Histologyis the branchof biology that studies tissues. The human body is composed offour basic types of tissues: the epithelial tissues, the connective tissues, the muscle tissuesand the nervous tissues.
Epitheliaare cellular sheets that line the cavitiesof organsand cover the body surface. It composed of closely aggregated polyhedral cells with strong adhesion to one another and attached to a thin layer of ECM.
The main functions of the epithelial tissue are covering and protecting the body surfaces, absorption, and secretion.
There are mainly two types of epithelial cells, according to the layer of the cells.: simple(one layer) or stratified(more than one layer). They can be further classified into squamous, cuboidal, and columnarcells according to the shape of the cells. Pseudostratifiedcells are those all attached to the basement membranewith nuclei at different levels which makes them seems like stratified (more than one layer) but actually not.
Keratinizationis also a common word for medical reading. When a cell is keratinized, it's filled with keratinand other substances, eventually lose its nucleusand organelles. Keratinized cells may slough off and be replaced by new cells from the basal layer.
The connective tissue will be discussed in the next chapter…