In Ross's book of histology it says that the mesothelium that includes all body cavities is made of simple squamous epithelium but in other places it says that in the gastrointestinal tract it is made of simple columnar epithelium. Is it that the trachea and the the gastrointestinal tract are not classed as cavities?
The peritoneum, the pleura, the pericardium, the tunica vaginalis testis and the tunica serosa uteri are made of mesothelium (simple squamous epithelium) .
The GI tube is made of a specialized tissue composed from four layers: mucosa, submucosa, muscularis externa and adventitia. The innermost layer (mucosa) has an epithelium that is stratified, squamous and non-keratinising, for protective purposes. The internal organs in the peritoneal cavity are covered with the visceral sheet of peritoneum which is the adventita layer .
Trachea is made of respiratory epithelium, which serves to moisten and protect the airways. It is lined with pseudostratified columnar epithelium with goblet cells that produce mucus .
Trachea, stomach and intestines are considered cavitary organs as opposed to parenchymatous organs (lung, kidney, liver).