Sunday 28 June 2015
Tissue: making cells work together
Tissue is the junction of similar cell
having a common origin, structure and function. The study of tissue is known as
histology
Human body is made up four different
types of tissues, which differ among themselves in composition and function.
The four basic types of tissues are:
·
Epithelium tissue
·
Connective tissue
·
Muscular tissue, and
·
Nervous tissues
Epithelium tissue:
Epithelial tissue covers the outer
surface of the some parts of the body, lines internal cavities, and many other glands.
The cells are closely arranged with little intercellular spaces and rest on a
basement membrane.
There are two types of epithelial
tissues namely:
·
Simple epithelium
·
Stratified epithelium
Simple epithelium is composed of single
layer of cells and present as lining for body cavities, ducts, and tubes.
On the basis of structure of cells
found in simple epithelium, the epithelium is categorized into three types:
Squamous- made up of polygonal and
flattened cells with irregular boundaries. Squamous epithelium is also called as pavement epithelium
because cells look like tiles on the floor. It is found in walls of blood
vessels, alveoli of lungs and kidney and forms a diffusion boundary and
regulates the diffusion of material through it.
Cuboidal- made up of cube shaped
cells and commonly found in tubular parts of nephrons and ducts of gland and
regulates secretion and absorption.
Columnar- made up of elongated/tall
and slender cells and found in the lining of stomach and intestine and like
cuboidal epithelium is involved secretion and absorption.
If the columnar and cuboidal cells bear
cilia on their free surface they are called ciliated epithelium.
These ciliated epithelium is found in
inner surface of bronchioles and fallopian tubes, where it is involved in
removal of particulate matter or mucus.
Stratified epithelium is made up of more than
one layer of cells and provide protection against chemical and mechanical
stresses. They are present on dry surface of skin, buccal cavity, pharynx,
inner lining of ducts of salivary glands and of pancreatic ducts.
The stratified epithelium
is named by the shape of the most apical layer of cells, closest to the free
space. For ex; if the cell shape is columnar (elongated/tall and slender cells)
then it is called as stratified columnar epithelium and if the cell shape is
polygonal/flattened then it is called as stratified squamous epithelium.
Pseudo
stratified epithelium: is made up of single layer of cells but appears to
be multi-layered due to variance in height and location of the nuclei in the
cells.
The pseudo stratified columnar
epithelium is found in respiratory tract where some of the cells have cilia.
Connective Tissue:-
Connective tissue is made up of
cells (fibroblasts, plasma cells, macrophages, adipose cells and mast cells) which
are dispersed in the matrix. The cells are loosely arranged with large amount
of intercellular spaces. The matrix consist of extracellular material which is
produced by the connective tissue cells. It consists of cells and fibers
enclosed in a ground substance. The matrix can be hard or soft or liquid.
The connective tissue provide
support and connect the tissues.
Based on the nature of matrix, the
connective tissue is classified into three types:
Ø Loose Connective Tissue
Ø Dense Connective Tissue
Ø Fluid
Connective Tissue
Loose Connective tissue: consists of cells and fibres loosely
arranged in a semi-fluid ground substance. It is found between many organs such
as the
dermis and subcutaneous layers of the skin as well as surrounding muscles where, it absorbs
shock and provide protection. It allows diffusion of salt, water and various
nutrients to adjacent cells and tissues. The adipose tissue and reticular
tissue are include under this group.
Areolar tissue:
It has cells and fibres loosely
arranged in a semi-fluid ground substance, present beneath the skin and serve
as support frame work for epithelium.
Adipose
tissue:
Adipose
tissue is found around some organs and joints. It forms a cushion for shock
absorption.
Adipose
tissue also insulates the body. Adipose tissue consists
of cells containing lipid (fat) called adipocytes. The lipid is used to store
energy to be used by the body if needed.
Reticular
tissue:
It is mesh like and provides
supportive frame work for organs such as liver, spleen, and bone marrow.
Dense
connective tissue:
It consist cells
embedded in hard matrix/dense matrix which is composed of calcium carbonate and
calcium phosphate. It forms the skeletal system of the body in all vertebrates.
The two major dense
connective tissues are cartilage and bone that allow the body to maintain its
posture and protect internal organs.
Fluid connective tissue:
Consist
of various specialized cells circulating in a watery fluid containing salts,
proteins and nutrients.
Blood
and lymph are fluid connective tissues.
Blood
contains fluid matrix called plasma, and cell formed elements such as erythrocytes
(RBC-red blood cells), Leucocytes (WBC-white blood cells) and platelets.
RBC
transport oxygen and some carbon-di-oxide. WBCs are responsible for defending
against infections and platelets are involved in blood clotting.
Muscular tissue:
Muscular tissue is made up of elongated
cells, these cells are called muscle fibres or myo-fibres.
The muscle fibres are specialized cells
capable of contraction and relaxation. This property is responsible for
movement of limbs and bending of the body.
Based on structure, function and
location, there are three types of muscular tissue:
Ø
Striped muscles
Ø
Unstriped muscles
Ø
Cardiac muscles
Striped muscles/Skeletal
muscles:
Striped muscles are made up of elongated,
cylindrical, multi-nucleated, unbranched muscle fibres with characteristics
striations or cross brands. Hence, they are also known as striated muscles. The
striped muscles are usually attached to bones and hence are also known as
skeletal muscles. They are voluntary muscles which are responsible for
locomotion, facial expression, body posture and other voluntary movements of
body.
Unstriped muscles:
Unstriped muscles are made up of
spindle shaped, elongated, uninucleated muscle fibres without striations.
Hence, they are also known as smooth muscles. Smooth muscle contraction is
responsible for involuntary movements of internal organs. They are found in the
wall of body cavity and in kidneys, blood vessels and glands.
Cardiac muscles:
Cardiac muscles are made up of
elongated, cylindrical and branched muscle fibres. It is involuntary muscle
which is found only in heart and are involved in rhythmic contractions and relaxation.
Nervous Tissue:
Neural tissue exerts greatest control
over the body’s responsiveness to changing condition. Nervous tissue is
involved in sending and receiving electrochemical signals that provide the body
with information. It is made up of two classes of cells i.e. neuron and
neuralgia.
Neurons are the conducting cell with
three main parts.
·
The cell body
·
Dendrities
·
Axon
The cell body contains
cell cytoplasm, organelles, and nucleus. Dendrities branch off the cell body
which appear like extensions and axon is the tail which extends from the neuron
body. Neuralgia act as supporting cell to the neuron, and modulate their
information propagation.
References:
1.
Text book of Anatomy and physiology by open stax college, vol
1: pg no-131-155.
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