Introduction of Basic Histology

EPITHELIAL TISSUE
Epithelium is a sheet of cells that covers the external surface of any solid structure and the internal surface of any hollow tubular (e.g. lumen/cavities) structure. Thus it serves as a barrier membrane separating the underlying tissue from various external and internal environments.

CLASSIFICATION OF EPITHELIAL TISSUE
On the basis of the function(s) performed, epithelial tissue can be broadly classifi ed into four types(fig. 1).
Connective tissue is one of the basic tissues which gives structural and metabolic support to other tissues and organs of the body. It connects other tissues.

GENERAL FEATURES
_ Connective tissue is made of:
(a) cells,
(b) fibres, and
(c) ground substance.
_ Unlike other tissues, the major constituent of connective tissue is its extracellular matrix. _ This extracellular matrix gives connective tissue its strength.
_ Although all types of connective tissue have the same basic structure, their physical properties depend on the composition of the extracellular matrix.

Connective tissue can broadly be classifi ed into following four categories:
A. Ordinary connective tissue
1. Loose areolar connective tissue
_ It is a vascular, delicate, fl exible connective tissue where the fi bres are loosely arranged.
_ It serves as a packing material by fi lling spaces between various tissue components of an organ and giving it a shape, e.g. subperitoneal tissue, endomysium, lamina propria.
2. Dense collagenous connective tissue
_ It is a tough tensile connective tissue where the collagen fi bres are densely packed giving strength and resistance to traction forces. It is of the following two types: