Health, Disease & Your Skin Summary & Study Notes

🩺 WHO Definition of Health

Health is a state of complete physical, mental, and social well-being, not merely the absence of disease or infirmity. This definition emphasizes a holistic approach beyond just treating illness.

🧩 Epidemiological Triangle

The Epidemiological Triangle describes three interacting components that cause disease: Host, Agent, and Environment. The host includes factors like age, genetics, immunity, and behavior. The agent can be a bacterium, virus, toxin, or trauma. The environment covers physical, social, and economic conditions that affect disease transmission.

🧭 Natural History of Disease — Leavell & Clark

The natural history has three main periods:

• Pre-Pathogenic Period: No disease yet; host, agent, and environment interact and risk factors may be present.
• Pathogenic Period: Disease processes begin. Early pathogenesis is subclinical (no symptoms). Discernible disease is clinical (signs and symptoms appear).
• Resolution Period: Outcomes include recovery, disability (permanent damage), chronic disease, or death.

🛡️ Three Levels of Prevention

• Primary prevention (Pre-Pathogenic): Prevent disease before it occurs. Examples: vaccination, healthy diet, exercise, seat belts, health education.
• Secondary prevention (Early Pathogenic): Early detection and treatment to stop progression. Examples: screening tests (mammograms, blood pressure checks).
• Tertiary prevention (Resolution): Reduce complications and disability. Examples: rehabilitation, chronic disease medications, physical therapy.

🔎 Signs vs. Symptoms

A sign is objective and measurable (e.g., fever, rash, swelling). A symptom is subjective and reported by the patient (e.g., pain, nausea, fatigue). Clinical assessment uses both for diagnosis.

🏥 Public Health: Definition & Goals

Public health is the science of protecting and improving the health of entire populations through education, policy, and research. Key goals: prevent disease, promote health, and prolong life.

🌍 SDG 3: Good Health and Well-Being

Sustainable Development Goal #3 aims for healthy lives and well-being for all by 2030. Targets include reducing maternal mortality, ending preventable newborn and child deaths, combating communicable diseases (HIV, TB, malaria), reducing premature mortality from non-communicable diseases, preventing substance abuse, and achieving universal health coverage.

⚠️ Risk Factors

Risk factors increase the likelihood of disease or injury. Modifiable risk factors can be changed (smoking, diet, physical activity, alcohol, stress). Non-modifiable risk factors cannot be changed (age, sex, genetics, family history, ethnicity).

📊 Disease Distribution Terms

• Endemic: Disease constantly present at expected levels in a region (e.g., malaria in some tropical areas).
• Epidemic: Sudden increase in cases above normal levels in a specific area (e.g., a localized flu outbreak).
• Pandemic: An epidemic that spreads across countries or continents (e.g., COVID-19).

🧍 Body Organization & Anatomical Planes

Three main planes: Sagittal (divides left/right), Frontal/Coronal (divides front/back), Transverse/Horizontal (divides upper/lower). Use these to describe locations and movements.

🫁 Body Cavities

Major cavities include cranial (brain), spinal (spinal cord), thoracic (heart, lungs, esophagus, trachea), abdominal (stomach, liver, intestines, kidneys, spleen), and pelvic (bladder, reproductive organs, rectum).

📍 Anatomical Directional Terms

Common terms: superior/cranial (toward head), inferior/caudal (toward feet), anterior/ventral (front), posterior/dorsal (back), medial (toward midline), lateral (away from midline), proximal (closer to attachment), distal (farther from attachment).

🧬 Four Main Tissue Types

• Epithelial tissue: Covers surfaces and lines cavities; forms glands. Types include simple vs. stratified and shapes like squamous, cuboidal, columnar.
• Connective tissue: Supports and protects organs. Examples: bone, cartilage, blood, adipose, ligaments, tendons.
• Muscle tissue: Produces movement. Types: skeletal (voluntary, striated), cardiac (involuntary, striated), smooth (involuntary, non-striated).
• Nervous tissue: Transmits electrical signals. Composed of neurons (signal transmitters) and glial cells (support).

🧴 Integumentary System (Skin)

Functions: protection from pathogens and UV, temperature regulation, sensation, vitamin D synthesis, and excretion via sweat. Skin layers:

• Epidermis: Outer stratified squamous epithelium, avascular; contains keratinocytes and melanocytes.
• Dermis: Connective tissue with blood vessels, nerves, hair follicles, sweat and sebaceous glands.
• Hypodermis: Subcutaneous adipose tissue for insulation, energy storage, and cushioning. Important proteins: melanin (pigment, UV protection) and keratin (waterproofing, hair and nails).

Common disorders: skin cancer (basal cell, squamous cell, melanoma), acne (clogged follicles), and wounds. Prevention includes sunscreen, hygiene, protective equipment, and regular checks.

🩸 Lymphatic System

Functions: returns excess tissue fluid to bloodstream, absorbs dietary fats, and defends against infection. Components: lymph, lymphatic vessels, lymph nodes, and major ducts (thoracic and right lymphatic duct).

Key organs/tissues: bone marrow (produces lymphocytes), spleen (filters blood), thymus (T cell maturation), tonsils/adenoids, and MALT (mucosa-associated lymphoid tissue). Disorders include lymphedema, lymphoma, and lymphadenopathy. Healthy habits: exercise, hydration, balanced diet, and avoiding tight clothing.

🛡️ Immune System Overview

Functions: defend against pathogens, recognize and destroy abnormal cells, and remember previous infections. Primary sites include bone marrow, spleen, and lymph nodes.

Major cell types: phagocytes (macrophages, neutrophils) that ingest pathogens, and lymphocytes (T cells destroy infected cells and coordinate responses; B cells produce antibodies).

Innate vs. Adaptive immunity:

• Innate immunity is non-specific, present at birth, and responds immediately (skin barrier, mucus, stomach acid, inflammation, phagocytes, fever).
• Adaptive immunity is specific, develops over time, responds slower (days), and creates memory (T cells, B cells, antibodies, vaccination).

📝 Study Tips

Review the epidemiological triangle and natural history diagrams. Match prevention levels to disease stages. Practice anatomical terminology with diagrams and label body cavities and planes. Compare and contrast the four tissue types and innate vs adaptive immunity. Use mnemonics to memorize cavities and planes, and draw structures for skin and lymphatic system for visual reinforcement. Good luck on your exam! 🎓