This is a section through the wall of the oral cavity, i.e., a
cheek or lip. It's cut vertically, and you are looking into it
from the left side.
Author: Dr. Thomas Caceci
This is a section through the wall of the oral cavity, i.e., a
cheek or lip. It's cut vertically, and you are looking into it
from the left side.
The oral side has a lining of stratified squamous epithelium. In most domestic animals this would be keratinized, often quite heavily; this image is from a primate, and it is not keratinized. The oral cavity side totally lacks any of the adnexal structures associated with skin: no hairs, sebaceous or sweat glands, etc. The skin side has these things, and as external integument, it's always keratinized to some degree.
The center of this specimen contains some of the buccal muscles, strands of skeletal muscle that are part of the muscle sheet underlying the skin. Here it's acting as the "tunica muscularis" for this part of the digestive tract. Many rodents, such as the Golden Hamster (Mesocricetus auratus) have cheek pouches for temporary storage of food. The cheek pouch muscles are very well developed. The hamster fills the pouch and then can contract the buccal muscle to dump the contents whenever he wants.
The place of continuity between the "dry" integument and the "wet" oral mucosa is located at the top of this section. This sort of transition point is a mucocutaneous junction. Mucocutaneous junctions exist in several other sites: the anus, the nostrils, the vulva and the urethra.
The
image at left provides a closer look at this region of the lip. To the right of
the junction the epithelium is keratinized, and continues to become typical integument;
to the leftit grades off into typical wet oral epithelium. Even when the oral
cavity is keratinized, there is a histologically distinct separation at this point.
Monkey lip; H&E stain, paraffin section, 20x and 100x
