An Idea On Connective Tissues

All living things, including bacteria, animals, and plants, have cells. Microorganisms are unicellular, whereas plants and animals are often multicellular. Multicellular organisms organise their cells into tissues. Tissues are made up of the same cell types that execute the same functions. They can be segregated into four major groups: epithelial, neural, connective, and muscular tissues. Originating from the mesoderm, the connective tissue is present throughout the body. As the name suggests, it connects other types of tissues all over the body.

Primary components of connective tissue

The 3 primary components of connective tissues are cells, fibres, and ground substances. The fibres and the ground substances comprise the extracellular matrix.

• Cells

The fibroblast is the primary connective tissue cell. Its purpose is to manufacture and maintain connective tissue’s ECM (extracellular matrix). Several other types of cells are present in addition to fibroblasts. These are immune system cells such as mast cells, macrophages, lymphocytes, and adipocytes. 

• Fibres

Three kinds of fibres can be found in connective tissues. They are collagen, reticular, and elastic fibres.

• Collagen

Collagen type I makes up the majority of collagen fibres. They are the most common protein fibres and provide tissues with varying levels of rigidity and strength.

• Reticular fibres

Collagen type III makes up the reticular fibres. They are fine, delicate fibres that create mesh-like arrangements in organs like the lymph nodes, spleen, and kidneys.

• Elastic fibres

Elastic fibres are composed of the protein elastin and allow tissues to stretch and flex. Skin, Lungs, large blood vessels, yellow ligaments, and elastic cartilages are the most common places where they can be identified. Varied forms of connective tissue result from different combinations and configurations of cell and protein fibres.

• Ground substances

It is a thick gel made of water, glycoproteins, glycosaminoglycans, and proteoglycans. These substances render the ground substance dense and bind a lot of water, allowing for hydration, nutrient diffusion, and tissue nourishment.

Types of connective tissue

Loose connective tissue

Cells are widely scattered in intercellular material, and fibres are loosely intertwined in a random pattern in the loose connective tissue. The following tissues have been classified as;

• Areolar connective tissue

It is the most basic connective tissue seen in animals’ bodies. The areolar connective tissue is a gelatinous and semifluid matrix that comprises hyaluronic acid, chondroitin sulphates, and mucin in a clear, semifluid state. Various connecting tissue types of cells and fibres are embedded in the matrix.

• Reticular connective tissue

Modified fibroblasts, also called reticular cells, make up the reticular connective tissues. Like the dense irregular connective tissues, the reticular connective tissues are arranged in an interwoven fine mesh-like network. Reticular meshes screen lymph and offer a setting for white blood cell passage and adhesion. As a result, it can be found in the lymph nodes, red bone marrow, and spleen.

• Adipose connective tissue

Adipose tissues are loose connective tissues primarily made up of adipocytes. Apart from adipocytes, it comprises adipose tissue macrophages, preadipocytes, vascular endothelial cells, and fibroblasts. Its primary function is to store and preserve energy as lipids, but it also insulates and cushions the body.

• Dense connective tissue

Compared to the loose connective tissue, the dense connective tissue has a lesser number of cells. Instead, collagen fibres are firmly packed into their extracellular matrix. Dense connective tissue is divided into two categories based on fibre arrangement.

• Dense regular connective tissue

Collagen fibres are positioned parallel to one another in dense regular types of connective tissue. This configuration gives the tissue a high level of unidirectional stress resistance. Examples of structures requiring this type of connective tissue are tendons and ligaments.

• Dense irregular connective tissues.

The collagen fibres are non-parallelly positioned in the dense irregular connective tissue, unlike the dense regular counterpart. This 3D network of fibres offers distension resistance to the tissue from all sides. E.g. dermis of the glands and skin, joint capsules, etc.

• Supportive connective tissue

It is one of the connective tissue types that supports and strengthens the soft body parts. It is also referred to as the skeletal connective tissue. Examples are the cartilages and bones in the body.

• Bones

Bones act as the primary support of a body. It has a rigid matrix composed of phosphorus and calcium.

• Cartilages

It is a non-porous, elastic tissue located at the ends of bones. Cartilages have a soft matrix.

• Fluid connective tissue

It is a connective tissue where the matrix is found in a liquid state. The fluid connective tissue is mainly concerned with nutrients transportation. Examples are lymph and blood.

• Blood

The circulatory system’s specialised connective tissue distributes dissolved materials and blood cells throughout the body via blood vessels. It has various cellular and extracellular constituents, like all connective tissue.

Functions of connective tissue

There are several vital functions of connective tissues in the body. They are as follows:

• Support: Connective tissues primarily support soft body parts by forming ligaments, tendons, sheaths, fascia, etc.
• Binding: Connective tissues connect or bind several other organs and tissues in the body.
• Storage: The connective tissues can store water, hormones, fats, calcium, growth factors, etc.
• Insulation: The adipose tissue acts as an insulator. Also, the connective tissues from the skin’s dermis aid in insulation.
• Transportation of nutrients: Blood, a fluid connective tissue, aids in transporting substances throughout the body.
• Allergic response and immunity: Mast cells are crucial in allergic reactions because they produce histamine when exposed to antigens. Macrophages, a highly specialised loose connective tissue that participates in phagocytosis, are another significant loose connective tissue. Histamine in basophils helps in type 2 immunity during parasite infection and allergic reactions. The two primary constituents of blood are red and white blood cells. Acute and chronic inflammation is caused by terminally differentiating white cells called neutrophils and lymphocytes.

Conclusion

The connective tissue is one of many basic forms of animal tissue alongside epithelial, muscular, and neural tissues. They are present in several forms like loose, dense, skeletal, and fluid connective tissues. They’re found all over the body and are connected to the primary tissues. Binding, supporting, protecting, insulating, storing reserve fuel, and transporting substances inside the body are their key activities.