Tissues
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 nonliving, intercellular materials that cells
produce. This substance is called the
matrix.
• Histology – the study of tissues
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
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
• 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.
• Epithelial functions include: protection,
filtration, lubrication, secretion, digestion,
absorption, excretion, transportation,
sensory reception, and reproduction.
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.
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.
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.
• Simple cuboidal epithelium consists of a
single layer of cube-shaped cells. It is
adapted for secretion and absorption.
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. (Ovary)
• 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. (trachea)
• 2) Pseudostratified nonciliated has no
cilia or goblet cells. (trachea)
Stratified Epithelial Tissue - at
least two layers of cells. Named
by shape of the cells in the
superficial layer.
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.
2) Stratified cuboidal epithelium consists
of several layers of cells in which the top
layer is cube-shaped. Fairly rare. Function is
mainly protective. (sweat glands)
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.
(saliva glands)
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.
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
•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.
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.
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.( Pituitary ,
thyroid, Parathyroid, Adrenals)
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.
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
General Features of C.T.
1) It consists of three basic elements :
cells
ground substance
fibers
Extracellular
Called the matrix
Noncellular
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.
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
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
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.
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.
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
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.
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
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.
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.
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.
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 wbc’s, sperm and
some bacteria. Injection of hyaluronidase
can speed the passage of drugs and fluid
through the tissue.
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.
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.
Dense connective tissue has fibers
as the dominant component.
Dense regular connective tissuecollagen 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.
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.
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.
Specialized Connective
Tissues:
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.
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.
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.
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.
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.
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.
Muscle Tissue
Skeletal
voluntary
cells are long
many nuclei
striated
Smooth
involuntary
short, spindle-shaped
single nucleus
nonstriated
Cardiac
involuntary
branched
single nucleus
striated
intercalated
disks
Nervous tissue
The nervous system consists of all nervous tissue in the body. It is divided
anatomically into the central nervous system and the peripheral nervous system.
Central Nervous System (CNS)
The CNS consists of the brain (encephalon), which is enclosed in the skull,
and the spinal cord, which is contained within the vertebral canal. Nervous
tissue of the CNS does not contain connective tissue other than that in the
meninges and in the walls of large blood vessels. Collagenous fibers or
fibrocytes/blasts are consequently not observed, which is quite unlike other
tissues. Because of the absence of connective tissue, fresh CNS tissue has
a very soft, somewhat jelly-like consistency. The two major classes of cells
that make up the nervous tissue are nerve cells, neurones, and supporting
cells, glia.
neurons :
Dendrites - (one or many) receive
incoming signals
Cell body