Anatomy vs. Physiology

Definitions and Distinctions

Anatomy and physiology are two closely related fields that form the foundation of medical and biological sciences. Anatomy focuses on the structure of body parts, while physiology examines their functions and how they work together to sustain life.

• Anatomy: Study of body parts, their shapes, positions, and relationships.

• Physiology: Study of how body parts function to maintain life-sustaining activities.

• Example (Liver):

  • Anatomy: Size, shape, location, blood/nerve supply.

  • Physiology: Bile production, nutrient regulation, metabolic functions.

Key Principles

Complementarity of Structure and Function

Structure and function are inseparable in biological systems. The physical characteristics of anatomical structures determine their physiological roles.

• Bones: Hardness provides support.

• Heart valves: Prevent backflow of blood.

• Thin lung walls: Enable efficient gas exchange.

Levels of Structural Organization

Hierarchy from Atoms to Organism

The human body is organized into increasingly complex levels, each building upon the previous.

1. Chemical: Atoms and molecules.

2. Cellular: Basic living unit.

3. Tissue: Groups of similar cells (e.g., connective, epithelial, muscle, nervous).

4. Organ: At least two tissue types, usually four.

5. Organ System: Organs working together.

6. Organismal: All systems combined to form the whole organism.

Cells: The Basic Unit of Life

Structure and Components

Cells are the fundamental structural and functional units of living organisms. Human cells share common features but differ in size, shape, and function.

• Three main parts:

  • Plasma membrane: Flexible outer boundary.

  • Cytoplasm: Internal fluid containing organelles.

  • Nucleus: DNA-containing control center.

• Cytoplasm includes:

  • Cytosol: Fluid portion.

  • Inclusions: Stored substances.

  • Organelles: Specialized structures performing cellular functions.

Major Organelles and Their Functions

• Membranous Organelles:

  • Endoplasmic Reticulum (ER):

    • Rough ER: Protein synthesis (ribosomes attached).

    • Smooth ER: Lipid metabolism, detoxification.

  • Golgi Apparatus: Modifies, packages, and directs proteins and lipids (three pathways: secretory vesicles, membrane proteins/lipids, lysosomes).

  • Peroxisomes: Detoxify (oxidase and catalase enzymes).

  • Lysosomes: Digestion and recycling, autolysis in damaged cells.

• Non-membranous Organelles:

  • Ribosomes: Protein synthesis.

  • Cytoskeleton: Structural framework, movement (microfilaments, intermediate filaments, microtubules).

  • Centrosomes & Centrioles: Organize microtubules, form cilia/flagella.

Cellular Extensions

• Cilia: Move substances across cell surfaces.

• Flagella: Propel cells (e.g., sperm).

• Microvilli: Increase surface area for absorption.

Extracellular Materials

• Fluids: Interstitial fluid, blood plasma, cerebrospinal fluid.

• Secretions: Saliva, mucus.

• Extracellular matrix: Glue-like support between cells.

Tissue: The Living Fabric

Types and Functions

Tissues are groups of cells similar in structure that perform common or related functions. There are four basic tissue types: epithelial, connective, muscle, and nervous tissue.

• Histology: Study of tissues.

• Each tissue type: Performs specific functions that maintain homeostasis.

Epithelial Tissue

Epithelial tissue is a sheet of cells that covers body surfaces or lines cavities. It is classified by the number of cell layers and the shape of cells.

• Main forms:

  • Covering and lining epithelium: On external and internal surfaces.

  • Glandular epithelium: Secretory tissue in glands.

• Characteristics:

  • Polarity: Apical and basal surfaces; apical often specialized.

  • Specialized contacts: Tight junctions, desmosomes.

  • Supported by connective tissue: Basement membrane (basal lamina + reticular lamina).

  • Avascular but innervated: Nutrients via diffusion.

  • Regeneration: High capacity for renewal.

• Classification:

  • Number of layers:

    • Simple epithelium: Single layer, absorption/secretion.

    • Stratified epithelium: Two or more layers, protection.

  • Shape of cells:

    • Squamous: Flat, scale-like.

    • Cuboidal: Box-like, cube.

    • Columnar: Tall, column-like.

Types of Epithelia

• Simple squamous: Lung alveoli, kidney glomeruli; rapid diffusion.

• Simple cuboidal: Kidney tubules, small glands; secretion/absorption.

• Simple columnar: Digestive tract, gallbladder; absorption/secretion.

• Pseudostratified columnar: Upper respiratory tract; secretion, movement of mucus.

• Stratified squamous: Skin, mouth, esophagus; protection.

• Stratified cuboidal/columnar: Rare, found in ducts of large glands.

• Transitional epithelium: Urinary bladder; stretches readily.

Glandular Epithelium

Glands are one or more cells that make and secrete a fluid. They are classified by site of product release and number of cells forming the gland.

• Endocrine glands: Ductless, secrete hormones into interstitial fluid/blood.

• Exocrine glands: Secrete products into ducts or onto surfaces (e.g., mucus, sweat, oil, saliva).

• Unicellular exocrine glands: Goblet cells, mucus cells.

• Multicellular exocrine glands: Composed of duct and secretory unit, classified by structure and mode of secretion.

Connective Tissue

Functions and Structural Elements

Connective tissue supports, protects, and binds other tissues together. It is the most abundant and widely distributed tissue type.

• Functions: Support, protection, insulation, transportation of substances.

• Structural elements:

  • Ground substance: Unstructured material filling space between cells.

  • Fibers: Collagen (strength), elastic (stretch), reticular (support).

  • Cells: Fibroblasts, chondrocytes, osteocytes, adipocytes, blood cells.

Summary Table: Levels of Structural Organization

Example Formula: Surface Area to Volume Ratio

The surface area to volume ratio is important in cell biology, affecting rates of diffusion and metabolic efficiency.

• Formula:

Additional info:

• Some content was inferred and expanded for clarity and completeness, such as the summary table and formula.

• Examples and definitions were added to ensure the notes are self-contained and suitable for exam preparation.