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Animal Biology - Animal Histology

Animal Histology

Animal Tissues:

Internal structure of animal is made up cells. Cells aggregate and forms tissue. Animal tissues are classified into four types on the basis of their functions – Epithelial tissue, Connective tissue, Muscle tissue and Nervous tissue.

EPITHELIAL TISSUE

The covering and protective tissues in the animal body are epithelial tissues. It covers most organs and cavities within the body and forms a barrier to keep different body systems separate.
Example: Skin, Lining of the mouth, lining of blood vessels, lung alveoli and kidney tubules


Characteristics of epithelial tissue:

·  Tightly packed and form a continuous sheet.
·  Small amount of cementing material is present between them and almost no intercellular spaces.
·  It plays an important role in regulating the exchange of materials between the body and the external environment and also between different parts of the body.
·  Matrix is either absent or negligible
·  Number of cells are large

Depending on the structures that correlate with their unique functions, epithelial tissues are classified into Simple and stratified epithelium.


Simple Epithelium: Cells are arranged in a single layer and does not contain matrix.

·  Squamous: Thin and flat tissue and forms a delicate lining.  They are arranged closely and jointed by cement material. Example: Lining of blood vessels, heart and lymphatic tubes
 
·  Columnar: Cells are broad and nucleus is oval in shape and is locatd in the centre or towards the narrow end
  Example: innerlining of alimentary canal, cystic duct

·  Cuboidal: Cube shaped cells and provides mechanical support and helps in secretion and absorption.
  Example: Kidney tubules

·  Glandular: Tissue folds inward and forms multicellular gland and secretes substances at the epithelial surface.


Stratified Epithelium: Cells are arranged in a many layers and are capable of cell division. Regions which are exposed to greater wear and tear such as epidermis of skin and lining of rectum are made up of stratified epithelium.

CONNECTIVE TISSUE

Connective tissues are loosely packed tissues embedded in an intercellular matrix which may be jelly like, fluid, dense or rigid. The nature of matrix differs in concordance with the function of the particular connective tissue. It connects or binds the organs and acts as filling or packing between organs.

Characteristics of connective tissue:

·  Number of cells is less as compare to epithelial tissue
·  Connect or binds the organs
·  Act as filling material between the organs
·  Intracellular substance is high
·  Responsible for cell division of preexisting cells


Types of connective tissue:

  1. Areolar Connective Tissue: It is found between the skin and muscles, around blood vessels and nerves and in the bone marrow. It fills the space inside the organs, supports internal organs and helps in repair of tissues. It has dense matrix which consists of a network of fibers and an unorganized, homogeneous intercellular secretion. Fibers are white or yellow. White fibers are made up of collagen and nonelastic, whereas yellow fibers are made up of elastin and are elastic in nature.

  1. Adipose tissue: Tissue present below the skin and between internal organs which contains fat globules. Fat inside the globules acts as an insulator.

  1. Compact Bone: Bone is a connective tissue and forms the framework that supports the body. It is strong and nonflexible tissue and embedded in a hard matrix that is composed of calcium and phosphorus compounds.

  1. Ligaments: Tissue present between two bones and is very elastic and has considerable strength. It contains very little matrix.

  1. Tendons: Tissue that connects muscles to bones and is fibrous with great strength but limited flexibility.

  1. Blood cells: Blood is another type of connective tissue which contains fluid matrix called plasma. Plasma contains red blood cells (RBCs), white blood cells (WBCs), and platelets. It also contains proteins, salts and hormones. Blood flows and transports gases, digested food, hormones and waste materials to different parts of the body.

MUSCULAR TISSUE:

Tissue consists of elongated cells and responsible for movement in our body is called muscular tissue.

Elongated cells present in muscular tissue are called as muscle fiber. Muscle also contains special proteins called contractile proteins, which contract and relax to cause movement


Type of Muscle fibers:

  1. Striated muscle: It is also called as a voluntary muscle as it moves by conscious will. They are mostly attached to bones and help in body movement so also called as skeletal muscle. Under microscope it shows light and dark bands or striations when stained appropriately and hence called as striated muscle. The cells of this tissue are long, cylindrical, unbranched and multinucleate.

  1. Smooth muscle: Muscles that controls the movement of food in the alimentary canal or the contraction and relaxation of blood vessels are smooth muscle or involuntary muscle. The cells are long with pointed ends and Uninucleate. They are also called unstriated muscles. They are spindle-shaped.

  1. Cardiac muscle: Muscles of the heart show rhythmic contraction and relaxation throughout life and called cardiac muscles. They are cylindrical, branched and uninucleate. It is the occurrence of connecting structures called intercalary discs near terminal regions of muscle fibers. Intercalary disc connects adjacent fibers.

NERVOUS TISSUE:

Highly specialized tissue for transmitting stimulus very rapidly from one place to another within the body is called nervous tissue. Nerve impulse allows animals to move rapidly in response to stimuli. The brain, spinal cord and nerves are all examples of nervous tissue. The cells are called nerve cells or neurons.

A neuron consists of a cell body with a nucleus and cytoplasm, from which long thin hair like parts arise. Usually each neuron has a single long part called the axon and many short branched parts called dendrites. An individual nerve cell may be up to a meter long. Many nerve fibers found together by connective tissue make up a nerve.

Nervous tissue establishes communication between different parts of the body, through conduction of nerve impulses.



Self study:

Q-1: Match the following

A B
Epithelial tissue Act as a filling or packing between organs
Muscle tissue Provides protection by covering over the body
Nervous tissue Transmits the nerve impulses between different parts of body
Connective tissue Associated with the movement of organs and the body

Answer:

A B
Epithelial tissue Provides protection by covering over the body
Muscle tissue Associated with the movement of organs and the body
Nervous tissue Transmits the nerve impulses between different parts of body
Connective tissue Act as a filling or packing between organs


Q-2: Tissue for transmitting stimulus very rapidly from one place to another within the body is called …………..

  1. Muscle tissue
  2. Skeletal tissue
  3. Nervous tissue
  4. Connecting tissue

Answer: Tissue for transmitting stimulus very rapidly from one place to another within the body is called nervous tissue

Q-3: Tissue present between two bones is called ……………..



  1. Ligament
  2. Tendoms
  3. Blood
  4. Areolar

Answer: Ligament is the tissue which is present between two bones and is elastic in nature.

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