An American Text-Book of Physiology Volume 1 (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1900 Excerpt: ...opens into the blood-vascular system at the junction of the left internal jugular and subclavian veins. The substances that take this route are distributed to the tissues by the blood, but it is to be noticed that, owing to the sluggish flow of the lymph-circulation (see section on Circulation), a relatively long time elapses after digestion before they enter the blood-current. The products that enter the blood directly from the alimentary canal are distributed rapidly; but in this case we must remember that they first pass through the liver, owing to the existence of 1 Zeitschrift fur physiologische Chemie, 1895, Bd. 21; 1896, Bd. 22, and 1897, Bd. 23. the portal circulation, before they reach the general circulation. During this passage through the liver, as we shall find, changes of the greatest importance take place. The physiology of absorption is concerned with the physical and chemical means by which the end-products of digestion are taken up by the blood or the lymph, and the relative importance of the stomach, the small intestine, and the large intestine in this process. Leaving aside the fats, whose absorption is a special case, the absorption of the other products of digestion was formerly thought to be a simple physical process. The processes of diffusion and osmosis, as they arc known to occur outside the body, were supposed to account for the absorption of all the soluble products. This belief is still held by many, but the facts known with regard to the absorption of the carbohydrates, proteids, and fats after the changes undergone during digestion are not wholly accounted for by the laws of diffusion and osmosis as they arc4 known to us (see p. 65 for a discussion of the nature of these processes). For the present at least it seems to b...