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.
The innumerable tiny fat drops drained off by the intestinal lymphatics or lacteals after an ordinary meal make their contents look white and milky, hence the name.* During fasting the lymphatics of the small intestine, like those in other parts of the body (see Chap. XIII.) convey a clear colorless liquid.
In the duodenum the bulk of food entering from the stomach is increased by the bile and pancreatic secretions poured out on it. Thenceforth absorption overbalances excretion, and the food-mass becomes less and less in bulk to the lower end of the ileum. The contractions of the small intestine drive on its continually diminishing contents, until they reach the ileo-colic valve, through which they are ultimately pressed. When the mass enters the large intestine its nutritive portions have been almost entirely absorbed, and it consists chiefly of some water, with the indigestible portions of the food and of the secretions of the alimentary canal. It contains cellulose, elastic tissue, mucin, and somewhat altered bile pigments; commonly some fat if a large quantity has been eaten; and some starch, if raw vegetables have formed part of the diet. In its progress through the large intestine the food-mass loses still more water, and the digestion of starch and the absorption of fats is continued. Finally the residue, with some excretory matters added to it in the large intestine, is expelled from the body.
How are emulsified fats carried off?
What are the lacteals? Why so called? Under what conditions do the lacteals not contain milky looking chyle?
In what part of the alimentary canal does absorption more than balance the amount of liquid poured out on the food?
What arc the constituents of the mass passing from the small into the large intestine? What changes does this mass undergo as it passes along the large intestine?
* From Latin, lac, milk.