Tissues

Tissues

Specialized Intercellular Junctions:
1. Tight Junctions: Close space between cells by fushing cell membranes
  1. Ex: Cells that line the small intenstine
2. Desmosomes: Bind cells by forming "spot welds"
  1. Ex: Cells of the outerskin layer (epidermis)
3. Gap Junctions: Form tubular channels b/w cells that allow the exchange of substances
  1. Ex: Muscle cells of the heart and digestive tract
Four Major Types of Human Tissue:
1. Epithelial Tissue
  1. Function: Protection, secretion, absorption, excretion
    1. Location: Covers body surface, covers and lines internal organs, compose glands
      1. Characteristics: Lacks blood vessels, cells readily divide, cells are tightly packed together
2. Connective Tissue
  1. Function: Bind, support, protect, fill spaces, stores fat, produces blood cells
    1. Location: Widely distributed throughout the body
      1. Characteristics: Mostly have a good blood supply, cells are farther apart than epithelial cells, extracellular matrix in between.
3. Muscle Tissue
  1. Function: Movement
    1. Location: Attached to bones, in walls of internal organs, heart
      1. Characteristics: Able to contract in response to specific stimuli.
4. Nervous Tissue
  1. Function: Conduct impulses for coordination, regulation, integration, and sensory reception.
    1. Location: Brain, spinal cord, nerves
      1. Characteristics: Cells communicate with each other and other body parts. Ex: Muscles
Epithelium
1. Location: Covers all free body surfaces, forms the inner lining of body cavities, lines hollow organs, major tissues of glands
2. The Basement Membrane anchors epithelium to connective tissue. Cancer cells secrete a substance that dissolves the basement membrane, enabling the cells to invade other layers (mestasis)
  1. Cancer cells also produce fewer adhesion proteins (help cells "stick" together) which allows them to spread into surrounding tissues.
Connective Tissue
1. Characteristics: Connects, supports, protects, provides frameworks, fill spaces, stores fat, produces blood cells, protects against infection, and helps repair damaged tissues.
2. Major Cell Types
  1. Fibroblasts produce collagen and elastic fibers.
  2. Macrophages are phagocytes ("eat cells")
  3. Mast cells may release heparin and histamine
3. 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
4. Usually have an extracellular matrix in b/w.
  1. This matrix consists of fibers and a ground substance (gel-like material)
5. Categories of Connective Tissue
  1. Connective Tissue Proper Includes
    1. Loose Connective Tissue
      1. Areolar: Forms thin membranes b/w organs and binds them together. Found beneath the skin and surrounds organs.
      2. Adipose: Stores fat, cushions, and insulates. Found beneath the skin; in certain abdominal membranes; and around the kidneys, heart, and various joints.
      3. Reticular: Thin branched reticular fibers. Supports the walls of the liver and spleen.
    2. Dense Connective Tissue
      1. Dense Regular: Strong collagen fibers that bind structures as parts of tendons and ligaments.
      2. Dense Irregular: Thicker, randomly distributed collagen fibers and is found in the dermis.
      3. Elastic: Elastic fibers that make up hollow internal organs like lungs and blood vessels.
6. Specialized Connective Tissue Includes
  1. Cartilage: Provides support. Consists of fibers and a gel like sub. Lacks a direct blood supply. So it is slow to heal.
  2. Bone: Matrix consists of mineral salts and collagen. Compact and spongy bones; heals rapidly.
  3. Blood: Composed of cells suspended in fluid. Produced in the tissues of hollow parts of certain bones.
Muscle Tissue
1. Muscle Tissue contracts, moving structures attached to it.
2. Muscle Cells are also called muscle fibers
3. Skeletal muscle makes up about 40% of body weight and smooth and cardiac muscle makes up about 10%.
4. 3 Types of Muscle Tissue
  1. Skeletal
    1. Function: Movement of body parts, facial expressions, writing, talking, signing, chewing, swallowing, and breathing.
    2. Muscles that contain skeletal muscle tissue are usually attached to bones.
    3. These musc. can be controlled consciously->nalso called volume muscle tissue.
    4. The cells are long, about 40 mm in length and and threadlike, less than .1 mm in width
    5. The cell has many nuclei: multinucleate.
    6. The cells contain striations: alternating dark and light cross markings.
    7. The muscle cells contract when stimulated by a nerve cell, then relaxes when it is no longer stimulated.
  2. Smooth Muscle
    1. Considered "smooth" bc it contains no striations.
    2. The cells are shorter than skeletal muscle cells and are spindled shaped
    3. Each cell contains one central nucleus.
    4. Found in the walls of internal hollow organs: stomach, intestines, bladder, uterus, blood vessels
    5. They are under involuntary control: moves food through digestive tract, constricts blood vessels, and empties the bladder.
  3. Cardiac Muscle
    1. Found only in the heart.
    2. The cells are striated, branched, joined end to end, and interconnected in a complex. network.
    3. Specialized intercellular junctions: the connection b/w cardiac muscle cells: called intercalated disc
    4. Under involuntary control.
      1. Pumps blood through the chambers of the heart and into blood vessels.
    5. Can cont. to function without nervous stimulation.
Nervous Tissue
1. Found in the brain, spinal cord, and peripheral nerves.
2. Basic cells called neurons and are very specialized.
  1. Neurons sense cert. types of changes in the surr.
  2. Neurons have dendrites which receive sensory info and transmit messages as an electrical signal to the axon. The axon sends the message to the next neuron or to muscles or glands.
3. Neuroglia Cell
  1. Supp. cells of the nervous tissue.
  2. Some of them bind and supp. nerv. tissue, and carry out phagocytosis ("eat cells")
    1. Helps protect nervous tissue by engulfing cellular debris, waste, and foreign material.
  3. Some are involved in cell to cell commun.

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