i think its mucus or something similar
Cells and muscles.
Smooth muscle lines most of the digestive system, especially the intestine.
digestive system is lined inside by non-keratinised stratified squamous epithelium some of which are ciliated
The bacteria that lines the inner stomach breaks down and makes the foods digestive, regardless of the acid it contains.
PeristalsisPeristalsis
Anatomy starts at the cellular level. (I'm going to use the digestive track for this example) First there are cells. Cells make up tissues (such as the tissue that lines the inside of your stomach). An accumulation of different tissues then makes an organ (ie. your stomach). An organ system would be a group of organs that work together, in this example it would be the digestive track: esophagus ...stomach...small intestine...colon..etc. And then finally, a group of organ systems makes up an organism, which would be you or me, a human!
The integumentary system includes your skin, and mucus that lines your stomach, intestines, and rectum.
Peristalsisis a radially symmetrical contraction and relaxation of muscles which propagates in a wave down the muscular tube, in an anterograde fashion. In humans, peristalsis is found in the contraction of smooth muscles to propel contents through the digestive tract. Earthworms use a similar mechanism to drive their locomotion.[1] The word is derived from New Latin and comes from the Greek peristallein, "to wrap around," from peri-, "around" +stallein, "to place".
Villi lines the small intestine. They are what absorb nutrients into the body from the food that's eaten and passes through the digestive system.
Mucous membranes line the digestive and respiratory tracts.
epithelium
Epithelial tissue lines the outer surface of the body and lines the hollow organs.