Maharashtra Board Class 11 Biology Chapter 10 Animal Tissue PDF Download

Animal Tissue

Tissue is a group of cells having same embryonic origin, structure and function. Various tissues combine together in an orderly manner to form large functional unit called organs. These organs combine together and form organ-system. The cells are of two types, somatic cells and germ cells. The word somatic is derived from the Greek word 'soma' means 'body'. All body cells of an organism except sperm and ova are somatic cells. The sperm and ova are germ cells. They belong to reproductive system.

Cells → Tissues → Organs → Organ systems → Body

Histology

The study of the structure and arrangement of tissue is called histology. There are four types of tissues present in animals namely epithelial, connective, muscular and nervous. Let us study each type in details.

Teacher's Note

Histology helps doctors understand diseases by looking at tissues under a microscope. For example, doctors take a small piece of skin to check if someone has a skin infection.

Exam Trick

Remember: Histo = tissue, logy = study. So histology means studying tissues. Think of it like using a magnifying glass to see very small things.

Points to Remember

There are four main types of tissues in animals.
Epithelial tissue covers the body surfaces.
Connective tissue supports and binds other tissues.
Muscular tissue helps the body move.
Nervous tissue carries messages in the body.

Epithelial Tissue

Epithelial tissue forms a covering on inner and outer surface of body and organs. The cells of this tissue are compactly arranged with little intercellular matrix. Cells rest on non-cellular basement membrane. Cells are polygonal, cuboidal or columnar in shape. Single nucleus is present at the centre or at the base. This tissue is avascular. It has good capacity of regeneration. Major function is protection and it also helps in absorption, transport, filtration and secretion. Epithelial tissue is classified into two types: Simple epithelium and Compound epithelium. Simple epithelium is made up of single layer of cells. Compound epithelium is made up of two or more layers of cells. Lowermost layer lies on basement membrane.

Simple Epithelial Tissue

1. Squamous Epithelial Tissue

Cells of this tissue are flat, thin, polygonal with serrated margin. Cells of this tissue fit together like tiles of footpath. Hence it is called pavement epithelium. Prominent spherical or oval nucleus is present at the centre of the cell. Function: Protection, absorption, transport, filtration, secretion. It is found in blood vessels, alveoli, coelom, etc.

Teacher's Note

Squamous epithelial tissue is very thin, like a thin sheet of paper. It helps oxygen pass through easily, just like how air passes through a screen window.

Exam Trick

Remember: Squamous = flat and thin. Think of squashed tiles on the floor - they are flat and fit together tightly.

Points to Remember

Squamous cells are very flat and thin.
They fit together like floor tiles.
Found in blood vessels and lungs.
Help with absorption and filtration.
Called pavement epithelium.

2. Cuboidal Epithelial Tissue

In this tissue, the cells are cuboidal in shape with a spherical nucleus at the centre. Function: Absorption, secretion. It is found in lining of pancreatic duct, salivary duct, proximal and distal convoluted tubules of nephron.

Teacher's Note

Cuboidal cells are shaped like small cubes. They are found in ducts that carry sweat or saliva from glands to other parts of the body.

Exam Trick

Remember: Cuboidal = cube-shaped. Think of a small dice or sugar cube to remember this shape.

Points to Remember

Cuboidal cells have cube-like shape.
Nucleus is in the middle of the cell.
Found in ducts and tubes of glands.
Help with absorption and secretion.
Present in kidney tubules.

3. Columnar Epithelium

Columnar epithelial cells are tall, pillar like. Inner ends of the cells are narrow while free ends are broad and flat. Free surface shows large number of microvilli. Nucleus is oval and is present in the lower half of the cell. Function: Secretion, absorption. It is found in inner lining of intestine, gall bladder, gastric glands, intestinal glands, etc.

Teacher's Note

Columnar cells are tall like pillars or columns in a building. The small finger-like structures (microvilli) on top help absorb food in the intestines.

Exam Trick

Remember: Columnar = column-shaped, like pillars. Think of tall columns in a temple - they are long and stand upright.

Points to Remember

Columnar cells are tall and pillar-shaped.
Have microvilli on the free surface.
Found in the intestines and stomach.
Help absorb food and nutrients.
Nucleus is in the lower half.

4. Ciliated Epithelium

Cells of this tissue are cuboidal or columnar. Free ends of cells are broad while narrow ends rest on a basement membrane. Free ends show hair like cilia. Nucleus is oval and placed at basal end of cell. Function: To create a movement of materials in contact in a specific direction and thus able to prevent entry of foreign particles in the trachea, push the ovum through oviduct. It is found in inner lining of buccal cavity of frog, nasal cavity, trachea, oviduct of vertebrates, etc.

Teacher's Note

Ciliated cells have tiny hair-like structures called cilia. These cilia move back and forth to push mucus and dust out of the lungs, keeping them clean.

Exam Trick

Remember: Cilia = hair-like. Think of tiny hairs that wave together to push things along, like a wave in a crowd at a stadium.

Points to Remember

Have hair-like structures called cilia.
Cilia move to push materials forward.
Found in the windpipe and lungs.
Help remove dust and germs.
Prevent harmful particles from entering.

5. Glandular Epithelium

Here, the cells may be columnar, cuboidal or pyramidal in shape. Nucleus is large and situated towards the base. Secretory granules are present in the cytoplasm. The glands may be unicellular (globlet cells of intestine) or multicellular (salivary gland) depending on the number of cells. Depending on mode of secretion, multicellular glands can be classified as duct bearing glands (exocrine glands) and ductless glands (endocrine glands).

Exocrine glands pour their secretions at a specific sites e.g. Salivary gland, sweat glands etc. Endocrine glands release their secretions directly into blood stream. e.g. thyroid gland, pituitary gland, etc. Function: Secrete the mucus that trap the dust particles, lubricates the inner surface of respiratory and digestive tracts, secretion of enzymes and hormones.

Teacher's Note

Glandular epithelium cells make and release substances like sweat, saliva, and hormones. For example, sweat glands in your skin produce sweat to cool your body.

Exam Trick

Remember: Exocrine = has a duct (like a tube), Endocrine = no duct, goes directly in blood. Think of exocrine as "exit-through-duct" and endocrine as "enters-blood".

Points to Remember

Glandular cells produce and release substances.
Exocrine glands have ducts like sweat glands.
Endocrine glands release into blood like thyroid.
Help with digestion and body temperature control.
Nucleus is at the base of the cell.

6. Sensory Epithelial Tissue

It is composed of modified form of columnar cells and elongated neurosensory cells. Sensory hairs are present at the free end of the cell. Function: It perceive external as well as internal stimuli. These are found in nose (Olfactory) Ear (Auditory hair cells) Eye (photoreceptors).

Teacher's Note

Sensory epithelial tissue helps us see, smell, and hear. For example, cells in your nose detect smells from food cooking in the kitchen.

Exam Trick

Remember: Sensory = senses. These tissues are found in nose, ear, and eye - the organs you use to sense the world.

Points to Remember

Found in nose, ears, and eyes.
Help us smell, hear, and see.
Have sensory hairs for detecting stimuli.
Connected to the nervous system.
Help us understand our surroundings.

7. Germinal Epithelial Tissue

Cells of this epithelium divide meiotically to produce haploid gametes. Ex.: Lining of seminiferous tubules, inner lining of ovary.

Teacher's Note

Germinal epithelial tissue makes sex cells (sperm and eggs). These cells divide in a special way to create reproductive cells that make babies possible.

Exam Trick

Remember: Germinal = germ cells = sex cells. These are in the ovaries and testes where babies are made.

Points to Remember

Makes sex cells like sperm and eggs.
Found in testes and ovaries.
Divides by meiosis.
Creates reproductive cells.
Important for having babies.

Cell Junctions

The epithelial cells are connected to each other laterally as well as to the basement membrane by junctional complexes called cell junctions.

Tight Junctions (TJs)

These junctions maintain cell polarity, prevent lateral diffusion of proteins and ions.

Adherens Junctions (AJs)

It is involved in various signaling pathways and transcriptional regulations.

Gap Junctions (GJs)

This intercellular connection allows passage of ions and small molecules between cells as well as exchange of chemical messages between cells.

Desmosomes (Ds)

These provide mechanical strength to epithelial tissue, cardiac muscles and meninges.

Hemidesmosomes (HDs)

Allow the cells to strongly adhere to the underlying basement membrane. These maintain tissue homeostasis by signaling.

Teacher's Note

Cell junctions are like the mortar between bricks in a wall. They hold cells together and help them communicate with each other, keeping your body working properly.

Exam Trick

Remember: Tight = seal together, Gap = pass messages, Desmo = give strength, Hemi = stick to basement. Each junction has a different job.

Points to Remember

Cell junctions connect cells together.
Tight junctions seal and protect.
Gap junctions allow communication.
Desmosomes provide strength.
Hemidesmosomes anchor to basement membrane.

Compound Epithelial Tissue

a. Stratified Epithelium

Nucleus is present in stratum germinativum. Cells at free surface become flat and lack nucleus called stratum corneum. Function: Protection. Ex.: Epidermis of skin, oesophagus cornea, vagina, rectum.

b. Transitional Epithelium

Structure of transitional epithelium is same like stratified epithelium. The cells can undergo a change in their shape and structure depending on degree of stretch. Function: Distension of organ. Ex.: Urinary bladder

Teacher's Note

Stratified epithelium is like layers of tiles - strong and protective, like the skin on your hand. Transitional epithelium can stretch and shrink, like a balloon filling with water.

Exam Trick

Remember: Stratified = many layers stacked up. Transitional = changes shape when stretched, like your bladder when you drink water.

Points to Remember

Stratified epithelium has many layers for protection.
Outer layer has no nucleus.
Found on skin and tongue.
Transitional epithelium can stretch and shrink.
Found in bladder and urinary organs.

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