Introduction to Anatomy & Physiology

Overview

Anatomy and physiology are foundational sciences for understanding the structure and function of the human body. Anatomy focuses on the form and relationships of body parts, while physiology explores how these parts work to sustain life. Together, they provide a comprehensive framework for medical and health sciences.

Form (Anatomy) Determines Function (Physiology)

Definitions and Principles

• Anatomy: The study of the structure of body parts and their relationships to one another.

• Physiology: The study of the function of body parts; how they carry out life-sustaining activities.

• Principle of Complementarity: Structure and function are inseparable; what a structure can do depends on its specific form.

Example: The sharp edges of incisors are ideal for cutting food, while the flat surfaces of molars are suited for grinding.

Reference Standards and Variability

• Reference values are based on a healthy young male (70 kg) or female (57 kg).

• Over 90% of anatomical structures match textbook descriptions, but minor variations exist (e.g., location of nerves or blood vessels).

• Extreme anatomical variations are rare and usually incompatible with life.

Sex vs. Gender

• Sex: Biological attributes based on chromosomes, gene expression, and hormone action; reflected in reproductive anatomy and physiology (male or female).

• Gender: Psychosocial construct including behaviors, expressions, and identities (e.g., man, woman, transgender, non-binary).

Topics and Subdivisions of Anatomy

Major Subdivisions

• Gross (macroscopic) anatomy: Study of large structures visible to the naked eye.

  • Regional anatomy: All structures in a specific area.

  • System anatomy: One organ system at a time (e.g., cardiovascular).

  • Surface anatomy: Internal structures as related to the overlying skin.

• Microscopic anatomy: Structures too small to see without magnification.

  • Cytology: Study of cells.

  • Histology: Study of tissues.

• Developmental anatomy: Structural changes throughout the lifespan.

  • Embryology: Developmental changes before birth.

Studying Anatomy

• Requires understanding anatomical terminology and using observation, manipulation, palpation, and auscultation.

• Medical imaging (e.g., X-ray, MRI, CT, ultrasound) allows non-invasive internal visualization.

Topics of Physiology

Major Subdivisions

• Based on organ systems (e.g., renal, neurophysiology, cardiovascular physiology).

• Often focuses on cellular and molecular events, including chemical reactions and physical principles (e.g., electrical currents, pressure).

Levels of Structural Organization

Hierarchy from Atoms to Organism

• Chemical level: Atoms combine to form molecules.

• Cellular level: Cells are made up of molecules and organelles.

• Tissue level: Groups of similar cells form tissues.

• Organ level: Organs are made of different types of tissues.

• Organ system level: Different organs work together closely.

• Organismal level: The human organism is made up of many organ systems.

The Body’s Organ Systems and Their Major Functions

Overview of the 11 Organ Systems

• Integumentary System: Protects body, synthesizes vitamin D, houses receptors and glands.

• Skeletal System: Supports and protects organs, forms blood cells, stores minerals.

• Muscular System: Allows movement, maintains posture, produces heat.

• Nervous System: Fast-acting control system, responds to stimuli.

• Endocrine System: Glands secrete hormones for regulation.

• Cardiovascular System: Transports blood, nutrients, gases, and wastes.

• Lymphatic System/Immunity: Returns leaked fluids, disposes of debris, houses immune cells.

• Respiratory System: Supplies blood with oxygen, removes carbon dioxide.

• Digestive System: Breaks down food, absorbs nutrients, eliminates waste.

• Urinary System: Eliminates nitrogenous wastes, regulates water, electrolytes, and acid-base balance.

• Reproductive System: Produces offspring.

Necessary Life Functions

Vital Functions for Life

• Maintaining boundaries: Separation between internal and external environments (e.g., plasma membranes, skin).

• Movement: Of body parts (skeletal muscles), substances (cardiac and smooth muscle), and cells.

• Responsiveness: Ability to sense and respond to stimuli (e.g., withdrawal reflex, breathing rate).

• Digestion: Breakdown and absorption of food.

• Metabolism: All chemical reactions in the body, including catabolism, anabolism, and cellular respiration.

• Excretion: Removal of wastes (e.g., urea, carbon dioxide, feces).

• Reproduction: Cellular division for growth/repair and production of offspring.

• Growth: Increase in size of body part or organism.

Survival Needs

Essential Requirements

• Nutrients: Chemicals for energy and cell building (carbohydrates, proteins, fats, vitamins, minerals).

• Oxygen: Required for metabolic reactions; survival without oxygen is limited to a few minutes.

• Water: Most abundant chemical in the body; necessary for chemical reactions and as a fluid base.

• Normal body temperature: Essential for proper metabolic reaction rates (optimal at 37°C/98.6°F).

• Appropriate atmospheric pressure: Required for adequate breathing and gas exchange.

Homeostasis

Definition and Importance

• Homeostasis: Maintenance of relatively stable internal conditions despite environmental changes; a dynamic equilibrium.

• Law of mass balance: The amount of a substance taken in must equal the amount lost to maintain constancy.

Homeostatic Control Mechanisms

• Involves three components: receptor (detects change), control center (determines set point and response), and effector (carries out response).

Negative Feedback

• Most common mechanism; response reduces or shuts off the original stimulus, returning variable to set point.

• Examples: Regulation of body temperature, blood glucose by insulin.

Positive Feedback

• Response enhances or exaggerates the original stimulus; variable changes in the same direction as the initial change.

• Usually controls infrequent events (e.g., labor contractions, blood clotting).

Feedforward (Anticipatory) Response

• Occurs in anticipation of a change (e.g., salivation and digestive juice release before eating).

Homeostatic Imbalance

• Disturbance increases risk of disease and contributes to aging.

• If negative feedback is overwhelmed, destructive positive feedback may occur (e.g., heart failure).

Anatomical Terms: Directions, Regions, and Planes

Anatomical Position and Directional Terms

• Anatomical position: Body erect, feet slightly apart, palms forward, thumbs away from body.

• Directional terms describe the location of one body part relative to another (e.g., superior, inferior, anterior, posterior, medial, lateral, proximal, distal, superficial, deep).

Orientation and Directional Terms Table

Regional Terms

• Axial part: Head, neck, and trunk (main axis).

• Appendicular part: Limbs (arms and legs).

• Regional terms designate specific areas within these divisions.

Body Planes and Sections

• Sagittal plane: Divides body into right and left parts (midsagittal = midline; parasagittal = offset from midline).

• Frontal (coronal) plane: Divides body into anterior and posterior parts.

• Transverse (horizontal) plane: Divides body into superior and inferior parts.

• Oblique section: Cuts made at angles other than 90° to the vertical plane.

Body Cavities and Membranes

Major Body Cavities

• Dorsal body cavity: Protects nervous system; includes cranial cavity (brain) and vertebral cavity (spinal cord), covered by meninges.

• Ventral body cavity: Houses internal organs (viscera); includes thoracic cavity (pleural cavities, mediastinum, pericardial cavity) and abdominopelvic cavity (abdominal and pelvic cavities).

Membranes in the Ventral Body Cavity

• Serosa (serous membrane): Thin, double-layered membrane covering ventral cavity surfaces.

  • Parietal serosa: Lines cavity walls.

  • Visceral serosa: Covers organs.

  • Serous fluid between layers reduces friction.

• Named for specific cavities: pleura (lungs), pericardium (heart), peritoneum (abdominopelvic organs).

Abdominopelvic Regions and Quadrants

• Medical personnel use four quadrants: RUQ, LUQ, RLQ, LLQ.

• Anatomists use nine regions: umbilical, epigastric, pubic (hypogastric), right/left inguinal (iliac), right/left lateral (lumbar), right/left hypochondriac.

Other Body Cavities

• Open to environment: oral, digestive, nasal, orbital, middle ear cavities.

• Closed: synovial cavities (joints, lined with synovial membrane).

Clinical Connections

• Homeostatic imbalance: Increases risk of disease, contributes to aging, and may lead to destructive positive feedback (e.g., heart failure).

• Clinical examples: Hiatal hernia (stomach protrudes through diaphragm), pleurisy (inflamed pleura), peritonitis (inflamed peritoneum), and "wrong site surgery" due to poor anatomical understanding.