Introduction to Anatomy & Physiology

Form Determines Function

In anatomy and physiology, the structure of a body part is closely related to its function. Understanding this relationship is fundamental to the study of the human body.

• Anatomy: The study of body structures and their relationships.

  • Gross (macroscopic) anatomy: Examines large, visible structures (regional, system, surface anatomy).

  • Microscopic anatomy: Studies structures too small to be seen with the naked eye (cytology, histology).

• Physiology: The study of body part functions, focusing on organ systems and cellular/molecular levels.

• Complementarity: Structure and function are inseparable; function always reflects structure.

Levels of Structural Organization

Chemical to Organism Level

The human body is organized in a hierarchy from the simplest to the most complex levels:

• Chemical level: Atoms and molecules.

• Cellular level: Smallest living units; organelles within cells perform specific functions.

• Tissue level: Groups of similar cells working together (e.g., muscle tissue).

• Organ level: Different tissues working together to perform a function (e.g., heart).

• Organ system level: Organs working together for a common purpose (e.g., digestive system).

• Organism level: The complete living being.

Major Organ Systems and Their Functions

• Integumentary system: Protection (skin, hair, nails); forms external covering, synthesizes vitamin D, houses receptors and glands.

• Skeletal system: Protection and support; forms blood cells, stores minerals.

• Muscular system: Movement, posture, heat production.

• Nervous system: Fast-acting control; responds to changes by activating muscles/glands.

• Endocrine system: Hormone secretion for regulation of processes.

• Cardiovascular system: Blood transport.

• Lymphatic system: Fluid balance, immunity.

• Respiratory system: Gas exchange.

• Digestive system: Nutrient breakdown and absorption.

• Urinary system: Waste elimination, water balance.

• Reproductive systems: Production of offspring.

Requirements for Life

Necessary Life Functions

• Maintaining boundaries: Separation of internal and external environments.

• Movement: Muscular contractions, movement of substances.

• Responsiveness: Ability to sense and respond to stimuli.

• Digestion: Breakdown and absorption of nutrients.

• Metabolism: All chemical reactions in the body.

• Excretion: Removal of wastes (e.g., urea, CO2, feces).

• Reproduction: Cellular (mitosis) and organismal (meiosis) levels.

• Growth: Increase in size.

Survival Needs

• Nutrients: Carbohydrates (energy), proteins (building blocks), fats (energy storage), minerals/vitamins (structural and metabolic roles).

• Oxygen: Required for ATP production.

• Water: Most abundant substance in the body (50-60% body weight).

• Normal body temperature: Necessary for chemical reactions.

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

Homeostasis

Definition and Mechanisms

Homeostasis is the ability to maintain a stable internal environment despite external changes. It involves all organ systems, especially the nervous and endocrine systems.

• Homeostatic control consists of three components:

  • Receptor: Detects changes.

  • Control center: Determines set point and response.

  • Effector: Produces the response.

• Negative feedback: Reduces or eliminates the original stimulus (e.g., regulation of blood sugar, body temperature).

• Positive feedback: Enhances the original stimulus (e.g., blood clotting, labor contractions).

Anatomical Terminology

Anatomical Position

• Body erect, feet apart, palms forward, thumbs away from body.

Directional Terms

• Describe body structure location relative to another.

• Always based on anatomical position.

• Right and left refer to the patient's right and left.

Planes and Sections

• Sagittal plane: Divides body into right and left parts.

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

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

Body Cavities and Membranes

• Dorsal body cavity: Protects nervous system (cranial and vertebral cavities).

• Ventral body cavity: Houses internal organs (thoracic and abdominopelvic cavities).

• Serous membranes: Double-layered membranes that secrete fluid to reduce friction.

Major Body Cavities Table

Cell Structure and Function

Cell Theory

• Cells are the smallest unit of life.

• All organisms are made of one or more cells.

• Cells arise from preexisting cells (mitosis/meiosis).

• Over 250 different cell types in the body.

Cell Components

• Plasma membrane: Selectively permeable barrier.

• Cytoplasm: Intracellular fluid and organelles.

• Nucleus: Control center, contains DNA.

Plasma Membrane Structure

• Phospholipid bilayer: Hydrophilic heads, hydrophobic tails.

• Cholesterol: Stabilizes membrane.

• Proteins: Integral and peripheral; involved in transport, communication, and recognition.

• Carbohydrates: Attach to proteins/lipids, function as name tags.

Cell Junctions

• Tight junctions: Impermeable, prevent passage between cells.

• Desmosomes: Anchor cells together, resist mechanical stress.

• Gap junctions: Allow communication and passage of small molecules.

Membrane Transport

• Passive transport (no energy):

  • Simple diffusion

  • Facilitated diffusion

  • Osmosis

• Active transport (requires energy):

  • Moves substances against concentration gradient

  • Includes vesicular transport (endocytosis, exocytosis)

Membrane Potential

• Voltage across the plasma membrane due to ion separation.

• Resting membrane potential: -50 to -90 mV, maintained by Na+/K+ pump.

• Only neurons and muscle cells can change membrane potential.

Cytoplasm and Organelles

• Cytosol: Fluid portion.

• Organelles:

  • Nucleus: Contains DNA, controls cell activities.

  • Mitochondria: Site of ATP synthesis.

  • Rough ER: Protein synthesis (with ribosomes).

  • Smooth ER: Lipid synthesis, detoxification.

  • Golgi apparatus: Modifies, sorts, packages proteins/lipids.

  • Lysosomes: Digestive enzymes, breakdown of waste.

  • Peroxisomes: Detoxify harmful substances.

Cellular Extensions

• Cilia: Short, numerous, move substances across cell surface.

• Flagella: Long, singular, propel the cell (e.g., sperm).

• Microvilli: Increase surface area for absorption (e.g., intestines).

Tissues

Overview

• Tissues are groups of cells working together for a related function.

• Four basic types: nervous, muscle, epithelial, connective.

Histology

• Study of tissues; involves fixation, sectioning, and staining.

• Microscopy: Light, transmission electron (TEM), scanning electron (SEM).

Epithelial Tissue

• Covers body surfaces, lines cavities, forms glands.

• Characteristics: Polarity, avascular but innervated, supported by basement membrane.

• Classified by layers (simple, stratified) and cell shape (squamous, cuboidal, columnar).

Table: Epithelial Tissue Types

Glandular Epithelium

• Specialized to secrete products (e.g., sweat, hormones).

• Endocrine glands: Secrete hormones into blood.

• Exocrine glands: Secrete products into ducts (e.g., sweat, saliva).

Connective Tissue

• Most abundant, widely distributed tissue.

• Functions: Support, protection, insulation, transport.

• Components: Cells, extracellular matrix (ground substance + protein fibers).

• Protein fibers:

  • Collagen: Thick, tough, strong, most abundant.

  • Elastic: Stretch and recoil.

  • Reticular: Fine, supportive networks.

Additional info: Some details, such as the full classification of tissues and the specifics of all organelles, have been expanded for academic completeness.