Tissue of Class 9
Animals, like plants are made up of different types of tissues which perform specific functions. For example, muscles contract and relax to bring about movement, blood carry substances (O2, CO2, food and waste materials), nerve cells respond to stimuli etc. Thus muscles, blood, nerves, etc are examples of tissues in our body.
Outline classification of Animal tissue:
The study of microscopic structure of tissues is called as Histology. Cells of a tissue are often held together by cell junctions.
- It occurs as a protective covering and consists of one or more layers of cells.
- The epithelium is not traversed by blood vessels.
- The epithelial tissue rests on non-cellular basement membrane.
- The cells are closely packed forming a continuous sheet and held together by intercellular junctions.
- The have small amount of cementing material between them and almost about no intercellular spaces. Thus, anything entering or leaving the body must cross at least one layer of epithelium. As a result, the permeability of the cells of various epithelia play an important role in regulating the exchange of materials between the body and the external medium and also between different parts of the body.
Types of epithelial tissue:
Based on cell layers and shape, epithelial tissues are further classified.
(a) Squamous Epithelium
Cells arranged end to end like tiles on a floor.
Cells are polygonal in surface view.
It forms the delicate lining of cavities (mouth, oesophagus, nose, pericardium, alveoli etc.) blood vessels and covering of the tongue and skin.
Epithelial cells are arranged in many layers (stratum) to prevent wear and tear in skin. This pattern is stratified squalors epithelium.
Squamous epithelium (a) Surface view (b) Vertical section.
(b) Cuboidal epithelium
They are cube like cells that fit closely, cells look like squares insection, but free surface appears hexagonal.
It is found in kidney tubules, thyroid vesicles & in glands (salivary glands, sweat glands).
It forms germinal epithelium of gonads (testes & ovaries)
It involves in absorption, excretion & secretion. It also provides mechanical support.
(i) Structure : It consists of single layer of pillar-like cells.
(ii) Occurrence : The columnar epithelium lines the stomach, intestine, gall bladder, etc
(d) Ciliated epithelium
- Structure : It consists of cuboidal or columnar cells that develops protoplasmic outgrowth called cilia on their free surfaces.
- Occurrence : Cuboidal ciliated epithelium lines certain parts of urinary tubules of the kidney. Columnar ciliated epithelium lines the nasal passage, oviducts, etc.
Ciliated columnar epithelium
This epithelium consists of columnar cells modified to secrete chemical sometimes a portion of the epithelial tissue bolds inward and a multicellular gland in formed. It lines the glands such as gastric glands, intestinal glands, etc.
Functions of Epithelial Tissue
- Squamous epithelium (both types) provides protection to underlying parts (organs) against mechanical injury, drying up, entry of germs, etc. It also helps in excretion, gaseous exchange, etc.
- Cuboidal epithelium helps in protection, mechanical support, absorption, excretion, etc.
- Columnar epithelium helps in absorption, secretion and protection. Columnar epithelium of intestine is meant for absorption of water and digested food.
- Ciliated epithelium helps in movement of mucus, urine, eggs, sperms, etc.
Muscles or muscle tissues consists of long cells. They are also called muscle fibres due to their elongated structure. The muscle cells are arranged parallely and contain special contractile protein which contract and relax in a definite direction. This brings about movement of body parts or limbs and locomotion of organism.
Types of Muscle Tissue
The muscle fibres are classified into three types.
(a) Striated Muscle or Skeletal Muscle: They are also called as voluntary muscles because these are under the control of one’s will. Muscle fibres or cells are multinucleated and unbranched. Each fibra enclosed by thin membrane which is called as sarcolemma.
Cytoplasm is called as sarcoplasm. These Muscles get tired & need rest.
Non striated muscles: They are involuntary muscles also called as smooth muscles. These muscle fibres are uninucleated & spindle shaped. They are not enclosed by membrane but many fibres are joined together in bundles. Such muscles are found in the walls of stomach, intestine, urinary bladder, bronchi, iris of eye etc. peristaltic movements in alimentary canal are brought about by smooth muscles.
Smooth muscle fibres
- They are so called because they are present only in the wall of the heart. They show striations.
- The fibres are short, cylindrical, branched and joined end to end to form a network.
- Each fibre is surrounded by sarcolemma and has a centrally located nucleus.
- Inter calated discs occur between the ends of fibres.
- Cardiac muscles are involuntary muscles and show rhythmic contraction and relaxation throughout life.
(ii) Occurrence : They are found in the wall of heart only.
Functions of Muscle Tissue:
- Striated muscles help in the movement of the body parts (arms, legs, neck) and locomotion.
- Unstriated muscles help in involuntary activities like passage of food through alimentary canal, flow of air through respiratory tract, flow of blood through the vessels, extrusive movements in urinary bladder, etc.
- Cardiac muscles bring about beating of heart and pumping of blood.
The name connective tissue suggests that it serves binding and joining of one tissue to another so that there is no interference between activities of different organs. The cells of connective tissue are living and slightly spaced, which in embedded in an intercellular non-living gel-like matrix.
Types of Connective Tissue:
Depending on the type of the matrix, jelly-like, dense (rigid) or fluid connective tissue is further classified.
(a) Connective Tissue Proper (Jelly-like matrix)
It is further divided.
(i) Areolar Tissue
- It is the most widely distributed connective tissue.
- It consists of jelly-like matrix, numerous fibres (white collagen fibres and yellow elastic fibres) and cells.
- This tissue fills spaces inside organs and is also found around blood vessels and nerves, between skin and muscles in bone marrow, etc.
Areolar connective tissue
(ii) Adipose Tissue
- This tissue consists of matrix packed with large, spherical fat cells (adipocytes) filled with fat globules.
- The matrix also contains macrophages, collagen and elastic fibres.
- Adipose tissue is found beneath the skin, in the covering of heart, kidney, etc.
(iii) White Fibrous Tissue
(iv) Yellow Elastic Tissue
Attachment of tendons and ligaments
(b) Skeletal Tissue (Dense or rigid matrix)
It is further classified into two types
- The hard matrix of bone is strengthened by fibres and hardened by calcium and phosphorus salts.
- Bone cells (osteocytes) are contained in lacunae which are arranged in concentric circles.
- The lacunae are traversed by nerves and blood vessels.
- Bones form the endoskeleton of vertebrates.
(a) T.S of long bone; (b) A bone cell
(c) Fluid or Vascular Tissue (fluid or liquid matrix)
It is further classified as
- It is the most important fluid connective tissue.
- The matrix of this tissue is called plasma which is a straw coloured fluid. The plasma contains 90% water and 10% of various organic and inorganic substances. The organic substances include proteins (albumin, globulin and fibrinogen), carbohydrates, lipids, etc.
- The blood has three types of cells.
- The Erythrocytes or Red blood corpuscles (RBC) are small biconcave cells without nucleus. They are packed with a transport protein called haemoglobin (red in colour) which carry O2 and CO2 to different parts of the body.
- The Leucocytes or White blood corpuscles (WBC) are round or irregular in shape. They possess lobed nucleus. They are colourless and may or may not have granules in their cytoplasm. There are five types of leucocytes-Eosinophil, Basophil, Neutrophil, Lymphocyte and Monocytes.
- The platelets are irregularly shaped, non-nucleated fragments of giant cells.
Human blood corpuscles (a) Erythrocytes (RBC); (b) Leucocytes (WBC); (c) Platelets
∙ Lymph is a colourless fluid similar in composition to blood except that it lacks RBC’s, proteins and contains less calcium and phosphorus. In lymph, WBCs are found in abundance.
The WBC’s exhibit amoeboid movement and the ones present in lymph can reach any part of the body and hence they form the defence system of the body.
Functions of connective Tissue:
- Connective Tissue Proper
- Areolar tissue supports internal organs and helps in repair of tissues.
- Adipose tissue stores fat, acts as an insulator.
- White fibrous tissue (tendons) and yellow elastic tissue (ligaments) serve to bind muscles to bones and bone to bone respectively.
- Skeletal Tissue
- Cartilage absorbs stresses, provides flexibility to the body parts and smoothens surface at joints.
- Bones anchors the muscles and provide levers for movement, support the body and for soft body parts and protect many delicate tissues and organs.
- Vascular Tissue
- (i) Blood
- Plasma serves the function of transport (nutrients, hormones, waste products, CO2, etc), regulates water-balance and body temperature.
- RBC helps in transport of O2.
- WBC acts as soldiers and scavengers.
- Platelets help in blood clotting.
- (ii) Lymph protects the body against infection and also transports nutrients.