Connective Tissue | Components, Function, Types

As the name implies, serves a “connecting” function. It supports and binds other tissues. Unlike epithelial tissue, connective tissue typically has cells scattered throughout the matrix. Connective tissue is one of four types in traditional classifications. It is mesodermal in origin and includes three basic components.

Definition: The collection of connective cells that maintain the body’s shape and promote internal cohesion is known as connective tissue. The connective tissues are made up of a variety of fibrous tissues, including bone, ligaments, tendons, cartilage, and adipose (fat) tissue, as well as the more specialized and well-known fibrous tissues.

Components of Connective Tissue

1. Cells

Cells are the living components of connective tissue having large intercellular spaces. These are mesodermal in origin and are of many kinds.

• Fibroblasts: They are spindle shaped, flattened cells, with long protoplasmic extensions. They have an oval nucleus. They produce fibers.
• Microphagous or Histocytes: They are large amoeboid cells with a kidney shaped nucleus. They are polymorphic in nature. They are polymorphic in nature. They engulf dead cells, bacteria or other foreign particles of tissue.
• Mast Cells: They are rounded or oval shaped cells with a small oval nucleus. These have granular cytoplasm. These secrete the chemicals heparin, histamine and serotonin. Heparin prevents clotting in the injured blood vessels. Histamine prevents the allergic and inflammatory reactions. Serotonin is a vasoconstrictor, steps the bleeding and raises blood pressure in blood vessels. It is produced by blood platelets.
• Fat cells: These are found scattered in cytoplasm. Each cell with a large droplet of lipid.

2. Fibres

They are found in a matrix scattered between the cells. They are secreted by fibroblast cells. They are of many kinds. There are proteins, non-living, and form the extracellular material. Fluid connective tissue i.e. blood devoid of fibres. The fibres are of three types; white fibres; yellow fibres and reticular fibres.

• White fibres: The white fibres are formed by a protein called collagen. These are abundantly found in the matrix of connective tissue. Usually, the white fibres are found in the matrix of connective tissue. Usually, the white fibres are found in bundles called fascia. They are flexible but inelastic and unbranched. It provides tenacity to the tissue.
• Yellow Fibres: The yellow fibres are formed by a protein, elastin. They are fewer in number and thicker than white fibres. They are found singly. They are flexible, elastic, and branched. These provide elasticity to the tissue.
• Reticular Fibres: The reticular fibres are formed by a protein reticulum. They are branched, inelastic and found as singly. They are found in very few in number.

3. Matrix

The ground substance or matrix is an amorphous, transparent, jelly, or solid structure. It mainly contains glycol-proteins and glycol-amino glycans, secreted by mast cells.

Functions of Connective Tissue

1. It joins various tissues together like skin with muscles and muscles ( muscular tissue ) with bone. So, also called binding tissue.
2. It forms various sheaths around the various organs, separating them, to prevent interference with each other, so it is a kind of packaging tissue.
3. The areolar tissue protects the body against wounds and infection. The microphagous cells of connective tissue ingest bacteria and dead cells to protect and clean the body.
4. The haemopoietic tissue produces the fluid connective tissue i.e. blood.
5. The adipose tissue stores the fat and insulate the body against heat loss. It also forms a cushion-like pad around some organs like eyeballs and kidneys as a shock-absorbing coat.
6. The supportive connective tissue forms a framework of the body, gives both strength and proper shape to the body.
7. The fluid connective tissue namely, blood and lymph carry materials from one part to another in the body. The lymphatic tissue helps the body to build immune by producing antibodies.

Types of Connective Tissue

On the basis of structure and function, the connective tissue is of three types and each type is further divided into many sub-types.

1. Proper Connective

Connective tissue proper is made up of a soft matrix which is of various types made from different tissues. It consists of jelly-like substances containing collagen fibres or yellow elastic fibres or both, together with the cells. These fibres are formed by fibroblasts.

On the basis of softness, rigidity, and degree of toughness, connective tissue proper is divided into loose and dense connective tissue.

Types of Proper Connective Tissue

1. Loose Connective Tissue Proper

Areolar tissue, or loose connective tissue (LCT), is a type of connective tissue. This organism’s cellular composition is extraordinarily diverse and rich in terms of diversity. In addition to the ground substance, the ECM consists of two primary types of protein fibers: elastic and reticular.

a. Areolar Tissue

Areolar tissue is the simplest and most widely distributed connective tissue. It consists of a jelly-like soft matrix having fibres and connective tissue cells. Fibres and other cells are:

• White Collagen Fibres ( made of collagen protein)
• Yellow Elastic Fibres ( made fo elastin protein)
• Fibrocytes : These are large flat cells, form white and yellow fibres
• Macrophages: These are irregular shaped cells with granules. They are actively phagocytic. i.e. engulfing bacteria and other foreign bodies.
• Mast cells: They produce heparin and histamine. The heparin prevents coagulation of plasma.

Functions of Areolar Tissue

• Acts as supporting and packing tissue
• Helps in combating foreign toxins

b. Adipose (Fat) Tissue

Adipose tissue is the modified areolar tissue. It consists of a large number of fat cells or adipocytes. Fibers are less absent. The fat cells are founded of polygonal with a thin layer of cytoplasm. The nucleus lies at one side, this tissue is found below the skin, heart, kidney, and eyeball.

Functions of Adipose Tissue

• Serves as an insulating layer (regulate body temperature) in mammals.
• Serves as a fat reservoir
• Acts as cushion as in the orbits or eye sockets, so that it prevents eye from injury.

2. Dense Connective Tissue Proper

Dense connective tissue is one that has fibers as the primary matrix element and is also referred to as dense fibrous tissue. A majority of the fibers are made up of type I collagen. Collagen fibers are sandwiched between rows of fibroblasts, the cells that produce the fibers. Tendons and ligaments, which are both made of dense connective tissue, are strong, rope-like structures.

Ligaments and tendons hold bones and muscles together at joints. Tendons contain fewer elastic fibers and are less flexible than ligaments. The lowest layers of the skin (dermis) are likewise made up of dense connective tissue, which is arranged in sheets.

Types Of Dense Connective Tissue

a. White Fibrous Tissue

It is a modified areolar tissue and consists of thickly packed white collagen fibres. These fibres are very tough and non-elastic. White fibres may run parallel to one another to form tendons that connect muscles with the bones. Matrix also contains fibroblasts. These tissues are found in the pericardium of the heart, the dura mater of the brain, the spinal cord, the cornea of the eyeball, the capsule of the kidney, and the coverings of cartilage and bone.

The function of White Fibrous Tissue

• Provides mechanical protection against stretch.

b. Yellow elastic tissue

It consists mainly of yellow elastic fibres. Their fibres are thick and branched. But it also contains some white fibres. Yellow elastic tissue may form a ligament that binds bone with bone.

The function of Yellow Elastic Tissue

• It provides streched and elasticity.

2. Supportive Connective Tissue or Skeletal Tissue

This is the supporting tissue that forms the endoskeleton of vertebrates. It supports the body and protects the delicate and vital organs from various injuries. Skeletal tissue are of two types: Cartilage and Bone

1. Cartilage

Cartilage is soft skeletal tissue in the vertebrate’s body. Typical cartilage consists of these like semi: sold matrix containing protein substances called chondrin. the matrix is secreted by an oval, a small group of cartilage cells called chondroblasts or chondrocytes. These cells are scattered in the matrix singly or in groups. These cells are scattered in the matrix singly or in groups. These cells are enclosed in fluid-filled spaces called lacunae. Cartilage is covered by thin and stiff perichondrium. It grows by the addition of new layers of the matrix to the outside.

Types of Cartilages

On the basis of the nature of the matrix, there are four types of cartilages:

1. Hyaline Cartilage: This types of cartilage is flexible. Its matrix is transparent, homogenous and tough. It covers joint srufaces, end of ribs, nose, and tracheal rings. In embryos of all vertebrates, it forms skeletal cartilages.
2. Elastic Cartilage: This type of catilage is more flexible. Its matrix has a network of numerious yellow elastic fibres. It is found in the external ear (pinna), external auditory canal of ear, epiglottis, eustachain tubes and tip of nose.
3. Fibro-Cartilage: Its matrix has aboudant white colagen fibres. it is the most resistant cartilage with less cells and matrix. It is found in intervertebral discs (pads) between mammalian vertebrae where it acts as cushions and in public symphysis around joints.
4. Calcified Cartilage: It is very hard, stuff and non:elastic. It is formed when hyaline cartilage gets impregnated with calcium (calcareous) in matrix. It is found in suprascapula of pectoral girdie, in pelvis of old frogs, in the heads of humerus and in vertebrae of sharks.

2. Bone

Bone is the specialized connective tissue that is very hard due to the decomposition of lime (CaCO) salts. the study of bones is called osteology. It forms the major part (roughly 2/3 of the body weight) of the body skeleton and provides the framework of the body. its matrix possesses bone cells called osteocytes. The matrix is formed of a protein called ossein. It is highly impregnated with inorganic salts, mainly calcium phosphate and calcium carbonate. The matrix contains 70% inorganic salts, mainly calcium phosphate and calcium carbonate. The matrix contains 70% inorganic salts and 30% fibrous protein ( ossein ).

Structure of Bone

A typical bone has the following structures.

1. Periosteum: It is the outermost covering of bone. It consists of undifferentiated bone cells.
2. Outer layer of osteoblast: Just below the periosteum is the outer layer of osteoblasts. There are flat connective cels that gice rise to bone cells.
3. Endosteum: The narrow cavity in the bone is formed by a thin layer of cells called endosteum.
4. Inner layer of osteoblasts: Outer layer of endosteum is formed of a continous layer of osteoblast cells similar to the outer osteoblasts.
5. Matrix: It covers the greater part of bone. It consists of various layers called lamellae. Each lamella has numerous small spaces called lacunae. Each lacuna encloses only the bone cell or osteocyte. each lacuna give off branching channel radiating in all directions called canaliculi. There canaliculi anastomose with other canaculi forming an interconnected system in the matrix.
6. Haversain System: Lamellae are arranged around a central canal called Haversian system or osteo. Various Haversian systems connected together by the canals of Volkman.

Types of Bones

On the basis of the type of matrix present, the bones have been classified into two types: Spongy bone and compact bone. However, the basic structure is the same.

1. Spongy Bone: it is present on the expanded ends of the long bones. It is filled with a soft tissue called red bone marrow. It lacks Haversian system.
2. Compact Bone: It is present on the shaft of the long bones. It is filled with fatty tissyue called yellow bone marrow. It has a number of Haversian systems.

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3. Fluid Connective Tissue ( Haemopoietic Tissue)

Blood and lymph are two types of fluid connective tissues. Cells move through a liquid extracellular matrix. All of the elements found in blood are derived from hematopoietic stem cells found in the bone marrow. It consists of both myeloid and lymphoid tissue which forms blood and lymph respectively. These fluid tissues are circulating in the body. They lack fibres.

Types of Blood Connective Tissue

1. Blood

It is one type of fluid connective tissue. It consists of plasma and corpuscles. A normal adult man contains 5:8 liter of blood in the body constituting 5:8% of the body weight. The blood is composed of two components:

Components of Blood

1. Blood Plasma: It is a pale yellow fluid and forms 55% of blood by volume. It is slightly alkaline, and contains various orgainc and inorganic materials in it.
   • Composition
     1. Water : 90 to 92%
     2. Dissolved solids: 8 to 10%
        • Proteins ( Serum albumin, Serum globulin, Fibrinogen) : 7%
        • Inorganic Constituents
        • Organic Constituents
        • Orgaic constituents
     3. Respiratory Gasses ( O₂ and CO₂ )
     4. Internal Secretions
   • Functions of Plasma
     • Transport: It transports digested food products, respiratory gases, excretory wastes, hormones, etc. inside the body.
     • Immunity: The immunoglobubins acts as antibodies and help the body to develop immunity.
     • Temperature Regulation: It distributes temperature in the body.
     • Maintenance of osmotic pressure: Serum albumin maintains the strong acids and bases hence act as acid:base buffers, thus maintaining the blood pH.
2. Blood Corpuscles (cells): These are following three types
   1. Erythrocytes or Red Blood Corpuscles (RBC)
   2. Leucocytes or White Blood Corpuscles (WBC)
   3. Thrombocytes or Blood Platelets

Functions of Blood

1. They transpoft oxygen from lungs to all parts of the body, and carries carbon dioxide producted by the tissue in the reverse direction.
2. They transport the soluble organic compounds form the small intestine to various part of the body.
3. They transport soluble excretory materials from tissues where they are producted to th eorgains of excretion.
4. They transport of metabloic by: products from areas of production to other parts of the body.
5. They transport hormones from the glands where they are produced to all parts of the body or certain target organs.

2. Lymph

Lymph is filtered blood without RBCs, WBCs, and platelets. It is a transparent, slightly yellowish, alkaline fluid. It contains glucose, salts, amino acids, vitamins in the same concentration as in plasma except for protein which is less in the lymph. It circulates in the body through lymph vessels and lymph hearts.

Function of Lymph

1. Lymph acts as a midel man which transport respiratory gases, food materials, hormones, etc.
2. Lymph nodes produce lymphocytes. It brings antibodies from lymph nodes to the blood.
3. It destroys the pathogens and foreign particle.
4. Lymph capillaries presentin the intestinal villi are called lacteals which are associated with absorption and fat soluble vitamins.
5. Lymph maintains the volume of blood in the body. As the volume of blood is reduced in the blood vascular syste, the lymp rushes from lymphatic system to the blood vascular system.

Conclusion

Connective tissue is a grouping of connective tissues that help to keep the body in shape and promote internal cohesion. The connective tissues are made up of a variety of fibrous tissues, such as bone, ligaments, tendons, cartilage, and adipose (fat) tissue, in addition to the more specialized and well-known fibrous tissues. We have discussed all connective tissue if you have any confusion about this topic then feel free to comment down.

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