Epithelial Tissue Types and Functions

Stratified Squamous Epithelia

• Multiple layers of cells, top layer is flattened (squamous)
• Found in areas exposed to abrasion (mouth, esophagus, skin)
• Skin is keratinized for protection, keeps cells durable and prevents dehydration
• Basal cells are stem cells, constantly divide, replacing cells at the surface

Simple Cuboidal Epithelia

• Single layer of cube-shaped cells
• Found in glands and ducts
• Specialized for absorption and secretion
• Example: Thyroid gland (secretes hormones), Kidney tubules (clean blood)

Stratified Cuboidal Epithelia

• Multiple layers of cube-shaped cells
• Relatively rare, found in sweat glands
• Secrete sweat when it's hot

Transitional Epithelia

• Can tolerate stretching and compression due to changing cell shape
• Found in urinary bladder
• When the bladder is empty, the cells are columnar shaped
• When the bladder is full, the cells flatten, becoming more squamous-like

Simple Columnar Epithelia

• Single layer of tall, column-shaped cells
• Found lining the digestive tract (stomach to anus)
• Specialized for absorption and secretion
• Contains goblet cells which produce mucus for lubrication

Stratified Columnar Epithelia

• Multiple layers with column-shaped cells on top
• Relatively rare, found in salivary gland ducts
• The apical layer is the defining feature for classification

Ciliated Pseudostratified Columnar Epithelia

• Single layer of cells with different heights, all anchored to the basement membrane
• Appears stratified, but is actually a single layer
• Found lining most of the respiratory tract
• Contains cilia which move mucus, trapping debris and sweeping it out of the body

Exocrine Glands

• Secrete substances to the outside world
• Merocrine Secretion:
  • Secretory vesicles exocytose their contents
  • Example: Goblet cells, saliva cells
• Apocrine Secretion
  • Apical portion of the cell breaks off, releasing the contents
  • Example: Mammary glands
• Holocrine Secretion
  • The entire cell fills with secretion, bursts, and releases the contents
  • Example: Sebaceous glands in the skin

Connective Tissues

• Connective Tissue Proper
  • Loose Connective Tissue
    • Areolar
      • Contains all fiber types (collagen, elastic, reticular)
      • Forms the lamina propria, supporting epithelial tissues
    • Adipose
      • Mostly fat cells (adipocytes) for energy storage and insulation
    • Reticular
      • Forms a delicate network of reticular fibers for support
  • Dense Connective Tissue
    • Dense Regular
      • Fibers arranged parallel for high tensile strength
      • Forms tendons (muscle to bone), ligaments (bone to bone)
    • Dense Irregular
      • Fibers interwoven for resisting tension from multiple directions
      • Found in the dermis of the skin
• Fluid Connective Tissues (Blood and Lymph)
  • Blood
    • Consists of plasma (the matrix) and blood cells
    • Responsible for transport of oxygen, nutrients, waste, and immune cells
  • Lymph
    • Forms from interstitial fluid entering lymphatic vessels
    • Returns fluid and proteins to the blood, transports fats, and contains immune cells

Body Membranes

• Mucous Membranes
  • Line cavities open to the external environment
  • Contain epithelial tissue and connective tissue (lamina propria)
  • Secrete mucus for lubrication and protection
• Serous Membranes
  • Line internal cavities not open to the external environment
  • Composed of mesothelium (simple squamous epithelium) and areolar tissue
  • Secrete serous fluid to reduce friction between organs
• Cutaneous Membrane (Skin)
  • Outermost layer of the body
  • Composed of stratified squamous epithelium and dense irregular connective tissue
• Synovial Membranes
  • Line freely movable joints
  • Composed of simple squamous epithelium and areolar tissue
  • Secrete synovial fluid to lubricate joints

Fasciae

• Superficial Fascia (Hypodermis)
  • Located between the skin and underlying organs
  • Composed of areolar and adipose tissue
  • Provides insulation and padding
• Deep Fascia
  • Forms a sturdy framework within the body
  • Composed of dense connective tissue
  • Attaches to capsules, tendons, and ligaments
  • Provides strength and support
• Subserous Fascia
  • Located between serous membranes and deep fascia
  • Composed of areolar tissue
  • Provides padding

Nervous Tissue

• Composed of neurons (excitable cells that transmit electrical signals) and glial cells (supporting cells)
• Functions of Neuroglia:
  • Provide structural support
  • Repair neural tissue after injury
  • Phagocytosis
  • Nutrient delivery
  • Regulate interstitial fluid composition

Muscle Tissue

• Consists of specialized contractile cells (muscle fibers)
• Types of Muscle Tissue:
  • Skeletal Muscle
    • Long, multinucleated fibers
    • Striated (due to protein arrangement)
    • Voluntary control
  • Cardiac Muscle
    • Branched, uninucleated fibers
    • Striated
    • Involuntary control
  • Smooth Muscle
    • Spindle-shaped, uninucleated fibers
    • Non-striated
    • Involuntary control