Unit 2: Tissues

Intercellular Junctions
1. Tight Junctions
  1. Close space between cells by fusing cell membranes
2. Desmosomes
  1. Bind cells by forming “spot welds” between cell membranes
3. Gap Junctions
  1. Form tubular channels between cells that allow the exchange of substances
Types of Tissues
1. Epithelial
  1. Function → protection, secretion, absorption, excretion
  2. Location → covers body surface, covers and lines internal organs, compose glands
  3. Characteristics → lack blood vessels, cells readily divide, cells are tightly packed together.
  4. Covers all free body surfaces - Forms the inner lining of body cavities - Lines hollow organs - Major tissue of glands
  5. Basement Membrane
    1. anchors epithelium to connective tissue
    2. Cancer cells
      1. secrete a substance that dissolves the basement membrane, enabling the cells to invade other tissue layers (metastasis)
      2. produce fewer adhesion proteins (help cells to “stick” together) which allows them to spread into surrounding tissues
  6. Lacks blood vessels, has cells that are tightly packed, and is continuously replaced.
  7. protects, secretes, absorbs, and excretes
  8. Classified according to cell shape and the number of cell layers.
    1. Simple Squamous Epithelium
    2. Simple Cuboidal Epithelium
    3. Simple Columnar Epithelium
    4. Pseudostratified Columnar Epithelium
    5. Stratified Squamous Epithelium
    6. Stratified Cuboidal Epithelium
    7. Stratified Columnar Epithelium
    8. Transitional Epithelium
    9. Glandular Epithelium
2. Connective
  1. Function → bind, support, protect, fill spaces, store fat, produce blood cells
    1. connect, supports, protects, provides frameworks, fills spaces, stores fat, produces blood cells, protects against infection, and helps repair damaged tissues.
      1. usually have considerable extracellular matrix between them
        consists of fibers and a ground substance
  2. Location → widely distributed throughout the body
  3. Characteristics → Mostly have a good blood supply, cells are farther apart than epithelial cells, extracellular matrix in between
    1. Major Cell Types
      1. Fibroblasts produce collagen and elastic fibers
      2. Macrophages are phagocytes (“eat cells”)
      3. Mast cells may release heparin and histamine
    2. Connective Tissue Fibers
      1. Collagen fibers have a great tensile strength.
      2. Elastic fibers are composed of elastin and are stretchy.
      3. Reticular fibers are fine collagen fibers.
    3. Categories of connective tissues
      1. Loose Connective Tissue
        Areolar
        forms thin membranes between organs and binds them together. Found beneath the skin and surrounds organs
        Adipose
        stores fat, cushions, and insulates. Found beneath the skin; in certain abdominal membranes; and around the kidneys, heart, and various joints.
        Reticular
        thin branched reticular fibers. Supports the walls of the liver and spleen
      2. Dense Connective Tissue
        Dense Regular
        strong collagen fibers that bind structures as parts of tendons and ligaments
        Dense Irregular
        thicker, randomly distributed collagen fibers and is found in the dermis.
        Elastic
        elastic fibers that make up hollow internal organs like the lungs and blood vessels
      3. Specialized Connective
        Cartilage
        Consists of fibers and a gel-like substances Lacks a direct blood supply, so it is slow to heal Found at the ends of various bones; in the ear; in the larynx; and in the pads between the bones of the spinal column, pelvic girdle, and knees
        Bone
        matrix consists of mineral salts and collagen. Compact & spongy bones. Heals rapidly
        Blood
        Composed of cells suspended in fluid. Produced in the tissue of hollow parts of certain bones.
3. Muscle
  1. Function → movement
  2. Location → attached to bones, in the walls of hollow internal organs, heart
  3. Characteristics → Able to contract in response to specific stimuli
    1. Muscle cells are also called muscle fibers.
    2. Skeletal muscle makes up about 40% of body weight & smooth and cardiac muscle makes up about 10%
  4. Skeletal
    1. Function - movement of body parts, facial expressions, writing, talking, singing, chewing, swallowing, and breathing.
    2. Muscles that contain skeletal muscle tissue are usually attached to bones.
    3. also called voluntary muscle tissue
    4. The cells are long → about 40 mm in length and threadlike → less than 0.1 mm in width.
    5. contain striations → alternating light and dark cross-markings
    6. multinucleate
    7. muscle cell contract when stimulated by a nerve cell, then relaxes when it is no longer stimulated
  5. Smooth
    1. contains no striations
    2. The cells are shorter than skeletal muscle cells and are spindled shaped.
    3. one central nucleu
    4. Found in the walls of hollow internal organs → stomach, intestines, bladder, uterus, blood vessels.
    5. under involuntary contro
  6. Cardiac
    1. Found only in the heart.
    2. The cells are striated, branched, joined end-to-end, and interconnected in a complex network.
    3. Each cell contains a single nucleus.
    4. Specialized intercellular junction → the connection between cardiac muscle cells → called intercalated disc
    5. These muscles are under involuntary control
    6. Can continue to function without nervous stimulation.
4. Nervous
  1. Function → conduct impulses for coordination, regulation, integration, and sensory reception
  2. Location → brain, spinal cord, nerves
  3. Characteristics → cells communicate with each other and other body parts
  4. Basic cells called neurons and are highly specialized.
    1. sense certain types of changes in their surroundings
    2. have dendrites, which receive sensory information and transmit the message as an electrical signal to the axon
      1. The axon sends the message to the next neuron or to muscles or glands
    3. Function is to coordinate, regulate, and integrate many body functions
  5. Neuroglia
    1. Supporting cells of the nervous tissue
    2. Some of the neuroglia bind and support nervous tissue.
    3. Some of the neuroglia carry out phagocytosis, which means “to eat cells”
    4. Helps protect nervous tissue by engulfing cellular debris, waste, and foreign material.
    5. Some of the neuroglia connect neurons to blood vessels.
    6. Some of the neuroglia are involved in cell-to-cell communication.

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Unit 2: Tissues

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