Cell Diversity

Overview of Cell Types

The human body contains over 200 distinct cell types, each specialized in structure and function. Cell diversity is essential for the wide range of physiological processes required for life.

• Epithelial cells: Hexagonal shape, form sheets, serve as barriers.

• Muscle cells: Elongated, contractile, enable movement.

• Nerve cells: Branched, transmit electrical signals.

• Blood cells: Round, transport gases and immune functions.

• Fat cells: Store nutrients.

• Macrophages: Fight disease.

Example: The hexagonal shape of epithelial cells allows tight packing, forming protective sheets.

Body Tissues

Classification of Tissues

Tissues are groups of cells with similar structure and function. The human body has four primary tissue types:

• Epithelial tissue: Covers surfaces, lines cavities, forms glands.

• Connective tissue: Supports, protects, binds, stores energy, provides immunity.

• Muscle tissue: Generates force for movement.

• Nervous tissue: Detects changes, transmits impulses, coordinates activities.

Epithelial Tissue

General Features

Epithelial tissue forms barriers and covers surfaces. It is avascular but has a nerve supply and regenerates easily.

• Protection: Skin epithelium protects against pathogens and chemicals.

• Absorption: Digestive tract epithelium absorbs nutrients.

• Filtration: Kidney epithelium filters substances.

• Secretion: Glandular epithelium produces sweat, mucus, etc.

Types of Epithelial Tissue

• Surface epithelium: Covers and lines surfaces.

• Glandular epithelium: Forms glands.

Classification by Layers

Epithelial tissues are classified by the number of cell layers:

• Simple epithelium: Single layer, functions in absorption, secretion, filtration.

• Stratified epithelium: Multiple layers, provides protection.

• Pseudostratified epithelium: Appears layered, nuclei at different levels.

Classification by Cell Shape

• Squamous: Flattened, allow rapid passage of substances.

• Cuboidal: Cube-shaped, function in secretion and absorption.

• Columnar: Tall, protect tissues, specialized for secretion and absorption.

• Transitional: Change shape, found in urinary organs.

Summary Table: Epithelial Types and Locations

Connective Tissue

General Features

Connective tissue supports, protects, and binds other tissues. It is characterized by an extracellular matrix and variable blood supply.

• Ground substance: Water, adhesion proteins, polysaccharides.

• Fibers: Collagen, elastic, reticular.

Types of Connective Tissue

• Bone: Hard matrix, osteocytes, protection and support.

• Cartilage: Flexible, chondrocytes, types include hyaline, fibrocartilage, elastic.

• Dense connective tissue: Tendons, ligaments.

• Loose connective tissue: Areolar, adipose.

• Blood: Fluid matrix, transport.

Areolar Tissue

Most widely distributed, soft, pliable, functions as packing tissue.

Bone Tissue

Composed of osteocytes in lacunae, hard matrix of calcium salts, collagen fibers.

Blood Tissue

Blood cells in plasma, transport of nutrients, wastes, gases.

Adipose Tissue

Fat cells dominate, insulates, protects, stores energy.

Muscle Tissue

Types of Muscle Tissue

• Skeletal muscle: Large, multi-nucleated, striated, voluntary movement.

• Cardiac muscle: Striated, branched, mono-nucleated, involuntary, intercalated discs, found in heart.

• Smooth muscle: Small, non-striated, involuntary, found in organs and blood vessels.

Nervous Tissue

Structure and Function

Nervous tissue is excitable and transmits electrical signals. It consists of neurons and neuroglia (support cells).

• Neurons: Specialized for communication, have dendrites, axon, and cell body.

• Neuroglia: Insulate, protect, and support neurons.

Functions: Receive and conduct impulses, detect changes, coordinate activities, maintain homeostasis.

Summary Table: Major Tissue Types

Additional info: The notes expand on brief lecture points to provide full academic context, including definitions, examples, and tables for classification and comparison. Images are included only when directly relevant to the explanation of cell and tissue structure and function.