Tissues

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Tissues
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Tissues

• A tissue is a group of similar cells that usually
  have a similar embryological origin and are
  specialized for a particular function.
• Tissue cells are often separated by non-living,
  intercellular materials that cells produce. This
  substance is called the matrix.
• Histology the study of tissues

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Four Principal Types of Tissues

• Epithelial covering and lining and glands
• Connective protects and supports, binds organs
  together, stores energy, and provides immunity
• Muscle movement
• Nervous transmits impulses that coordinate body
  activities

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Feature of Epithelial Tissue

• Closely packed cells with little extracellular
  material
• Epithelial cells are arranged in continuous
  sheets, in single or multiple layers
• Epithelial cells have an apical (free) surface,
  which is exposed to body cavity, lining of
  internal organ or exterior of body, and a basal
  surface which is attached to a basement membrane

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• Cell junctions are plentiful, providing secure
  attachments among cells.
• Epithelia are avascular, blood vessels are
  located in nearby connective tissue exchange of
  materials occurs by diffusion.
• Epithelia adhere firmly to nearby connective
  tissue by means of the basement membrane .
• Epithelia have a nerve supply.
• Epithelia have a high capacity for renewal (high
  mitotic rate) since it is subjected to wear and
  tear.

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• Epithelial functions include protection,
  filtration, lubrication, secretion, digestion,
  absorption, excretion, transportation, sensory
  reception, and reproduction.

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Covering and Lining Epithelium

• Epithelial layers are arranged as
• simple epithelium -(one layer), where diffusion,
  osmosis, filtration, secretion and absorption
  occur.
• stratified epithelium (several layers), protects
  underlying tissue from wear
• pseudostratified epithelium (one layer that
  appears as several) because nuclei at different
  level not all cells reach the surface those
  that do have cilia or secrete mucus.

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Cell Shapes

• squamous (flat) for diffusion
• cuboidal (cubelike) - produce secretions and
  function in absorption
• columnar (rectangular) - protect underlying
  tissue, may have cilia, secretion or absorption.
• transitional (variable) - change in shape from
  flat to columnar due to distention, expansion or
  movement of body parts.

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Classification is by number of layers and cell
shape (top layer)

• Simple squamous epithelium consists of a single
  layer of flat cells. It is adapted for
  diffusion, osmosis and filtration and is found in
  lungs and kidneys. Endothelium lines the heart,
  blood vessels, and lymph vessels and forms the
  walls of capillaries.

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• Simple cuboidal epithelium consists of a single
  layer of cube-shaped cells. It is adapted for
  secretion and absorption.

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Simple columnar epithelium comes in two
forms Nonciliated simple columnar epithelium - a
single layer of nonciliated rectangular cells.
Also functions in secretion and absorption.
Specialized cells containing microvilli perform
absorption. Goblet cells secrete mucus Ciliated
simple columnar epithelium consists of a single
layer of ciliated rectangular cells. Aids in
movement.
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• Pseudostratified columnar epithelium has only
  one layer but gives the appearance of many. All
  cells are anchored to the basement membrane, but
  some do not reach the surface.
• 1) Psuedostratified ciliated - has cilia and
  goblet cells Functions in secretion and movement.
• 2) Pseudostratified nonciliated has no cilia or
  goblet cells.

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Stratified Epithelial Tissue - at least two
layers of cells. Named by shape of the cells in
the superficial layer.
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Stratified squamous epithelium several layers
of cells in which the top layer is flat, bottom
layers vary from cuboidal to columnar. Its
function is protection (against abrasion). Basal
layers continually replicate. a) Nonkeratinized
variety lines the mouth, vagina and anus remains
moist b) Keratinized variety forms contains
protein keratin - outer layer of skin.
waterproof, resistant to friction, helps repel
bacteria.
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2) Stratified cuboidal epithelium consists of
several layers of cells in which the top layer is
cube-shaped. Fairly rare. Function is mainly
protective. 3) Stratified columnar epithelium
consists of several layers of cells in which the
top layer is rectangular. Also uncommon. Usually
basal layers are shortened, irregular polyhedral
cells. It protects and secretes.
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4) Transitional epithelium consists of several
layers of cells whose appearance is variable,
whether stretched or relaxed. It lines the
urinary bladder, and parts of the ureters and
urethra. It is capable of stretching. Tight
junctions in theses areas prevent leaks and
diffusion.
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Glandular Epithelium

• A gland is a single cell or a mass of epithelial
  cells adapted for secretion.
• There are two types depending on how the cells
  release the substances they produce Exocrine
  glands and endocrine glands

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• 1) Exocrine glands secrete into ducts or directly
  onto a free surface. Their secretions include
  mucus, sweat, oil, ear wax and digestive
  enzymes.
• Structural classification of exocrine glands
• multicellular glands - most glands, have a
  distinctive appearance. Communicates with the
  surface
• unicellular glands - single celled. goblet
  cells. No ducts.

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Functional classification of glands Holocrine -
accumulate secretions in cell, cell dies, and is
discharged with its contents as a glandular
secretion. The discharged cell is replaced by a
new cell. ex. sebaceous or oil gland in
skin Merocrine - most exocrine glands, form
secretion and discharge by exocytosis. Apocrine
glands - secretions accumulate near the top,
which pinches off to form secretion. Cell repairs
itself and repeats. ex. mammary glands.
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Endocrine glands - called ductless glands
discharge their secretions into the intracellular
fluid, where it diffuses into the blood stream.
These secretions are hormones, or chemical
messengers, which regulate many bodily
functions.
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Connective Tissue

• Connective tissue is the most abundant and
  widely distributed tissue in the body .
• All connective tissues have the same embryonic
  origin- from mesodermal cells called mesenchyme.
  

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The functions of connective tissue

1. Binding, attachment and support (bones, tendons
   and ligaments, organs)
2. Protection- bones and adipose tissue
3. Insulation - adipose tissue
4. Storage - of energy and fat soluble substances
5. Transportation - blood

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General Features of C.T.
1) It consists of three basic elements
cells ground substance
Extracellular fibers Called the
matrix Noncellular
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2) Does not occur on free surfaces such as
linings, except for the joint cavities which are
lined by areolar connective tissue. 3) Except
for cartilage, it has a nerve supply. 4) Usually
highly vascular, except for cartilage (avascular)
and tendons which have a small blood supply.
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5) Matrix may be fluid, semifluid, gelatinous,
fibrous, or calcified. It is usually secreted
by the connective tissue cells (except for blood)
and adjacent cells, and determines the qualities
of the tissue. (hard, rubbery, fluid, etc.) 6)
Cells can usually divide
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Cells of Connective Tissue Immature cell names
end in - blast. These cells can reproduce and
form the matrix Mature cell names end in
-cyte. These cells have a reduced ability to
divide and form matrix. Fixed cells - appear in
tissues in stable numbers Wandering cells - found
in tissues only in response to infection or injury
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Fibroblasts - most common type of fixed cell.
They secrete the matrix particularly the fibers
of the matrix. Macrophages develop from
monocytes. Phagocytize bacteria or cell debris.
Wandering macrophages leave the blood and wander
to infected tissues , while fixed macrophages
remain in certain tissues and organs. Important
in infection and immunity.
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Mast cells are found along blood vessels and
produce histamine, which dilates small blood
vessels during inflammation. They contain
heparin, an anticoagulant. Also involved in
allergic responses.
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Cells specific to a particular type of connective
tissue Adipocytes - store triglycerides.
Insulate and cushion Osteocytes (osteoblasts)
- bone Chondrocytes (chondroblasts) -
cartilage leukocytes and erythrocytes (
hemocytoblast)- blood
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Fibers Collagen fibers made of collagen.
Collagen fibers are tough and only slightly
elastic.. They often occur in bundles with the
fibers parallel to one another, which gives great
tensile strength. Collagen is found in most
connective tissues, esp. bone, tendons, and
ligaments.
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Elastic fibers are composed of a protein called
elastin and glycoprotein framework. They are
very stretchy and branch and join to form a
network. They provide strength to tissues, but
allows the tissue to be flexible and stretchy.
They are found in skin, blood vessels, and lungs
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Reticular fibers are composed of collagen and
glycoprotein. They provide support and form
loose networks of fibrous tissue. They are found
around fat cells, nerve fibers, and skeletal and
smooth muscle cells. They also form the stroma or
supporting framework of many soft, nonmuscular
organs such as the spleen and lymph nodes. These
fibers also help form the basement membrane.
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Ground substance can contain a variety of large
molecules. Some are which are complex
combinations of polysaccharides and proteins.
Some of these are hylauronic acid , chondroitin
sulfate, and keratan sulfate. Other molecules in
the matrix are adhesion proteins. Adhesion
proteins anchor cells in position and to provide
traction for movement of cells. The ground
substance supports and binds cells together, and
provides a medium for the exchange of materials.
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Types of Connective Tissues Connective Tissue
Proper Loose Connective Tissue or Areolar
connective Tissue - It is loosely arranged, it
is found wrapping organs and under skin, and
holds and conveys tissue fluid. Contains
primarily fibroblasts, but also macrophages,
adipocytes and some blood cells. It contains all
three fiber types, randomly arranged.
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The ground substance is fluid, semifluid or
gelatinous. This tissue contains hyaluronic acid,
which is thick and may slow the passage of some
drugs. Hylauronidase is an enzyme produced by
wbcs, sperm and some bacteria. Injection of
hyaluronidase can speed the passage of drugs and
fluid through the tissue.
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adipose tissue- cells are adipocytes, and
specialize in storing fat. Adipocytes are tightly
packed, and very little matrix . They
accumulate under the skin and yellow marrow of
long bones. Functions in energy reserves,
insulation, protection, and support.
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reticular connective tissue - consists of
reticular fibers and fibroblasts and forms the
supporting framework for cells in the liver,
spleen, lymph nodes and bone marrow.
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Dense connective tissue has fibers as the
dominant component. Dense regular connective
tissue- collagen fibers are arranged in parallel
bundles which makes this tissue flexible, but
resistant to stretching. Fibroblasts are found in
rows between the fibers. Found in tendons and
ligaments. Blood supply is poor.
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Dense irregular connective tissue - also has
collagen fibers and fibroblasts, but the
collagen fibers are thicker and arranged
irregularly. (Like felt material) This tissue
usually forms sheets, and resists pulling in
many directions. It is found in heart valves,
around cartilage, bone, muscles, dermis of skin,
and around some organs.
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Elastic connective tissue consists of elastic
fibers and fibroblasts. Very elastic. It is
found in the lungs, walls of arteries, bronchial
tubes and in the attachments between the
vertebrae.
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Specialized Connective Tissues
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Cartilage has a dense network of collagen fibers,
which gives strength, and elastic fibers. The
matrix contains chondroitin sulfate, which is
rubbery and gives cartilage resilience. Cells
are chondrocytes, and are found in lacuanae.
Surface of cartilage is surrounded by
perichondrium, where blood vessels are located.
No blood supply in the cartilage itself.
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Hyaline cartilage - (gristle) most abundant
cartilage, and weakest. It has very fine
collagen fibers and a resiliant gel as its ground
substance. It is found in the embryonic skeleton,
at the ends of bones , in the nose, and in
respiratory structures. It is flexible, allows
movement, reduces friction, absorbs shock and
provides support. Important in bone growth and
repair.
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Elastic cartilage - has condrocytes in a
network of elastic fibers. It maintains the shape
of organs such as the epiglottis of the larynx,
auditory (Eustachian) tubes, and external ear.
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Fibrocartilage contains visible bundles of
collagen fibers and combines strength and
rigidity. Also acts as a shock absorber. It is
found in the pubic symphysis, intervertebral
discs, and menisci (cartilage pads) in joints.
It is the strongest cartilage.
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Bone (osseous tissue) consists of
collagen fibers (flexibility) , mineral salts
(that contribute to the hardness of bone) and
cells called osteocytes. It is covered by the
periosteum and lined by the endosteum. It can be
compact or spongy depending on how the matrix and
the cells are organized. The basic unit of
compact bone is the osteon or Haversian system.
It supports, protects, helps provide movement,
stores minerals, and houses blood-forming
tissue.
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Blood (vascular tissue) consists of plasma and
formed elements (erythrocytes, leukocytes, and
platelets). Functionally, its cells transport
oxygen and carbon dioxide, carry on phagocytosis,
participate in allergic reactions, provide
immunity, and bring about blood clotting.
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Muscle Tissue
Skeletal Smooth Cardiac voluntary
involuntary involuntary cells are long short,
spindle-shaped branched many nuclei single
nucleus single nucleus striated nonstriated st
riated intercalated disks
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Nervous tissue neurons Dendrites - (one or
many) receive incoming signals Cell
body Axon - (one) transmits outgoing
signals neuroglia protective and supporting
cells
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