Introduction to Anatomy & Physiology: Organ Systems and Tissues

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Anatomy vs. Physiology

Definitions and Distinctions

Anatomy and physiology are foundational disciplines in the study of living organisms. Anatomy focuses on the structure of organisms and their parts, while physiology examines the function of those structures.

Anatomy: The study of the structure (form) of organisms and their parts. Example: Parts of the heart
Physiology: The study of the function of organisms and their parts. Example: Cardiac cycle (how the heart contracts)

Levels of Organization in the Human Body

Hierarchical Structure

The human body is organized into several levels, each with increasing complexity:

Organism (e.g., human)
Organ system (e.g., cardiovascular system)
Organs (e.g., capillary)
Tissues (e.g., epithelial tissue)
Cell (e.g., squamous epithelial cell)
Organelle (e.g., mitochondria)
Molecule (e.g., DNA)
Atom (e.g., oxygen)

Organ Systems

Overview and Functions

Organ systems are groups of organs working together to perform common functions. Each system is typically made of at least two tissue types. For example, the heart contains connective, muscle, epithelial, and nervous tissues, all working together to pump blood as part of the cardiovascular system.

Examples of organ systems: lungs, skin, reproductive organs, brain

Major Organ Systems and Their Functions

System	Structure	Function
Skeletal	Rigid bones, cartilage, tendons, ligaments	Structural support, anchor points for muscles, blood cell production
Cardiovascular	Heart, blood vessels	Transport of nutrients, gases, wastes, cells
Respiratory	Respiratory passages, lungs	Exchange of gases (O2 and CO2)
Digestive	Alimentary canal, associated organs	Ingestion, breakdown, absorption of nutrients
Muscular	Skeletal muscles	Voluntary movement, posture
Urinary	Kidney, bladder, urethra	Excretion of nitrogenous wastes, pH and water balance
Endocrine	Gland tissues	Hormone production, regulation of body functions
Reproductive	Ovaries/testes and related structures	Production of gametes, reproduction
Integumentary	Skin, hair, nails	Protection, temperature regulation, vitamin D synthesis
Lymphatic	Lymph nodes, vessels, thymus, spleen	Fluid balance, immunity
Nervous	Brain, spinal cord, nerves	Information processing, control of responses

Tissues

Definition and Categories

Cells are the universal building blocks of all living things. Tissues are groups of similar cells that work together to perform a specific function. In multicellular organisms, tissues are classified into four major categories:

Epithelial tissue
Connective tissue
Muscle tissue
Nervous tissue

Components of Tissues

Cells: Produce and maintain the extracellular matrix. Examples include fibroblasts, osteocytes, cardiac muscle cells.
Extracellular matrix: Can be liquid, jelly-like, or solid. Consists of:
- Ground substance: Water with dissolved substances (e.g., carbohydrates, ions)
- Protein fibers: Collagen, elastin

Vascularization of Tissues

Well-vascularized tissues: Have capillaries in the extracellular matrix, providing nutrients and oxygen for repair. These tissues heal quickly.
Poorly vascularized or avascular tissues: Lack capillaries; nutrients and oxygen must diffuse in, so healing is slower.

Epithelial Tissue

Structure and Classification

Epithelial tissue lines, protects, and covers surfaces, tubes, and cavities. It is avascular (no blood vessels) and classified by:

Number of layers of cells
Shape of cells
Presence or absence of cilia

Types of Epithelial Tissue

Simple epithelium: One layer of cells attached to a basement membrane. Good for rapid exchange (e.g., lungs, capillaries).
Stratified epithelium: Two or more layers attached to a basement membrane. Found in areas needing protection (e.g., esophagus, skin).

Shapes of Epithelial Cells

Squamous: Flat/pillow-shaped
Cuboidal: Cube-shaped
Columnar: Tall/column-shaped

Ciliated Cells

Some columnar epithelial cells have cilia (finger-like folds of cell membrane) that:

Increase surface area for membrane transport
Sweep fluid or mucus

Functions of Epithelial Tissues

Simple squamous: Delicate lining, efficient diffusion
Stratified squamous: Tough lining/covering, protection
Cuboidal: Secretion (tubules/ducts/glands)
Columnar: Secretion and absorption (digestive tract)

Connective Tissue

Structure and Function

Connective tissue consists of cells and an extracellular matrix. It fills spaces between tissues/organs, connects tissues, stores and transports substances, and provides support.

Types of Connective Tissue

Type	Structure	Function
Loose (areolar)	Sparse cells in loose collagen/elastin matrix	Flexible support, absorbs fluid during swelling
Loose (adipose/fat)	Adipose cells packed with fat, little matrix	Energy storage, insulation, cushioning
Dense (fibrous, avascular)	Dense collagen/elastin matrix, poor blood supply	Tendons, ligaments, strength
Cartilage (hyaline)	Irregularly shaped cells in jelly-like matrix	Flexible support, cushioning in joints
Bone	Oval cells in concentric rings, solid matrix of calcium salts/collagen	Rigid support, blood cell production
Blood	Red/white blood cells, platelets in liquid matrix (plasma)	Transport of dissolved molecules

Summary Table: Epithelial Tissue Classification

Type	Layers	Shape	Example
Simple squamous	1	Flat	Lung alveoli
Stratified squamous	2+	Flat	Skin, esophagus
Simple cuboidal	1	Cube	Kidney tubules
Simple columnar	1	Column	Digestive tract lining

Key Terms and Concepts

Basement membrane: Protein-rich layer anchoring epithelial cells
Extracellular matrix: Non-cellular material surrounding cells, providing structural and biochemical support
Vascularization: Presence of blood vessels in tissue
Cilia: Hair-like projections aiding movement of substances

Additional info:

Many epithelial cells need frequent replacement due to friction and mechanical stress.
Connective tissue types vary in vascularization, affecting healing rates.
Blood is considered a connective tissue due to its origin and function.