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ANIMAL BIOCHEMISTRY 



Cardiac gland 

 region 



FIGURE 17-1. Diagram of the stomach of a horse. (Courtesy of W. B. Saunders Co.) 



food is swallowed, the additions tend to occupy the central region 

 since the wall is covered. Salivary action continues in this mass until 

 gastric juice is admixed by the muscular activity of the stomach. 



A continuing gentle contraction in the cardiac region presses the 

 stomach contents toward the pylorus. In this latter region peristaltic 

 waves slowly move the material toward the pyloric valve, which 

 responds to a high acidity by opening momentarily and allowing a 

 small quantity of liquid or semiliquid material to pass through. 

 On closing, the valve temporarily reverses the general flow and aids 

 in mixing the contents of the pylorus. Intermittent operation of this 

 sphincter both aids in gastric digestion by prolonging the exposure 

 time in the stomach and controls the admission of material into the 

 intestine. 



The musculature of the stomach is controlled by a highly organized 

 nerve network providing synchronized activity. Since the network 

 has a connection with the vagus system, strong emotion can inhibit 

 normal stomach movements. Cramps and vomiting represent reflex 

 responses to abnormal stimuli. 



Secretion of gastric juice appears to be controlled by reflex re- 

 sponses to eating and to a lesser extent to the specific local chemical 

 effects of meat components and degradation products. The rate of 

 gastric secretion rises rapidly after a meal to a maximum in about 2 

 hours and then declines steadily. It seems probable that secretion 

 occurs at low levels even for long periods without food and that the 

 entire process is at least partially under hormone control. Although 

 extensively studied, the mechanisms and control of gastric secretion 

 are but poorly understood. 



