Introduction
Definition of Tissues
Tissues are collections of cells that share a similar structure and work together to perform specific functions in the body. For instance, muscle tissue is made up of elongated cells that are designed to contract and allow movement. Organs, the functional units of the body, are then formed by the organised combination of different tissues. The interplay between cells and the extracellular matrix (ECM) is fundamental to the organisation and function of tissues. The ECM, consisting of various macromolecules, provides structural support, facilitates nutrient transport, and influences cellular behaviour.
Classification of Tissues:
There are four primary types of tissues that make up the human body: epithelial, connective, muscular, and nervous.
Epithelial Tissue: This tissue forms sheets of closely packed cells with strong adhesion to one another and a thin layer of ECM. Epithelial tissue serves to cover body surfaces, line internal organs and cavities, and forms glands. It is classified by the number of cell layers (simple or stratified) and the shape of the cells in the surface layer (squamous, cuboidal, or columnar).
Connective Tissue: This tissue is characterised by an abundance of ECM produced by its cells. Connective tissue provides support, binds structures together, and protects organs. It is classified into various types based on the composition and arrangement of its cells, fibres, and ground substance. These include loose connective tissue, dense connective tissue (regular and irregular), cartilage, bone, blood, and lymph.
Muscle Tissue: Muscle tissue is composed of elongated cells specialised for contraction. This allows for movement of the body or its organs. It is classified into three types: skeletal muscle (voluntary control), smooth muscle (involuntary, found in the walls of internal organs), and cardiac muscle (involuntary, found in the heart).
Nervous Tissue: This tissue is composed of cells with long, fine processes specialised to receive, generate, and transmit nerve impulses. Nervous tissue coordinates body functions. It is classified into neurons (conducts nerve impulses) and neuroglia (support and protect neurons).
General Properties of Tissues
Cellularity: Tissues are primarily composed of cells, though the amount of extracellular matrix varies.
Specialisation: Each tissue type has unique structural characteristics and is specialised to perform specific functions.
Connectivity: Tissues are interconnected to form organs, and organs work together in systems to maintain overall bodily function.
Vascularity: The level of blood supply varies among tissues. Connective tissues are typically well-vascularized, while cartilage has a limited blood supply.