Tissues

• Tissues

  • There are four (4) primary or major tissue types:
  • Epithelial Tissue
  • Connective Tissue
  • Muscle Tissue
  • Nervous Tissue
• Epithelial Tissue


  • Cover organs and the body
  • Line body cavities
  • Line hollow organs
  • Have a free surface (apical surface)
  • Have a basement membrane
  • Are avascular
  • Cells readily divide
  • Cells tightly packed
  • Cells often have desmosomes
  • Function in protection, secretion, absorption, and excretion
  • Classified according to cell shape and number of cell layers
• Simple squamous epithelium


  • Single layer of flat cells
  • Substances pass easily through
  • Line air sacs
  • Line blood vessels
  • Line lymphatic vessels
• Simple cuboidal epithelium


  • Single layer of cube-shaped cells
  • Line kidney tubules
  • Cover ovaries
  • Line ducts of some glands
• Simple columnar epithelium


  • Single layer of elongated cells
  • Nuclei usually near the basement
  • Sometimes possess cilia
  • Sometimes possess microvilli
  • Often have goblet cells
  • Line uterus, stomach, intestines
• Stratified Epithelium


  Multiple layers of squamous/cuboidal cells
• Stratified squamous epithelium


  • Most common stratified epithelium in the body, usually consists of many cell layers
• Stratified cuboidal epithelium


  • Typically has just two cell layers with (at least) the surface cells being cuboidal in shape
• Stratified columnar epithelium


  • Columnar cells, but its basal cells vary in size and shape. Both of these epithelia are fairly rare in the body, found mainly in the ducts of large glands
• Transitional epithelium


  • Many cell layers, cube-shaped and elongated cells, line urinary bladder, ureters, and part of urethra
• Connective Tissues


  • Most abundant tissue type
  • Many functions: bind structures, provide support and protection, serve as frameworks, fill spaces, store fat, produce blood cells, protect against infections, help repair tissue damage
  • Have an extracellular matrix
  • Have varying degrees of vascularity
• Connective Tissue Fiber Types Present (Matrix)

  • Collagenous fibers - Thick, composed of collagen, great tensile strength
  • Reticular fibers - Very thin collagenous fibers, highly branched, form supportive networks
  • Elastic fibers - Bundles of microfibrils embedded in elastin, fibers branch, elastic, found in vocal cords and air passages
• Loose Connective Tissue

  • Areolar Connective Tissue - Supports, cushions, and nourishes various organs and tissues, contains immune cells, edema
  • Reticular Connective Tissue - Composed of reticular fibers, supports internal organ walls, walls of liver, spleen, lymphatic organs
  • Adipose Tissue - Adipocytes, cushions, insulates, stores fats, beneath skin, behind eyeballs, around kidneys and heart
• Dense Connective Tissue


  • Packed collagenous fibers, elastic fibers, few fibroblasts, bind body parts together, tendons, ligaments, dermis, poor blood supply
• Cartilage


  • Hyaline cartilage - Most abundant, ends of bones, nose, respiratory passages, embryonic skeleton
  • Elastic cartilage - Flexible, external ear, larynx
  • Fibrocartilage - Very tough, shock absorber, intervertebral discs, pads of knee and pelvic girdle
• Bone (Osseous Tissue)


  • Solid matrix, supports, protects, forms blood cells, attachment for muscles, skeleton, produced by Osteocytes in lacunae
• Blood


  • Fluid matrix called plasma, red blood cells, white blood cells, platelets, transports, defends, involved in clotting
• Muscle Tissues


  • Highly specialized to contract, or shorten, three types: skeletal, smooth, cardiac
• Skeletal muscle


  • Attached to bones, striated, voluntary
• Smooth muscle


  • Walls of organs, skin, walls of blood vessels, involuntary, non-striated
• Nervous Tissue


  • Found in brain, spinal cord, and peripheral nerves, sensory reception, conduction of nerve impulses, functional cells are neurons, neuroglial cells support and bind nervous tissue components
• Neurons


  Transmit electrical impulses, have a cell body, dendrites, and an axon
• Neuroglia


  Support and protect neurons, six types: astrocytes, microglial cells, ependymal cells, oligodendrocytes, satellite cells, and Schwann cells
• Tissue Repair (Wound Healing)


  Inflammation sets the stage, granulation tissue forms, regeneration and fibrosis effect permanent repair
• Tissue repair, or wound healing, occurs in two major ways: by regeneration and by fibrosis
• Regeneration is the replacement of destroyed tissue by the same kind of cells
• Fibrosis involves repair by dense (fibrous) connective tissue, that is, by the formation of scar tissue
• Cell/Tissue Modifications

  • Neoplasms - abnormal cell growths (benign/malignant or cancerous); result from lack of control of cell division
  • Hyperplasia - increase in size; results when tissue is repeatedly and strongly stimulated or irritated
  • Atrophy - decrease in size; results when organ is not stimulated
  • Metastasis - The formation of new masses at other body sites
  • Carcinogens - Radiation, mechanical trauma, certain viral infections, and many chemicals (tobacco tars, organic solvents such as mineral spirits)