell counts
• HIV PrEP/HAART: antiretroviral medication for treatment

Major Histocompatibility Complex (MHC)

• Allows the body to differentiate between self and non-self antigens on cell surfaces.
• Enables adaptive immunity.
• Also known as human leukocyte antigens (HLA).