THE TISSUE- ENGLISH
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TISSUE-
Tissues are group of cells which perform similar task and
are similar in size and shape. In human
body we have four types of tissues
Ø Epithelial
tissue or epithelium
Ø Connective
tissue
Ø Muscle
tissue
Ø Nervous
tissue.
EPITHELIAL TISSUE=
• Epithelial
tissues are thin sheet like tissues that cover all the exposed surfaces of the
body. They form the external skin, the inner lining of the mouth,
digestive tract, secretory glands, the lining of hollow parts of every organ such
as the heart, lungs, eyes, ears, the urogenital tract,
as well as the ventricular system of the brain and central
canals of the spinal cord.
• The
cells are very closely packed and the intercellular substance, called the matrix,
is minimal. The cells usually lie on a basement membrane, which is an
inert connective tissue made by the epithelial cells themselves. Epithelial
tissue may be:
• simple:
a single layer of cells
• stratified:
several layers of cells.
SIMPLE
EPITHELIAL TISSUE-
When the epithelium is composed of a single layer of
cells arranged on basement membrane, it is called simple epithelial tissue. The
types are named according to the shape of the cells, which differs according to
their functions. The more active the tissue, the taller the cells.
Simple epithelial tissue is further classified into
3 types-
Ø Squamous epithelium- It is composed of
a single layer of flattened cells arranged on a basement membrane. The cells fit closely together like flat
tiles, forming a thin and very smooth membrane across which diffusion easily
occurs. It forms the lining of the
following structures:
heart – where it is known as
endocardium
alveoli of the lungs
lining the collecting ducts of
nephrons in the kidneys
Ø Cuboidal
epithelium- This consists of cube-shaped cells fitting closely together lying
on a basement membrane Cuboidal epithelium is actively involved in secretion,
absorption and excretion. It forms the kidney tubules and is found in some
glands.
Ø Columnar
epithelium- This is formed by a single layer of cells, rectangular in shape, on
a basement membrane . It lines many organs and often has adaptations that make
it well suited to a specific function. The
lining of the stomach is formed from simple columnar epithelium .
The surface of the columnar
epithelium lining the small intestine is covered with microvilli . Microvilli provide a very large surface area
for absorption of nutrients from the small intestine.
In the trachea, columnar
epithelium is ciliated and also contains goblet cells that secrete mucus .This
means that inhaled particles that stick to the mucus layer are moved towards
the throat by cilia in the respiratory tract. In the uterine tubes, ova are
propelled along by ciliary action towards the uterus.
STRAITIFIED
EPITHELIAL TISSUE-
• Stratified epithelia consist of several layers
of cells of various shapes. Continual cell division in the lower layers pushes cells above nearer and nearer
to the surface, where finally they are shed.
• Basement
membranes are usually absent. The main function of stratified epithelium is to
protect underlying structures from mechanical wear and tear
Straitified epithelial tissue is further classified into
2 types-
Ø Straitified squamous epithelium- This
is composed of a number of layers of cells. In the deepest layers the cells are
mainly columnar and, as they grow towards the surface, they become flattened
and are then shed. This process continue in our whole life.
Straitified squamous epithelial
tissue is further classified into 2
types-
Keratinised stratified squamous epithelium- This is found on dry surfaces subjected to
wear and tear, such as skin, hair and
nails. The surface layer consists of dead epithelial cells that have lost their
nuclei and contain the protein keratin. This forms a tough, relatively
waterproof protective layer that prevents drying of the live cells underneath.
The surface layer of skin is rubbed off and is replaced from below
Non-keratinised stratified squamous epithelium - This
is found on dry surfaces subjected to wear and tearThis protects moist surfaces
subjected to wear and tear, and prevents them from drying out, such as the
conjunctiva of the eyes, the lining of the mouth, the pharynx, the oesophagus
and the vagina.
Ø Transitional epithelium - This is composed of several layers of
pear-shaped cells. It is found lining the urinary bladder and allows for
stretching as the bladder fills.
Ø CONNECTIVE TISSUE=
Ø The
connective tissue cells are more widely separated from each other than in
epithelial tissues, and intercellular
substance (matrix) is present in considerably larger amounts. There are usually
fibres present in the matrix, which may be of a semisolid jelly-like
consistency or dense and rigid, depending upon the position and function of the
tissue.
Most types of connective tissue have a good blood supply.
Major functions of connective tissue are:
• Binding
and structural support
• Protection
• Transportation
• Insulation.
• The
following cells are present in
connective tissue-
>Fibroblasts >Macrophases
>Fat cells >Lymphocytes
>Mast cells
Types of connective tissues are:
-Areolar tissue -Adipose
tissue
-Lymphoid tissue -Fibrous
tissue
-Elastic tissue -Cartilage
tissue
-Bone tissue and -Blood
• AREOLAR TISSUE- Areolar (loose) connective tissue is found
between many organs where it acts both to absorb shock and bind tissues
together. . The matrix is semisolid with many fibroblasts and some fat
cells (adipocytes), mast cells and macrophages widely separated by elastic and
collagen fibres. It is found in almost every part of the body, providing
elasticity and tensile strength.
• It
connects and supports other tissues, it is found:
• under
the skin
• between
muscles
• supporting
blood vessels and nerves
• in
the alimentary canal
• in
glands supporting secretory cells.
• ADIPOSE TISSUE- Adipose tissue consists of fat cells (adipocytes), containing
large fat globules, in a matrix of areolar tissue There are two types: white and brown.
• White
adipose tissue is most abundant. It can appear yellow and owes its color to
carotene and related pigments from plant food. White fat contributes mostly to
lipid storage and can serve as insulation from cold temperatures and mechanical
injuries. White adipose tissue can be found protecting the kidneys and
cushioning the back of the eye.
• This
is present in the newborn. It has a more extensive capillary network than white
adipose tissue. When brown tissue is metabolised, it produces less energy and
considerably more heat than other fat, contributing to the maintenance of body
temperature. In some adults it is present in small amounts.
• LYMPHOID TISSUE- This tissue, also
known as reticular tissue, has a semisolid matrix with fine branching reticulin
fibres. It contains reticular cells and white blood cells (monocytes and
lymphocytes). Lymphoid tissue is found in lymph nodes and all organs of
the lymphatic system
• FIBROUS TISSUE- This tissue is made up
mainly of closely packed bundles of collagen fibres with very little matrix.
Fibrocytes (old and inactive fibroblasts) are few in number and are found lying
in rows between the bundles of fibres.
• Fibrous
tissue is found:
• forming
ligaments, which bind bones together as an outer protective covering for
bone, called periosteum as an outer protective covering of some
organs, e.g. the kidneys, lymph nodes and the brain forming muscle sheaths,
called muscle fascia (see Fig. 16.52, p. 408), which extend beyond the
muscle, to become the tendon that attaches the muscle to bone.
ELASTIC TISSUE-
Elastic tissue is capable of considerable extension and recoil. There are few
cells and the matrix consists mainly of masses of elastic fibres secreted by fibroblasts.
It is found in organs where stretching or alteration of
shape is required, e.g. in large blood vessel walls, the trachea and bronchi,
and the lungs.
• CARTILAGE TISSUE- Cartilage is firmer
than other connective tissues; the cells are called chondrocytes and are
less numerous. They are embedded in matrix reinforced by collagen and elastic
fibres. There are three types:
• Hyaline cartilage, -Hyaline cartilage
is a smooth bluish-white tissue. The chondrocytes are in small groups within
cell nests and the matrix is solid and smooth. Hyaline cartilage provides
flexibility, support and smooth surfaces for movement at joints. It is found:
on the ends of long bones that form joints, forming the costal cartilages which
attach the ribs to the sternum, forming part of the larynx, trachea and
bronchi.
• Fibrocartilage
- This consists of dense masses of white collagen fibres in a matrix similar to
that of hyaline cartilage with the cells widely dispersed. It is a tough,
slightly flexible, supporting tissue found: as pads between the bodies of the
vertebrae, the intervertebral discs between the articulating surfaces of
the bones of the knee joint, called semilunar cartilages on the rim of
the bony sockets of the hip and shoulder joints, deepening the cavities without restricting .
• Elastic
fibrocartilage.- This flexible tissue consists of yellow elastic fibres
lying in a solid matrix. The chondrocytes lie between the fibres. It provides
support and maintains shape of, e.g. the pinna or lobe of the ear, the epiglottis
and part of the tunica media of blood vessel walls.
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