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Nurussama Patel
In this assignment I am going to describe the main tissue types of the body
which are epithelial, connective, muscle and nervous tissues. Each of these four
tissues has an individual structural features and particular functions which are
joined together to produce functioning organs. Also I am going to describe the
roles they play in any two organs of our body.
Epithelial tissue
Firstly I am going to talk about epithelial tissue. Epithelial covers the lining of
the body surfaces both internal and external. The outer layer of the skin is
formed from the epithelial tissue and also the inner lining of digestive area and
blood vessels. The cells of the epithelial tissue are tightly packed and rest on a
thin basement membrane as the below picture shows. The free surface of the
epithelium is exposed to air or fluid. There are no blood vessels present.
Epithelial tissues are classified according to the shape of the component cells
and the cells are arranged into one or more layers.
Epithelial tissue can be divided into two groups; simple and compound. Simple
epithelial is where there is an epithelial tissue of one cell thick whereas if the
epithelial tissues are two or more cells thick then it’s known as compound
epithelial. The types of simple epithelial are squamous, cuboidal and columnar.
Squamous is thin, flat and square shaped and they form the lining cavities such
as the mouth blood vessels. Cuboidal are square or cuboidal shaped and they are
found in glands and in the lining of kidneys. Lastly the columnar is column shaped
and the cells appear rectangular in side view with the nucleus displaced toward the
base of the cell. All of these three are shown in the picture below.
The compound epithelial tissue is where the linings have to continue wear and
tear, the epithelia are composed of many layers of cells and they are called
compound epithelium. The top cells are flat and scaly and it may or may not be
keratinised which contains a tough, resistant protein called keratin. The
mammalian skin is an example of dry, keratinised, stratified epithelium.
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Compound epithelium
Connective tissue
Secondly I am going to talk about the connective tissue. Connective tissues are
fibrous tissues. They are made up of cells separated by non-living material,
which is called extracellular matrix. Connective tissue gives shape to organs and
holds them in place. Both blood and bone are examples of connective tissue.
Connective tissue is a "connecting" function. It supports and binds other tissues.
Connective tissue has cells scattered throughout an extracellular matrix.
Regular connective tissue
Dense connective tissue is characterized by an abundance of fibres with
fewer cells, as compared to the loose connective tissue. It is also called fibrous
or collagenous connective tissue because of the abundance of collagen
(collagenous) fibres. Little intercellular substance is present.
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Cartilage
Cartilage is a somewhat elastic, pliable, compact type of connective tissue. It is
characterized by three traits: lacunae, chondrocytes, and a rigid matrix. The
matrix is a firm gel material that contains fibres and other substances. There are
three basic types of cartilage in the human body: hyaline cartilage, elastic
cartilage and fibrocartilage. In this laboratory, you will examine the most common
type of cartilage, the hyaline cartilage. Most of the skeleton of the mammalian
fetus is composed of hyaline cartilage. As the fetus ages, the cartilage is gradually
replaced by more supportive bone. In the mammalian adult, hyaline cartilage is
mainly restricted to the nose, trachea, bronchi, ends of the ribs, and the
articulating surfaces of most joints. The function of the hyaline cartilage is to
provide slightly flexible support and reduce friction within joints. It also provides
structural reinforcement.
Areolar connective tissue
Microscopic view of Areolar
connective tissue
Areolar connective tissue is the most widespread connective tissue of the
body. It is used to attach the skin to the underlying tissue. It also fills the
spaces between various organs and thus holds them in place as well as cushions
and protects them. It also surrounds and supports the blood vessels.
The fibres of areolar connective tissue are arranged in no particular pattern but
run in all directions and form a loose network in the intercellular material. Collagen
(collagenous) fibres are predominant. They usually appear as broad pink bands.
Some elastic fibres, which appear as thin, dark fibres are also present.
The cellular elements, such as fibroblasts, are difficult to distinguish in the
areolar connective tissue. But, one type of cells - the mast cells are usually
visible. They have course, dark-staining granules in their cytoplasm. Since the
cell membrane is very delicate it frequently ruptures in slide preparation,
resulting in a number of granules free in the tissue surrounding the mast cells.
The nucleus in these cells is small, oval and light-staining, and may be obscured
by the dark granules.
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Adipose connective tissue
Microscopic view of adipose connective tissue
The cells of adipose (fat) tissue are characterized by a large internal fat droplet,
which distends the cell so that the cytoplasm is reduced to a thin layer and the
nucleus is displaced to the edge of the cell. These cells may appear singly but are
more often present in groups (Figure 11). When they accumulate in large numbers,
they become the predominant cell type and form adipose (fat) tissue.
Adipose tissue, in addition to serving as a storage site for fats (lipids), also pads
and protects certain organs and regions of the body. As well, it forms an insulating
layer under the skin which helps regulate body temperature.
Blood
Blood is considered a connective tissue for two basic reasons: (1)
embryologically, it has the same origin (mesodermal) as do the other connective
tissue types and (2) blood connects the body systems together bringing the
needed oxygen, nutrients, hormones and other signaling molecules, and removing
the wastes. In circulating blood two different cell types are found: enucleated
erythrocytes or red blood cells and nucleated leukocytes or white blood cells.
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Bone
Bone tissue is a specialized form
of connective tissue and is the
main element of the skeletal
tissues. It is composed of cells
and an extracellular matrix in
which fibers are embedded. Bone
tissue is unlike other connective
tissues in that the extracellular
matrix becomes calcified.
FUNCTIONS OF BONE
TISSUE
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The skeleton is built of bone tissue. Bone provides the internal support of
the body and provides sites of attachment of tendons and muscles,
essential for locomotion.
Bone provides protection for the vital organs of the body: the skull
protects the brain; the ribs protect the heart and lungs.
The hematopoietic bone marrow is protected by the surrounding bony
tissue.
The main store of calcium and phosphate is in bone. Bone has several
metabolic functions especially in calcium homeostasis.
Nervous tissue
Nervous tissue is the main component of nervous system including the brain,
spinal cord, nerves. The nervous tissue regulates and controls the body function.
Nervous tissue has two types, one is neurones and the second is neuroglia.
Nervous tissues that stem throughout the body are all made up of specialised of
nerve cells called neurones. Neurones are stimulated and passed on impulses very
quickly.
Neurons are classified as either motor, sensory, or interneurons. Motor
neurons carry information from the central nervous system to organs, glands,
and muscles. Sensory neurons send information to the central nervous system
from internal organs or from external stimuli. Interneurons send signals
between motor and sensory neurons.
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Neurones
Cell Body
Neurons contain the same cellular components as other body cells. The
central cell body is the largest part of a neuron and contains the
neuron's nucleus, associated cytoplasm, and other cell structures. The
cell body produces proteins needed for the construction of other parts
of the neuron.
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Axons - typically carry signals away from the cell body. They are long
nerve processes that may branch out to show the signals to different
areas. Some axons are wrapped in an insulating coat of glial cells called
oligodendrocytes and Schwann cells. These cells form the myelin covering
which indirectly support in the transfer of impulses as myelinated nerves
can carry out impulses quicker than unmyelinated nerves Axons end at
the joint known as synapses.
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Dendrites - carry signals toward the cell body. Dendrites are usually
more numerous, shorter and more split than axons. They have many
synapses to receive signal messages from nearby neurons.
Neuroglia: Collectively, cells that structurally and metabolically support
neurons. They make up about half the volume of nervous tissue in vertebrates.
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The neuroglial cells are found in the parenchyma which is a functional part of
brain and spinal cord and these are classified as:
Macroglia, of neural origin, including astrocytes, oligodendrocytes,
and glioblasts.
Microglia, of mesodermal origin.
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Muscle tissue
Muscle tissue has an ability to relax and contrast and so bring about movement
and work in many parts of the body. There are other movements in the body too
which are especially for the survival of the organism such as the heart beat.
Muscles can be divided into three main groups according to their structure, e.g.:
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Smooth muscle tissue.
Skeletal muscle tissue.
Cardiac (heart) muscle tissue.
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Smooth muscle tissue is made up of thin
muscle cells and fibres. These fibres are
pointed at their ends and each has a single,
large, oval nucleus. Each cell is filled with a
specialised cytoplasm, the sarcoplasm and is
surrounded by a thin cell membrane, which is
the sarcolemma. They are not arranged in a
definite striped pattern, as in skeletal muscles.
Smooth muscle fibres connect to form layers
of muscle tissue rather than bundles. Smooth
muscle is involuntary tissue; it is not controlled
by the brain. Smooth muscle forms the muscle
layers in the walls of organs such as the
digestive tract (intestines).
Smooth muscle tissue
Skeletal muscle is a form of striated muscle tissue and it is
voluntarily controlled. Most skeletal muscles are attached to
bones by bundles of collagen fibers which are known as
tendons.
Skeletal muscle is made up of each component known as
muscle fibers. These fibers are formed from the fusion of
developmental myoblasts (a type of cell that gives rise to a
muscle cell). The muscle fibers are long and cylindrical.
This is a single tissue only found in the walls of the
heart. Cardiac (Heart) Muscle Tissue shows some of
the characteristics of smooth muscle and some of
skeletal muscle tissue. Its fibres like those of skeletal
muscle have cross-striations and contain a lot of nuclei.
However like smooth muscle tissue, it is involuntary.
Cardiac muscle differs from striated muscle in terms
of length because they are shorter and the sarcolemma
is thinner and not clearly visible. There is only one
nucleus present in the centre of each cardiac fibre.
The spaces between different fibres are filled with
areolar connective tissue which contains blood
capillaries to supply the tissue with the oxygen and
nutrients.