STUDY OF DIFFERENT KINDS OF ANIMAL TISSUES BY TEMPORARY MOUNT PREPARATIONS

Objectives
 To familiarize the students with the concept of tissues. To categorize the animal tissues based on structure and function. To understand the structure and functions of different kinds of animal tissues. To make the temporary preparations of animal tissues. To differentiate among the various kinds of tissues.

Introduction

All of you have learnt in your previous classes that cells are the building blocks of organisms, which comprise the body of all living organisms. These carry out all the necessary functions of the body and are thus, essential for the sustenance of an individual. In unicellular organisms, different parts of the same cell perform all the vital functions, but in multicellular organisms, the cells group together in a well organized manner to perform these functions.

The complexity and number of these cells increase with the advancement of the body organization. For example, the number of cells in simple multicellular organisms, like Hydra, Planaria, etc. may be only in thousands, whereas, the human body is composed of billions of cells to perform various functions. How do these billions of cells function together or co-ordinate with each other? In fact, the cells exhibit a division of labour. The cells undergo the process of differentiation and acquire a great variation in their shape, size, structure and function. The similar cells remain grouped together, function as a unit and perform a specific function, while different types of cells carry out different functions.

The groups of similar cells having identical origin and structure; and which perform a specific function are called tissues.

For example:

• Muscle cells form muscle tissue which causes movement of a body part.
• Nerve cells form nervous tissue responsible for the transmission of the messages.
• Blood cells and plasma collectively form another tissue, blood.

The tissues are further organized in a specific proportion and pattern to perform the specific function and form an organ. When two or more organs perform a common function by their interaction, they collectively form an organ system.

Thus, cells, tissues, organs and organ systems split the work in such a way that they exhibit a division of labour and contribute to the survival of the body as a whole. In this practical, you will prepare the temporary mounts of different kinds of animal tissues to study their structure and differentiate between them.

The term tissue was introduced by a French surgeon, Bichat (1771-1802).

A separate branch for the study of tissue was proposed by an Italian biologist, Marcello Malpighi (1628-1694).

The branch for the study of tissues was named as Histology by Mayer (1819-?)

ANIMAL TISSUES

You may be surprised to know that the complex body of multicellular animals is made up of only four basic types of tissues. Can you name them? These are as follows:

1.Epithelial Tissue: The cells of epithelial tissue cover surfaces, line blood vessels or are modified to form gonads. This tissue acts as a barrier and participates in absorption and secretion.

2.Connective Tissue: The cells of this tissue form cartilage, bone, blood, etc. This tissue participates in organization and maintenance of the structure of an individual.

3.Muscular Tissue: The muscle cells are contractile in nature and assist in movement.

4.Nervous Tissue: The cells of nervous tissue form brain, spinal cord, and nerves. It helps in communication within the body.

In this Practical, you will study each of these tissues by preparing temporary mounts. Before that, let us study about the structure and functions of each of these in brief.

EPITHELIAL TISSUE

Epithelial tissue popularly called epithelium exists as a continuous layer on the entire body surface of the animals. It also lines most of the closed cavities within the body and all the passages that lead to the exterior, such as the lining of mouth cavity, oesophagus, trachea, ureters, etc. As a result, each surface remains either in the contact with the air on the outer side or certain fluid present in the cavities.

Structure of Epithelium:

Epithelium is a continuous sheet of adherent cells. It is characterized by the presence of tightly-packed cells with very little or without any intercellular material. The cells of epithelium are bound at the base by a non-cellular basement membrane. It contains a special form of matrix protein (Collagen) and separates epithelium tissue from other tissues.

Functions of Epithelium:

a) Protection: Epithelium is mainly a protective tissue. It protects the underlying cells from the adverse environmental conditions such as desiccation, injury, exposure to chemical and pathogens. It also protects the hollow cavities and organs from the adverse effects of mechanical trauma and noxious substances.

b) Absorption: The epithelial lining of the alimentary canal helps in the absorption of different substances such as, water and nutrients.

c) Secretion: A few epithelial cells secrete a variety of substances, e.g. sweat, enzymes, saliva, hormones, etc.

d) Excretion: The epithelium present in the excretory system helps in the elimination of waste products.

e) Reproduction: The epithelial tissue lining the reproductive organs secretes gametes and help in reproduction.

f) Sensation: Some epithelial cells aid in the nerve transmission and help in the receipt of stimulus, such as the cells of taste buds, olfactory epithelium, and the ear.

Classification of Epithelium:

The epithelial tissue comprises of either only one layer of cells (Simple Epithelium) or two or more than two layers (Stratified Epithelium). Further, epithelium can be categorized into different types based on the shape and function of cells. These are as follows:

a)Squamous Epithelium

It is made up of a thin layer of flat cells with often irregular, but sometimes smooth margins. Each cell has a centrally located spherical nucleus. Squamous epithelium lines the mouth cavity, blood vessels, heart, nose, pleural cavity, etc. It protects the underlying parts, facilitates the movement of organs, forms a selectively permeable surface for filtration and secretes biologically active molecules.

b)Cuboidal Epithelium

Cuboidal epithelium consists of cube-like cells with centrally located nucleus but appear polygonal in section. It forms the inner lining of kidney tubules, ducts of sweat glands, alveoli of lungs, thyroid vesicles and germinal layer of ovary. Cuboidal epithelium is mainly a mechanical tissue and helps in absorption, excretion and secretion.

c)Columnar Epithelium

The columnar epithelium consists of tall, pillar-like cells (taller than broad). The cells have oval and basal nuclei. The epithelium often has a prominent striated border with microvilli present at the free end of the cells which increase its surface area. Columnar epithelium forms the lining of stomach, intestine, gall bladder and oviducts. It helps in the absorption and secretion of substances across the epithelial barrier.

d)Glandular Epithelium

Glandular epithelium consists of columnar to cuboidal cells specialized for secretory functions. It may consist of isolated cells (unicellular glands) or a cluster of cells (multicellular glands). The glands may release their secretions through ducts (exocrine) or without any ducts (endocrine). Glandular epithelial cells are present in the pancreas, adrenal, thyroid, sebaceous glands, salivary glands and mammary glands, etc.

e)Ciliated Epithelium

Ciliated epithelium comprises cuboidal or columnar cells bearing numerous cilia or protoplasmic threads on their free surface. This epithelium is mainly present in the fallopian tubes, and organs of respiratory tract, such as trachea, bronchi, and bronchioles. The cilia help in the movement of particles or mucus over the epithelial surface. For example, they guide the released ova in the oviducts to the uterus and move mucus over the surface in the respiratory tract.

CONNECTIVE TISSUE

Connective tissue, also known as supportive tissue, is the most abundant and widely distributed tissue in the body of animals forming 30% of the body.

Structure of Connective Tissue:

Unlike the epithelial tissue, it possesses only a few cells, such as fibroblasts, plasma cells, lymphocytes, macrophages, adipocytes and mast cells. These cells are embedded in a considerable amount of intercellular matrix containing three types of fibres; collagen, elastic and reticular fibres.

Functions of Connective Tissue:

a) Connective tissue serves to connect and supports different tissues or organs of the body so that they function as a single integrated unit. b) It forms a packing material around the organs to prevent their displacement by the body movements.

Classification of Connective Tissue:

Connective tissue can be of different types based on the occurrence of cell types and the nature of matrix. These are as follows:

a) Loose or Areolar Connective Tissue

Areolar tissue is the most common tissue containing all the three fibres in the matrix. The cells present in most numerous numbers are macrophages and fibroblasts. It fills spaces between the tissues, provides mechanical support to them and surrounds blood vessels. It also provides defense with the help of macrophages and participates in the tissue repair with the help of macrophages.

b) Dense Connective Tissue

Dense connective tissue contains fewer cells and predominantly collagen fibres. It is found in the capsule of spleen, testes, within blood vessels, etc. certain type of dense tissue forms tendons and ligaments in the body. Tendons are fibrous and inelastic tissues which attach muscles to bones, while ligaments attach two bones with each other and are flexible in nature.

c) Adipose Connective Tissue

Adipose tissue is dominated by adipocytes or fat cells filled with fat droplets. The intercellular matrix contains collagen and elastic fibres. This tissue is mainly found beneath the skin, around the kidneys and adrenals, in the bone marrow, cervical regions and axillary regions. It is the largest repository of energy and serves as a fat reservoir. It also shapes the body surface, acts as a shock absorber, fills spaces and maintains body heat.

In a man of normal weight, adipose tissue represents 15-20% of the body weight. In a woman of normal weight, it forms 20-25% of the body weight.

d) Skeletal Connective Tissue

Skeletal connective tissue forms the endoskeleton of the body and provides mechanical support. Based on the flexibility, it can exist as flexible cartilage or hard and rigid bone. Cartilage, unlike bone, does not have any blood or nerve supply. Cartilage consists of chondrocytes embedded in the lacunae (cavities) in the matrix. Matrix is hard due to the deposition of inorganic salts of calcium. Depending on the types of fibres present in the matrix, cartilage can be hyaline, fibrous or elastic. Cartilage is present in the surfaces of movable joints, wall of respiratory tract, ear pinna, etc. Cartilage provides flexibility to the tissues, facilitates bone movements, and gives mechanical support. Bone comprises osteocytes, and calcified matrix containing salts of calcium, magnesium and ossein protein. Bone cells are arranged in concentric layers around the lacunae, forming bone lamellae. The lamellae have small channels called Haversian canals which communicate with a large central bone cavity known as bone marrow. Bones form the skeleton of the body, support vital organs, form blood cells, and help in body movements.

e) Fluid Connective Tissue

It is a vascular tissue which helps in the transport of nutrients, respiratory gases, wastes, etc. within the body. It includes blood and lymph. Can you name the vascular tissues of the plants? Blood is the chief fluid connective tissue consisting of plasma (55%) and blood cells (45%). Plasma consists of 90% water and 10% inorganic salts, proteins and other nutrients. Blood cells are of three kinds-erythrocytes (red blood cells/RBC), leucocytes (white blood cells/WBC) and thrombocytes (Platelets). RBCs are enucleated biconcave discs, contain haemoglobin (Hb), are red in colour and help in the transport of oxygen to the body cells. WBCs are amoeboid, colourless, lack Hb and are nucleated. These are phagocytic in functions and protect the body against foreign organisms. Platelets are enucleated, colourless fragmentations of the large cells. They help in blood coagulation and help in wound healing. Lymph is a straw-coloured fluid. It has similar composition like that of blood except that it lacks RBCs and large protein molecules. The chief cellular component of the lymph is lymphocytes which are responsible for the immune response in the body.

Occurrence of blood cells in the blood

S. No. Blood cell Occurrence 1. Erythrocytes 4.5-5.0 Million/mm3 2.

    a)
b)
c)
d)
e)


Leucocytes Neutrophils Lymphocytes Eosinophils Basophils Monocytes

6-8 Thousands/mm3 0-1% 1-5% 20-30% 2-5% 60-68% 3. Thrombocytes 2-4 Lakhs/mm3

MUSCULAR TISSUE

Muscles constitute the ‘flesh’ of the body. These are contractile in nature and cause the movement of the body by contraction and expansion.

Structure of the Muscle Tissue:

Muscle tissue is made up of long, cylindrical fibres, called muscle cells. These are held together by connective tissue and contain contractile proteins, actin and myosin. The muscle fibres are present in bundles and may be nucleated or lack nucleus completely.

Function of the Muscle Tissue:

The muscles, as you learnt just now, are responsible for the contraction and expansion of the organs, body, etc.

a) All the voluntary movements of the body, such as walking, running, picking things, talking etc. take place because of the muscle contraction and expansion only.

b) Not only this, muscle tissues also help in carrying out the involuntary functions such as, vision, respiration, ingestion, micturition, pumping of blood, etc.

The list is endless. Try to find out the other functions of muscle tissue and prepare a list. Categorize the functions into voluntary and involuntary functions.

Classification of the Muscle Tissue:

The muscle cells can be three types, based on their structure, function and location.

a)Skeletal Muscles

Skeletal muscles are named so because they join two bones and help in movement of the body. They have been assigned other names also, which are:

(i)Striated Muscles, because each fibre possesses alternate dark and light bands, which give them striated appearance.

(ii)Voluntary Muscles, because they work at our will.

Skeletal muscle fibres are cylindrical, elongated, non-tapering and multinucleated. These do not branch and run parallel to one another longitudinally. These provide force for the voluntary movements and are thus, present in all those body parts which we can move at our will.

b)Smooth Muscles

Smooth muscles are elongated, spindle-shaped and have non-tapering ends. These have a single nucleus located centrally in each fibre. Smooth muscles are also called as

(i)Unstriated Muscles, because they do not exhibit any bands or striations. What are these bands? Do you know?

(ii)Involuntary Muscles, because they can not work at our will and are thus, not under our control.

(iii) Visceral Muscles, as they are present in all visceral organs, except heart.

Smooth muscles are responsible for peristalsis in the GI tract, emptying of bladder, child birth, bile secretion, and the amount of light entering our eyes, etc. Find out more functions and write down in your notebook.

c)Cardiac Muscles

Cardiac muscles are confined to only heart and thus, called so. Cardiac Muscles are similar to cardiac muscles in structure and; in functions they are similar to smooth muscles.

Like skeletal muscles, cardiac muscles are striated, cylindrical, non-tapering. However, unlike them, their fibres are small, branched and uninucleated. In addition to the normal striations, cardiac muscle cells have densely stained bands called intercalated discs. These connect the fibres and permit to contract as a unit. Consequently, if one cell receives a signal to contract, its neighbouring cells also contract.

Cardiac muscles are involuntary in functions like smooth muscles. They exhibit rapid and characteristic rhythmic contractions and work continuously without taking any rest.

Enumerate at least six differences between three types of muscle fibres, you studied in the above section.

NERVOUS TISSUE

Nervous tissue is a highly specialized tissue which consists of basic units, called nerve cells or neurons.

Structure of a Neuron:

A neuron consists of three parts; cyton, dendrites and axon.

a) Cyton or cell body contains cytoplasm, a central nucleus and certain characteristic particles, called Nissl’s Granules. Is there any significance of these particles?

b) Dendrites are short and branched processes that arise from cyton.

c) Axon is a single long fibre covered by a delicate sheath termed as neurilemma and branches terminally into short branches, axon terminals. A few axons are covered by a white, fatty myelin sheath interrupted at intervals by constrictions, termed Nodes of Ranvier.

Functions of Neurons:

The neurons are concentrated in brain and spinal cord, from where 43 pairs of nerves arise. Out of these, 12 pair of nerves arises from brain and are called cranial nerves while the remaining originate from spinal cord and are thus, called spinal nerves. The neurons are specialized for receiving and transmitting impulses. The impulses are received by dendrites which carry them towards cyton, which further transmits them to the axon and the axon terminals. The axon terminals of each neuron communicate to the dendrite of another neuron at synapse where they release neurotransmitters from their knob-like ends. Acetylcholine is one of such neurotransmitters.

Classification of Neurons:

a)Based on Functions

(i) Afferent or Sensory Neurons: These are located outside the CNS and carry information from tissues and organs to it.

(ii) Efferent or Motor Neurons: They are also located mostly outside the CNS and carry the information from CNS to the effector cells.

(iii) Interneurons or Association Neurons: These lie entirely in the CNS and connect afferent and efferent neurons.

b)Based on Structure

(i) Unipolar Neurons: These are without dendrites and have a very short, single process which is divided into proximal and distal fibres.

(ii) Bipolar Neurons: These have two processes, one axon and one dendrite. They function as receptor cells in the sense organs.

(iii) Multipolar Neurons: These are the typical neurons with a long axon and two or more branched dendrites.

In this Practical, you will prepare a temporary mount of one of each kind of tissues.

Epithelial tissue: Squamous Epithelium

Connective Tissue: Blood

Muscular Tissue: Skeletal Muscle

Nervous Tissue: Neurons

EVALUATE YOURSELF

Q1. Why do the cells exhibit diversity in shapes and sizes?

Q2. Categorize the animal tissues based on their structures and functions.

Q3. Name the animal tissue found:

a) between a muscle and a bone.

b) at the surface of human skin.

c) in the human heart.

d) in the calf and arms.

e) in the stomach wall.

f) in adrenals and thyroid.

Q4. What is the significance of microvilli present at the surface of ciliated epithelium?

Q5. Name the different kinds of cells present in the connective tissue.

Q6. Differentiate between bone and cartilage.

Q7. What are the different kinds of muscle cells present in human beings? Tabulate their differences and draw the diagrams.

Q8. How is connective tissue responsible for providing immunity to our body?

Q9. Where will you find the following?

a) Areolar connective tissue

b) Ligaments

c) Ciliated epithelium

d) Smooth muscles

e) Cartilage

Q10. What would happen, if our limbs had only smooth muscles?

Q11. How does a neuron transmit message to another neuron?

Q12. How many pairs of nerves originate from the spinal cord?

Q13. Write one function of the following.

a) Cuboidal epithelium

b) Lymph

c) Dense Connective tissue

e) Chondrocytes

Q14. Categorize the neurons based on their functions.

EXPERIMENT 1: TO PREPARE A TEMPORARY MOUNT OF SQUAMOUS EPITHELIUM FROM HUMAN CHEEK CELLS

REQUIREMENTS

Chemicals: Methylene Blue, Glycerin Glassware: Glass slides, Cover slips Equipments: Compound Microscope Miscellaneous: Needle, Tooth pick, Blotting paper, Distilled Water

METHODOLOGY

1.Wash your mouth cavity with clean water. 2.Take a clean tooth pick and scrape the inner side of your cheek with the blunt end softly. Take care not to hurt yourself. 3.Place the scraped material on a clean and dry glass slide in a drop of water. 4.Spread the material with the help of needle. 5.Pour 2-3 drops of methylene blue on the material and leave it undisturbed for a few minutes. 6.Wash the material with distilled water and blot extra water and glycerin. 7.Put a few drops of glycerin and cover by a cover slip. Take care to avoid the entry of any air bubbles in the material. 8.Remove extra glycerin with the help of blotting paper. 9.Observe the slide under the low power and then high powers of the compound microscope.

OBSERVATIONS

The cheek cells are squamous in shape with irregular outlines. The cytoplasm of the cell is stained light blue. Each cell has a distinct spherical nucleus present within the cytoplasm, which is stained deep blue.

INFERENCE

The inner lining of the human cheek is made up of squamous epithelium, which protects the underlying parts from the mechanical injury and the presence of harmful chemicals.

PRECAUTIONS

1. Scrap the inner side of your cheek with the blunt end of tooth pick.

 2. Spread the material evenly.
3. Do not over-stain the material.
4. Avoid the entry of any air bubbles in the mounted material.


TROUBLE SHOOTERS

If you obtain very dark stain, keep the material in stain for lesser time and de-stain your slide by washing the material thoroughly with water, taking care that the material does not flow with the water. However, if you obtain very light stain, place the material in stain for more time.

 Work in progress, expect frequent changes. Help and feedback is welcome. See discussion page.