Definition of tissue , types of tissues and functions of the tissue
Definition of tissue
A group of cells having the same origin similar shape and specific or common generalized function is known as a tissue.
•Histology ------> study of tissue
Types of tissue
The tissue are different and are broadly classified into four types
1. Epithelial tissue
2. Connective tissue
3. Muscular tissue
4. Nervous tissue
1. Epithelial tissues
• Epithelial tissues form the covering or lining to the free surface of the body .
• They perform vital function like protection excretion, glandular secretion and absorption.
• The epithelial cells contain minimal extra cellular material but they are arranged on a basement membrane.
Epithelium is further classified as
• Simple epithelium
• compound epithelium
• Simple epithelium
It consists of a single layer of cells it is further divided into for types
• Simple Squamous epithelium
• Simple Cuboidal epithelium
• Simple Columnar epithelium
• Simple Ciliated epithelium
Squamous epithelium
It consists of a flat cells arrangement edge to edge as in a mosaic .this type of epithelium covers the alveoli of lungs pericardial pleural and peritoneal cavity .
Cuboidal epithelium
The cells are cubical. They are arranged basement membrane.
It is found in the distal convoluted tubules of the kidney.
Columnar epithelium
It consists of tall piller like cells arranged in basement membrane .
It is found in in lungs and ducts of glands .
Ciliated epithelium
The cells may be cuboid are columnar. But they are contain hair like structure called Cilia present in free border that is cells lining the trachea
Their function is to move articles are mucus in specific direction over the epithelium. They are mainly present in the the inner surface of hollow organs like bronchioles and fallopian tubes .
• Compound epithelium
It is also known as stratified epithelium
It consists of of several layers of cells. It is present in surfaces where there is considerable wear and tear.
Depending on the type of cells present stratified epithelium is further classified into
--> stratified squamous epithelium
--> stratified cuboidal epithelium
--> stratified columnar epithelium
2. CONNECTIVE TISSUE
Connective tissue most abundant and widely distributed in the body of complex animals.
They are named connective tissue because of their special function of linking and supporting other tissues of the body.
Connective tissue serve to connect or bind together different organs or different parts of body .
Connective tissues are classified as :
• Loose connective tissue or Areolar tissue
It is most widely distributed tissue in the body . It is loose irregular connective tissue.
It connects the skin to the underlying structures . Also it fills unoccupied spaces between organs .
It is found between muscles , blood vessels and nerves .
• Dense fibrous tissue
This tissue has compactly arranged fibres with greatly reduced interspace .
The cells are less in number than areolar tissue . This type of tissue is present in dermis of skin .
• Adipose tissue (fatty tissue )
It contains large rounded cells and cytoplasm is loaded with fat .
The nucleus of the cells is pushed towards the periphery e.g. subcutaneous tissue of skin.
• Cartilage
It has a tough , gelatinous and elastic matrix formed of chondrin .
The cells are more or less round and lie un groups of four embedded in the matrix .
• Bone
It is the hardest connective tissue. Bones contain high concentration of salt like calcium phosphate and calcium carbonate .
A bone generally consists of :
--> Periosteum is membrane of fibrous tissue covering the the surface of a bone .
--> Compact bone is a hard dance substance found below the periosteum .
--> Spongy bone is a spongy , porous tissue.It forms the interior of mature bone.
--> Bone marrow is a soft material which fills the hollow interior of a mature bone . It is of two types -
° Yellow bone marrow which is a fatty tissue
° Red bone marrow from which the cells of blood are developed .
3. MUSCULAR TISSUE
MYOLOGY : Study of muscles
Muscle is a tissue which has the power of contraction of muscles produces moments .
All muscle contain bundles of fibres which run in the same direction .
Muscles are classified into three types :
Skeletal muscle or Striated
It is voluntary in nature and under the control of will power. It forms the flesh of limbs and trunk. It contains and unbranched fibres called myofibrils .
These fibres are cylindrical in shape containing distinct striations and number of nuclei each fibre is surrounded by a thin membrane called sarcolemma .
Smooth muscle or non-striated
It is involuntary in nature because it is not controlled will . It is present internal organs like stomach , intestine and uterus .
It contains long , spindle shaped fibres with the central nucleus. The fibres are not striated and are not covered by any membrane but they are joined together by a loose connective tissue .
These muscles are controlled by autonomic nervous system .
Cardiac muscle
It is found only in the heart .It consists of short cylindrical and branched fibres.
The nucleus is centrally placed . The striations are vague .
The cardiac muscle is not controlled by will that is involuntary in nature . But it contracts automatically in a rhythmic manner.
4. NERVOUS TISSUE
NEUROLOGY : Study of nervous system
Neural tissue exerts the greatest control over the body's responsiveness to changing conditions. Neurons the unit of neural system are excitable cells .
The neuroglial cell which constitute the rest of the neural system protect and support neurons.
Nervous tissue is composed of three kinds of matter
- Gray matter which forms the nerve cell.
- White matter which forms the nerve fibres
- Neuroglia which is a supporting tissue it holds together and supports nerve cells and fibres .
NEURONE :
It is the unit with which the nervous system is composed of. It consists of nerve cell ,axon and dendrite.
Myelin sheath
It is the sheath which covers and protects the axon of some nerves. Nerves which contain this sheath are called as medullated nerves.
Nerves which do not contain this sheath are called as non-medullated nerves. The medullated nerves contain nuclei .
The nucleus lies in between the myelin sheath and outer covering called neurilemma.
Node of Ranveir is the interruption found in the myelin sheath at regular intervals.
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