What is connective Tissue?
The unique characteristic of connective tissue is the occurrence of a variety of cells which are embedded in a large quantity of intercellular substance, called matrix. The connective tissue supports, protects and binds together other tissues. These tissues are mesodermal in basis, and form bones, tendons, ligaments and cartilage of the skeleton. Blood and lymph are other forms of connective tissue.
Connective Tissue Classification
Connective tissues are of three types on the basis of the nature of intercellular matrix. Those are
i) Connective tissue proper
ii) Skeletal tissue
iii) Vascular tissue.
Connective tissue proper
Connective tissue proper is characterized by the presence of soft matrix and has the following sub-types:
a) Areolar tissue
b) Adipose tissue
c) White fibrous tissue
Skeletal connective tissue
Skeletal tissue is characterized by a tough matrix and forms the supportive framework of the body, protects the vital organs and affords surfaces for the attachment of muscles. The two types of skeletal tissues are cartilage and bone.
The cartilage is a solid but semi-rigid and flexible connective tissue. The cells of cartilage are called chondrocytes. Three main types of cartilage are recognized on the basis of nature and percentage of fibers in the matrix :
a) Hyaline cartilage,
b) White fibro-cartilage
c) Yellow elastic cartilage.
Bone is a highly calcified, hard and rigid connective tissue and consists of none cells or osteocytes that are widely separated from one another by a considerable amount of intercellular substance. According to structure bones are of two types : compact bones and spongy bones.
Vascular connective tissue
The examples of vascular connective tissue are Blood and lymph. Both circulate in the body and are responsible for the transportation of materials from one place to another. Vascular connective tissue also plays an important role in the defense mechanism of the body. In contrast to other connective tissues, the intercellular substance (matrix) of blood is liquid, called plasma. The cellular components, known as corpuscles, float freely in plasma. Plasma is a slightly alkaline, somewhat viscous aqueous solution with a complex composition and forms about 30-35% of the total extra-cellular fluids (ECF).
Corpuscles are of three main types, those are:
iii) Blood platelets.
About 55% of the total volume of blood is plasma, most of the remaining part is made up of erythrocytes; and leucocytes and platelets account for less than 1% of the volume. There are about 5 million erythrocytes in one cubic millimeter of blood, but only 7,000 leucocytes in the same volume.
The size and shape of erythrocytes vary in different classes of animals. In mammals, they are non-nucleated (except camels and llama, where they are nucleated) circular discs, having a diameter of 7-8 µm and seem biconcave in side view. In mammals, erythrocytes are devoid of all cell organelles. Erythrocytes contain a red colored protein, called hemoglobin that plays a significant role in carrying oxygen from lungs to all tissues of the body.
Vascular connective tissue, Leucocytes are enormously important cells as they provide defense mechanism to the body against infections. Leucocytes are nucleated cells devoid of haemoglobin and contain various organelles. The two types of leucocytes have been recognized on the basis of the presence or absence of granules in their cytoplasm. Those are:
Depending on the staining characteristics of their granules, granulocytes are of the three types, viz. neutrophils, eosinophil, and basophils. In neutrophils, the nucleus is quite variable in shape and consists of several lobes. The granules of neutrophils stain lightly with both acidic and basic dyes. The nucleus of the eosinophil has two or three lobes that are joined by delicate strands. Its granules stain brightly with acid dyes and possess digestive enzymes. The nucleus of basophils is S-shaped. Its granules stain with basic dyes.
Agranulocytes are of the following two types, viz. lymphocytes and monocytes. Lymphocytes provide defense to the body against invasion of bacteria and other organisms. In contrast to granulocytes and monocytes, which directly attack invading organisms, lymphocytes destroy them by producing antibodies.
Vascular connective tissue, blood platelets are non-nucleated, biconvex, disc-like bodies and are concerned with the clotting of blood. Lymph is a transudate from blood and contains the same proteins as in plasma but in lesser amounts and in somewhat different proportions. It does not have any RBC, but lymphocytes are present in a large numbers. Lymph carries materials from the tissues into blood stream and destroys micro-organisms.