TYPES OF TISSUES

A tissue is a group of cells designed to perform a particular function. There are four types of tissues.

1. Epithelium (Epithelial tissue) - These are cells that line surfaces of biological structures, such as lining of the intestine or the skin covering.

There are three types of epithelial tissues classified based on their shapes:
(a) Squamous epithelium - flat cells
(b) Cuboidal epithelium - Look like cubes
(c) Columnar epithelium - Look like columns or pillars

They can also be classified based on the number of layers:
(a) Simple epithelium: Only one layer of cells
(b) Stratified epithelium: Many or multiple layers of cells
(c) Pseudoepithelium: This epithelium has only one layer but appears under the microscope as multiple layers
(d) Transitional epithelium -This epithelium has many layers of cells with various shapes. It lines the ureters and bladder and functions in the distension of these structures.

Some of the cuboidal/columnar epithelial tissues have hairlike structures on the surface called cilia.
The function of the cilia is to move substances along the surface of the tissue.

•  For example, the columnar ciliated epithelium can be found in the respiratory tract where it moves mucus to the throat.

It is also good to know that some epithelial tissues produce secretions. They are called glandular tissues.

Types: 

• Endocrine are ductless glands, secreting chemical messengers (hormones) directly into the blood or lymph.
• Exocrine are glands that secret products into a duct. Examples: sweat and sebaceous (oil) glands, salivary, liver, pancreas, mammary, and mucous glands.

2. Muscle tissue: There are three types of muscle tissues. 

• Cardiac muscle - found in the heart; they are branched striated muscles
• Skeletal muscles - they move bony parts of the body; they are unbranched striated muscles
• Smooth muscles - found in the internal organs such as the intestines, uterus, etc; they are non-striated muscles.

Diagram of the muscle tissues.

Tip for the exam: You should know the diagram of the various muscle tissues and their functions.

3. Nervous tissue: The basic unit of the nervous tissue is the neuron. 

Diagram of the neuron.

4. Connective Tissue

• Functions: binding and support, protection, insulation, transportation
• Examples of connective tissue cell types:
• Connective tissue proper - fibroblasts/fibrocytes (ligaments, tendons, adipose tissue, etc.)
• Cartilage - chondroblast/chondrocyte
• Blood - hemocytoblast/hemocyte
• Bone - osteoblast/osteocytes

Tip for the exam: You should know the examples of connective tissues.