Tissues

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Tissues
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Tissue

• A group of similar cells, usually of similar
  embryonic origin, that function together to carry
  out specialized activities

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Histology

• The science that deals with the study of tissues
• Pathologist a scientist who specializes in
  laboratory studies of cells and tissues to make
  accurate diagnoses. A pathologist examines
  tissues for any changes that might indicate
  disease.

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Types of Tissues

• Epithelial Tissue
• Covers body surfaces lines body cavities, hollow
  organs and ducts forms glands
• Connective Tissue
• protect and supports the body and its organs,
  binds organs together, stores energy reserves as
  fat, provides immunity
• Muscular Tissue
• Generates the force needed to make body
  structures move
• Nervous Tissue
• Detects changes inside and outside the body and
  initiates and transmits nerve impulses that
  coordinate body activities to help maintain
  homeostasis

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Cell Junctions

• Points of contact between plasma membranes of
  different cells that join them into functional
  units.

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Epithelial Tissue

• AKA Epithelium
• 2 types
• Covering and Lining Epithelium
• Forms the outer covering of the skin and some
  internal organs. It also lines body cavities,
  blood vessels, ducts, and the interiors of many
  of the body systems.
• Glandular Epithelium
• Makes the secreting portion of glands

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General Features of Epithelium

• 1. Closely packed cells with little extracellular
  material between them arranged in sheets
• 2. Surfaces
• Apical Surface exposed to a body cavity, the
  outside of the body or lining an internal organ
• Lateral Surface Face adjacent cells
• Basal Surface bottom layer attached to a
  basement membrane (extracellular structure
  composed mainly of fibers located between
  epithelium and underlying connective tissue)

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General Features of Epithelium

• 3. Avascular no blood vessels. Epithelial
  cells must get their nutrients from underlying
  connective tissue through diffusion
• 4. Innervated (have a nerve supply)
• 5. High mitotic rate high capacity for cell
  division because of wear and tear and injury

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Covering and Lining Epithelium Cell Shapes

• Squamous flat cells that attach to each other
  like tiles
• Allows for rapid passage of substances through
  them
• Cuboidal cells are as tall as they are wide,
  sometimes contain microvilli
• Function in Secretion and Absorption
• Columnar Taller than they are wide, sometimes
  contain microvilli or cilia
• Function in Secretion, Absorption and Protection
• Transitional Cells that have the ability to
  change shape from Cuboidal to Squamous and back
  as organs stretch

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Simple Epithelium

• A single layer of cells found in areas where
  diffusion, osmosis, filtration, secretions and
  absorption occur

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Simple Squamous Epithelium

• A single layer of flat cells that resembles a
  tile floor when viewed from the apical surface
• Nucleus is a flattened oval found in the center
  of the cell
• Found where filtration or diffusion take place,
  not found in areas of high wear and tear

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Simple Squamous Epithelium

• Endothelium simple squamous that lines the
  heart, blood vessels and lymphatic vessles
• Mesothelium simple squamous that lines serous
  membranes (lines cavities not open to the outside
  of the body, like the abdomen or thorax)

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Simple Cuboidal Epithelium

• Single layer of cube shaped cells
• Found on the surface of the ovary, the lens of
  the eye and lining of glands as well as the
  secreting portion of glands
• Function in Secretion and Absorption

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Simple Columnar Epithelium

• Single Layer of Column Shaped Cells
• 2 Forms cilliated and noncilliated

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Non-cilliated Simple Columnar Epithelium

• Contains absorptive cells and goblet cells
• Absorptive Cells have microvilli to increase
  surface area
• Goblet Cells modified Columnar cells that
  secrete mucus at the apical surface
• Lines most of the GI tract, ducts of glands and
  gallbladder

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Ciliated Simple Columnar Epithelium

• Cells with cilia at the apical surface, usually
  interspersed with goblet cells
• Mucus secreted by goblet cells forms a thin layer
  over the cell surface which is moved by the
  ciliated cells.
• Found in the respiratory tract

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Stratified Epithelium

• Contains 2 or more layers of cells used for
  protection of underlying tissue in area where
  there is a lot of wear and tear
• The name of the tissue depends on the shape of
  the cell on the apical layer

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Stratified S quamous Epithelium

• Cells in the apical layer are flat
• Cells in the deep layers vary in shape
• Basal cells continuously undergo mitosis
• As they move farther from the basal layer they
  become dehydrated and harder

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Keratinized Stratified Squamous Epithelium

• Tough layer of keratin is deposited on the top
  layers to help protect the skin and underlying
  tissues from microbes, heat and chemicals

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Nonkeratinized Stratified Squamous Epithelium

• Does not contain keratin
• Found on the lining of the mouth, esophagus, and
  tongue

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Stratified Cuboidal Epithelium

• Fairly Rare
• 2 or more layers of cells, apical layer is
  cuboidal
• Found in sweat glands

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Stratified Columnar Epithelium

• Fairly Rare
• 2 or more layers of cells, the top layer is
  columnar
• Found in excretory ducts of some glands and some
  mucous membranes

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Transitional Epithelium

• Varies in appearance depending on whether the
  organ it lines is distended or relaxed.
• Looks similar to stratified cuboidal except the
  top layer is large and rounded

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Pseudostratified Columnar Epithelium

• Appears to have several layers because the nuclei
  of the cells are at various depths.
• All of the cells are attached to the same
  basement membrane so there is only 1 layer of
  cells

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Glandular Epithelium

• Functions in Secretion
• A gland consists of one cell or a group of cells
• Endocrine Glands secretions enter the
  interstitial fluid
• Hormones
• Exocrine Glands secrete their products into
  ducts (tubes) that empty at the surface of the
  covering/lining epithelium
• Mucus, oil, earwax, digestive enzymes

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