Grade 12 Zoology Note

Animal tissues

Chapter-1 Animal tissue

A cell is a basic unit of body. Many cells form a tissue. A tissue may be defined as the Group of cells that may be or may not be similar in structure but are specialized to perform specific functions.  Cells having similar in structure, origin and functions. The study of tissue is called histology.    

Types of tissues

 On the basis of structure and function there are four types of animal tissue. They are:

1.Epithelial tissues

These tissues forms covering of the various body parts on outside as well as the internal organs and body species inside. These epithelial tissues are secretary, glandular and sensory in functions. On the basis of Shape of cell layers the are of two types. They are;




i.Simple epithelium


The simple epithelium tissue is composed of a single layer of cells. the cell rest on a basement membrane. They are of following types;

a.Simple squamous epithelium:

 This is made up of thin, flat and hexagonal cells. A large central rounded nucleus contain by each cell. It is usually forms a covering around coelom. Its main function is help in protection, absorption, filtration and exchange of gases.

b.Simple cuboidal epithelium:

 This tissue consists of cubical cells. These cell lies on a basement membrane. It forms the lining on kidney tubules, sweat glands, salivary glands, gut lining, testis and overy.This tissue involves in secretion, absorption and excretion. They are also two types, ciliated cuboidal and Brush bordered cuboidal. The cubical cells have cilia on the free surfaces and brush bordered cuboidal types of cell have microvilli at free the end of cells.

c.Simple columnar epithelium:

 These columnar epithelium consist of tall columnar cells. These cells are placed side by side forming a layer. It forms the lining of the stomach, gastric glands, intestinal glands, gall bladder, ureter and uterine wall. This tissue involves in protection, secretion etc. They are of two types. Cells having cilia on the surfaces called ciliated columnar and cells having microvilli at free ends of the cells called brush bordered columnar.

d.Pseudo-stratified epithelium:

 The stratified epithelium is formed of columnar cell. The cell remain deep but do not reach the free surface. It is found in the lining of trachea, large bronchi, and ducts of some glands. Its function as protection against dust particles entering the respiratory tract.

ii.Stratified or compound epithelial tissues:

 These tissues is formed of several layers of epithelial cells. It is called multilayered tissue. They are of following types;

a.Stratified squamous epithelium:

It is type of tissue in which the upper layer consists of large flat polygonal or squamous cell. It is also of two types namely Ketratinised stratified epithelium which is found on hair, claws and nails. and Non ketratinised stratified epithelium found on wet surfaces like in buccal cavity, pharynx, vegina, etc.

b.Stratified cuboidal epithelium:

It is the type of tissue in which the outer most layer consists of cuboidal cells which is found on sweet glands, salivary glands, pancreatic gland, female urethra, etc.

c.Stratified columnar epithelium:

 In this type the outer layer of tissue consists of tall columnar cells. However, the lower layer germinative cells are cuboidal type. It is found on the lining of ducts mammary glands, lining of vasa-defferentia, trachea and bronchi.

d.Transitional epithelium:

 Transitional epithelium is composed of several layer. It is capable in extension which has the capacity to search and relax. It is found on urinary bladder, ureters, uterus, etc.

Modified epithelium:

Some epithelium cells are modified for specialized functions. These are;

1.Ciliated epithelium:

 It is modified form of columnar or cuboidal cells which bear cilia help in conduction of mucus and other substances. It is found in trachea, bronchi, sperm ducts etc.

2.Sensory epithelium:

 It is the modified columnar cells found in tongue and nasal cavities which are sensitive in nature.

3.Germinal epithelium: These are the modified cuboidal cells found in testa and ovary. These can divide and develop in to gametes by meiosis.

4.Glandular epithelium:

These are modified columnar cells which form glands.

Types of glands:

1.Based on the kind of secretion and duct present

a.Unicellular glands:

These glands occur as a single cell, scattered in the columnar cells e.g. goblet cell, mucus secreting cells.

b.Multicellular glands:

These are formed of many cuboidal cells, which form  many tubular invagination e.g. Sweet gland gastric glands etc.

2.Besed on the kind of secretion and duct present

a.Exocrine glands:

These are the glands which pour secretion through the ducts their respective sites of action e.g. Salivary, tear, gastric and intestinal glands.

b.Endocrine glands:

These glands do not possess ducts and pour their secretions directly in to the blood vessels. Their secretions are hormones.

3.Based on the shape and complexity they are of two types;

a.Simples glands:

These glands have a single unbranched duct. In this types of gland the  secretory part could be in the form of tubes or sacs. Various form of simplest glands are as,

i.simple tubular glands: found in intestinal crypts.

ii.simpe coiled tubular glands: found in simple sweet glands of mammals.

iii.simple branched  tubular glands: found in lining gastric and brunner’s  glands.

iv.simple alveolar  glands: mucous secreting gland of frog.

v.simple branched alveolar glands: found in sebaceous or oil gland of mammals.

b.Compound glands: These glands have number of ducts forming a branching pattern. The different forms of compound glands are;

i.Compound tubular glands: found in the salivary glands.

ii.Compound alveolar glands: found in the mammary glands, pancreatic glands, etc.

iii.Compound tubular-alveolar glands: found in the parts of salivary and mammary glands.

d.Based on the mode of secretion;

a.Merocrine glands:

In these glands, the secretions are discharged on its cell surface by diffusion without losing any of its cytoplasm.

b.Apocrine glands:

In these glands, the cell loses a part of its cytoplasm while  releasing its secretions.

c.Holocrine glands:

In these  glands, the entire cell, when filled with secretary  products, breaks down in order to in order to release its secretions.

e.Based on the nature of secretion;

a.Mucous glands:

These are the glands which secretes the mucus. It is present in the goblet cells in the intestine.

b. These are the glands which secretes a clear watery fluid. These cells are termed as serocytes.

c.Mixed glands:

Some glands are made of both mucocytes and serocytes and hence produce both kinds of secretion e.g. gastric glands and pancreatic glands.

2.connective tissues:

The cells of connective tissue are separated by non-living material. Connective tissue binds and supports body parts, protects, fills spaces, stores fat (for energy), and transports materials.



                     Fig; some connective tissues



1.Bind the different cells or tissues together.

2.Store lipids or fat globules in the cells in adipose.

3.Form skeleton to support frame work of a body.

4.insulate the body.

5.replace dead and damage tissues.

6.Trasport material from one place to another in the body.

Structure of connective tissue:

Connective tissue is composed primarily of two elements: cells and a matrix. The types of cells found in connective tissue vary depending on the type of tissue they support. For example, red and white blood cells are found in blood, which is a fluid connective tissue. Adipocytes are fat cells found in adipose tissue, or fat. and fibroblasts are cells found in large quantities in many different types of connective tissues.

The matrix can be thought of as the substance in which the cells are embedded. The matrix can be fluid, semifluid, gelatinous, or ground substance and protein fibers. A ground substance is a supportive medium made of water and large molecules. There are three types of protein fibers found within the matrix.

Collagen fibers are very strong and provide flexibility. Elastic fibers are very stretchy and assume their original shape after being stretched. Finally, reticular fibers are very thin and provide support for many soft organs and blood vessels.

Connective tissues are divided in to three types;

1.Proper connective tissue;

Connective tissue proper, the second broad category of connective tissues, contains a variety of types.  All possess visible protein fibers embedded in a fluid ground substance. On the basis of softness, rigidity and degree of toughness, they are two types;

a.Loose connective tissue proper:

they are also of two types;

i. Areolar tissue:

 These tissues are Loose, irregularly arranged connective tissue, that consists of collagenous and elastic fibers, a protein polysaccharide ground substance, and connective tissue cells e.g. white collagen fibres, yellow elastic fibres, fibrocytes, macorophages, mast cells. Areolar tissue acts as supporting and packing tissues.


ii. Adipose tissue:


  Fig; Adipose tissue

Adipose tissue, or fat, is an anatomical term for loose connective tissue composed of adipocytes. Its main role is to store energy in the form of fat, although it also cushions and insulates the body.

b.Dense connective tissue proper: They are also of two types they are;

i.White fibrous tissue:

One of the specific types of connective tissue is fibrous connective tissue. This high-strength, slightly stretchy tissue consists mainly of collagen, a protein which is known for providing strength and stability. The two other main components  are water and polysaccharides, which are complex strands of carbohydrates, which also provide Protection and support.

ii.yellow elastic tissue:

yellow elastic tissue or yellow fibers are bundles of proteins  found in extracellular matrix  of connective tissue and produced by fibroblasts and smooth muscle cells in arteries. These fibers can stretch up to 1.5 times their length, and snap back to their original length when relaxed.

2.Supportive connective tissues:

These skeletal tissues support the body and protect the delicate and vital organ from various injuries. They are of two types;


Cartilage is a type of connective tissue composed of special cells known as chondrocytes  along with collagen or yellow elastic fibers. The fibers and the cells are embedded in a firm gel like matrix. Cartilage is not as hard and rigid as bone. It is much more flexible and elastic. There are three types of cartilage;

1.Hyaline cartilage

2.Fibrous cartilage

3.Elastic cartilage


1.Hyaline cartilage:

This type of cartilage has very thin fibers having same refractive index as the matrix of the cartilage and thus these fibers are not seen. Hyaline cartilage is the articular cartilage of long bones, sternum, ribs etc. Its color is bluish white and it is flexible.

2.Fibrous cartilage:

This type of cartilage has numerous white fibers. It is present in the symphysis pubis, and sternoclavicular joint etc. Its color is glistening white and the appearance is opaque.

3.Elastic cartilage:

This type of cartilage has numerous yellow elastic fibers. It is present in the ear pinna, external auditory meatus, Eustachian tubes, and epiglottis etc. Its color is yellowish and the appearance is opaque.


A bone is a rigid organ that constitutes part of the vertebral skeleton. Bones support and protect the various organs of the body, produce red and white blood cells, store minerals and also enable mobility. Bone tissue is a type of dense connective tissue. Bones come in a variety of shapes and sizes and have a complex internal and external structure.

Structure of bone:

A typical weight-bearing bone has an outer membrane called the periosteum. The actual bone has an outer layer of denser bone called compact bone, and an inner layer of more honeycombed bone called trabecular bone. Compact bone has structures called osteons, or the haversian system. Osteocytes (bone cells) are found between the lamellae. Trabecular bone is a network of interconnected mineralised matrix, with the hollows between filled with bone marrow.
Bones also contain nerves, blood vessels, and other non-bone structures.
Biochemically, the bone matrix is composed of collagen fibres, and depositions of hydroxyapatite that form the mineral component of the bone.

3.Fluid connective tissue:

It consists of both myeloid and lymphoid tissue which forms blood and lymph respectively.


It is one type of fluid connective tissue. It consists of plasma and corpuscles.




a.Blood plasma:

Blood plasma is the pale-yellow liquid component of blood that normally holds the blood cells in whole blood in suspension. It makes up about 55% of the body's total blood volume. It is the intravascular fluid part of extracellular fluid (all body fluid outside of cells).


i.Water:                      90 – 92%

ii.Dissolved solid:       8 – 10%

iii.Respiratory gases:  O2 and CO2

iv.Internal secretions:  Antibodies and various enzymes.

Function of plasma:

The function of blood plasma is that of carrying the white blood cells, platelets and red blood cells suspended within it. Plasma helps with maintaining a proper pH balance and operates as the exchange system of both sodium and potassium within the body. The immunoglobulin act as antibodies and help the body to develop immunity.

2.Blood corpuscles (cells):

A blood cell, also called a hematocyte, is a cell produced by hematopoiesis and normally found in blood. In mammals, these fall into three general categories:

1.Red blood cells or Erythrocytes (RBC):

Red blood cells primarily carry oxygen and collect carbon dioxide through the use of hemoglobin, and have a lifetime of about 120 days. In the process of being formed they go through being a monopotent stem cell. They have the job alongside the white blood cells of protecting the healthy cells.

2 White blood cells or Leukocytes (WBC):

White blood cells are cells of the immune system involved in defending the body against both infectious disease and foreign materials. Five different and diverse types of leukocytes exist, but they are all produced and derived from a multipotent cell in the bone marrow known as a hematopoietic stem cell. They live for about 3 to 4 days in the average human body. Leukocytes are found throughout the body, including the blood and lymphatic system.

3.Platelets or Thrombocytes :

Platelets, or thrombocytes or yellow blood cells, are very small, irregularly shaped clear cell fragments (i.e. cells that do not have a nucleus containing DNA), 2–4 µm in diameter. The average lifespan of a platelet is normally just 5 to 9 days. Platelets are a natural source of growth factors.

Functions of blood:

Blood has three main three  functions:


Blood transports the following substances:

1.Gases, namely oxygen (O2) and carbon dioxide (CO2), between the lungs and rest of the body.

2.Nutrients from the digestive tract and storage sites to the rest of the body.

3.Waste products to be detoxified or removed by the liver and kidneys.

4.Hormones from the glands in which they are produced to their target cells.

5.Heat to the skin so as to help regulate body temperature.


Blood has several roles in inflammation:

1.Leukocytes, or white blood cells, destroy invading microorganisms and cancer cells.

2.Antibodies and other proteins destroy pathogenic substances.

3.Platelet factors initiate blood clotting and help minimise blood loss.


Blood helps regulate:

1.pH by interacting with acids and bases.

2.Water balance by transferring water to and from tissues.


Lymph is the fluid that circulates throughout the lymphatic system. The lymph is formed when the interstitial fluid (the fluid which lies in the interstices of all body tissues) is collected through lymph capillaries. It is then transported through lymph vessels to lymph nodes before emptying ultimately into the right or the left subclavian vein, where it mixes back with blood.

Function of Lymph:

1.Lymph acts as a "middle man" which transports oxygen, food materials, hormones, etc2.Body cells are kept moist by the lymph.

3.Lymph nodes produce lymphocytes. Lymph takes lymphocytes and antibodies from the lymph nodes to the blood.

4.It destroys the invading microorganisms and foreign particles in the lymph nodes.

5.It absorbs and transports fat and fat soluble vitamins from the intestine

6.It brings plasma portein macromolecules synthesized in the liver cells and hormones produced in the endocrine glands to the blood.



3.Muscular tissue:

Fig; a.Unstriped muscles, b. few fibres enlarged, c.Cardiac muscles

Muscle tissues are derived from the mesodermal layer of embryonic germ cells in a process known as myogenesis. There are three types of muscle, skeletal or striated, cardiac, and smooth. Muscle action can be classified as being either voluntary or involuntary. The muscular tissue is used for movement of arms or limbs for location. There are three kinds of muscles. they are;

a.Unstriated (unstriped or involunatory muscles):

1.These muscles are spindle-shaped tapering at both ends with numerous fine longitudinal myofibrils.

2.Each myofibril contains a single oval nucleus at the middle. There is no sarcolemma.

3.The fibre being bounded merely by its plasma membrane.

4.They exhibit slow but prolonged contraction. These muscles are not fatigued.

5.They are also called  as involuntary muscles.

b.Straiated(Striped or skeletal or voluntary muscles):

1.These muscles are long and cylindrical fibres with blunt ends.

2.Each fibre is bounded by an elastic sarcolemma and contains many acentric nuclei.

3.In the vertebrates these muscles are attached to the skeleton. So, they are called skeletal muscles.

4.These muscles fatigue or tried quickly.

5.They are found in body wall, limbs, tongue, pharynx, beginning of the oesophagus.

c.Cardiac muscles:

1.These muscles are only located in the heart wall.

2.These contract rhythmically but do not get fatigue.

3.They consist of cylindrical fibres interconnected by oblique bridges and forming a continuous contractile network.

4.The cardiac muscles are myogenic.

5.Structurally, these muscle form intermediate type wall having the properties of both striped and unstriped muscles.

4.Nervous tissues:

Nervous tissue form the nervous system of animals. It control and coordinates the body functions. It is ectodermal in origin. It consists of neurons, which have two very important basic properties, respectively, excitability and conductivity.


A neuron also known as a neurone  or nerve cell which is an electrically excitable cell that processes and transmits information through electrical and chemical signals.  These signals between neurons occur via synapses, specialized connections with other cells. Neurons can connect to each other to form neural networks. Neurons are the core components of the nervous system, which includes the brain, spinal cord which together comprise the central nervous system (CNS)–and the ganglia of the peripheral nervous system (PNS) . Specialized types of neurons include: sensory neurons which respond to touch, sound, light and all other stimuli affecting the cells of the sensory organs that then send signals to the spinal cord and brain, motor neurons that receive signals from the brain and spinal cord to cause muscle contractions and affect glandular outputs, and interneurons  which connect neurons to other neurons within the same region of the brain or spinal cord in neural networks.

                                   Fig. Structure of neurons


Types of nerve fibres:

A.On the basis of structure, nerve fibres are of two types;

1. myelinated or meduallated nerve fibres:

These fibres have myelin sheath. These are found in white matter of brain and spindal cord, cranial and spindal nerves.

2. Non- myelinated nerves:

These are fibres without myelin sheath. These are found in gray matter of brain and spinal cord.

B.On the basis of function of nerve impulses, they are of two types;

1.Afferent nerve fibres:

These conduct nerve impulses from sense organ to the CNS.

2.Efferent nerve fibres:

These conduct nerve impulses from CNS to the body organs. These are also called motor nerve fibres.

C.Based on the number of their processes, these are of three types;

1.Unipolar: These neuron have only one axon with dendrites.

2.Bipolar: These neuron have two processes take their origin from the cell body.

3.Multipolar: these neuron have many processes.

Neuroglia or glia cells:

Glial cells, sometimes called neuroglia or simply glia. They  are non-neuronal cells that maintain homeostasis, form myelin, and provide support and protection for neurons in the brain and peripheral nervous system.


1.To surround neurons and hold them in place

2.To supply nutrients  and oxygen to neurons

3.To insulate one neuron from another

4.Act as phagocytes and kill microorgains.

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