Animal Histology: Cells and Tissues

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Animal Histology Cells and Tissues
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Tissues

• How do we define tissue?
• Tissues are groups of specialized cells that work
  together for a particular function.
• There are four types of tissue.
• Epithelial (covering)
• Connective (support)
• Muscle (movement)
• Nervous (control)

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Epithelial Tissues

• Epithelial tissues cover body surfaces.
• Outer layer of skin and the lining of organs
• Also found in glandular tissue
• Play roles in absorption, filtration, secretion,
  and protection against foreign substances

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Special Characteristics of Epithelium

• Have one free (unattached) surface or edge
  called the apical surface
• basement membrane

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Classification of Epithelium

• According to the number of cell layers
• Simple (one layer of cells)
• Stratified (more than one cell layer)

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Classification of Epithelium

• According to the shape of cells
• Squamous (cells flattened like scales)
• Cuboidal (cube-shaped)
• Columnar (shaped like columns)

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Simple Squamous Epithelium

• Simple squamous (SS) tissue is composed of flat,
  scale-like cells that usually forms membranes
• It lines the walls of blood vessels, and the
  lining of the heart, lung, and peritoneal
  cavities.

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Simple Cuboidal Epithelium

• This tissue is composed of a single layer of
  cube-like cells.
• It lines the walls of kidney tubules, covers the
  surface of ovaries, and is common in glands and
  their ducts.

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Simple Columnar Epithelium

• This tissue is composed of a single layer of tall
  cells.
• It often includes mucus-producing goblet cells.
• It often lines the digestive tract.

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Pseudostratified Columnar Epithelium

• Although this tissue appears stratified, it is
  actually composed of a single layer of cells of
  different types.
• Although their nuclei are found at different
  levels, each cell adjoins the basal membrane
  (BM).
• This tissue lines the larger respiratory
  passageways.
• It is often ciliated (arrows).

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Pseudostratified Columnar Epithelium

• Main functions absorption and secretion
• Ciliated variety lines respiratory tract
• Mucus produced by goblet cells traps dust and
  other debris
• Cilia propel mucus upward and away from the lungs

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Stratified Squamous Epithelium

• The outer layers of cells appear flat, but the
  inner cells vary in shape from cuboidal to
  columnar.
• Stratified squamous epithelium serves as a
  barrier to the outside environment in locations
  such as the skin, mouth, and esophagus.

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Stratified Cuboidal Epithelium

• Stratified cuboidal epithelium (SC) is found in
  the ducts of sweat glands and surrounds the
  follicles of ovaries (shown below).

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Transitional Epithelium

• Shape of cells depends upon the amount of
  stretching
• It lines organs of the urinary system.

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Ciliated Epithelium

• Some epithelial membranes are made up of cells
  with cilia, to move mucus along the surface.
• Ciliated epithelia in the trachea, for example,
  sweep debris out of the respiratory tract.

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Glandular Epithelium

• A gland is defined as one or more cells
  responsible for secreting a particular product
• Two major gland types
• Endocrine gland
• Ductless since secretions diffuse into blood
  vessels
• All secretions are hormones
• Examples include pancreas, ovaries, testes
• Exocrine gland
• Secretions empty through ducts to the epithelial
  surface
• Include sweat and oil glands

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Glandular Epithelium
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Connective Tissue

• Connective tissue differs from other tissues in
  that it contains large amounts of extracellular
  matrix.
• Extracellular matrix is nonliving material that
  surrounds living cells
• It is found everywhere and includes the most
  abundant and widely distributed tissue

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Connective Tissue

• Connective tissues function to
• bind other tissues together
• provide support
• provide nourishment
• store wastes
• repair damaged tissues
• These tissues are generally well vascularized
• Exceptions tendons, ligaments, cartilage
• The exceptions are avascular

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Extracellular Matrix

• Two main elements
• Ground substance
• Mostly water along with glycoproteins and large
  polysaccharide molecules
• May be liquid, gel-like, or rock-hard
• Fibers
• Collagen fibers (high strength)
• Elastic fibers (stretch and recoil)
• Reticular fibers (fine fibers, internal
  skeleton)

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Types of Connective Tissue

• Bone
• Various types of cartilage
• Adipose tissue
• Dense and loose connective tissue
• Blood

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Bone (Osseous Tissue)

• Composed of
• Bone cells in lacunae (cavities)
• Hard matrix of calcium salts
• Large numbers of collagen fibers
• Used to protect and support the body

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Hyaline Cartilage

• Most common type of cartilage
• Composed of collagen fibers hidden by a rubbery
  matrix with a glassy blue-white appearance
• Found in the larynx, attaches ribs to sternum,
  at the end of many bones
• Entire fetal skeleton before birth

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Elastic Fibrocartilage

• Elastic
• Provides elasticity
• Supports the external ear
• Fibrocartilage
• Highly compressible
• Forms cushion-like discs between vertebrate

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Dense Connective Tissue

• Dense connective tissue contains a large number
  of fibers with only a few cells.
• Fibers shown here are all running parallel to
  each other, and no cells are present.
• Tendons (muscle to bone) and ligaments (bone to
  bone) are composed of dense connective tissue.

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Loose Connective Tissue

• Loose connective tissue has few fibers, a number
  of cell types, and a large amount of matrix.
• It functions to bind epithelia to underlying
  tissues.
• Includes areolar, adipose, reticular connective

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Areolar Tissue

• Most widely distributed connective tissue
• Soft, pliable cobwebby tissue that cushions and
  protects the bodys organs it wraps
• Holds internal organs together and in their
  proper positions
• Under microscope matrix appears as empty space,
  reservoir of water and salts

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Edema

• When a body region is inflamed, the areolar
  tissue in the area soaks up the excess fluid like
  a sponge, and the area swells and becomes puffy.

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Adipose Tissue

• Adipose cells are bundled together by connective
  tissue.
• Each cell appears as a clear space, representing
  the site of the large drop of lipid (fat) before
  it dissolved during preparation of the microscope
  slide.
• The nuclei appear as small disks on the periphery
  of cells.
• Functions to insulate the body, protect organs,
  and fuel storage

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Reticular Connective Tissue

• Consists of a delicate network of interwoven
  reticular fibers
• Forms the stroma (internal framework) which can
  support free blood cells in lymphoid organs
  (lymph nodes, spleen, bone marrow)

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Blood (Vascular Tissue)

• Consists of blood cells surrounded by nonliving,
  fluid matrix called blood plasma
• Fibers only visible during blood clotting
• Functions as a transport medium for materials

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Muscle Tissue

• Muscle is a contractile tissue.
• There are three types of muscle
• Skeletal
• Cardiac
• Smooth
• Main function is to produce movement.

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Skeletal Muscle

• Under voluntary control
• Contracts to pull on bones or skin
• Produces gross body movements or facial
  expressions
• Characteristics of skeletal muscle cells
• Striated (stripe-like pattern)
• Multinucleate (more than one nucleus)
• Long, cylindrical

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Cardiac Muscle

• Under involuntary control
• Found only in the heart
• Function is to pump blood
• Characteristics of cardiac muscle cells
• Cells are attached to other cardiac muscle cells
  at intercalated disks
• Striated
• One nucleus/cell

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Smooth Muscle

• Under involuntary muscle
• Found in walls of hollow organs such as stomach,
  uterus, and blood vessels
• Characteristics of smooth muscle cells
• No visible striations
• One nucleus/cell
• Spindle-shaped cells

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Nervous Tissue

• Nervous tissue, which occurs throughout the body,
  receives and transmits stimuli.
• It converts a stimulus, whether chemical or
  physical in nature, into an electrical impulse
  that is conducted by neurons.
• Nervous tissue also consists of glia, which are
  the various types of supporting cells in the
  nervous system.

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Cerebellum

• The surface of the cerebellum is highly
  fissured.
• Outer layer is the molecular layer, which
  contains some glial cells but consists mostly of
  neuronal processes (dendrites and axons).
• Darkly stained area is the granular layer and is
  composed mostly of nerve cell bodies of tiny
  granule cells (a neuron type) along with some
  larger Golgi cells (another neuron type).
• Between the molecular and granular layers lies
  the Purkinje layer.

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How Histology Can Be Used
(One example)
Immunohistochemistry is used to reveal BrdU
(brown), a thymidine analog that is incorporated
in cells undergoing S phase. Cells stained brown
were caught in the act of DNA synthesis. These
cells are found in the hippocampus, one of the
only brain regions where new neurons are formed.
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Immunofluorescence labeling shows new neurons in
the hippocampus. Green is BrdU (the marker that
labels cells undergoing S phase), red is a NeuN
(a neuron-specific marker), and blue is GFAP (a
glial marker). Cells co-labeled green and red
are new neurons.