Epithelial Tissue Overview

Epithelial Tissue

• Forms the outer layer of skin and internal structures
• Two types: Covering/Lining and Glandular
• Covering/Lining: Forms the outer layer of skin and internal organs
• Glandular: Forms glands of the body
• Functions:
  • Physical protection: Epithelial tissue protects underlying structures from damage. For example, the lumen of the urinary bladder is lined with epithelial tissue.
  • Absorption: Epithelial tissue facilitates the absorption of nutrients, such as in the kidney.
  • Sensation: Epithelial tissue can detect stimuli and transmit signals to the nervous system. For example, the epithelium of the eyeball is involved in sensation.
  • Secretion: Epithelial tissue produces and releases substances, like sweat, earwax, and saliva.
  • Gland Classification:
    • Endocrine Glands: Secrete hormones directly into the bloodstream (e.g., thyroid, pituitary gland)
    • Exocrine Glands: Secrete products through ducts onto epithelial surfaces (e.g., sweat, earwax, saliva)
• Structure:
  • Apical Surface: The free surface exposed to the exterior environment or cavity of an organ
    • Often has microvilli or cilia
  • Basal Surface: The anchored lower surface.
  • Basal Lamina: An adhesive sheet beneath the basal surface that joins epithelial tissue to connective tissue.
• Classification:
  • Arrangement of Layers:
    • Simple: A single layer of cells
    • Pseudostratified: Appears stratified but all cells touch the basement membrane
    • Stratified: Multiple layers of cells
  • Cell Shape:
    • Squamous: Thin and flattened
    • Cuboidal: Cube-shaped
    • Columnar: Tall and column-shaped
• Epithelial Tissue Rule of Thumb:
  • More layers = more protection
  • Single layer = easier for substances to permeate
  • Cilia often help move substances or are involved in sensation.

Connective Tissue

• Supports body structures
• All connective tissue develops from mesenchyme
• Four main types:
  • Connective Proper
  • Cartilage
  • Bone
  • Blood
• Functions:
  • Support: Connective tissue provides structural support for the body. For example, intervertebral discs are made of fibrocartilage.
  • Bind: Tissues are held together by connective tissue. For example, tendons are dense regular connective tissue.
  • Storage: Connective tissue can store energy and water. For example, adipose tissue stores fat.
  • Transport: Connective tissue carries nutrients, gases, and waste products throughout the body. For example, blood carries red blood cells, white blood cells, and platelets.
  • Protection: Connective tissue protects organs and other tissues. For example, the pectoral girdle (clavicle and scapula) protects the shoulder region.
  • Immune Protection: Connective tissue plays a role in the immune system. For example, bone marrow produces immune cells.
• Types:
  • Loose Connective Tissue:
    • Areolar:
      • Cells found in areolar:
        • Fibroblast, Defense cell, adipose cell
      • Characteristics:
        • Strong, flexible, and resistant to stretch
        • Tough but flexible, branching/lattice pattern
        • Allows for stretch and recoil
      • Ground Substance:
        • Colorless, viscous solution that:
          • Supports cells
          • Binds cells together
          • Provides a medium for exchange
      • Defense Cells:
        • Breakdown invading pathogens
        • Part of the second line of defense after epithelial tissue
        • Examples: macrophage, plasma cell, mast cell, eosinophil, neutrophil
      • Adipose Cells:
        • Mainly lipids:
          • Energy storage
          • Cushioning and protection
          • Involved in some hormone production
    • Adipose: Primarily composed of lipid cells
    • Reticular: Found in "hollow organs" as a supporting framework.
  • Dense Connective Tissue:
    • Regular: Densely packed, parallel collagen fibers, resulting in very strong tissue.
    • Irregular: Predominantly collagen fibers arranged in an irregular or mesh-like pattern, providing strength in multiple directions.
    • Elastic: Contains both collagen and elastic fibers, allowing for stretch and recoil.

Cartilage

• Chondrocyte: A cartilage cell that develops from a chondroblast
  • Contains collagen + elastic fibers + ground substance
• Perichondrium: A dense connective tissue covering most cartilage.
• Strong but pliable, often contains chondroitin sulfate
• Types:
  • Hyaline:
    • Most common type with a high concentration of fine collagen fibers
    • Precursor to the skeletal system in a fetus
    • Found at the ends of long bones (articular cartilage)
    • Most hyaline cartilage has perichondrium (except articular cartilage)
  • Elastic:
    • Composed of both collagen and elastic fibers, making it more flexible.
    • Has an outer perichondrium.
  • Fibrocartilage:
    • Chondrocytes and collagen fibers arranged in parallel rows.
    • No perichondrium.

Bone

• Supports, protects, and houses blood-forming cells.
• Relatively tough, composed of collagen and calcium.
• Compact Bone: Dense, solid bone tissue.
• Spongy Bone: A porous type of bone tissue that contains red bone marrow.

Blood

• Consists of plasma and cells (white blood cells, red blood cells, platelets).
• Its primary function is to transport to support tissues (blood carries substances throughout the body).

Membranes (Epithelia + Connective Tissue + Basement Membrane)

• Skin:
  • Also known as the "cutaneous membrane"
  • Two layers:
    • Epidermis: Outer layer of skin, composed of epithelial tissue.
    • Dermis: Inner layer of skin, composed of connective tissue.
• Mucous:
  • Epithelial tissue + Loose connective tissue + goblet cells
• Serous:
  • Simple epithelia + Areolar connective tissue
  • Produces a thin, watery fluid to lubricate surfaces.
• Synovial:
  • Lines joint cavities
  • Secretes synovial fluid for lubrication

Epithelial Tissue

• Covers the outer layer of skin and internal structures
• Forms the glands of the body
• Functions include:
  • Physical protection
  • Absorption
  • Sensation
  • Secretion
• Two types:
  • Covering / Lining Epithelium
  • Glandular Epithelium

Glandular Epithelium

• Secretes products directly into bloodstream or into ducts
• Two types of glands:
  • Endocrine
  • Exocrine

Endocrine Glands

• Secrete their products directly into the bloodstream
• Examples:
  • Thyroid
  • Pituitary gland

Exocrine Glands

• Secrete their products into ducts
• Examples:
  • Sweat glands
  • Earwax glands
  • Salivary glands

Structure of Epithelial Tissue

• Apical Structure:
  • Free surface exposed to the exterior environment or cavity of the organ
  • Often have microvilli or cilia
• Basal Surface:
  • Anchored lower surface
• Basal Lamina:
  • Adhesive sheet beneath the basal surface
  • Joins epithelial tissue to connective tissue

Classifying Epithelial Tissue

• Classified by arrangement of layers:
  • Simple
  • Pseudostratified
  • Stratified
• Classified by cell shape:
  • Squamous
  • Cuboidal
  • Columnar

Epithelial Tissue Rule of Thumb

• More layers equal more protection
• Single layers are easier for substances to permeate
• Cilia are often helpful in moving substances or involved in sensation

Connective Tissue

• Supports body structures
• All connective tissue develops from Mesenchyme
• Four types:
  • Connective Proper
  • Cartilage
  • Bone
  • Blood

Connective Tissue Functions:

• Support:
  • Examples: Intervertebral discs containing fibrocartilage
• Bind:
  • Examples: Dense regular connective tissue of a tendon
• Storage:
  • Examples: Adipose tissue showing adipocytes of white fat
• Transport:
  • Examples: RBC, WBC & platelets
• Protection:
  • Examples: Pectoral Girdle: Clavicle and Scapula
• Immune Protection:
  • Examples: Bone Marrow

Types of Connective Tissue (Loose vs. Dense)

Loose Connective Tissue

• Contains:
  • Areolar
  • Adipose
  • Reticular

Areolar Connective Tissue

• Contains:
  • Fibroblast
  • Defense cell
  • Adipose cell
• Characteristics:
  • Strong, flexible, and resistant to stretch
  • Tough but flexible, branching / lattice
  • Allows for stretch and recoil
• Ground Substance:
  • Colorless, viscous solution
  • Supports cells
  • Binds cells together
  • Provides a medium for exchange
• Defense Cell:
  • Breaks down invading pathogens
  • Second line of defense after epithelia
  • Examples: macrophage, plasma cell, mast cell, eosinophil, neutrophil
• Adipose Cells:
  • Mainly lipids
  • Energy storage
  • Cushion / protect
  • Some hormones

Adipose Connective Tissue

• Primary cell type is lipid

Reticular Connective Tissue

• Found in "hollow organs" as a supporting framework

Dense Connective Tissue

• Contains:
  • Regular
  • Irregular
  • Elastic

Regular Connective Tissue

• Collagen fibers run parallel, densely packed, very strong

Irregular Connective Tissue

• Mostly collagen fibers, irregular / mesh pattern
• Provides strength in multiple directions

Elastic Connective Tissue

• Collagen and elastic fibers
• Allows for stretch and recoil

Cartilage

• Chondrocyte = cartilage cell
  • Develops from chondroblasts
    • Collagen + elastic fibers + ground substance
• Perichondrium = dense CT, covers cartilage
• Makes solid but somewhat pliable
  • Chondroitin sulfate
• Contains:
  • Hyaline
  • Elastic
  • Fibrocartilage

Hyaline Cartilage

• Most common type
• High concentration of fine collagen fibers
• Precursor to skeletal system in fetus
• Found at ends of long bones (articular cartilage)
• Most hyaline has perichondrium (not articular)

Elastic Cartilage

• Composed of both collagen and elastic fibers
  • More elastic, so it is more flexible
• Has outer perichondrium

Fibrocartilage

• Chondrocytes and collagen fibers are arranged in parallel rows
• No perichondrium

Bone

• Supports, protects, houses blood forming cells
• Relatively tough
• Contains only collagen and calcium
• Contains:
  • Compact
  • Spongy

Blood

• Contains plasma and cells (WBC, RBC, Platelets)
• Function is to transport to support tissues (blood carries stuff in it to all over the body)

Membranes

• Epithelia + Connective Tissue + Basement Membrane
• Contains:
  • Skin
  • Mucous
  • Serous

Skin Membrane

• "Cutaneous membrane"
• Two layers:
  • Epidermis
  • Dermis

Mucous Membrane

• Epithelial + Loose connective tissue + goblet cells

Serous Membrane

• Simple epithelia + areolar connective tissue
• Produces thin, watery fluid to allow easy motion over surfaces