Structural Organisation In Animals CBSE CLASS - 11th NEET BIOLOGY.pdf

Structural Organisation
in Animals
Class 11th
neharohtagi1
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Introduction
In unicellular organisms, all functions like digestion, respiration & reproduction are performed
by a single cell.
In the complex body of multicellular animals, the same basic functions are carried out by
different groups of cells in a well organised manner.
The body of a simple organism like Hydra is made of different types of cells and the number of
cells in each type can be in thousands.
The human body is composed of billions of cells to perform various functions.

Germ Layers
The Germ Layers are formed in the earliest of embryonic development.
Types of Germ Layers
Ectoderm Endoderm Mesoderm
Give rise to the
skin and nervous
system
Forms lining of
digestive and
respiratory system
Forms bones,
muscles and
connective tissue

Tissues
Tissues is group of similar cells along with intercellular substances perform a specific function.
Study of tissues is called ‘Histology’.
The term ‘Tissues’ was given by Mayer.
It was 1 found in Coelentrates.
st
These tissues are organised in specific proportion and pattern to form an Organ.
When two or more organs perform a common function by their physical and chemical interaction,
they together form Organ System. Cells, tissues, organs and organ systems split up the work in
a way that exhibits division of labor and contribute to the survival of the body as a whole.
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Animal Tissues
The structure of the cells vary according to their function. Therefore, the tissues are
different and are broadly classified into four types:
Epithelial tissue Connective tissue Muscle tissue Nervous tissue
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Epithelial Tissue
A Epithelial Tissue is composed of one or more layers of cells that provide a covering or lining
for some parts of the body.
An epithelium (pl.: epithelia) has two surface, Free Surface, which faces either a body fluid or
the outside environment and thus provides a covering or a lining for some part of the body and
Basal Surface is in contact with the Basement Membrane.
The cells are arranged compactly with little intercellular matrix. It is Avascular and Highly
Regenerative.
Role of Epithelial Tissue:
Performs different functions such as protection, filtration, secretion and absorption.
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Basement Membrane
It is secreted by both epithelium and
connective tissues.
The basement membrane is Acellular and made
up of two laminae.
Role of Basement Membrane:
The primary function is that it lies
underneath the epithelial tissue, provinding
support and seperating it from the
connective tissue beneath.
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Classification E.T.
Types of Epithelial Tissues
(on the basis of number of cell layers)
Simple Epithelium Compound Epithelium
Cuboidal Epithelium
Columnar Epithelium
Simple Epithelium Keratinized Epithelium
Non - Keratinized Epithelium
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Simple Epithelium
Simple epithelium is composed of a single layer
of cells and functions as a lining for body
cavities, ducts, and tubes.
On the basis of structural modification of the
cells, simple epithelium is further divided into
three types:
Simple Squamous Epithelium
Simple Cuboidal Epithelium
Simple Columnar Epithelium
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Simple Squamous Epithelium
The squamous epithelium is made of a single
thin layer of flattened cells with irregular
boundaries (Tesselated Epithelium).
They are found in the walls of blood vessels
and air sacs of lungs and are involved in
functions like forming a diffusion boundary.
It is also known as Pavement Epithelium due to
it’s tile - like appearance.
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Simple Cuboidal Epithelium
Single Layer of cube like cells resting on a
basement membrane.
The nucleus is situated centrally.
Found in ducts of Glands and Tubular part of
Nephron.
Its main function are Secretion and
Absorption.
It is also known as Germinal Epithelium, is a
thick layer of cells that lines the sex organs
(Testes & Ovary) during the embryonic stages.
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Modification in Cuboidal E.T.
Microvilli covered surface of Simple Cuboidal.
Brush Border Cuboidal Epithelium Ciliated Cuboidal Epithelium
Found in PCT of the nephron.
Cilia covered surface, facilitate movement.
Found in Respiratory Tract.
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Simple Columnar Epithelium
It is composed of tall and slender cells.
The nucleus is situated at the base.
Free surface may have microvilli.
Its main function are Secretion and
Absorption.
Found in lining of stomach, intestine and gall
bladder.
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Modification in Columnar E.T.
Microvilli covered surface of Simple Columnar
Brush Border Columnar Epithelium Ciliated Columnar Epithelium
Found in Stomach Lining.
Cilia covered surface, facilitate movement.
Found in Bronchioles and Fallopian Tube.
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Glandular Epithelium
It is a kind of epithelial tissue that produces and releases a variety of secretory products.
Some of the columnar or cuboidal cells get specialised for secretion and are called Glandular
Epithelium.
They are mainly of two types: (On the basis of no. of cells)
Unicellular Multicellular
Goblet Cells of Alimentary Canal Salivary Gland
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Glands
It secrete mucus, saliva,
earwax, milk, digestive
enzymes and other
products.
These Products are
released through ducts
and tubes.
They do not have ducts.
Their products are called
Hormones, which are
secreted directly into the
fluid bathing the gland.
These glands have both
exocrine and endocrine
part.
For eg: Pancreas because
it secretes the hormone
Insulin into the blood
(endocrine) and digestive
juices in stomach through
ducts(exocrine).
Exocrine Glands Endocrine Glands Heterocrine Glands
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Compound Epithelium
Compound epithelium is made of more than
one layer (multi-layered) of cells.
They cover the dry surface of the skin, the
moist surface of buccal cavity, pharynx,
inner lining of ducts of salivary glands and of
pancreatic ducts.
It has a limited role in Secretion and
Absorption.
Their main function is to provide protection
against Chemical and Mechanical Stresses.
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Cell Junctions
All cells in epithelium are held together with little intercellular material.
Adhering Junctions
In nearly all animal tissues, specialised junctions provide both structural and functional links
between its individual cells.
Gap Junctions Tight Junctions
Perform cementing
to keep neighbouring
cells together
Help to stop
substances from
leaking across a tissue.
Facilitate the cells to communicate
with each other by connecting the
cytoplasm of adjoining cells.
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Connective Tissue
Connective tissue are the most abundant and widely distributed in the body of complex
organisms.
Features of Connective Tissue:
Mesodermal in origin.
Perform special function of Linking and Supporting.
Abundant intercellular matrix.
All C.T. (except Blood), secrete fibres of structural proteins called Collagen Fibres.
The fibres provide strength, elasticity and flexibility to the tissue.
These cells also secrete modified polysaccharides, which accumulate between cells and
fibres and act as matrix (ground substance).
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Cells ofConnective Tissue
Fibroblast: Cells that produce and secrete fibres and
matrix.
Macrophages: They are also known as Phagocytes,
help in engulfing and digesting microbes.
Mast Cells: They are like Basophils of blood in
structure and function. They secrete histamine,
serotonin, heparin and matrix.
Adipose Cells: They are also called Adipocytes or fat
cells, contain large globules of fat.
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Fibers ofConnective Tissue
Collagen Fibres: are the most widespread, white in
colour and are made up of collagen protien. They are
Flexible and have High Tensile Strength.
Elastic Fibres: are yellow in colour, form a network.
They are made up of elastin protien. They retain
their original shape and size once force is removed.
Reticulate Fibres: are made up of reticulin protien.
They are delicate. Elasticity is absent. These are
mainly distributed in Lymphoid Organs.
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Matrix of C.T.
The extra-cellular fluid may be solid, liquid or gel, that is, it can be soft, dense and
mineralised, fluidy or fibre - free.
The ground substance is made up of an organic substance (usually a protien) and an inorganic
substance (usually a mineral or water).
Matrix is composed of mucopolysaccharide (modified polysaccharide) which is present in the
form of hyaluronic acid.
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Classification of C.T.
Loose CT Dense CT Specialised CT
Areolar
Tissue
Adipose
Tissue
Regular
Tissue
Irregular
Tissue
Skeletal CT Fluid CT
More matrix, less fibres Less matrix, more fibres Cartilage
Bone
Blood
Lymph
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Areolar Loose C.T.
It contains fibroblasts, macrophages and
mast cells.
It serves as the framework for skin.
Areolar tissue is present beneath the skin.
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Adipose Loose C.T.
It is also a Loose C.T., present beneath the skin.
It act as the insulation layer (Blubber of Whale).
The cells of this tissue are specialised to store fats.
The excess nutrients which are not used immediately
are converted into fats and stored in the tissue.
Adipose tissue is present around eyes, heart and
kidney.
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Dense Regular C.T.
In the dense regular connective tissues, the collagen fibres are present in rows between many
parallel bundles of fibres.
For e.g. - Tendons and Ligament
Tendon Ligament
Joins Skeletal Muscles to
Bones.
Joins bone to bone.
Consist of Collagen Fibres.
Consist of Collagen and
Elastin Fibres.
Provide more strength. Provide Flexibility.
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Dense Irregular C.T.
Dense irregular connective tissue has fibroblasts
and many fibres (mostly collagen) that are oriented
differently.
This tissue is present in the skin.
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Cartilage
The intercellular material of cartilage is solid
and pliable and resists compression.
Cells of this tissue (chondrocytes) are
enclosed in small cavities (Lacunae) within the
matrix secreted by them. Most of the
cartilages in vertebrate embryos are replaced
by bones in adults.
Cartilage is present in the tip of nose, outer
ear joints, between adjacent bones of the
vertebral column, limbs and hands in adults.
Main function is to act as a shock absorber.
Cartilage gives shape, support and structure
to body tissue.
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Bones
Bones have a hard and non-pliable ground substance rich in calcium salts and collagen fibres
which give bone its strength. The bone marrow in some bones is the site of production of RBCs.
The bone cells (osteocytes) are present in the spaces called lacunae.
Functions of Bone are:
Support: Bones form the framework of
body and contribute to the alignment.
Protection: Protect softer tissues and
organs.
Movement: They interact with skeletal
muscles to bring about movements.
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Blood
Blood is a fluid connective tissue containing
plasma, red blood cells (RBC), white blood cells
(WBC) and platelets.
It is the main circulating fluid that helps in
the transport of various substances.
Functions of Blood is:
Transportation of O to lungs and tissues.
2
Form clots to prevent excess blood loss.
Carry cells and Antibodies which fight
against infections.
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Lymph
Lymph is a colorless fluid that circulates
throughout the Lymphatic system.
The main role of the lymphatic system is to act
as a filter against microbes, organic waste and
toxins.
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Muscle Tissue
Features of Muscular Tissue:
Mesodermal in origin.
Each muscle is made of many long, cylindrical fibres arranged in parallel arrays. These
fibres are composed of numerous fine fibrils, called myofibrils.
Muscle fibres contract (shorten) in response to stimulation, then relax (lengthen) and
return to their uncontracted state in a coordinated fashion.
Their action moves the body to adjust to the changes in the environment and to maintain the
positions of the various parts of the body.
In general, muscles play an active role in all the movements of the body.
The special properties of a Muscle Tissue are: Excitability, Contractility, Extensibility and
Elasticity.
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Skeletal Muscle
Skeletal muscle tissue is closely attached to
skeletal bones.
In a typical muscle such as the biceps, striated
(striped) skeletal muscle fibres are bundled
together in a parallel fashion.
A sheath of tough connective tissue encloses
several bundles of muscle fibres.
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Smooth Muscle
The smooth muscle fibres taper at both ends
(fusiform) and do not show striations.
Cell junctions hold them together and they are
bundled together in a connective tissue sheath.
The wall of internal organs such as the blood
vessels, stomach and intestine contains this
type of muscle tissue.
Smooth muscles are ‘involuntary’ as their
functioning cannot be directly controlled.
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Cardiac Muscle
Cardiac muscle tissue is a contractile tissue
present only in the heart.
Cell junctions fuse the plasma membranes of
cardiac muscle cells and make them stick
together
Communication junctions (intercalated discs)
at some fusion points allow the cells to
contract as a unit, i.e., when one cell receives a
signal to contract, its neighbours are also
stimulated to contract.
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Neural Tissue
Neural tissue exerts the greatest control over the body’s responsiveness to changing conditions.
Neurons are the unit of neural system and are
excitable cells.
The neuroglial cell which constitute the rest
of the neural system protect and support
neurons.
It make up more than one half the volume of
neural tissue in our body.
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Conduction of Impulse
When a neuron is suitably stimulated,
an electrical disturbance is generated
which swiftly travels along its plasma
membrane.
Arrival of the disturbance at the
neuron’s endings, or output zone,
triggers events that may cause
stimulation or inhibition of adjacent
neurons and other cells.
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Organ and Organ System
The basic tissues mentioned above organise to form organs which in turn associate to form
organ systems in the multicellular organisms.
Morphology refers to study of form or externally visible features.
Each organ in our body is made of one or more type of tissues. For e.g: Heart consists of all the
four types of tissues, i.e., epithelial, connective, muscular and neural.
The complexity in organ and organ systems displays certain discernable trend. This discernable
trend is called evolutionary trend.
Anatomy is used for the study of morphology of internal organs in the animals.
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Structural Organisation In Animals CBSE CLASS - 11th NEET BIOLOGY.pdf

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