Animal Tissues

On the basis of the functions they perform, there are four different types of animal tissues. They are:

1. Epithelial Tissue

2. Connective Tissue

3. Muscular Tissue

4. Nervous Tissue

Epithelial Tissue

• Epithelial tissues provide the covering and protection for the organs and cavities of the animal body. It forms the outermost layer of the body. Anything that enters or leaves the body must cross this layer of tissues.

• The epithelium also acts as a barrier to keep different body systems separate.

• There is a basement membrane, an extracellular fibrous membrane between the epithelium and the underlying tissues.

• These are found in the skin, the lining of the mouth, and the lining of blood vessels, lung alveoli, and kidney tubules.

Characteristics of Epithelial Cells

• They are tightly packed to form a continuous layer.

• There is a basement membrane to separate the epithelial tissue from the underlying tissue.

• There is a small amount of cementing material between the cells, and there are no intercellular spaces.

• They are permeable to control the exchange of materials between the body and its surroundings and within the body.

Types of Epithelial Tissues

There are different types of epithelia in correlation with their unique functions. They show structural differences.

Type	Characteristics	Location
Squamous	Very thin and flat to form a soft lining. These are selectively permeable for transportation. Squamous cells are arranged in layers to prevent wear and tear. Multilayered squamous tissues are called stratified squamous.	Skin, linings of blood vessels, lung alveoli, mouth, esophagus, etc.
Columnar	It is column-shaped. It performs the movement of materials across the epithelial barrier. Columnar epithelium with cilia is called ciliated columnar epithelium. Cilia are hair-like projections on the outer surfaces of epithelial cells that can move and thus push the mucus to clear it.	The respiratory tract, the inner lining of the intestine, etc.
Cuboidal	Cube-shaped cells. It provides mechanical support. It performs absorption and secretion.	Forms the lining of kidney tubules and ducts of salivary glands.

Glandular Epithelium

Sometimes, a portion of epithelial tissue folds inward to form multicellular glands. These are called glandular epithelium. They can secrete substances at the epithelial surface.

Connective Tissue

In connective tissue, cells are loosely spaced and embedded in an intercellular matrix. The matrix may be jelly-like, fluid, dense, or rigid. The function of particular connective tissue is related to the nature of its matrix. Connective tissues are of different types based on their structure and function:

Type of connective tissues	Functions
Blood	It has a fluid matrix called plasma. Plasma contains proteins, salts, and hormones. It contains 90-92% of water. Red Blood Cells (RBC), White Blood Cells (WBC), and Platelets are found in plasma. Blood flows through all parts of our body. It helps in the transportation of respiratory gases, digested food, hormones, and waste materials to different parts of the body.
Bone	It is strong and non-flexible tissue in the body.  It anchors the muscles. It supports and protects the main organs of the body. It cannot be bent. Bone cells are embedded in a hard matrix that is composed of calcium and phosphorus compounds.
Ligaments	These are tough fibrous tissue that connects bones to each other. These are very elastic with considerable strength. It contains very little matrix.
Tendons	These are fibrous connective tissue with less flexibility and greater strength. These connect muscles to bones.
Cartilage	These have widely spaced cells. This solid matrix is composed of proteins and sugars. These are smooth and more flexible than bones. These smoothen the bone surfaces at joints. Found at joint tips and in ears, nose, trachea, and larynx. These can be bent.
Adipose Tissue	Fats are stored in this tissue. Found below the skin and between internal organs. These cells are filled with fat globules. It acts as an insulator as it stores fat.
Areolar Connective Tissue	It is found between the skin and muscles, around nerves and blood vessels, in the bone marrow, etc. Space between the organs is filled with it. It supports internal organs. It helps in the repair of tissues.

 

 

Activity

Take a drop of blood on a slide and observe different cells present in it under a microscope.

  1. Red Blood Cells (RBCs)

  2. White Blood Cells (WBCs)

  3. Platelets

Muscular Tissue

• Muscular tissue is responsible for movement in our body.

• It consists of elongated cells, also called muscle fibers.

• Voluntary muscles are muscles that can be moved according to conscious will.

• Involuntary muscles are muscles that cannot be moved according to our will.

• Muscles contain contractile proteins, which contract and relax, causing movement.

• Muscles can be classified into three categories: skeletal, smooth, and cardiac

Type of muscle and location	Cell characteristics	Nature of functioning
Skeletal muscles are attached to bones. Example: Limbs	Fibers are long cylindrical, unbranched, and multinucleate. Alternate light and dark bands or striations. Also called striated muscles.	Voluntary, i.e., can be moved according to our will. Enables movement at joints. Contracts and relaxes rapidly. Stimulated by the nervous system.
Seen in the wall of hollow organs, vessels, and respiratory passageways. Examples: The alimentary canal, blood vessels, the iris of the eye, ureters, bronchi, etc.	Muscle cells are long with pointed ends (spindle-shaped) and uninucleated. No dark and light bands. Also called unstriated muscles	Involuntary, i.e., cannot be moved according to our will. Produces peristalsis Contracts and relaxes slowly. May sustain contraction.
Seen in the wall of the heart.	Muscle cells are cylindrical, branched, and uninucleated. Intercalated discs between cells. Striated.	Involuntary, i.e., cannot be moved according to our will. Pumps blood out of the heart. Self-excitatory but influenced by the nervous system and hormones. Rhythmic contraction and relaxation.

Compare the structures of different types of muscular tissues. Note down their shape, number of nuclei, and position within the cell in the table given below:

Nervous Tissue

The cells of the nervous tissue are called nerve cells or neurons. A neuron is the basic building block of the nervous system. Neurons are highly specialized to respond to stimuli and transmit information throughout the body. Nervous tissue is found in the brain, spinal cord, and nerves. Many nerve fibers bound by connective tissue make up a nerve. The signal that passes along the nerve fiber is called a nerve impulse. Nerve impulses allow us to move our muscles as and when we want to. The functional combination of nerve and muscle tissue makes organs move rapidly in response to stimuli.

Structure of Neuron

• The length of each neuron may be up to one meter long.

• It consists of a cell body in which the nucleus and cytoplasm are found.

• From the cell body, lengthy, thin, hair-like processes arise. These are called dendrites.

• It has a single long part called an axon.

• Axons are protected by a protective covering called the myelin sheath.

• Axon splits into branches. Each branch ends with a swelling called a nerve terminal.

• Nerve terminals, or axon terminals, connect the neuron to the target cells.

• Neurons receive impulses through dendrites. It passes through the axon and reaches the axon terminal, which in turn transmits the impulse to the target cells.

• They communicate information in both chemical and electrical forms.

Summary

• Tissue is a group of cells similar in structure that perform a specific function.

• There are two main types of plant tissues: meristematic and permanent.

• The dividing tissue that is responsible for the growth of plants is known as meristematic tissue.

• Depending on the region where they are present, meristematic tissues are classified as apical, lateral, and intercalary.

• Meristematic tissues take on a specific role and lose the ability to divide and form permanent tissue.

• Permanent tissues are classified as simple and complex tissues.

• Simple, permanent tissue is made up of only one type of cell.

• Complex, permanent tissue is made up of more than one type of cell.

• The entire surface of a plant has a protective outer covering called the epidermis.

• Small pores in the epidermis of a leaf are called stomata and are enclosed by guard cells.

• Parenchyma, collenchyma, and sclerenchyma are three types of simple tissues.

• Xylem and Phloem are two types of complex tissues.

• The xylem consists of tracheids, vessels, xylem parenchyma, and xylem fibers.

• The phloem is made up of sieve cells, sieve tubes, companion cells, phloem fibers, and phloem parenchyma.

• On the basis of the functions they perform, the different types of animal tissues include epithelial tissue, connective tissue, muscular tissue, and nervous tissue.

• Depending on shape and function, epithelial tissue is classified as squamous, cuboidal, columnar, ciliated, and glandular.

• The different types of connective tissues in our body include blood, bone, tendon, ligament, cartilage, areolar tissue, and adipose tissue.

• The three types of muscle tissues are striated, unstriated, and cardiac.

• Nervous tissue is made of neurons that receive and conduct impulses.

• A neuron consists of a cell body, an axon, and a dendrite.

  

Frequently Asked Questions

Q1: How many types of animal tissues are there?

Ans: Animal tissues can be categorized into four main types: epithelial tissue, connective tissue, muscle tissue, and nervous tissue.

Q2: What is epithelial tissue?

Ans: Epithelial tissue covers the surfaces of the body, both internal and external. It forms protective barriers, lines organs, and facilitates the exchange of substances. Examples include skin, the lining of the digestive tract, and the inner surfaces of blood vessels.

Q3: What is connective tissue?

Ans: Connective tissue supports and connects different structures in the body. It includes various types such as bone tissue, cartilage, adipose tissue (fat), and blood. Connective tissue provides structural support, protection, and the transportation of nutrients.

Q4: What is muscle tissue?

Ans: Muscle tissue is responsible for movement. There are three types: skeletal muscle (voluntary movement), smooth muscle (involuntary movement of internal organs), and cardiac muscle (involuntary movement of the heart).

Q5: What is nervous tissue?

Ans: Nervous tissue is involved in communication and coordination within the body. It consists of neurons, which transmit electrical signals, and glial cells, which support and protect neurons. The nervous tissue forms the basis of the nervous system.