Study the digestive system on a microscopic level on The Human Protein Atlas website - these images are excellent, labeled, and you can click to zoom in. The Apologia text specifically looks at stomach and liver, so I've linked those here, but the Protein Atlas website has samples from all the major organs in the human body.
CLICK HERE to view the stomach lining.
CLICK HERE to view the liver.
(click on the image and zoom in)
Dissection of Human Cadaver Digestive System
*Warning: This educational video does contain images of a human cadaver used for a Human Anatomy and Physiology class*