126 



THE HUMAN MECHANISM 



So far as is known, these movements are aroused by the 

 distention of the intestine with food and possibly by chemical 

 stimulation of the muscular coat by substances formed within 



the tube. The presence of solid in- 

 digestible material also favors the 

 movements. 



33. Absorption is the name given 

 to the passage of digested food 

 materials from the cavity of the 

 intestine into the blood. The word 

 itself perhaps suggests that the 

 products of digestion are received 

 into the blood without change, as 

 a sponge might absorb a mixture 

 of peptids, amino-acids, sugar, fatty 

 acids, soaps, and inorganic salts. 

 Such, however, is by no means the 

 case, and the actual physical and 

 chemical processes of absorption are 

 complicated far too complicated 

 to be discussed here. Suffice it to 

 say that the intestine is not lined 

 by a dead membrane but by living 

 cells, and through these guardian 

 cells the products of digestion must 

 pass to enter the blood (see Fig. 59). 

 In their passage through these cells 

 teal. Observe that the products some o f the digestive products are 



of digestion must first be ex- .. , . .. ,, t , 



acted upon chemically so that they 

 enter the blood in forms more 

 available to the tissues of the 

 body. The object of the whole process of alimentation, 

 digestion, and absorption would seem to be that of sup- 

 plying food to the muscle fiber, the gland cell, the nerve 

 cell, etc., through the blood as an internal medium or 



FIG. 61. The intestinal struc- 

 tures concerned in absorp- 

 tion 



In one villas is shown the close 

 network of blood vessels im- 

 mediately under the lining 

 membrane ; in the other villus, 

 the central lymphatic, or lac- 



posed to absorption by the 



blood vessels before they can 



enter the lacteal 



