Epithelial Tissue and Connective Tissue

Introduction

Animals and plants are different from unicellular organisms in that they exhibit a higher level of organisation. The cells are organized to form tissues in animals and plants. The tissues are specialised in their origin, function and structure. In this tutorial, we will be learning about epithelial and connective tissue in animals.

What is a Tissue?

Tissue refers to a group of cells which exhibit similar origin, function and structure. In animals, there are four types of tissues present, and the structure of these tissues depends on their function.

The types of tissues present in animals are −

• Epithelial Tissue

• Connective Tissue

• Muscle Tissue

• Nerve Tissue

In this tutorial, we will be learning about the epithelial and connective tissue present in animals.

Epithelial Tissue

Epithelial Tissue forms the covering for all the organs both internal and external, body cavities, hollow organs etc. by forming a thin layer of tissue called the epithelium. The epithelium is the major tissue in the glands.

Epithelial tissue is highly permeable and also acts as a barrier for preventing the entry of microorganisms.

The main functions of epithelial tissue are protection, sensation, absorption and excretion. The epithelium is further divided into two types.

• Simple Epithelial Tissue

• Compound Epithelial Tissue

Let us discuss these two types in detail below.

Simple Epithelial Tissue

Simple epithelial tissues are composed of single-layered cells and form the lining of various cavities, ducts and tubes in the body.

Based on the cell structure, simple epithelial tissue is of three types −

Squamous Epithelium

Squamous epithelium is single-layered and composed of flat cells having irregular boundaries. Squamous epithelium forms the linings of alveoli and blood vessels.

Cuboidal Epithelium

The characteristic feature of cuboidal epithelium tissue is that the tissue is made up of cube-shaped cells. The example of cuboidal epithelium tissue are tissues lining the ducts of the salivary glands and those forming the lining of the kidney tubules.

Columnar Epithelium

The columnar epithelium consists of column-shaped epithelial tissues. They are tall and slender in appearance. These are epithelial tissues that form the lining of the stomach and intestine.

In some organs, the columnar and cuboidal epithelial cells have cilia which are helpful in the movement of material in hollow organs like the respiratory tract.

The columnar and cuboidal epithelia that are specialised to perform secretions are called the glandular epithelium.

Compound Epithelial Tissue

The compound epithelium is multi-layered in its structure and the main function of this class of epithelial tissue is to provide protection. Its role in secretion is limited.

Skin is an example of compound epithelial tissue which protects the body from different kinds of stresses such as mechanical and chemical stress.

Connective Tissue

Connective tissue refers to those tissues which are involved in connecting and supporting the other tissues and organs. Connective tissues are the most found tissues in an organism.

There are three types of connective tissue which are as follows −

Loose Connective Tissue

This type of connective tissue is present where both elasticity and support are required. Blood vessels, muscles and nerves all are having wrapping of loose connective tissue. In association with the adipose tissue, the loose connective tissues form the subcutaneous layer under the skin.

A few examples of loose connective tissue are areolar tissue, adipose tissue and reticular connective tissue.

Dense Connective Tissue

In this type of tissue, the fibres and fibroblast cells are tightly packed and are therefore less flexible than the loose connective tissue. The main function of dense connective tissue is to provide support and transfer force to the bones

There are two types of dense connective tissue based on the arrangement of collagen fibres, namely: Dense regular tissue and Dense irregular tissue.

The dense regular tissue has a regular arrangement of fibres which enhances the tensile strength of the tissue. Examples of dense regular tissue are ligaments and tendons.

The dense irregular tissue has an irregular or random arrangement of fibres which makes them complex and also enhances elasticity, this type of arrangement also provides uniform strength in all directions. An example of such tissue is tissues found in the dermis of the skin.

Specialised Connective Tissue

The function of specialised connective tissue is to support internal organs and also in circulation. The following are some examples of specialised connective tissue.

Cartilage

The function of cartilage is to act as a secondary skeleton. It is mostly present in the body at the time of development of an embryo. It is replaced by bones upon reaching adulthood. But, there are certain organs that need cartilage to function and examples are the nose, external ear, between the bones of the spinal cord or the vertebral column.

Bone

Bone is considered the strongest connective tissue and its function are to provide shape and posture to the body, and also to protect the internal organs.

Blood

Blood is a fluid connective tissue and the functions of blood are to transport oxygen, minerals, fats and other nutrients throughout the body and also help in providing defence against infection. It also contains important factors that help in clotting.

Lymph

The function of lymph is to transport absorbed fats into the blood, which otherwise cannot enter directly, it also provides defence against infection and helps the body get rid of toxins and various waste materials.

Conclusion

Animal tissues are of four types and the structure of tissues depends on their function. We have discussed the epithelial and connective tissue and their types here.

FAQs

Qns .1 What are the four types of animal tissues?

Ans. The four types of animal tissues are epithelial tissue, connective tissue, muscle tissue and nerve tissue.

Qns .2 What are the different types of epithelial tissue?

Ans. There are two different types of epithelial tissues are simple epithelial tissue and compound epithelial tissue.

Qns .3 What are the types of simple epithelial tissue?

Ans. There are three types of simple epithelial tissue namely, squamous epithelium, cuboidal epithelium and columnar epithelium.

Qns .4 What are some examples of fluid connective tissue in animals?

Ans. Blood and Lymph are the fluid connective tissue present in animals.