What are Tissues?
A group of cells with similar shape and function are termed as tissues. They form a cellular organizational level intermediate in between the cells and organ system. Organs are then formed by combining the functional groups of multiple tissues.
There are different types of tissues in different organs. For example, in human beings, there are four basic types of tissues:
- Epithelial Tissue,
- Connective Tissue,
- Muscular Tissue and
- Nervous Tissue.
Study of Tissues
The study of tissue is known as histology and study of disease related to tissue is known as histopathology. The classical tools for studying tissues is by embedding and sectioning using the paraffin block.
Animal tissues are basically grouped of four types:
- Connective Tissue
- Muscle Tissue
- Nervous Tissue
- Epithelial Tissue
The collection of tissues are joined in structural units to serve a common function of organs. The main purpose of all these four tissues is differ depending on the type of organism. For example, the origin of the cells comprising a particular tissue type also differs.
Connective Tissues: A fibrous tissues made up of cells separated by non-living material, called as an extracellular matrix. This tissue gives shape to the organs and holds them in place. For example, blood, bone, tendon, adipose, ligament and areolar tissues.
Classification of Connective Tissues
- Fibrous Connective Tissue.
- Fluid Connective Tissue.
- Skeletal Connective Tissue.
Muscle Tissue: They are involved in producing force and generating motion, either for the locomotion or for the movement within internal organs. There are three types of muscle tissue:
- Skeletal Muscle – they are typically attached to bones
- Cardiac Muscle – found in the heart.
- Visceral or Smooth Muscle – they are found in the inner walls of organs.
Nervous Tissue: They are the main tissue components of the brain and spinal cord in central nervous system. While, in the peripheral nervous system, the neural tissue forms the cranial nerves and spinal nerves.
Epithelial Tissue: They are formed by cells which cover the external parts of the body organs and lines the organ surfaces such as the surface of the skin, the reproductive tract, the airways, and the inner lining of the digestive tract.
Plant tissues are broadly categorized into three tissue systems:
- Epidermis Tissues – cells formed from the outer most surface of the leaves.
- Vascular Tissues – involved in transporting fluid and nutrients internally.
- Ground Tissue – involved in producing nutrients by photosynthesis and preserve nutrients.
Types of Plant Tissues
Plant tissue is divided into two types:
- Meristematic tissues.
- Permanent tissues.
Meristematic Tissue: It consists of actively dividing cells, which leads to increase in length and thickness of the plant.
Meristematic Tissue is classified as:
- Apical Meristem.
- Lateral Meristem.
- Intercalary Meristem.
Permanent Tissues – A group of cells which are similar in origin, structure and in function. They are involved in complete growth and differentiation during the ineffective of meristematic activity.
There are three types of permanent tissues:
- Simple Permanent Tissues.
- Complex Permanent Tissues.
- Special or Secretory Tissues.
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