Animal Tissues

Biswarup Majumder | Bio-World
Introduction
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Animal Tissue - Types
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Polarity - Epithelium is arranged so there is one free
surface (apical surface) and one attached surface
(basal surface).
Cellular nature – Cells in epithelium fit closely together
side by side and sometimes atop each other to form sheets
of cells. These sheets are held together by specialized
junctions.
Supported by connective tissue – Attachment to a layer
of connective tissue at the basal surface forms a layer
called the basement membrane, an adhesive layer formed
by secretions from the epithelial cells and the connective
tissue cells.
Avascular – Epithelium typically lacks its own blood supply.
Regeneration – Epithelium cells can regenerate if proper
nourished.
Absence of nerves (except for a few axons in the deeper
layers).
Biswarup Majumder | Bio-World 3
Epithelial Tissue
An epithelium is a sheet of cells that covers a body surface or
lines a cavity.
Epithelium forms the coverings of surfaces of the body such
as Skin, Mouth, Nasal cavity (Ectodermal), Lines internal body
surface such as GI tract, Lungs, Urinary bladder and vagina
(Endodermal) and Lining of blood vessels, lymphatic and heart
(Endothelial cells derived from Mesoderm).
It serves many purposes, including protection, adsorption,
excretion, secretion, filtration, and sensory reception.
Characteristics :

Epithelial Tissue - Types
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(a) On the basis of arrangement of cells
1. Simple epithelium :
2. Compound or Stratified epithelium :
3. Pseudostratified epithelium :
4. Transitional epithelium :
Cells are found in a single layer attached to the basement
membrane.
Cells are found in 2 or more layers stacked atop each other.
Pseudostratified epithelium appears to be more than one
cell thick since the nuclei lie at different heights, but in
fact it is single layer of cells, in contact with the basement
membrane.
Cells are rounded and can slide across one another to allow
stretching.
Epithelial Tissue - Classification
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(b) On the basis of shape
1. Squamous epithelium : (Latin, squama - scale)
2. Cuboidal epithelium :
3. Columnar epithelium :
- Flat, thin, scale-like cells,
- Cells that have a basic cube shape.
- Typically the cell’s height and width are about equal.
- Tall, rectangular or column shaped cells.
- Typically cells are longer than width.
Epithelial Tissue - Classification
Squamous Cuboidal Columnar
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Names of epithelial tissues include a description of both their shape and their
number of cell layers. The presence of cilia may also be identified in their
names. For example, simple squamous describes epithelium consisting of a
single layer of flat cells. Pseudostratified columnar ciliated epithelium
describes a single layer of tall, ciliated cells of more than one size.
Simple Epithelium
It consists of a single layer of epithelial cells resting on a
basement membrane, and is present on those areas where
absorption is more, but wear and tear is less.
Simple epithelium consists of the following types :
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Stratified epithelium is named after the shape of the outermost cell layer. Thus, stratified
squamous epithelium has outermost layers of squamous cells, even though some inner
layers consist of cuboidal or columnar cells.
Compound Epithelium
It consists of a many layers of epithelial cells of different
shapes representing newly formed and mature cells. The
superficial layer grows outward from below. Basement
membranes are usually absent. Their main function is to protect
underlying structure from mechanical wear and tear.
Compound epithelium consists of the following types :
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The cells of glandular epithelium tissue are generally columnar
or cuboidal. The glandular epithelium tissue can be classified
into two types :
(a) According to presence or absence of ducts :
(b) According to number of cells :
Exocrine Glands – Salivary glands, Liver etc.
Endocrine Glands – Thyroid gland, Pituitary gland etc.
Mixed Glands – Pancreas.
Glandular Epithelium
Unicellular – Goblet cells.
Multicellular – Salivary glands.
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Types of Exocrine Glands
(a) According to their structure :
(b) According to their function :
Merocrine Secretion
Apocrine Secretion
Holocrine Secretion
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Connective Tissue
Characteristics :
Connective tissue ranges from avascular to highly vascular.
Composition : Composed mainly of nonliving extracellular
matrix that separates the cells of the tissue.
Location : It is present in between different tissue and
organs. It can be found in and around the body organs.
skeletal tissue present in the form of bone and cartilage,
and fluid connective tissue as blood and lymph are
connective tissue.
Functions :
Establishing the structural framework of the body.
Transporting fluid and dissolved materials.
Protecting organs.
Supporting, surrounding and connecting other tissues.
Storing energy.
Defending the body from microorganisms.
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Connective Tissue - Types
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Connective Tissue Proper
Loose connective tissue :
Dense connective tissue :
The cells in the matrix are widely distributed and the
fibres are loosely woven.
It generally connects and support various tissues and
organs and helps them to resist strain and displacement.
The fibres dominate over the cells and the matrix in
quantity.
The fibres may be regularly or irregularly arranged.
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Areolar Tissue
They binds tissues together.
They engulf bacteria and damaged and dead cells.
They secrete heparin and histamine. Heparin is an
anticoagulant while histamine causes inflammation reaction.
They produces antibodies.
Structure :
Functions :
These are simplest and most widely distributed connective
tissues.
It has homogenous, transparent, semi-fluid and gelatinous
matrix.
Matrix contain various types of cells (fibroblast,
macrophages, mast cells, lymphocytes, fat cells, plasma
cells) and fibres (white collagen fibres, yellow elastic
fibres).
Fibres are loosely arranged and there is space between
fibres, areolae, which derives its name.
Found in continuous layers beneath skin, space between
many organs, between muscles, peritoneum and
mesenteries.
Location :
Areolar tissue makes the skin elastic and
helps it to withstand pulling strain.
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Adipose Tissue
As it synthesize, stores and metabolizes fat, it is a
considerable source of energy.
It acts as a shock absorbers around kidney, heart, and eye
balls.
It prevent heat loss by forming insulating layer.
Structure :
Functions :
It is a modified form of areolar tissue that contain large
number of fat cells ( Adipocytes cells).
Adipocyte is a large, spherical or oval shaped cell, with
large fat droplet causing shifting of nucleus to periphery of
the cell.
2 types of adipocytes - white adipocyte - contain a single
large fat droplet and Brown adipocyte - contain number of
small fat droplets.
Found beneath skin in dermis, mesenteries, around kidney,
heart and eye balls.
Location :
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Reticular Tissue
They are mostly phagocytic cells, helps in defense
mechanism of the body.
Structure :
Functions :
It is a modified areolar tissue that contains large number
of stellate shape reticular cells floating in fluid matrix.
Reticular cells has number of cytoplasmic processes which
are interconnected to form reticular network.
Reticular cells secretes reticular fibres.
Found-lymph glands, spleen, liver , bone marrow, thymus and
tonsils.
Location :
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White Fibrous Tissues
Structure :
It contains fibroblast cells and collagen fibres and very
few amount of matrix.
The dense network of collagen fibres gives great strength.
It occur in two forms - (i) tendon and (ii) Sheath
Tendon is the thick bundle of collagen fibres running
parallel to each other, giving strong, flexible but
inextensible strength. It joins skeletal muscles to bones.
Sheath is the bundles of collagen fibres lies in a criss-cross
manner. It is present in pericardium of heart, dura matter,
cornea, capsule of kidney, spinal cord. It also forms
covering of cartilage and bones.
Yellow Fibrous Tissues
Structure :
These tissues contains numerous and closely packed yellow
elastic fibres.
Elastic fibres are long, straight and branched, they are
elastic and flexible.
They are present in Ligament, also present in wall of blood
vessel, vocal cords, respiratory passage and lungs.
Ligament – It is composed of yellow elastic fibres and some
collagen fibres. It join two bone together.
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Supportive Connective Tissue
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Carilage
It is tough, hard but a flexible connective tissue. It can
resist strain and can absorb mechanical shock.
It consists of solid or semisolid matrix in which cartilage
cell (chondrocytes) and fibres are embedded.
Cartilage is enclosed in a sheath of white fibrous
connective tissue called Below the perichondrium, there
is layer chondroblast cell, which form chondrocytes.
Chondrocytes are dispersed in the matrix and occur in
the fluid filled space called lacunae.
Each lacunae contain 2-4 chondrocytes. Each
chondrocytes is a large, angular cell with distinct
nucleus.
The matrix lacks the blood vessels.
Structure :
Depending upon matrix, cartilage are of 3 types :
Types :
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Bone
It is supportive and protective tissue.
The matrix is solid and calcified (70% salts of calcium and
phosphate: hydroxyapatite, 30 %fibrous protein; Ossein).
Bone cell (Osteocyte) and collagen fibre are embedded in
solid matrix.
Each bone is enclosed in a layer of white fibrous
connective tissue, called periosteum.
Matrix is arranged in concentric circles called lamellae.
Number of osteoblast cell and osteocytes are arranged
in between the lamellae, in the fluid filed space called
Lacunae.
Each lacunae has fine cytoplasmic processes
called canaliculi, which connect with other lacunae.
Osteoblast are active bone cell, while osteocytes are
inactive osteroblats
Structure :
Types :
1. Compact bone
Outside of the bone.
Supportive tissue of the body.
Is the part we call the skeleton.
2. Spongy bone
Tissue inside the bone.
Strong, but light weight.
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Fluid Connective Tissue
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Blood
Composition :
Functions :
Blood is called a fluid connective tissue because it develops
from the mesoderm of the embryo like any other typical
connective tissue and connects all the organ systems of the
body by transporting oxygen, nutrients, hormones, etc., and
removing wastes from these organs.
22

Lymph
Lymphatic System
Lymph acts as a “middle man” which transports oxygen, food materials,
hormones, etc. to the body cells and brings carbon dioxide and other
metabolic wastes, from the body cells to blood and then finally pours the
same into the venous system.
Lymph is similar in composition to blood plasma except that it
lacks red blood cells, platelets, plasma protein required for
clotting and other macromolecules found in blood.
The lymphatic tissue includes the lymph nodes, spleen, tonsils,
adenoids and the thymus (an organ in the chest that is
particularly large during infancy).
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Summary Table
24

Muscular Tissue
Muscles are made up of highly specialized thin and
elongated cells called muscle fibres.
The muscle fibres contains specialized cytoplasm
called sarcoplasm that contain network of the
membrane called sarcoplasmic reticulum.
The muscle fibres may be bounded by the cell
membrane called sarcolemma.
Each muscle fibre may contain numerous longitudinal
fibrils called myofibrils.
Basic Physiological Property of Muscular Tissue
Contractibility
Excitability
Extensibility
Elasticity
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Muscular Tissue - Types
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Skeletal Muscle Tissue
Skeletal muscle is called "striated" because of its
appearance consisting of light and dark bands visible
using a light microscope.
A single skeletal muscle cell is long and
approximately cylindrical in shape, with many nuclei
located at the edges (periphery) of the cell.
Movement of the skeleton under conscious control,
including movement of limbs, fingers, toes, neck, etc.
Movement of tissues of facial expression under
conscious control, e.g. ability to smile and to frown.
Structure :
Function :
Skeletal or striated muscles constitute about 50% of the body
weight.
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Smooth Muscle Tissue
Unlike Skeletal and Cardiac muscle tissue, Smooth muscle
is not striated.
Smooth muscle fibers are small and tapered - with the
ends reducing in size, in contrast to the cylindrical shape
of skeletal muscle.
Each smooth muscle fiber has a single centrally located
nucleus.
Contractions of smooth muscle constrict the vessels they
surround.
This is particularly important in the digestive system in
which the action of smooth muscle helps to move food
along the gastrointestinal tract as well as breaking the
food down further.
Smooth muscle also contributes to moving fluids through
the body and to the elimination of indigestible matter
from the gastrointestinal system.
Structure :
Function :
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Cardiac Muscle Tissue
Cardiac muscle fibers are striated, branched
(sometimes described as Y-shaped), and have a single
central nucleus.
These fibers are attached at their ends to adjoining
fibers by thick plasma membranes called
intercalated discs.
Pumping of blood through the heart : Alternate
contraction and relaxation of cardiac muscle pumps.
Structure :
Function :
De-oxygenated blood through the Right Atrium and Right
Ventricle to the lungs, and
Oxygenated blood through the Left Atrium and Left
Ventricle to the aorta, then the rest of the body.
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Nervous Tissue
Nervous tissue is the main tissue component of the two
parts of the nervous system; the brain and spinal cord of
the central nervous system (CNS), and the branching
peripheral nerves of the peripheral nervous system (PNS),
which regulates and controls bodily functions and activity.
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Neuron
Structure :
The cell body is the enlarged portion of the neurons that
contains the nucleus. It is the “nutritional centre” of the
neuron where macromolecules are produced. The cell body
also contains densely staining areas of rough endoplasmic
reticulum known as Nissl Bodies that are not found in the
dendrites or axon.
Dendrites (from the Greek dendron = tree branch) are thin,
branched processes or structure that extend from the
cytoplasm of the cell body. Dendrites provide a receptive
area that transmits electrical impulses to the cell body.
The axon is a longer process that conducts impulses away
from the cell body. Axons vary in length from only a
millimeter long to up to a meter or more (for those that
extend from the CNS to the foot). The origin of the axon
near the cell body is an expanded region called the axon
hillock; it is here that nerve impulses originate. Side
branches called axon collaterals many extend from the
axon.
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Myelinated & Non-myelinated Axons
Myelinated nerves, which are the most common type in humans, conduct
action potential much faster than the unmyelinated nerves.
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Synapse
Synapse is a junction between the axon terminal of one neuron
and the dendrite of the next neuron. It is separated by a small
gap known as synaptic cleft.
A synapse is formed by the membranes of a pre-synaptic
neuron which may or may not be separated by a gap called
synaptic cleft. Chemicals involved in transmission of impulses
at chemical synapses are called neurotransmitters.
There are two types of synapses :
a) Electrical synapses
b) Chemical synapses
In electrical synapses, the pre and post synaptic neurons lie in
close proximity to each other. Hence the impulse can move
directly from one neuron to another across the synapse. This
represent faster method of impulse transmission.
In chemical synapses, the pre and post synaptic neurons are
not in close proximity. They are separated by a synaptic cleft.
The transmission of nerve impulses is carried out by chemicals
such as neurotransmitters.
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Neuron - Types
(a) On the basis of the structure
(b) On the basis of function
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Neuroglia
Neuroglia (neuro = nerve; glia = glue) or neuroglial cells are
specialized cells found in the brain and spinal cord supporting
the neurons and their fibres.
About 50 percent of all brain cells are neuroglial cells.
They provide a variety of functions for brain tissue. They
support the metabolic and signaling functions of neurons.
Neuroglia also contribute to the organization and formation of
a barrier between the blood and the brain. The other function
of neuroglia is participation in creating an inflammatory
response in injured neural tissues, including phagocytosis of
cellular debris.
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Ependymal cells
These cells are arranged as an epithelial layer, one cell
thick, which lines the ventricles (cavities of the brain) and
the central canal of the spinal cord.
The cells vary from squamous to columnar according to
their location. Their free surface bears numerous
microvilli and cilia.
The microvilli help in the absorption of cerebrospinal fluid.
The movements of the cilia contribute the flow of the
cerebrospinal fluid.
The ependymal cells possess one or more long processes
towards opposite side which penetrate the nervous tissue.
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Neurosecretory cells
Neurosecretory cell, a type of neuron, or nerve cell, whose
function is to translate neural signals into chemical stimuli.
Such cells produce secretions called neurohormones that
travel along the neuron axon and are typically released into
the bloodstream at neurohemal organs, regions in which
the axon endings are in close contact with blood capillaries.
Neurosecretory cells are present in most multicellular
animals and are usually distinguished from other neurons
by the unusually large size of the cell nucleus, axon
endings, and the cell itself.
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Biswarup Majumder | Bio-World 38
Animal Tissues - Summary

Animal Tissues

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