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Unit 6 – Animal Tissues Class 12 Biology Notes

6.1 Animal Tissues: Introduction; Types of animal tissues: epithelial, connective, muscular and nervous (structure, functions & location of different sub-types). (8 teaching hour)

Animal tissue

Tissue :-

A group of cell which are similar in structure, similar in origin and espicalized for the particular function is know as tissue.

The term tissue L. texere - to weave was given by Nehemiah Grew with reference to the plant anatomy. This term was introduce in histology by a French anatomist and physiologist Mari Francois Xavier Bichat (1771 - 1802). He is considere as the founder father of animal histology.

• The branch of biology concerned with the study of microscopic anatomy of cell & tissues of plants & animal is called histology. (histos = web, logis = study) or microanatomy.
• The person who specilized the science of Histology is called histiolized.
• And italian scientist Marcello malpighii is the founder father of histology.
• The term histology was given by August mayer.

Types of tissue :-

There are 4 major types of tissue they are

1. Epithelial tissue
2. Muscular tissue
3. Connective tissue
4. Nervous tissue

1. Epithelial tissue :- (Greek epi- over / upper, thelium - covering)

• The word epithelium was introduced by Ruysch.
• An epithelium is a tissue composed of one or more layers of cells covering the external surface of body of viscera (internal organs). [Diagram labels: Cementing matter, Basement membrane]
• Epithelia arises from all the three primary germ layers, ectoderm, mesoderm & endoderm of the embryo.
• for ex: the epidermis arises from the ectoderm, coelomic epithelium from mesoderm & epithelial lining of alimentary canal from the endoderm. (ie Ectothelium, mesothelium, endothelium).
• The tissue consist of various shape and closely arranged in one or more layers forming continuous sheet & lack the intercellular space.
• The cell are helid together by cementing substance which is made up of Carbohydrates derivative. (hyaluronic acid, mucopolysaccharides)
• The epithelia rest on a thin lower most non cellular layer called basement membrane.
• The epithelia general lack blood vascular (avascular) but still have good power of repair after injury.
• The receive usefull material & transfer waste material to the blood flowing in blood vessel across the basement membrane.

Function of epith.

1. As it covers the surface it protect the under line tissue from mechanical injury drying up, entry of germs (infection), harmful chemicals.
2. Formation of Exoskeleton :- It produces many useful exoskeletal structure such as scales, feathers, hairs, claws, hoofs in tetrapod vertebrates.
3. Secretion :- Epithelial lining the cavities give rise to gland that provide valuable secretion such as mucus, gastric juices.
4. Selective Barriers :- The epithelial checks the absorption of harmful material.
5. Respiration :- Epithelium of lungs alveoli brings about exchange of co2 & o2 betⁿ blood & air.
6. Reproduction :- Germinal epithelium of the seminiferous tubules & ovaries produces spermatozoa & ova respectively.
7. Regeneration :- The ability of epithelia to regenerate quickly help in the healing of wounds.
8. Sensation :- Sensory epithelium in sense organ. eg. nasal chamber, pick up stimuli from environment & send to nerve impulse & finally to CNS.
9. Absorption :- Epithelial lining of intestine absorbs the digested food.

Types of epithelial tissue :-

On the basis of layering, shape structure & function it is divided into 3 types.

• Simple (one layer of cell) -> Simple Squamous epithelium, cuboidal, Columnar (ciliated, Brush-bordered), Pseudostratified
• Compound (many layers of cells) -> Stratified (Stratified Squamous, Stratified Cuboidal, Stratified Columnar), Transitional
• Specialized (for particular function) -> Germinal, Sensory, ciliated, Glandular

1) Simple Epithelial tissue

• It consist of single layer of cell.
• All the cell rest on the basement membrane.
• Being extermely thin it is more effective as sensory or absorbtive surface.
• It is not very effective as protective lining.
• It is a various types : On the basic of shape & arrangement.

a) Simple squamous epithelium :-

• It is formed of flattened scale like (Squama - scale). Usually polygonal cell which consist a centraly placed large nucleus.
• It contains litter cytoplasm.
• The tissues have irregular margin called Tessellated margin.
• The cells are so closely fitted together that they look like tiles or mosaic also called pavement epithelium.
• The are located in alveolar linning (air sac) of lungs, bowman's capsule of kidney, inner linning of blood vessels & linning of blood capillaries.
• These epithelia survive for easy exchange of material by diffusion across them.

[Diagram labels: Tessellated margin (Irregular), cell bounded, Nucleus, Basement membrane, cytoplasm]

b) Simple cuboidal epithelium :-

• These are cube-like cells hence called cuboidal.
• The height & breadth of epithelial tissue are same.
• Each cell consist of central spherical nucleus surrounded by cytoplasm.
• The tissue lie on the basement membrane.
• They are located in tubular part of nephron in kidney, salivary gland, sweat gland, thyroid gland & ciliary muscle of eye.
• Its main function is absorption, secretion, excretion, accomodation of lens & gamet formation.
• Cuboidal epithelium also covers the ovaries & lines the sperm producing tubules of testes also called germinal epithelium & produces new cells for the formation of gamet.

[Diagram labels: Cuboidal epithelial cells, basement membrane]

c) Simple Columnar Epithelium :-

• These are tall, columnar or pillar like cells with nucleus at the basal & their height exceeds their wide.
• They are single layer linning that rest upon the basement membrane.
• free surface may have cillia or microvilli.
• The It is located in stomach, Intestinal villi, fallopian tube, Gall bladder, Ureter, & Renal tubule.
• The main function is absorption, conduction, stroage & excretion.

[Diagram labels: columnar Epithelium cells, Basement membrane. a) Simple ciliated epithelia found in uterus & help in conduction. b) Simple brush micrepithelium - Helps in absorption]

d) Pseudostratified epithelium :-

• It is one layer of columnar cell but appear to be in two layers due to nuclei at different level so, it is called pseudostratified epithelium.
• All the cells rest on basement membrane.
• Such cells are cilliated.
• It is found in lining of trachea & primary bronchi, RT & nasal epithelium.
• Due to cillia fallopian tube cillia pushes ova toward the uterus, mucus trap the bacteria & dust particles. The ciliary beat expel them in outward direction & filtration.

[Diagram labels: Tall cell (long duct/passage), Nuclei, Basement membrane, Goblet cell (mucus cell), Basal cell, cillia. fig: Pseudostratified epithelium]

2) Compound Epithelial tissue :-

• It consist of many layer of cells only the lower layer rest on the basement membrane.
• They are thicker and stronger than the simple epithelial tience provide better protection to the underline tissue.
• The surface exposed to air such as skin epidermis, protect from chemical & microbieal infection, friction & damages, cornea of eye, inner surface of mouth, esophagus etc.
• It is a following types

a) Stratified squamous epithelium :-

• The upper layer are flattene cell Hence called squamous epithelium. These epithelia consist of many layer of cells & cells may be columnar & cuboidal. The main function of this epithelium is protection.
• It is of 2 types.

i) keratinized squamous epithelium

• This tissue has heavy deposit of the insoluble protein called keratin in dead superfical cells. So it is called impermeable to water & highly resistant to absortion (Protect under lying tissue). It is located in external surface of epidermis of skin, nail, clow, horns etc.

[Diagram labels: Flattened cells, Polygonal / Basal cells, Columnar cells, keratinized layer, Flattened cell, Polygonal / Basal cells, Cuboidal cell, Basement membrane. a) keratinized b) Non-keratinized]

ii) b) Non-keratinized squamous epithelium

• It occurs at wet surfaces where abration occurs but there is no risk of drying. Such epithelia forms the cornea of eye, Inner surface of eyelid & lining of buccal cavity, lower part of pharynx, vagina. It helps in protection & conduction.
• The squamous cell of surface layer do not lose their nuclei & keratin is absent.

b) Stratified Cuboidal epithelium :-

• These have top layer (2 layer) of cuboidal cells & it rest on basement membrane. It is found in lining of salivary duct, Pancreatic duct & sweat duct. It also form the epidermis (scales) of fishes & tails of Urodela (Ex Salamander). Its function is to protect from mechanical or chemical stress & also help in conduction.

[Diagram labels: cuboidal cells, columnar cells, Basement membrane]

c) Stratified Columnar Epithelium :-

• These have layer of columnar cells over many layers of cuboidal cells. They are found in lining of duct of mammary gland & part of urethra. It covers epiglottis.
• This help in secretion & protection from mechanical & chemical stress.

[Diagram labels: columnar cells, Cuboidal cells, Basement membrane]

d) Transitional Epithelium (urothelium) :-

• There is no basement membrane.
• This epithelium consist of 2 to 6 layers of cells. The cells of deepest layer are columnar, in middle is polygonal & upper is of large & globular cells.
• The cells are stretchable.
• It is found in Renal Pelvis, Urinary bladder, ureter.
• They have thick membrane with thin region that fold when the bladder contracts.
• It helps in urine conduction & storage.

[Diagram labels: Flat cells, polygonal cell (2-6 layer), Cuboidal cells, Connecting on smoth muscle]

3) Compound Specialized epithelium

The cuboidal & columnar epithelium are modified to perform other function than the protection. They are following type.

a) Ciliated epithelium :-

• The cells of epithelium are made up of columnar & cuboidal epithelium but their margin are ciliated. Due to presence of cilia it conduct different product of tissue. They are found in fallopian tube, vasa differentia, nasal chamber.
• Its function is conduction, Receive sensitivity (ie dectect smell) & filtration.

[Diagram labels: cilia, Nucleus, B.M]

b) Sensory epithelium :-

• It is the modified form of simple columnar epithelium.
• Each cell is elongated slender and its inner end remains connected with nerve fibres & outer with sensory hairs.
• These cells receive external stimuli & transmit nerve impulse to brain.
• They are found in sense organ & receive sensitivity & makes body aware of them.
• It is found in retina, taste bud, nasal chamber & Organ of corti.

[Diagram labels: Sensory epithelium, nerve cell]

c) Germinal epithelium :-

• It is the modified cuboidal epithelium & have power to divide to form gamet (spermatozoa & ova). By reproduct.
• In male it is found in seminiferous tubules of testes where as in female it is found in other line of ovary.

d) Glandular epithelium :-

• These are modified form Cuboidal cell that have power of synthesis & secretion of imp chemical substance in the body such as Gastric juice, intenstinal hormone.

Gland : A cell, tissue or organ which secretes a useful material is known as gland.
- The gland develop from the epithelial tissue.

Secretion : A gland may secret protein pancrease, lipid -adrenal gland, mixture of carbohydrates & protein, mixture of all material (mammary gland).

Types of Glands

The Glands are classif...

Based on site of secretion

According to the site where the secretion is released they gland are of 3 types: exocrine, endocrine & Heterocrine.

1) Exocrine :-

The exocrine send their secretion through the duct to the site of action. These includes salivary gland, gastric gland, intestinal gland, tear gland, oil gland, sweet gland, mammary gland.

2) Endocrine

The endocrine gland lack duct. They discharge their secretion called hormone into the blood that carries to the target organ. They include Thyroid, parathyroid, Pituitary gland.

3) Heterocrine Gland

The heterocrine gland have exocrine & endocrine part. The former send it secretion by duct & later one release it product directly into blood. Eg pancrease.

B. Based on mode of secretion :-

The glands are 3 types.

1) Merocrine gland :-

The secretion leaves the cell through cell membrane & the cell contact remains intact on cell surface. Ex Goblet cell, sweat gland.

ii) Apocrine glands :-

The secretion are stored in the apical part of cell which brust & release the secretion along with some part of cytoplasm. Ex mammary gland.

iii) Holocrine glands :-

The whole cells fills with a secretion & latter breaks down & is shed as secretion. Ex Sebaceous gland (oil gland).

[Diagram labels: Merocrine gland, Apocrine gland, Holocrine gland, fig: Types of Glands regarding mode of secretion.]

C. Based on the involvement of single or many cells :-

According to the involvement of one or many cells the exocrine gland may be categorized as unicellular or multicellular exocrine glands.

1) Unicellular exocrine gland :-

It consist of simple cell which represents a single gland & is called unicellular gland. This Includes.

• a) mucous cells (goblet cells or mucocytes) :- They secrete mucous. They are common in columnar epithelium of intestine.
• b) Serous cells :- It may secrete clear, watery fluid containing enzyme. They are present in gastric gland.

2) Multicellular glands :-

The multicellular glands are formed by proliferation & sinking in of the glandular epithelium into the underlying connective tissue. They consist of secretory part & duct both formed by epidermal cells. It is of,

i) Tubular glands :-

The glands have tube like secretory parts. They may be simple or compound. The simple tubular gland may be straight, coiled or branched & opens into a single duct. But has numerous secretory part the opens into single duct. Ex: The gland present in male frog's nuptial pad & crypts of lieberkuhn in the human ileum are simple straight tubular gland.

• Sweat gland in mammalian are also simple coild tubular gland.

[Diagram labeled: coild simple tubular gland]

iii) Saccular gland

These gland has wide spherical secretory part (the acinus or alveolus) at the inner side of tubular duct. It may be branched or unbranched.

eg: the cutaneous (mucous) gland of frog are simple, unbranched saccular gland.

The oil gland or exocrine part of the pancrease.

II Muscular tissue (musculus - muscle) :-

• It is the strong contractile tissue that has power to produce movement in the body. Generally it is mesodermal in origin (embryonic mesoderm). It makes up of 40% mammals body weight.
• It is made up of large no. of muscular unit cell knows as muscle fibers.
• The muscle fibers held together by connective tissue which support the muscles fibers & its capillary supply o2 and nourishment to them.
• The sarcoplasm is largely is occupied by fine longitudinal, parallel protein threads called myofibril.
• The fibers remain covered by thin membrane called sarcolemma.
• The cytoplasm of the cell is called sarcoplasma.
• The study of muscular tissue is called myology / sarcology.

function of muscular tissue :-

-> The muscular tissue play a multiple role in animal body :-

1. It bring about movement of body parts & locomotion of organism.
2. It also support bone & other structure.
3. Muscles are also responsible for the heartbeat, for the flow of blood, lymph through vessels and passage of food through alimentary canal and flow of air through respiratory trace.
4. Facial expression & gesture :- also depends on muscles.
5. Maintaince of equilibrium & favourable resting posture.

Types of muscular tissue :-

On the basis of structure it is of three types :-

a) Striated (striped / skeletal / voluntary) muscles :-

• The striated muscles are found attached to the skeleton in the face, head, trunk & limbregion & so called skeletal muscles. They are under our control of our will so called voluntary muscles.
• The muscle fibres are arranged in bundles called fasciculi.
• Each muscle fibres is elongated cell & surrounded by sarcolemma.
• These fibres are multinucleated (syncytial).
• This cytoplasm contains abundant myofibrils.
• Myofibril contains alternately arranged dark & light bands.
• The dark band is made up of myosin protein & light band is made up of actin protein.
• They bring about movement of the animals.

[Diagrams labeled: sarcolemma, dark band (H)-myosin, Sarcoplasm, Nucleus, H-line (Hensen's disc), Dark band, sarcolemma, z-line (Krause's membrane)]

b) Unstriated (Involuntary / unstriped / smooth / visceral) muscles :-

• A smooth muscles consist of sheet of densely packed elongated fibre bound by connective tissue.
• Each muscle fibre is spindle shaped / tapering at both the ends & uninucleate.
• It has no sarcolemma so it is covered by plasma membrane.
• Each muscle fibre contains numerous fine contractile myofibril.
• The myofibrils do not form dark & light band so called unstriped fibres.
• They are found in the walls of visceral organs (internal organs) like stomach, intestine, uterus, urinary bladder, blood vessels so called visceral muscles.
• The visceral muscle contracts slowly but can remain contracted for a long time without getting fatigued (tired) it also relaxes slowly.
• So, they are not easily tired. It remains under the control of autonomic nervous system hence called involuntary muscles.

Functionally, the smooth muscles is of 2 types :-

i) Single unit smooth muscles :-

The single unit smooth muscle have fibres that are closely joined together have poor nerve supply & they contract as a single unit. They occur in the wall of hollow organ such as digestive tract, uterus, ureter, urinary bladder.

ii) Multi - unit smooth muscles :-

The multiunit smooth muscles have fibres which aren't closely joined.

• They have rich nerve supply.
• They contract more or less independently as separate unit.
• They occure in dermis of skin, iris of eye & walls of large blood vessels.

[Diagram labeled: plasma membrane, Nucleus, cytoplasm]

c) Cardiac muscular tissue :-

• The cardiac muscle is largely confined to the wall of heart. It also occur in the wall of the pulmonary veins & superior venacava ie myocardium of heart.
• It is short, cylindrical cells with flat ends & branched.
• They are covered by plasma membrane.
• These muscle fibres are interconnected with each other by oblique bridge called intercalated disc.
• They are intermediate between striped & unstriped muscles tissue.
• Similar to striped muscle they contain dark & light bands & similar to the unstriped muscular tissue, each fibre contains single center nucleus.
• Its unique ability is to generate its own wave of excitation that can pass directly from fibre to fibre ie systolic & distole.
• They are tireless muscular tissue & show rhythmic continuous movement throughout the life.
• They are under of both C.N.S and A.N.S.
• The fibres contains numerous mitochondria, Glycogen and E.R as they need a large amount of energy.

[Diagram labeled: myofibril, connective tissue, Nucleus, Intercalated disc, plasma membrane. fig: Cardiac muscle]

Difference betⁿ

III Connective Tissue :-

- It is mesodermal in origin.

• The tissue that bind and hold other tissue together in the organ or protected by providing support is called connective tissue.
• It consist of 3 compound components.
  1. Cell :- It is the living component & widely seperated from each other & has large inter cellular spaces.
  2. Matrix :- It form basic ground tissue & support cells and tissue. It may be lipid (blood), semi-solid (fat), solid (bones).
  3. Fibers :- These are non-living product which is form by protein thread like structures. It is of 3 types.
     1. white collagen fibres :- It is highly elastic. It is made up of collagen.
     2. Yellow collagen fibres :- It is made up of elastic protein. It is branched. It is elastic & flexible. It is randomly distributed in ground tissue.
     3. Reticulate fibres :- Made up of Reticulin protein. It is fine, short, thread like network called reticulate fibre. It is weak.

-> function of connective tissue :-

• It binds various tissue together like skin with muscle & muscle with bone.
• The areolar tissue protects the body against wound & infection.
• The adipose tissue store fat & insulate body against heat loose.
• The bone marrow forms various blood cells.
• The lymphatic tissue helps the body to build immunity by producing antibodys.
• The supportive tissue forms shape & framework of the body.
• It transport various substance from one part to another part of the body.
• It fights pathogena, foreign toxin & protect the body.
• The lymphocytes eat up the debris.

-> Types of connective tissue :-

-> Depending on the kind of matrixie present, the connective tissue have been divide into various 3 types :-

• Connective tissue proper (matrix - semisolid)
  • Loose (no. of cell > no. of fibre) -> Areolar tissue, Adipose, Reticulate
  • Dense (No of fibres > No of cells) -> Tendon (muscle to bone), ligament (bone to bone)
• Supportive / skeletal tissue (matrix - solid)
  • Bone -> Trabecular / spongy bone, compact bone
  • Cartilage -> Hyaline cart, elastic, white fibrous, calcified
• Vascular or fluid tissue (Haemopoietic tissue)
  • Blood
  • lymph

1) Connective tissue proper :-

The connective tissue proper posses a soft gel-like matrix, less rigid & shows varying of toughness.

• It is composed of proteoglycans which are complex carbohydrate linked to protein.
• They mainly connect one tissue to another & forms protective sheath around organs.
• It is generally divided into loose & dense connective tissue.

A) loose connective tissue :-

It contains cells widely dispersed in matrix & has fibres loosely wooven in random manner. It is subdivided into. a) Areolar tissue b) Adipose tissue c) Reticular tissue.

a) Areolar tissue

• The matrix is homogenous & semisolid nature plasma.
• It is the most abundant & widely distributed proper connective tissue.
• It is jelly like consist of transparent stiky matrix which consist of four type of cells & two types of fibres.

[Diagram labels: fibroblast, elastic fibre, collagen fibre (bundle), mast cell, macrophage (histiocyte)]

i) Cells :-

• fibroblast -> spindle shaped cells -> synthesizes fibres & helps in healing.
• Mast cell -> small sized (rounded), nucleus bean shaped. Produces heparin, histamin, serotonin (vaso-constrictor ie. stop bleeding & increases blood pressure).
• Macrophage (Histiocyte) -> large sized, phagocytic cell, engulf microorganism increase immunity.
• Plasma cells (cartwheel wall) -> oval cell and cytoplasm radiates. It secrete antitoxin to neutralize foreign particle.

ii) fibres :-

• white collagen fibres :- The collagen fibre are in bundle & runs parallel to the cell. The bundle intersect each other. It is tough and rigid made up of collagen protein.
• Yellow elastic fibre :- flexible & elastic made up of elastin protein.

The gap between two fibres is called Areola due to pressure of this areolae is called Areolar tissue.

functions :-

• It provides immunity.
• It produces fibres.
• It give flexibility & elasticity.
• It provide protection also that it cover the organ from all the side like packing material & provide cushion around soft organs that acts as soft shock absorber.