Chapter 4 Notes
Epithelial and Connective Tissue

Histology: the study of tissues

1. Definition

• a tissue is a group of similar cells with
  intercellular material that together perform a specific function.
• Four basic tissues and germ layer derivative
              1. Epithelial tissue:      ectoderm, endoderm, mesoderm
              2. Connective tissue:    mesoderm
              3. Muscle tissue:         mesoderm
              4. Nervous tissue:       ectoderm

 Epithelial Tissue

2. Characteristics

• Function - protect, absorb, secrete
• Exist in sheets of cells (membranes)
• No blood supply
• Contain an inferior basement membrane
      - anchors epithelial tissue to connective tissue below
      - is composed of connective tissue fibers and
         intercellular substance
• Types of Epithelial Cells
      - Squamous - flat, irregular cells
      - Columnar - column-shaped with oval nucleus at base of cell
      - Cuboidal - relatively square; central nucleus
• Method of Classifying Epithelial Tissue
      - by cell type
      - by number of cell layers
              simple - one cell layer
              stratified - multiple cell layers
• Epithelial tissue online comparison

3. Types of Epithelial Tissue

Simple Squamous epithelium

•   Structure - single layer of flat, squamous cells
•    Function - flattened cells emphasize ability to absorb
•    Location - air sac (alveoli) of lungs, capillary walls,
                      covering of organs, part of kidney that filters blood

Simple cuboidal epithelium

• Structure - single layer of cuboidal cells
• Function - absorption, secretion
• Location - kidney tubules, lines cornea & lens of eye,
                   Thyroid gland

Simple columnar epithelium

• Structure  - single layer of columnar cells
                  - may contain the following specialized structures
                      a. Goblet cells - specialized for mucus secretion
                      b. Microvilli with perpendicular projections for
                      absorption
                      c. Cilia in respiratory tract
• Function - protection, secretion, absorption
• Location - lining of digestive tract, gall bladder and part
                   of uterine tubes & respiratory tract

Keratinized stratified squamous epithelium

• Structure - multiple layers of three epithelial cell
  types, superficial cells, dehydrate, fuse, and
  fill with keratin, a yellow, horny material
                  - basal layer undergoes mitosis
• Function - protection of living cells below
                  - first line of defense
• Location - surfaces constantly exposed to air; skin

Nonkeratinized stratified squamous epithelium

• Structure - multiple layer of three epithelial cell
                    types; contains mucous glands
• Function - protection from abrasion
• Location - lining of mouth, esophagus, vagina

Pseudostratified columnar epithelium

• Structure - single layer of columnar cells with
                    appearance of multiple layers
                  - may contain goblet cells and cilia
• Function - protection, trap dust particles
• Location - lining of trachea, male reproductive
                   ducts, ducts of some glands

 Transitional epithelium

• Structure - all 3 types of cells with rounding of outer layer
• Function - allow for stretch (distension)
• Location - lining of urinary bladder and ureters

Glandular Epithelium

• Definition - specialized group of epithelial cells that function in secretion
• Formation of Glands
  - epithelial cells grow downward into the supportive tissue
  - cells proliferate and differentiate
  - endocrine glands
          - cells that detach from epithelium 
          - ductless
          - secretions are released into blood stream       
  - exocrine glands
          - cells that retain their connection with the epithelial surface
          - duct is present
          - secretion released onto surface of epithelium
          -types of exocrine glands
                  1. Halocrine - cell dies and releases content
                                       - sebaceous gland
                  2. Merocrine - secretion released without any damage to cell
                                       - sweat gland, pancreas, salivary
                  3. Apocrine - secretion pinches off from cell
                                      - mammary gland

Histology online sites

Connective Tissue

4. Characteristics

• Function - support and binding
• Cells are scattered among fibers and a matrix
• Vascular
• Arises from embryonic mesenchyme
• Matrix varies from fluid to solid, holds fibers and cells
  in place while determining the function of the tissue
• Fibers are made from three proteins
• Types of fibers
          a. Collagenous  - contains the protein collagen,
                                  - fibers are strong and flexible
          b. Reticular fibers - fine branching fibers form
                                        a supporting framework
          c. Elastic fibers  - protein is elastin, fibers have
                                      strength and elasticity
• Types of Connective Tissue Cells
          a. Fibroblast     - produces fibers & matrix
                                  - most numerous
                                  - involved in repair and growth
          b. Fibrocyte      - mature fibroblast
                                  - maintenance
          c. Macrophages - defense, phagocytosis
          d. Plasma cells - source of circulating antibodies
          e. Mast Cell - releases heparin, an anti-coagulant
                                  - releases histamine, dilates small blood vessels
          f. Fat Cell - stores triglycerides
                                  - signet ring shape

5. Types of Connective Tissue

Areolar connective tissue (areolar)

• Structure  - collagenous & elastic fibers
                  - all 6 types of connective tissue cells
                  - fluid matrix contains hyaluronic acid
                     which aids in diffusion
• Function   - covers organs
                  - holds blood vessels & nerves in place
                  - widely distributed
                  - nutritive role
                  - second line of defense
• Location  - mucous membranes
                  - between tissue of body organs
                  - with adipose tissue forms subcutaneous layer

Dense connective tissue

• Structure  - collagenous fibers predominate
                  - cells are fibroblasts and macrophages
                  - dense matrix
• Function  - provides strength
• Location  - fibers arranged in parallel bundles for strength
                  - tendons (attaches muscle to bone)
                  - ligaments (holds bones to joints)
                  - fibers irregular for stretch aponeuroses (fasciae)
                      and capsules of organs

Elastic connective tissue

• Structure  - free branching elastic fibers, few fibroblasts
• Function   - allows expansion and recoil
• Location  - lungs, trachea, arteries, aorta

Reticular connective tissue

• Structure  - mainly reticular fibers, thin matrix
• Function   - holds cells of loose organs together
• Location   - liver, spleen, bone marrow

Adipose connective tissue

• Structure  - collagenous and elastic fibers
                  - all six connective tissue cells
                  - fibroblasts specialize as fat cells
                      (central fat vacuole thin cytoplasm)
                  - associated with areolar connective tissue
• Function   - food reserve for energy
                  - prevents loss of body heat
• Location   - around most organs
                  - beneath skin
                  - marrow of long bones

Cartilage

• General characteristics
      1. cells are chondrocytes
      2. matrix is semisolid containing chondroitin
      3. lacuna - a depression in matrix which houses chondrocytes
      4. perichondrium - connective tissue membrane around cartilage
      5. no blood supply
• Types

Hyaline cartilage

• Structure  - invisible fine collagenous fibers
                  - two chondrocytes housed in each lacunae
                  - thick gelatinous ground substance
• Function  - acts as a model for embryonic bone
                      formation, prevents tissue damage
                      from friction. Provides shape to nose
                      and respiratory passages
• Location   - covering bone ends at joints
                  - tip of nose
                  - between rib and sternum (costal)
                  - epiphyseal plate
  
  Fibrocartilage

• Structure  - collagenous fibers arranged in parallel bundles
                  - chondrocytes sandwiched between bundles
• Function   - provides strength
• Location   - intervertebral discs, pubic symphysis

Elastic cartilage

• Structure - many elastic fibers
• Function  - allows for bending with return to original shape
• Location  - external ear, larynx and eustachian tubes

Bone tissue

• General Characteristics
          - organic matter - 35% (cells & fibers)
          - inorganic material - 65% (matrix & calcium salts)
• Types of bone cells
              1. osteocytes - maintenance of intercellular material (matrix)
              2. osteoblasts - peripheral bone forming cells
              3. osteoclasts - internal, actively destroy bone matrix
• Classification of bone according to structure
• 
              1. Compact bone
                  - arranged into concentric rings called Haversian systems
                  - provides strength
                  - is external & solid
                  - Haversian system consists of:
  
                          lamella - concentric ring of matrix
                          lacuna - openings between lamellae for osteocytes
                          osteocytes - mature bone cell
                          Haversian canal - in center of lamella; houses vessels
                          Canaliculi - radiating channels between lacuna
                                      and Haversian canal for nutrients and wastes
                          Volkmann canal - crosswise canals from Haversian canal
                                      to exterior containing blood vessels and nerves
• 

                        2. Spongy bone
                            - irregular lattice work of bone called trabecula
                            - spaces filled with red bone marrow
                            - osteocytes trapped within calcium matrix

    Connective Tissue Lab