This section is from the book "The Human Body: An Elementary Text-Book Of Anatomy, Physiology, And Hygiene", by H. Newell Martin. Also available from Amazon: The Human Body.
Through its whole extent the mucous membrane lining the digestive tube is traversed by very closely packed tubes of two kinds, the blood and lymph vessels. Matters ready for absorption pass through or between the cells covering the surface of the mucous membrane, and then through the very thin walls of the smallest blood and lymph vessels; and by these vessels are conveyed to larger channels with thicker walls, which all ultimately lead to the heart. From the heart the digested and absorbed food is distributed to every organ of the body.
Absorption from the Mouth, Pharynx, and Gullet is but slight. Some water, some common salt, some sugar, and some grape sugar (made from starch by the action of saliva) are no doubt taken up during the processes of chewing and swallowing. But the time which elapses between taking a mouthful of food and its transference to the stomach is usually too short to allow the occurrence of any considerable absorption.
Why should dyspepsia never be neglected?
What tubes are found in the mucous membrane of the alimentary canal? How do dissolved foods enter them? Where are the absorbed matters carried? To what parts are they finally distributed?
What foodstuffs are partly absorbed in mouth, pharynx, and gullet? Why does not any great amount of absorption take place in those parts?