Difference Between Connective Tissue and Epithelial Tissue
The basic structural and functional unit of all living organisms is the cell. When different cells are oriented or grouped together to perform a common function, it is referred as a tissue. The cells are often physically aligned and connected with each other through intercellular matrix. Connective tissue and epithelial tissue are the most predominant forms of tissue, which are located across different organs in our body. These tissues often interact with each other for the viability and functioning of an organ. Connective tissue is the major supporting tissue in our body. The other functions of connective tissue are to connect or separate different types of tissues or organs. The major components of all connective tissue (except blood and lymph) are elastin, type-1 collagen, ground substances and cellular component. Connective tissues are broadly classified as connective tissue proper and special connective tissue. The classification is based on the type and orientation of the cells in the tissue (Ross 2011). The classification of connected tissue is represented as:
Fig 1: Reflects different types of Connective Tissues
Connective tissue originates from the mesoderm of the embryo. The cells are spread through an extracellular fluid and contain ground substances. These substances include glycosaminoglycans, proteoglycans, keratin sulphate and chondroitin sulphate. Connective tissues primary provides the vascular framework through which oxygen and nutrients are transported to different parts of the body. The adipose tissue helps to provide insulation to our body. Elastin and collagen present in the lungs helps to maintain lung compliance (elastic recoil). Collagen and reticular fibres helps to bind different tissues with one another. Various neoplasms (potential for cancer) are associated with connective tissue (Ross 2011).
Epithelial tissue or epithelium is located on the lining of different organs. They are mainly classified into simple and compound epithelium. When the epithelial tissues are one cell thick they are referred as simple epithelium. However, when the epithelium is multilayered it is referred as compound epithelium. Simple epithelial is also further divided into various types. The classification is based on the type and morphology of the cells. When the cells are wider than their height, they are referred as squamous epithelium (Ross 2011).
When the height and width of the cells are nearly same, they are referred as cubical epithelium. If the heights of the cells are larger than the width of the cells, they are referred as columnar epithelium. When the simple epithelial cells are oriented in such a way so the nuclei of different cells are arranged in different orientations, it is referred as pseudo-stratified (lack of true stratification) epithelium. On the other hand, when the epithelium is made of multi-layered cells, it is referred as compound epithelium. Transitional epithelium is a type of compound epithelium, where the cells undergo rapid changes in morphology. This means one type of cell is changed to the other. Epithelial tissue originates from the ectoderm of an embryo. The main functions of epithelium are secretion (hormones and mucus), absorption (through villi) and protection. A comparison of connective and epithelial tissue is provided below:
|Features||connective tissue||epithelial tissue|
|Function||Structural, connective||secretion (hormones and mucus), absorption (through villi) and protection|
|Classified as||Connective Tissue Proper and Specialized Connective Tissue||simple and compound epithelium|
|Arrangement of cells||Not aligned in layers||Aligned as single or multi-cellular layers|
|Composition||Elastin, collagen and chondroitin, fibrous||Chiefly fibrous|
|Supported by blood vessels||Yes||No|
|Presence of Basement membrane||No||Yes|
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Ross M, Pawlina W (2011). Histology: A Text and Atlas (6th ed.). Lippincott Williams & Wilkins. pp. 158–197.