Biology 104 Human Digestive System Anatomy

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Digestive system Biology 104

Accessory organs – these are not part of the alimentary canal, but are important organs 

for digestion. 


Inferior to the stomach and posterior to the small intestine is the pancreas.  The 

pancreas is a long, irregularly-shaped gland, with superficial resemblance to cottage 

cheese.   Some of its products, like the hormones insulin and glucagon, are dumped into 

the blood as they are needed. (Thus, the pancreas is an endocrine gland.)   The pancreas 

also produces enzymes that catalyze protein digestion.  These enzymes which are 

released as needed into the duodenum through a duct.  Thus, the pancreas is also an 

exocrine gland.   


     Bile produced in the liver also empties into the duodenum.  Ducts from the liver and 

gall bladder join to form the common bile duct which enters the anterior side of the 


duodenum right next to the pylorus.  Bile emulsifies fats, and the digestion of fats does 

not begin until they reach the small intestine.   


The small intestine loops back and forth, and fills much of the abdominal cavity.  

The small intestine is held in place by fan-like folds of connective tissue (mesentery) that 

contain many blood vessels.    Why would so many blood vessels be attach to the small 

intestine?   (Think about the major reason we have a digestive system)      





















































Find where the small intestine is attached to the large intestine and you will find 

3-way junction with the colon (a.k.a.  large intestine ).  A dead end tube or sac, the 

caecum, will be on one side of the junction. The colon is on the other side (the small 

intestine is, of course, the third).   In humans there is a relatively short caecum off of 

which an even thinner extension is found   This dead end tube, about as big around as a 

pencil and a couple of inches long, is the  





The colon has three regions, each named  for its orientation.  Within the ascending 

colon material moves upward.   Within the transverse colon material moves from right to 

left, and within the descending colon, material moves inferiorly toward the rectum.    


The distal portion of the colon extends into the true pelvis, which is the cylinder 

surrounded by bone in the center of the pelvis.   The colon ends at the sigmoid colon and 

then the rectum.  The external opening of the rectum is the anus.   (Sigmoid means 

“similar to sigma” or “similar to the letter S” as that part of the colon makes a few zig-

zags on its way to the rectum.) 


Let‟s review the passage of food through the alimentary tract:  If you swallow a piece of 

gum that you don‟t digest, list all the organs, in order, that the gum passes through: 


Mouth      












































  anus 
















IDENTIFY the following structures in the human torso model on the attached 

drawing:  esophagus, liver,  stomach, cardiac end of stomach, pyloric end of stomach, 

duodenum, pancreas, common bile duct, ascending colon, transverse colon, descending 

colong, caecum, vermiform appendix, and rectum.  



















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