3 classes1. simple endoderm1 layer, few think upper layers dermisa. squamousb. cuboidalc. columman2. stratified ectodermmany layers thika. squamousb. columman3. gland endodermdistirctdig. gland (cottage cheese)-globular: not uniform in textureEpithelial is one of the four types of tissues in the body. There is also muscular, nervous, and connective tissues. The best way to describe epithelial tissues is that they occur in parts of the body that need protection from the external environment. An analogy would the be the tiles on the space shuttle.3 classes1. simple endoderm1 layer, few think upper layers dermisa. squamousb. cuboidalc. columman2. stratified ectodermmany layers thika. squamousb. columman3. gland endodermdistirctdig. gland (cottage cheese)-globular: not uniform in texture1- non penetrable to vessels 2- penetrated by nerves 3- lines cavities and surfaces 4- lie on basement membrane 5 compacted cells with little inter-cellular space.Characteristics of epithelial tissue: Epithelial tissue lies on a basement membrane. That means that underlying the cells that are the cellular component of the epithelial tissue, there is a layer of acellular ("a-" means not, so "acellular" means not cellular) material. This basement membrane can be thought of as a sticky layer to keep the epithelial cells attached to whatever underlies them. The bottom edge of the epithelial tissue abuts the basement membrane; this bottom edge is called the basal surface. The edge of the epithelial tissue that faces the lumen (or the outside world) is called the apical surface.Other characteristics:1. Cells within this tissue readily divide to make more cells. This helps this tissue recover after any sort of abrasions occur.2. This tissue does not have any vasculature. This means that there are no blood vessels within it. This should make sense, since epithelial tissue is likely to get damaged by material moving against it-- and you don't want to bleed everytime something bangs into your skin or everytime you swallow something rough.3. The cells within this tissue are firmly attached to each other. As a border-tissue, if the cells weren't adherent to one another, it would be a leaky border. This would be no good-- liquids from inside of us would drip out! Yuck! So the cells all make the type of junctions with each other called tight junctions.