Answer:
The small intestine is part of the entire GI tract, and it is central in food absorption, more than anything else, as it is covered with microvili that will absorb the nutrients from the food that has been mixed with enzymes and been broken up by the movements along the GI tract, before it reached the small intestine. As such, the answers would be:
1. Motility is the process by which food, turned first into a bolus, and later on into chyme, is pushed along the GI tract, broken into smaller sections to maximize surface exposure to enzyme activity, mixed with all the necessary enzymes for nutrient extraction and, finally, expulsion of waste, and water extraction from the several chemical, and mechanical processes, against the food that was processed. In the small intestine, motility also plays a vital role as through segmentation and peristalsis, the chyme is mixed with such substances as the bile, which breaks down fatty acids, pancreatic juices, which break down glucose, and others. While segmentation continues separating the chyme into smaller portions so that more enzymes can act on it, peristalsis will ensure that the chyme comes into contact with the microvilli of the small intestine, where the actual absorption will take place.
2. The different mechanisms by which the chyme is mixed with secretions from the accesory glands: pancreas, liver and gallbladder, are: circular motions of small portions of the muscular layer of the small intestine, to further break apart the chyme that entered into the duodenum. Next, the liver produces bile and sends it to the gallbladder, who also adds extra enzymes to bile to be able to not just break apart fat, but also finish breaking up the proteins. The second movement is segmental contractions, which will further mix bile with the chyme, but it will also allow for pancreatic juice to mix with the chyme once those two come into contact, further down the line, and almost reaching the ileum. Once there the third movement, although they are not in order, but happen at the same time during the digestion and absorption process, is peristaltic contractions. These will propel the chyme towards the large intestine, but as it does so, the movement propels the nutrients towards the villi, which will capture them and pass them on to the bloodstream, or the lymphatic system, in the case of fats.
