Animal Tissue

Definition: Tissue is a group of similar cells having intercellular substance between them performing a specific function. Human body is made of a nine different types of system. Each system is made of many organs and each organ is composed of four different types of tissue.

Types of Animal Tissue

On the basis of structure and function, animal tissues are four types:

A. Epithelial Tissue

An animal tissue which makes outermost protective covering of the body, organs body cavities and body is known as epithelial tissue. On the basis of structure and function epithelial tissues are:

1. Simple epithelium
2. Stratified epithelium
3. Specialized or modified epithelium

1) Simple Epithelial Tissue

An epithelial tissue which is made of a single layer of cell is known as simple epithelial tissue. On the basis of shape of cell simple epithelial tissue are four types:

1. Squamous simple epithelial tissue
2. Cuboidal simple epithelial tissue
3. Columnar simple epithelial tissue
4. Pseudostratified simple epithelial tissue

a) Squamous Simple Epithelial Tissue

The simple epithelial tissue which is made up of single layer of thin and flat cells is known as squamous simple epithelial tissue. In this tissue cell is hexagonal in shape and remains attached together like mosaic. It rests on the floor of the room. Each cell contains centrally located nucleus.

Location: It is found on the lips of mouth, inner Bowman’s capsule of the kidney etc.

Function: It helps in protection, filtration and gaseous exchange.

b) Cuboidal Simple Epithelial Tissue

The simple epithelial tissue which is made up of a single layer cube shaped cell is known as cuboidal simple epithelial tissue. It is shaped like side by side and each cell contain centrally located nucleus.

Location: They are found in the duct of glands, duct of excretory and duct of reproductive organs.

Function: They help in protection and secretion etc.

c) Columnar Simple Epithelial Tissue

It is made up of elongated or tall column shaped cell. It is cell like side by side and rest over the basement membrane. They are found on lining of stomach, intestine and mammary gland. Function: they help in protection, absorption and secretion.

d) Pseudostratified Simple Epithelial Tissue

In this type of tissue cell are present in single layer but size of cell different. The nucleus of the cell lies at different position. It looks like multilayer, hence it is called pseudostratified.

Location: It is found in the inner lining of nasal chamber and bronchi etc.

Function: It helps in protection, secretion, filtration and excretion.

2) Stratified or Compound Epithelial Tissue

An epithelial tissue which is made up many layer of cells is known as stratified epithelial tissue. On the basis of shape of cell on the outermost layer it is four types.

a) Squamous Stratified Epithelial Tissue

The stratified epithelial tissue which contain squamous cell in outermost layer is known as squamous stratified epithelial tissue. Its inner layer are either made up of cuboidal or columnar cell.

Types on the basis of presence or absence keratin protein on outermost layer:

Keratinized Squamous Stratified Epithelial Tissue

The squamous stratified epithelial tissue which contains dead cell or keratin protein on its outermost layer is known as keratinized. It is found on the skin containing hair and nails. It makes water proof layer of the body.

Non-keratinized Squamous Stratified Epithelial Tissue

This type of tissue does not contain keratin protein or dead cell in its outermost layer but contains living cell. It is found on wet part of body like oral and buccal chamber, oesophagus and female vagina.

b) Cuboidal Stratified Epithelial Tissue

The stratified epithelial tissue which contains cube shaped cell on its outermost layer is known as cuboidal stratified epithelial tissue. Its inner layer are either made up columnar or squamous. It is found on the lining of large duct of gland.

c) Columnar Stratified Epithelium Tissue

The stratified epithelial tissue which contain columnar cell in outermost layer is called columnar stratified. Its lower layer are either cuboidal or squamous. It is found in the duct of mammary gland, lining of vas deferens, trachea and bronchi.

d) Transitional or Plastic Epithelium Tissue

The stratified epithelium tissue which allows the stretching of body organ on which have expansion of body organ is known as transitional epithelium. In this tissue cells are arranged in such a way where lowermost layer is made up of cube shaped cells, middle layer are made up of oval shaped cell and outermost layer are made up of dome-shaped cell. It is found on the wall of urinary bladder, ureter and urethra.

3) Modified or Specialized Epithelial Tissue

The epithelium tissue which perform other function than the protection are called modified epithelial tissue.

i) Ciliated Epithelium

They are modified cuboidal or columnar cell which contain cilia on its free margin. It is known as ciliated epithelium. They are found on the lining of trachea, bronchi and inner wall of fallopian tube. They help in filtration of dust particles, conduction of dust particles in respiratory tract and in fallopian tube it help in conduction of ovum.

ii) Germinal Epithelium

They are modified cuboidal epithelium which produce gametes (sperms or ova). They are found on the outer surface of ovary and inner lining of seminiferous tubules of the testes.

iii) Sensory Epithelium

It is the modified columnar tissue which perceive the different kinds of stimulus. They are found in the sense organs.

iv) Glandular Epithelium

They are modified cuboidal or columnar epithelium which produce juice is known as glandular epithelium. They are found in glands.

Glandular Epithelium

Types on the Basis of Number of Cells

1. Unicellular gland: It is made up of single cell. For eg. goblet cell or mucus secreting cell.
2. Multicellular gland: It is made up of many cells. Eg: salivary gland.

On the Basis of Number of Duct

1. Simple gland: Those gland which contain single duct to conduct juice is known as simple gland, for eg. sweat gland.
2. Compound gland: Those gland contain many duct to conduct juice, for eg. salivary gland.

On the Basis of Presence and Absence of Duct as well as Nature of Juice

• Exocrine gland: Those gland which contain duct and juice of them contain enzymes are called exocrine gland. For eg. salivary gland.
• Endocrine gland: They secrete their juice directly into the blood. Their juice contain hormone. Eg: pituitary gland.
• Mixed gland: Those gland which are both exocrine and endocrine in nature are known as mixed gland. They secrete both enzyme and hormones. For eg: pancreas gland.

Types of Gland on the Basis of Mode of Secretion

• Merocrine gland: Those gland which secrete juice without the loss of any part of cell cytoplasm. For eg. salivary gland.
• Apocrine gland: Those gland which secrete juice by the loss of some part of cell cytoplasm. For eg. mammary gland.
• Holocrine gland: Those gland which secrete juice by the loss of whole part of cell cytoplasm. For eg. sebaceous gland, oil gland.

On the Basis of Nature of Secretion

• Mucous gland: Those gland which secrete mucus only are called mucous gland. For eg. goblet cell found in intestine.
• Serous gland: Those gland which secrete clear watery fluid are called serous gland. For eg. sweat gland.
• Mixed gland: Those gland which secrete mucus and watery fluid are called mixed gland. For eg. salivary gland.

B. Connective Tissue

An animal tissue which connect or binds different type of tissue together in organ is known as connective tissue. In connective tissue cells are widely separated and in between the cell non-living substance is present called matrix.

Types of Connective Tissue

1. Proper connective tissue
2. Skeletal connective tissue
3. Fluid connective tissue

1) Proper Connective Tissue

It is the main connective tissue. It contains jelly like matrix. It binds different types of tissue together.

Types of proper connective tissue:

1. Loose proper connective tissue
2. Dense proper connective tissue

Loose Proper Connective Tissue: Areolar Tissue

It is the most widely distributed proper connective tissue. Its jelly-like matrix contains three types of cells and two types of fibre.

Cells

• Macrophage: It is a large irregular shaped cell. It engulfs microorganism and protects from disease.
• Fibrocyte: They are small and flat shaped cell. They manufacture different types of fibre.
• Mast cell: They are small and oval shaped cell. They produce heparin and histamine.

Fibres

• White collagen fibre: They are tough and rigid protein fibre. They are made up of collagen protein.
• Yellow elastic fibre: They are highly flexible and elastic in nature. They are made up of elastin protein.

Functions of Areolar Tissue

• It binds muscle fibres with muscle fibre.
• It engulfs microorganisms and protects body from infection.
• Mast cells produce heparin and histamine. Heparin prevents clotting of blood while histamine increases lumen of blood vessel.

Adipose Tissue

It is a modified areolar tissue. Its jelly-like matrix does not contain any types of fibre but all the cells are modified into fat storing cell called adipocyte or fat cell. It is unilocular. Its cytoplasm is more adipose tissue rich in lipid called fat tissue.

Functions

• It binds skin with muscles.
• It stores fat as a reserve food.
• It makes cushion around the vital organs like around kidney, around eyeball, around heart etc.
• It also helps to regulate body temperature.

Dense Proper Connective Tissue

Those proper connective tissue which contain large amount of fibres in their matrix are called dense. It is two types:

a) White Collagen Fibrous Tissue

It is a modified areolar tissue. Its jelly-like matrix contains a large number of white collagen fibres. Other types of cell and fibres are absent.

Function: It binds muscles with the bones so that it is called tendon.

b) Yellow Elastic Fibrous Tissue

It is also modified areolar tissue. Its jelly-like matrix contain yellow elastic fibres in large amount and fibrocyte. Other types of cell and fibres are absent.

Function: It connects or binds bone with bones at the joints hence it is also called ligament.

2) Skeletal Connective Tissue

The connective tissue which contain solid matrix between the cell is known as skeletal connective tissue. It is two types:

1. Cartilage
2. Bone

a) Cartilage

It is the soft skeletal connective tissue. It contains cheese like solid matrix.

• Shape and size of cartilage are dependent with all the type of cartilage made up of same internal structure.
• It consists of following parts.
• All the cartilage are externally covered by tough and rigid fibrous connective tissue called perichondrium. It protects the internal part of cartilage.
• In below the perichondrium, cartilage contain white cheese-like solid matrix.
• Matrix of cartilage is made up of chondrin protein.
• Matrix of cartilage contain many oval shaped fluid filled spaces called lacunae.
• Each lacunae contain one or more cartilage cell called chondrocytes.
• This chondrocyte synthesized the cartilage protein called chondrin protein.

Types of Cartilage

A) Hyaline or Glass-like Cartilage

Those cartilage which are slightly flexible or less elastic are called hyaline cartilage. Matrix of this cartilage contain clear and white collagen fibres. They are found on the end of the ribs and in flap of nose and tracheal rings.

B) White Fibrous Cartilage

Those cartilage which are rigid and non-elastic are called white cartilage. Matrix of this cartilage contain large amount of white collagen fibrous. They are found on the end of the ribs and between the vertebrae of backbone.

C) Yellow Elastic Cartilage

Those cartilage which are highly elastic and elastic in nature are called yellow elastic cartilage. Matrix of this cartilage contain large amount of yellow elastic fibres. They are found in ear pinna, tip of nose, epiglottis, eustachian tube.

D) Calcified Cartilage

Those cartilage which are very hard like a bone are known as calcified cartilage. Matrix of this cartilage contain calcium carbonate. They are found on suprascapula of the pectoral girdle of frog.

b) Bone

The skeletal connective tissue which contain stone like matrix is known as bone. They are the hardest connective tissue. Hardness of bone is due to deposition of calcium carbonate and magnesium carbonate.

• Bone is a living tissue because it contain living cell called osteocyte.
• Osteocyte produce nonprotein called ossein protein.
• Ossein protein is found in matrix and constitutes about 30% weight of matrix.
• Remaining 70% weight of matrix is occupied by inorganic salt like carbonate and phosphate of calcium and magnesium.

Functions of Bone

• It makes frame work of the body.
• It protects vital and delicate organ of the body.
• It provides surface area for the attachment of muscles.
• It manufactures new blood cells.
• It helps in locomotion.
• It acts as a store of minerals because it stores excess minerals present in the body.

Internal Structure of Bone

Shape and size of bones are different but all the type of bone are made up of same internal structure.

1. Periosteum: It is the outermost protective covering of the bone. It is made up of tough and rigid fibrous tissue.
2. Outer layer of osteocytes: It lies just below the periosteum and is made up of single layer of flat cells. It manufactures new bone cells (osteocytes) and supplies them into matrix.
3. Matrix: It lies between outer and inner layer of osteoblast. It is composed almost all parts of the bone. Matrix of bone contains ossein protein and is very hard due to decomposition of calcium carbonate and magnesium carbonate. Matrix of bone is arranged into many layers called lamellae. Each lamella contains many oval irregular shaped fluid filled spaces called lacunae. Each lacuna contains single bone cell called osteocyte. It produces ossein protein.
4. Inner layer of osteoblast: It is also thick below the matrix and is made up of single layer of flat cell and produces new bone cells.
5. Bone marrow: Inner cavity of bone is hollow called marrow cavity. Wall of marrow cavity contain soft tissue called bone marrow.

Types of Bone Marrow

• Red bone marrow: It is red in colour and found in spongy bone. It manufactures new blood cells: RBC and platelets.
• Yellow bone marrow: It is white/yellow in colour. It is found in compact bone. It stores fat as a reserve food.

Haversian System

In the compact bone, matrix contains long and narrow canal called Haversian canal. Haversian canal contains blood vessels and nerve fibres. Around it supplies oxygen and nutrients to osteocytes. The branching system formed in the matrix by the Haversian canal, its blood vessels and extension of lacuna is called Haversian system.

Difference Between Red Bone Marrow and Yellow Bone Marrow

Difference Between Spongy Bone and Compact Bone

Difference Between Cartilage and Bone

3) Fluid Connective Tissue

The connective tissue which contain liquid like matrix is known as fluid connective tissue. Due to fluid like matrix it flows in the blood stream and connects hence it transport different materials in the body.

On the basis of type of colour, it is of two types:

1. Blood
2. Lymph

A) Blood

It is a red fluid connective tissue. Adult healthy man contains about 5 to 6 litre volume of blood. It is composed of plasma and blood cells.

1) Plasma

It is a pale yellow and slightly alkaline (7.2–7.4 pH). It constitutes about 55% volume of the blood. It is composed of 90–92% water and about 10% dissolved solutes.

a) Organic Solutes

They are vitamins, amino acid, fatty acid, glucose, salt, urea, creatine, hormone, globulin, fibrinogen etc.

b) Inorganic Solutes

NaCl, KCl, Ca++, Na+, Mg++, bicarbonate, NaHCO₃, KHCO₃, O₂, CO₂ etc.

2) Blood Cells (Blood Corpuscles)

The cells floating over the blood plasma is known as blood cell. They are three types:

Erythrocyte / Red Blood Cells (RBC)

• They are found in largest number.
• 1 mm³ blood contains about 4.5 to 5.5 million RBC.
• They are biconcave in shape.
• They do not contain nucleus and cell organelles.
• They are formed in red bone marrow.
• Average life span of RBC is about 110 to 120 days.
• Old and dead RBC are destroyed in the liver and spleen.
• The process of formation of RBC is called erythropoiesis.
• Reduction of RBC is called erythropenia and increase is called anaemia in the source note.
• It contains red pigment called haemoglobin.
• Due to presence of haemoglobin RBC transport O₂ and CO₂ respiratory gases.

Leucocytes / White Blood Cells (WBC)

• They are the largest blood cell.
• They are least in number but irregular in shape.
• They contain nucleus and cell organelles.
• 1 mm³ cube of blood contains about 4 thousand to 11 thousand WBC.
• Life span varies from few hours to 14 days.
• They are found in red bone marrow and lymph node.
• Dead and white WBC are destroyed in liver and spleen.
• They are the soldier of the body and protect the body from foreign organism by destroying them.
• Process of formation of WBC is called leucopoiesis.
• Excess formation of WBC is known as disease called leukemia (blood cancer).

Types of WBC

Types of WBC shown in the source include granulocytes and agranulocytes.

Granulocytes

• Neutrophils: About 60–70% of WBC. They engulf microorganisms.
• Eosinophils / Acidophils: About 2–5%. They destroy toxins and are involved in allergic reaction.
• Basophils: About 0.5–1%. They contain heparin and histamine.

Agranulocytes

• Lymphocytes: About 20–25%. They produce antibodies against microorganisms.
• Monocytes: About 2–8%. They engulf microorganisms and act as phagocytes.

Thrombocytes (Platelets)

• They are the smallest blood cells.
• Shape of cell is star, sphere or spindle.
• They do not contain nucleus.
• 1 mm³ of blood contains 1.5 to 4.5 lakh number of platelets.
• They are found/formed only in bone marrow.
• Life span of platelets is about 7 days.
• Dead and old platelets are destroyed in liver and spleen.
• They contain blood clotting protein called prothrombin and help in clotting of blood at injured parts.
• Formation of platelets is thrombopoiesis.
• Reduction of platelets in the blood is called thrombopenia.

Functions of Blood

1. Blood is a main transporting medium and it transports various substances from one part of body to other parts.
2. It transports nutrient substances from elementary canal to all over body tissue.
3. It transports metabolic wastes from all over the body to the kidney.
4. It transports hormones from endocrine gland to target organ.
5. It transports respiratory gases O₂ and CO₂ from all over the body to lungs and from lungs to all over the body.
6. It transports heat from liver to all over the body.
7. It protects body from infection of microorganisms because it either engulfs or destroys microorganisms.
8. It helps in clotting of blood at injured parts and prevents loss of blood.
9. It maintains osmotic pressure of the tissue.
10. It maintains pH level of body fluid.

Lymph

Lymph is a filtered blood without RBC and platelets. It is also called intercellular fluid. It is similar to blood plasma and colourless. Lymph also flows through vessel called lymph vessel. Lymph vessel contain one or more called lymph node. Lymph node produce a type of WBC called lymphocyte. Lymph also does not contain plasma protein called fibrinogen.

Functions of Lymph

1. It acts as a middle man between body cells and blood.
2. Lymph vessel present in intestine helps in absorption of lipid.
3. It transports different materials from one part of body to the other parts.
4. It contains WBC so that it provides immunity to the body.
5. When blood is lost from the body then lymph enters into the blood and maintains volume of the blood.

C. Muscular Tissue

An animal tissue which brings the movement of body organ is known as muscular tissue. Muscular tissue is made up of thread like cell called muscle fibre.

• Membrane of muscle fibre is called sarcolemma and cytoplasm of muscle fibre is called sarcoplasm.
• Sarcoplasm contains fine fibres called myofibrils.
• Study of muscular tissue is called myology.

Types of Muscular Tissue

On the basis of structure and function muscular tissue are three types.

1) Striated or Striped or Skeletal or Voluntary Muscular Tissue

1. It is made up of long and cylindrical shaped muscle fibre with blunt end.
2. Each muscle fibre contains fine fibrils in their cytoplasm called myofibrils.
3. Its myofibrils contain alternately arranged dark and light bands so that it is also called striped muscular tissue.
4. Dark band is made up of myosin protein but light band is made up of actin protein.
5. Each muscle fibre contains many nuclei so that it is also called multinucleated muscular tissue.
6. This type of muscular tissue always remains attached with skeleton of the body so that it is also called skeletal muscular tissue.
7. It is a tired muscular tissue and it tires very quickly.
8. It is controlled by central nervous system: brain and spinal cord.
9. It is under the control of will so called voluntary muscular tissue.
10. It is found on the neck, tongue and limbs.

2) Unstriped or Unstriated or Involuntary or Smooth / Visceral Muscular Tissue

1. It is made up of spindle shaped muscle fibre having pointed end.
2. Its myofibrils do not contain alternately arranged dark and light band.
3. Each muscle fibre contains single nucleus.
4. Due to absence of dark and light band it is also called unstriped or smooth muscular tissue.
5. It is a tired less muscular tissue and shows continuous movement throughout the life.
6. It is found on the visceral organs like liver, kidney, lungs, intestine, stomach etc.
7. It is controlled by autonomic nervous system.
8. It is not under the control of will.

3) Cardiac Muscular Tissue

1. It is a special type of muscular tissue only found on the wall of heart.
2. It is intermediate between striped and unstriped muscular tissue, similar to striped muscular tissue. It contains light and dark band. Similar to unstriped muscular tissue each muscular fibre contains single nucleus.
3. In cardiac, all the muscular fibres are interconnected to each other by an oblique bridge.
4. One muscle fibre separated from another by an intercalated disc.
5. It is also a tired less muscular tissue and shows rhythmic continuous movement throughout the life from birth to death.
6. It is controlled by both autonomic nervous system and central nervous system in the source note; it is also not under the control of will.

D. Nervous Tissue

An animal tissue which control, coordinate, regulate the functioning body organ and system is nervous tissue. Nervous system of all animal is made up of nervous tissue.

Types of Nervous Tissue

1. Neuron
2. Neuroglia
3. Ependymal cell
4. Neurosecretory cell

1) Neuron

It is the main nervous tissue. Neuron is the longest cell of the body and some neuron are more than one meter in length. Neuron has the special property of excitability and conductivity.

Structure of Neuron

Neuron is the longest cell of the body. It is differentiated into two parts:

1. Cyton or cell body
2. Cytoplasmic extension

1) Cyton or Cell Body

It is the main part of neuron. It contains both nucleus and cytoplasm. Its cytoplasm contains special type of granules called Nissl’s granules.

2) Cytoplasmic Extension

From the cyton cytoplasm is extended outward called cytoplasmic extension. It is two types:

a) Dendron

Short cytoplasmic extension are known as dendron. Generally they are many in number and each dendron divides into fine branches called dendrites. Dendron and dendrites are afferent in nature and conduct the message towards the cyton.

b) Axon

Long cytoplasmic extension is called axon. It is always single. Axon also divides into branches called terminal arborization. Each terminal arborization ends into round swelling called synaptic button.

In most of the neuron axon is externally covered by sheath of fatty called fatty sheath or myelin sheath. If myelin sheath is present then it is broken down at various points called node of Ranvier. Axon carries the message away from the cyton.

The fatty sheath is externally covered by a cell called Schwann cell. Those neurons which contain myelin sheath are myelinated neuron. They are found in white part of brain and spinal cord.

Types of Neuron on the Basis of Myelin Presence or Absence

Types of Neuron

On the Basis of Number of Cytoplasmic Extensions

1) Unipolar Neuron

Those neuron which contain a single cytoplasmic extension are called unipolar neuron. They are found in the peripheral nervous system.

2) Bipolar Neuron

They have two cytoplasmic extensions: one is dendron and other is axon. They are found in retina of eye and nose.

3) Multipolar Neuron

They have many cytoplasmic extensions out of them one is axon and remaining are dendron. They are found in central nervous system.

On the Basis of Function

1) Afferent or Sensory Neuron

Those neuron which carry the message from different part of the body to the brain or spinal cord are known as afferent neuron. For eg: optic nerve.

2) Efferent or Motor Neuron

Those neuron which carry the message from brain or spinal cord to all over the body organ is known as efferent or motor neuron. For eg: oculomotor nerve.

3) Mixed Neuron

Those neuron which are both afferent and efferent in nature are known as mixed neuron. For eg: all spinal nerve.

Neuroglia or Glial Cell

They are star shape and small size non-nervous tissue found around the neuron. They are ten times more than neuron and occupy half weight of the brain and spinal cord.

Functions of Neuroglia

1. They insulate one neuron from other neuron.
2. They act as packing material.
3. They bind all the neurons together.
4. They provide nutrition to the neuron.
5. They help in memory process.
6. They engulf the microorganism.

Ependymal Cell

The simple epithelial tissue which is found on the wall of ventricles of brain and spinal cord is known as ependymal cell. It helps in protection.

Neurosecretory Cell

The nervous tissue which produce neuro hormone is known as neurosecretory cell. Neurohormone control the pituitary gland.

Synapse

Neurons are never attached together but contain a gap between axon of one neuron and dendron of another neuron. This gap or junction between the two neuron is known as synapse.