290 



THE MAINTENANCE OF THE INDIVIDUAL 



lies between the mucous and muscular layers. The latter is made up 

 of three layers of involuntary muscles, an inner, poorly developed 

 obUque layer over which lies a circular layer that in turn is enclosed 

 by an outer layer of longitudinal muscles. The fourth or outermost 



coat is known as the serosa, 



ynoufh 



capillar 

 lumen 



parietal' 

 cells 



tissoe ^ 



:^'J> 



A typical gastric gland. Explain the 

 functioning of each part. 



which is continuous with the 

 peritoneum and as such covers 

 both organs and their associ- 

 ated glands. This covering is 

 moist and serves not only as 

 a protection but also facilitates 

 the movement of one portion 

 over the other. 



Food in order to reach the 

 stomach must be rolled into 

 boluses and then swallowed. 

 This is a complicated reflex 

 movement which apparently 

 may be more or less volun- 

 tarily initiated as the bolus 

 passes into the pharyngeal 

 region, past the trap door (epi- 

 glottis) which covers the open- 

 ing into the larynx and trachea. 



Failure of this flap to close properly results in food "going down the 

 wrong way," when the mass is expelled after a paroxysm of choking 

 and coughing. 



Liquids and soft foods reach the stomach in about 0.1 second while 

 more solid boluses are passed along by a series of slow-moving wavelike 

 contractions, called peristalsis. Boluses require about six seconds to 

 reach the stomach. The entrance of food into the stomach is prob- 

 ably controlled by the cardiac sphincter. Solid food may remain 

 in the stomach for several hours. One of the first noteworthy obser- 

 vations of this process was made upon Alexis St. Martin, a Canadian 

 voyageur who was studied by Beaumont in 1847. The adventurer 

 had a permanent opening into his stomach as a result of a gunshot 

 wound, which permitted direct observation of processes going on within 

 the stomach. These and other studies indicate that the fundus largely 

 fimctions as a reservoir which retains the bulk of the food while the 

 more muscular pyloric portion churns it, forcing it periodically into 



