TISSUE LEVEL OF ORGANIZATION

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TISSUE LEVEL OF ORGANIZATION

• A tissue is a group of cells that have a common
  embryonic origin and function together to carry
  out specialized activities.

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Tissues

• The various tissues of the body are classified
  into four major tissue types. They are
  epithelial, connective, muscle and nervous.
• All tissue develop from three primary germ
  layers ectoderm, mesoderm and endoderm.
• Epithelial-ectoderm, mesoderm and endoderm
• Connective and muscle-mesoderm
• nervous tissue-ectoderm

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Cell Junctions

• Most epithelial cells and some muscle and nerve
  cells re tightly joined into functional units.
• Cell junctions are contact points between the
  plasma membranes of tissue cells.
• Tight junctions-form fluid-tight seals between
  cells.
• Desmosomes-fasten cells to one another or the
  basement membrane
• gap junctions-permit electrical or chemical
  signals to pass between cells.

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Epithelial Tissues

• Lining tissues
• single or multi-layered
• apical surface and basal surface
• avascular
• nerve supply
• highly mitotic
• several functions

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Epithelial tissue functions

• Protection
• Filtration
• Lubrication
• Secretion
• Digestion
• Absorption
• sensory reception

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Classification of Epithelial Tissues

• Simple
• squamous
• cuboidal
• columnar

• Stratified
• sqamous
• cuboidal
• columnar
• transitional

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Simple squamous epithelium

• Single layer of thin and flat cells
• locationlining of blood vessels, air sacs of
  lungs, Bowmans capsule of kidneys
• function diffusion, secretion, filtration

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Simple cuboidal epithelium

• Cube-shaped cells
• found in the lining of kidney tubules, covers
  surface of ovary, lens of eye
• function secretion and absorption

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Simple columnar epithelium(nonciliated)

• Cells are elongated
• ciliated or non-ciliated.
• location GI tract, ducts of many glands and
  gall bladder
• function absorption and secretion

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Startified squamous epithelium

• Several layers of cells
• flat on top and cuboidal or columnar at the
  bottom
• layer of skin, lining of mouth, esophagus, vagina
  and tongue
• protection
• keratinized or non-keratinized

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Stratified cuboidal epithelium

• Rare type of epithelium
• Two or more layers of cells
• ducts of sweat glands and part of male urethra
• protection

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Stratified columnar epithelium

• Also uncommon
• Several layers of cells
• lines part of urethra, glands,anal mucous
  membrane,conjunctiva of eye
• protection and secretion

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Transitional epithelium

• Several layers thick
• appearance of superficial layer varies
• urinary bladder, ureter and urethra
• permits distention

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Glandular Epithelium

• Function is in secretion.
• A gland may consist of one cell or a group of
  highly specialized cells that secrete substances
  into ducts, onto a surface ot into the blood.
• Glands are classified as being exocrine or
  endocrine.

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Exocrine Glands

• Secretions reach the skin surface or lumen of
  organs.
• Secretions include sweat, mucus, oil, ear wax,
  and digestive enzymes.
• Eg. Sweat gland, salivary glands.
• Unicellular (goblet cells) or multicellular
  (sweat gland, salivary glands).
• Divided into Holocrine, merocrine and apocrine
  glands.

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Endocrine Glands

• Ductless glands
• secretions enter the extracellular fluid and then
  directly diffuse into the bloodstream.
• Secretions are called hormones which regulate
  many metabolic and physiological functions to
  maintain homeostasis.
• Eg. Pituitary, thyroid, adrenal.

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Connective Tissues

• Most abundant body tissue
• Bind cells and organs together
• consists of cells, ground substance and fibers
• has a nerve supply (except for cartilage)
• and is highly vascular ( except for cartilage,
  tendons and ligaments)

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General Features

• Contain three basic elements cells, ground
  substance and fibers.
• Do not usually occur on free surfaces.
• Have a nerve supply.
• Highly vascular.
• Matrix which may be fluid, semi-fluid,
  gelatinous, fibrous or calcified is usually
  secreted by the connective tissue cells

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Connective tissue cells

• Cells in connective tissue are derived form
  mesenchymal cells.
• The cell types are
• fibroblasts-secrete matrix
• macrophages-perform phagocytosis
• plasma cells-secrete antibodies
• mast cells-produce histamine
• adipocytes-store fat
• white blood cells-migrate from blood in response
  to infections.

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Connective Tissue Matrix

• Ground Substance Supports cells, binds them
  together and provides a medium through which
  substances are exchanged between the blood and
  cells.
• Hyaluronic acid lubricates joints and maintains
  shape of eyeball
• Chondroitin Sulfate cartilage, bone, skin
• Dermatan Sulfate skin, tendons, blood vessels
• Keratan Sulfate bone, cartilage, cornea of eye.

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Matrix of Connective Tissue

• The ground substance and fibers make up the
  matrix.
• The ground substance includes hyaluronic acid,
  chondroitin sulfate, dermatam sulfate, keratan
  sulfate, adhesion proteins.
• The fibers are
• collagen fibers in bone, tendons and ligaments
• elastic fibers (made of elasin, fibrillin,) in
  skin, blood vessel walls and lungs.
• Reticular fibers (made of collagen and
  glycoproteins) fat cells, nerve fibers, muscle.

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Classification of Connective Tissue

• Embryonic connective tissue
• mesenchyme
• mucpus connective tissue
• Mature connective tissue
• loose connective tissue
• dense connective tissue
• cartilage
• bone
• blood

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Types of mature connective tissue

• Loose connective tissue
• areolar connective tissue
• adipose tissue
• reticular connective tissue
• dense regular and dense irregular connective
  tissue
• cartilage hyaline, fibrocartilage and elastic
• bone or osseus tissue
• blood and lymph

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Membranes

• An epithelial membrane consists of an epithelial
  layer overlying a connective tissue layer.
• Mucous membrane lines cavities that open to the
  exterior such as the GI tract.
• Serous membrane line closed cavities and cover
  the organs in the cavities such as pleura,
  pericardium, peritoneum.
• The cutaneous membrane is the skin.
• Synovial membranes line joint cvaities, bursae
  and tendon sheaths.

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Muscle Tissue

• Muscle tissue consists of fibers that are
  specialized for contraction. It provides
  motion, maintains posture and produces heat.
• The three types of muscle tissue are
• skeletal muscle attached to bones and is
  striated. Voluntary action.
• Smooth muscle found in the walls of hollow
  internal structures, is nonstriated and action is
  involuntary.
• Cardiac muscle forms most of the heart wall, is
  striated and its action is also involuntary.

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Nervous Tissue

• There are two types of nerves cells that make up
  the nervous system- neurons and neuroglia.
• Neurons are the nerve cells. They receive
  stimuli, convert stimuli into nerve impulses and
  conduct nerve impulses. They consist of a cell
  body and axons and dendrites.
• The neuroglia are the protective and supporting
  cells.