Introduction to Anatomy and Physiology

Anatomy and physiology are foundational sciences for understanding the structure and function of the human body. This chapter introduces the organization of the body, the relationship between structure and function, and the terminology used in the field.

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 work to carry out life-sustaining activities.

• Principle of Complementarity: Structure always reflects function; what a structure can do depends on its specific form.

Anatomical variability exists among humans, but most structures match textbook descriptions. Extreme variations are rare and usually incompatible with life.

Subdivisions of Anatomy

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

• Regional anatomy: Examines all structures in a particular area of the body.

• System anatomy: Focuses on one organ system at a time.

• Surface anatomy: Studies internal structures as they relate to the overlying skin.

• Microscopic anatomy: Examines structures too small to be seen with the naked eye (includes cytology—the study of cells, and histology—the study of tissues).

• Developmental anatomy: Traces structural changes throughout the lifespan (includes embryology—developmental changes before birth).

Studying Anatomy

• Requires understanding anatomical terminology and using tools such as observation, manipulation, palpation (feeling organs with hands), and auscultation (listening to organs with a stethoscope).

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

Subdivisions of Physiology

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

• Often focuses on cellular or molecular events and chemical/physical principles (e.g., electrical currents, pressure, lever systems).

The Body’s Organization: Levels of Structural Organization

The human body is organized into hierarchical levels, from the simplest chemical components to the entire organism.

• Chemical level: Atoms combine to form molecules.

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

• Tissue level: Groups of similar cells perform a common function.

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

• Organ system level: Organ systems consist of different organs that work together closely.

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

The Body’s Organ Systems and Their Major Functions

The human body contains 11 organ systems, each with specific functions essential for survival.

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

• Skeletal System: Supports and protects organs, provides a framework for muscles, forms blood cells, and stores minerals.

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

• Nervous System: Fast-acting control system; responds to internal and external changes.

• Endocrine System: Glands secrete hormones that regulate growth, reproduction, and metabolism.

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

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

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

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

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

• Reproductive System: Produces offspring; male and female systems have distinct structures and functions.

Requirements for Life

Necessary Life Functions

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

• Digestion: Breakdown of food into absorbable units.

• Metabolism: All chemical reactions in the body, including catabolism (breakdown) and anabolism (synthesis); cellular respiration produces ATP.

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

• Reproduction: Cellular division for growth/repair; organismal reproduction produces offspring.

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

Interrelationships Among Body Organ Systems

Organ systems work cooperatively to maintain life. Cells depend on organ systems to meet survival needs.

Survival Needs

• Nutrients: Carbohydrates (energy), proteins (cell building), fats (energy storage), vitamins and minerals (chemical reactions and structure).

• Oxygen: Essential for energy production; 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: Required for proper metabolic reactions (typically 37°C/98.6°F).

• Appropriate atmospheric pressure: Needed for adequate breathing and gas exchange in the lungs.

Homeostasis: Maintaining Stable Internal Conditions

Definition and Importance

• Homeostasis: Maintenance of relatively stable internal conditions despite continuous 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

• Regulated by the nervous and endocrine systems.

• Three essential components:

  • Receptor (sensor): Monitors environment and responds to stimuli.

  • Control center: Determines set point and response.

  • Effector: Carries out the response (muscle or gland).

Types of Feedback

• Negative feedback: Most common; response reduces or shuts off the original stimulus, returning the variable to its set point (e.g., regulation of body temperature, blood glucose).

• Positive feedback: Response enhances or exaggerates the original stimulus; usually controls infrequent events (e.g., labor contractions, blood clotting).

Homeostatic Imbalance

• Disturbance of homeostasis increases risk of disease and contributes to aging.

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

Anatomical Terms: Body Directions, Regions, and Planes

Anatomical Position and Directional Terms

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

• Directional terms describe the location of one body part relative to another (e.g., lateral, medial, superior, inferior).

Regional Terms

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

• Appendicular part: Limbs (arms and legs) attached to the axis.

• Regional terms specify particular areas within these divisions.

Body Planes and Sections

• Sagittal plane: Divides body into right and left parts; midsagittal is exactly in the midline, parasagittal is offset.

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

• Transverse (horizontal) plane: Divides body into superior (top) and inferior (bottom) 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 the nervous system; includes cranial cavity (brain) and vertebral (spinal) cavity (spinal cord), covered by meninges.

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

Membranes in the Ventral Body Cavity

• Serosa (serous membrane): Thin, double-layered membrane; parietal serosa lines cavity walls, visceral serosa covers organs. The space between contains serous fluid for lubrication.

• Specific serous membranes:

  • Pleura: Lungs

  • Pericardium: Heart

  • Peritoneum: Abdominopelvic organs

Abdominopelvic Regions and Quadrants

• Clinicians use four quadrants: right upper (RUQ), left upper (LUQ), right lower (RLQ), left lower (LLQ).

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

Other Body Cavities

• Open cavities: Oral, nasal, orbital, and middle ear cavities (exposed to environment).

• Closed cavities: Synovial cavities (joints, not exposed to environment).

Summary Table: The Eleven Organ Systems and Their Major Functions

Key Equations

• Law of Mass Balance:

• ATP Production (Cellular Respiration):

Additional info: Where content was inferred or expanded, it is based on standard academic knowledge for introductory Anatomy & Physiology courses.