Connective Tissue

Introduction

Connective tissue is one of the four basic types of tissues systems present inside an animal body. It is developed from the mesoderm of the embryo. The connective tissue function is as the name suggests to connect different parts of the body and hold them as one unit. Hence, the connective tissue is found in between other tissue systems as well including specialised systems such as the nervous system. The cell types of connective tissue examples include fibroblasts, macrophages, mast cells, leukocytes, and adipocytes.


Define Connective Tissue

The term “connective tissue” was coined by Johannes Peter Müller in 1830 even though it was already categorized as a separate tissue system a century before. From the simple attempt to define connective tissue, in the introduction, they can be defined as groups of tissues responsible for maintaining the form of the body and the structural integrity of the organs by providing cohesion and internal support. As given already, it is present all over the body and also in between other tissues. It is also present in the central nervous system within the three outer membranes surrounding and enveloping the brain and spinal cord

There are three components of connective tissue - the fibres which are both elastic and collagenous, the ground substance of connective tissue, and the specialized connective cells. Some of the scientific authorities also consider the blood and the lymph as connective tissue because they partially hold the connective tissue meaning of connecting the entire body because of their own network of flow within the body. But they are different from typical connective tissues since they do not contain any fibres. 


Types of Connective Tissues

Connective tissue is widely classified into two types - the connective tissue proper and special connective tissue. They are further explained as follows:

Connective Tissue Proper: There are two types of connective tissue proper which are typified as loose connective tissue and dense connective tissue. This classification is based on the ratio of the ground substance of connective tissue to the fibrous tissue. This means that the loose connective tissue proper has more ground substance as compared to the fibrous tissue whereas the dense connective tissue has more fibrous connective tissue than the loose connective tissue. Connective tissue examples of this type include areolar tissue, reticular tissue, and adipose tissue. Examples of dense connective tissue include tendons and ligaments. As a matter of fact, the dense connective tissue is further divided into dense regular and dense irregular connective tissue. The difference is that the dense connective tissue is ordered in a parallel fashion given tensile strength to tendons and ligaments in one direction while the dense irregular connective tissue forms dense fibre bundles providing strength in all directions.

Special Connective Tissue: While talking about connective tissue systems people sometimes ask a general question - is cartilage a connective tissue?. The answer is yes. Cartilage is a special connective tissue. The cartilage connective tissue comes under the classification of special connective tissue along with reticular connective tissue, adipose tissue, bone and blood. Another of the connective tissue examples that are included in this category are the fibrous, elastic and lymphoid tissues. The fibroareolar tissue and fibromuscular tissue is a combination of the fibrous and areolar tissue and fibrous and muscular tissue, respectively. 


Characteristics & Components of Connective Tissue

Many forms of connective tissue are made up of type I collagen fibres, which make approximately 25% of human protein content and play a primary role in the connective tissue function. These collagen fibres are fixed in the intercellular spaces by the ground substance which is a clear, colourless and viscous fluid containing glycosaminoglycans and proteoglycans. 

Some of the connective tissue such as the adipose tissue and the blood is different in this sense as they are not made up of fibres. Even though the adipose tissue isn't made up of collagen fibres they are held together in a group by collagen fibres and sheets. This combination provides mechanical cushioning to the body by keeping the fat tissue under compression and in place. The components of connective tissue - the fibre proteins and ground substance together create the entire matrix for connective tissue.

As part of the components of connective tissue the fibre types are explained below: 

Fibres

Usage

Made Up of

Where in the Body?

Collagen

Binding of bones and tissues to each other and one another

𝛼 - polypeptide chains 

Ligaments, skin, tendons, cornea, cartilage, etc. 

Elastic

Recoiling of arteries, lungs and other such organs

Elastic microfibril and elastin

Extracellular matrix

Reticular

Scaffolding other cell types

Type III collagen 

Bone marrow, liver, lymphatic organs


Functional and Clinical Importance of Connective Tissue

The connective tissue function varies depending on the cell type and fibrous material present. For example, the loose and dense connective tissue found in the fibroblasts and collagen fibres is responsible for providing a medium for the transfer of oxygen and nutrients from the capillaries to cells and the diffusion of carbon dioxide and waste materials from the cells to back in the circulatory system

The dense regular connective tissue which as told earlier is responsible for providing tensile strength in organised structures, also provides tear and stretch resistance to the tendons, ligaments, aponeuroses and in specialised organs such as the cornea. The function of elastic fibres made from fibrillin and elastin is also to provide stretch resistance in walls of large blood vessels and particular ligaments (ligamentum flavum).

When asked to name the connective tissue from which the connective tissue of an adult is formed, the answer to be given is the Mesenchyme tissue. It is a type of connective tissue found in the developing organs of the embryo that differentiate into all the mature connective tissues.

Certain specialised cells of the immune system of the kind of macrophages, mast cells, plasma cells, eosinophils are found randomly distributed around the loose connective tissue for starting an immune response upon detection of antigens as soon as possible. 

There are many kinds of disorders as well related to connective tissue. The name of connective tissue disorders as few examples are shown below:

  • Connective tissue neoplasms or connective tissue tumours: Hemangiopericytoma, and Malignant peripheral nerve sheath tumours

  • Congenital Diseases: Marfan syndrome, Ehlers-Danlos Syndrome

  • Deficiency Diseases: Scurvy caused due to Vitamin C deficiency leads to insufficient collagen production

  • Fibromuscular Dysplasia: Abnormal growth in the artery walls

Thus, from the given information in the article, it is clear that the connective tissue plays a vital role in maintaining the structural integrity of the body and performing functions responsible for the diffusion of essential nutrients and substances. The images of certain kinds of connective tissue are shown below:


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FAQs (Frequently Asked Questions)

1. What are the Three Types of Connective Tissue?

Ans: The connective tissue can be mainly classified into two types: the connective tissue proper and specialized connective tissue. The connective tissue proper is further classified into two types - the loose connective tissue and the dense connective tissue. Thus, in other words, the connective tissue is classified into three types as loose connective tissue, dense connective tissue and specialized connective tissue.

2. What are the Connective Tissues?

Ans: Connective tissues are one of the four basic tissues systems found in an animal body. They are responsible for providing structural support and integrity to the entire body and make the body function as a single unit. Along with the support they also provide protection to other tissues and organs in the body. Examples of connective tissues include adipose tissue, bone, blood, cartilage, etc.