Biology 104 Human Digestive System Anatomy

stomach.  Locate the cardiac end of the stomach near the diaphragm where the 

esophagus enters the stomach.  It is named the „cardiac end‟ because it is the end closest 

to the  heart.  There is a weak muscle here called the cardiac sphincter that keeps food 

in the stomach from splashing on to the esophagus.  The stomach walls secrete HCl as 

well as pepsin, an enzyme that catalyzes the breakdown of some proteins. 

 

What would be the result of the contents of the stomach splashing onto the esophagus?   

(There‟s a common name for this occurrence. )  

 

 

 

At the posterior end of the stomach is a constriction where the stomach joins the 

anterior end of the small intestine.  This constriction between the stomach and small 

intestine is the pyloric sphincter, which is a circular muscle (a sphincter) that controls 

the movement of acidic chyme from the stomach to the small intestine.  It allows just a 

little bit of stomach contents to move into the small intestine at a time.   As the stomach‟s 

peristaltic waves push food from the cardiac end to the pyloric end, the pyloric sphincter 

will open and let a bit of partially digested food into the small intestine. 

 

What is different about the stomach contents that makes it important to have gate-

like muscles at either end of the stomach ? 

 

 

 

 

 

The anterior end of the small intestine is the duodenum – so named becasue it is 

about 12 inches long in the average human. (Latin for twelve is „duocecim.‟)  The small 

intestine on the model is not loose as it is in real life.  In a living person it is actually a 

tube about 3 meters long.    The duodenum begins at the pylorus of the stomach, extends 

to the right side of the abdomen, then loops back to the left half of the body, passing close 

to the stomach and spleen.