Connective Tissue

Connective Tissue

It is one of the most abundant and widely distributed tissue. It provides structural frame work and gives support to different tissues forming organs. The components of the connective tissue are the intercellular substance known as the matrix, connective tissue cells and fibres. The matrix forms the main bulk of the connective tissue. The main function of the connective tissue is binding, supporting and packing together different organs of the body. It prevents the organs from getting displaced by body movements.

Connective tissue is classified as follows

i. Connective tissue proper (Areolar and Adipose tissue)

ii. Supportive connective tissue (Cartilage and Bone)

iii. Dense Connective tissue (Tendons and Ligaments)

iv. Fluid connective tissue (Blood and Lymph)

i. Connective tissue proper

Connective tissue proper consist of collagen bres, elastin bres and broblast cells.

a. Areolar tissue

It has cells and fibres loosely arranged in a semi fluid ground substance, matrix takes the form of fine threads crossing each other in every direction leaving small spaces called areolae. The matrix consists of collagen fibres, elastin fibres and fibroblast cells. It joins skin to muscles, fills space inside organs and is found around muscles, blood vessels and nerves. The matrix of this tissue plays an important role in diffusion of oxygen and nutrients from small blood vessels. It also helps in repair of tissues after injury and fixes skin to underlying muscles.

b. Adipose Tissue

Adipose tissue is the aggregation of fat cells or adipocytes and serves as fat reservoir. Each fat cell is a spherical or oval adipose cell and contains a large droplet of fat.

The fat cells are arranged into lobules separated by partitions of collagen and elastin fibres. They are found in subcutaneous tissue, between internal organs around the heart and kidneys. They keep the visceral organs in position and act as shock absorbers around the kidneys and eye balls. They also regulate the body temperature by acting as insulator.

ii. Supportive Connective Tissue

The supporting or skeletal connective tissues forms the endoskeleton of the vertebrate body. They support the body, protect various organs and help in locomotion. The supportive tissues include Cartilage and Bone.

a. Cartilage

They are soft, semi- rigid, flexible and are less vascular in nature. The matrix is composed of large cartilage cells called chondrocytes. These cells are present in fluid filled spaces known as lacunae.

Cartilage is present in the tip of the nose, external ear, end of long bones, trachea and larynx. It smoothens the surface at joints. It provides support and flexibility to the body parts.

b. Bone

It is solid, rigid and strong, non-flexible skeletal connective tissue. The matrix of the bone is rich in calcium salts and collagen fibres which gives the bone its strength. The matrix of the bone is in the form of concentric rings called lamellae. The fluid filled spaces present between the lamellae are called lacunae in which are present the bone cells called osteocytes that communicate with each other by a network of fine canals called canaliculi. The hollow cavities of spaces are called marrow cavities filled with bone marrow. They provide shape and structural framework to the body. Bones support and protect soft tissues and organs.

iii. Dense Connective Tissue

It is a fibrous connective tissue densely packed with fibres and fibroblasts. It is the principal component of tendons and ligaments.

a. Tendons

They are cord like, strong, structures that join skeletal muscles to bones. Tendons have great strength and limited flexibility. They consist of parallel bundles of collagen fibres, between which are present rows of fibroblasts.

b. Ligaments

They are highly elastic structures and have great strength which connect bones to bones. They contain very little matrix. They strengthen the joints and allow normal movement.

iv. Fluid connective tissue

The blood and the lymph are the fluid connective tissues which link different parts of the body. The cells of the connective tissue are loosely spaced and are embedded in an intercellular matrix.

a. Blood

Blood contains corpuscles which are red blood cells (erythrocytes), white blood cells (leucocytes) and platelets. In this fluid connective tissue, the blood cells move in a fluid matrix called plasma. The plasma contains inorganic salts and organic substances. It is a main circulating fluid that helps in the transport of substances.

Red blood corpuscles (Erythrocytes)

The red blood corpuscles are oval shaped, circular, biconcave disc-like and lack nucleus when mature (mammalian RBC). They contain a respiratory pigment called haemoglobin which is involved in the transport of oxygen to tissues.

White blood corpuscles (Leucocytes)

They are larger in size, contain distinct nucleus and are colourless. They are capable of amoeboid movement and play an important role in body’s defense mechanism. WBC’s are of two types

i. Granulocytes (with granules in the cytoplasm)

ii. Agranulocytes (without granules in the cytoplasm).

Granulocytes have irregular shaped nuclei and cytoplasmic granules. They include the neutrophils, basophils and eosinophils. Agranulocytes lack cytoplasmic granules and include the lymphocytes which have a spherical nucleus and the monocytes which have a large nucleus indented on one side. They engulf or destroy foreign bodies and neutralise their harmful effects.

Blood platelets

They are minute, anucleated, fragile fragments of giant bone marrow called mega karyocytes. They play an important role in blood clotting mechanism.

b. Lymph

Lymph is a colourless fluid filtered out of the blood capillaries. It consists of plasma and white blood cells. It mainly helps in the exchange of materials between blood and tissue fluids.