As befits the active vertebrate lifestyle, there are many specializations of this tube along its length. The three main organic molecules we eat are carbohydrates , proteins , and lipids . Although digestion is ultimately done at the cellular level, the specialized vertebrate gut allows for extracellular digestion inside the lumen of the digestive tract. As you have already seen in lab dissections, different vertebrates have different specializations in their digestive tracts, depending on diet. A tongue may serve various purposes.
Lips help to hold food in.
The oral cavity is connected to a pharynx , or common region for both airway and food path. As a vertebrate swallows food, involuntary peristalsis passes the food along. Its length depends on neck length. One modification at its distal end in birds is a crop or storage area. Lining the gut from here on is an increasingly specialized mucosa or epithelial lining, involved in different digestive purposes.