Epithelial tissues form the covering on all internal and external surfaces of your body. The tissues are made up of epithelial cells. It also lines body cavities including hollow organs. The function of epithelium includes protection, secretion, and absorption.

There are 3 types of epithelial cells based on their shape:
1. Squamous epithelium cells appear flat and sheet-like.
2. Cuboidal epithelium cells appear cube-like.
3. Columnar epithelium appear column-like, which means they are taller than they are wider.

There are also types which based on their arrangements:
1. Simple – one layer of cells
2. Stratified – made up of more than one layer of cells
3. Transitional – a type of stratified epithelium that transitions from cuboidal when relaxed to squamous when stretched.
4. Pseudostratified – closely packed cells that appear to be arranged in layers but of different sizes. They are actually just one layer and is distinguishable by the presence of goblet cells.

Source:
Epithelium: What It Is, Function & Types. (2021). Cleveland Clinic. https://my.clevelandclinic.org/health/articles/22062-epithelium#:%7E:text=The%20epithelium%20is%20a%20type,the%20major%20tissue%20in%20glands.

Organs where these tissues can be found:
1. Transitional epithelium – urinary bladder, ureters, urethra, and ducts of the prostate gland.
2. Stratified squamous epithelium – skin, esophagus, mouth, and vagina
3. Ciliated pseudostratified columnar epithelium – trachea and upper respiratory tract.

Source:
Epithelial Tissue | Boundless Anatomy and Physiology. (n.d.). Lumen. https://courses.lumenlearning.com/boundless-ap/chapter/epithelial-tissue/