Connective tissue is animal tissue and is formed from cells. Its function is connecting different tissues, supporting tissues, and organs. Connective tissue can be divided into three types based on the arrangement of the cells. The types are Loose, Dense, and Specialised connective tissue. Loose connective tissue functions to keep the organs in their specific location. It consists of the extracellular matrix (Commonly regarded as ECM), collagen fibre, elastic fibre, and reticular fibres. Dense connectives form the tendons and ligaments, which help connect bones and tissues. They are known to have high collagen fibre density. Adipose tissue, bone, lymph, etc., fall under the specialised tissues category.
Connective Tissue Structure
Connective tissue is formed from 3 types of fibres:
- Collagen fibres are collagen fibrils that weave through tissues in a wavy pattern. Flexible proteoglycans make up these parallel fibrils, which give a significant mechanical property. They are known to provide adequate resistance to any pulling force. Collagen weaves its way through loose connective tissue in a parallel pattern before combining to form a larger bundle. To form a three-dimensional meshwork, they split from one another and reunite at various locations. Ligaments and tendons are Dense connective tissue. It is constructed from densely packed collagen fibres.
- Reticular fibres are also known as argyrophilic fibres. They are found throughout the human body. The most common areas where they can be found are the base of epithelial tissue, adipose cells, Schwann cells, muscle cells, etc. The reticular fibres are thin and dark made of a number of fibrils. The fibrils are parallel to the college fibres and form a mesh. The fibrils’ mesh-like arrangement results in the fibres’ formation below the basal lamina layer.
- Elastin fibres are elastic. They can stretch under pressure and regain their original shape once the pressure is removed. Elastic recoil is a distinguishing attribute of these fibres. Elastin is a loose connective tissue that determines the organisation and distribution of the fibre. The presence of concentrated elastin fibres in the arterial wall aids in the maintenance of constant blood pressure. The lungs and urine bladder, for example, are distensible and contractible organs that contain fibres. These fibres form a strong bond with the basal lamina hence regarded as the functional and structural unit capable of supporting tissues.
Embryology
Connective tissue is somatic mesodermal in origin. Scleraxis is a transcription factor. It is activated by inductive signals from the sclerotome and myotome present in its surrounding. Many fibroblast factors, along with transforming growth factor-beta (TGF Beta), are the main factors involved in the synthesis of tendons, a dense connective tissue. Tendon progenitor cells form collagenous fibrils, which develop in various directions to produce the tendon fascicle. Tendon fibroblasts are present in the tendon between collagen fibres.
Blood Supply
Various forms of connective tissue have different blood flow patterns. Tendons and ligaments are avascular. That is, they do not contain vessels in them. They’re primarily made up of densely packed collagen fibres that don’t require blood and don’t have any metabolic activity. However, these collagen fibres contain living cells that require a blood supply.
Muscle Connective Tissue
Fibre is made up of individual muscle cells that have been joined together. These fibres are grouped to form a fascicle. The fascicles are then further grouped to form the whole muscle. Every muscle cell, fibre, and fascicle contains connective tissues. Endomysium is a basement membrane that forms a mesh-like structure from the collagen fibres. The endomysium connects muscle cells to their adjacent muscle cells at the molecular level. Perimysium surrounds the fascicles and connects to the epimysium. It surrounds the whole skeletal muscle with the dense connective tissue (tendon). The collagenous network begins at the endomysium and expands to the perimysium and tendon, which helps in effective muscular contraction. The mesh of collagen fibre starts from the endomysium to the perimysium and the tendon. This whole arrangement of the fibres is the key reason for effective and strong muscle contraction.
Connective Tissue in Nerves
All peripheral nerve filaments are protected by 3 connective tissue that forms a covering around the nerve filaments. The peripheral nerve is surrounded by a thick layer of connective tissue known as the epineurium. The epineurium comprises several nerve fascicles, each of which is encircled by the perineum.
Conclusion
Connective tissue is a type of animal tissue that maintains the structure of the body and its organs while also providing cohesion and internal support. It can also store fat, transport nutrients, etc. Connective tissue is formed from a cluster of similar types of cells that combine to form a specific tissue. The origin of connective tissue is from the mesoderm, composed of collagen and elastin. Based on the types of cells and their arrangement, the connective tissue is divided into three types: Loose, Dense and Specialised connective tissue.
This tissue is known for providing support to tissues, organs, and different body parts. It also protects them from damage and dislocation. It is also known for storing fats. It is known to move substances from 1 tissue to another. It can also move substances between the organs.