Epithelium is one of the four basic types of tissues in your body and is composed of epithelial cells. These cells act as the first contact point of your body to things like viruses, allergens, toxins, nutrients, and physical stimuli (heat or pressure). As such, they perform many important jobs:
- Protect the underlying tissues from damage due to radiation, toxins, microbes, and physical trauma.
- Absorption of nutrients and other molecules, specifically in the digestive tract.
- Secrete substances into the body or out of the body. Examples include hormones, sweat and mucus.
- Aid in the sensation of pain, heat, cold and itch.
Epithelium can be found in a number of locations in your body and the types of epithelium at each of these locations can vary depending on the function that it needs to perform.
- Simple squamous – single layer of flat cells. Lines the alveoli in your lungs and the vessels of your body.
- Simple cuboidal – single layer of cube shaped cells. Lines your glands as well as the ducts in your kidneys.
- Simple columnar – single layer of column shaped cells. These line airways, digestive tract, bladder and the uterus. They often have hair like projections called cilia.
- Stratified squamous – multiple layers of flat cells. Lines your mouth, esophogus, and vagina.
- Stratified cuboidal – multiple layers of cube cells. Lines salivary glands and mammary glands (in the breasts).
- Stratified columnar – multiple layers of column cells. Lines some glands and the male urethra.
- Pseudostratified columnar – single layer of column cells that looks like multiple layers. Lines trachea and larger airways.
Your skin is a special type of stratified squamous cells called keratinized cells. Keratin makes your skin cells harder and waterproof which makes them well suited to act as your body’s armour.
(Header image credit: Servier Medical Art)