Shoulder

Brachium

Antebrachium

Facial and Masticatory Muscles

Thorax and Heart

Brain

Body Wall

Hip and Thigh

Shank and Foot

Digestive System

Urinary and Reproductive Systems

Hip and Tail

Digestive system of the Rat (Rattus norvegicus)

Photos and text by Yu Jin Kim and Ana Panduro

The dissection part of this lab was very simple.  We made an incision on the ventral side of our rat starting at the diaphragm and continuing all the way down to the base of the tail, opening up the abdominal cavity. 

The organ that is most cranially situated in the abdominal cavity is the liver.  One of the important functions that the liver performs is regulating the normal glucose level in blood.  When an excess of glucose enters the body with intake of food, the liver takes up the glucose and stores it until it is needed again as glucose level in blood declines.  Another important function of liver is bile secretion.  Bile helps digestion by dissolving  fats and fat-soluble vitamins.  The production of bile helps eliminate waste products.  The fetal pig had a very large liver because the liver develops early.  It has to work when the animal is very young.   

The stomach is situated caudal to the rib cage in the left part of the abdominal cavity.  The stomach has a few different roles in the digestion process.  First, it can act as a storage place.  When a lot of food is consumed at once, the stomach holds it until enzymes and acid break it down.  Another function of the stomach is liquefaction of food.  Lastly, the stomach releases ground food into the small intestine for further digestion and absorption.  The rat has a relatively large stomach for its body size and the rabbit also had a large stomach in relation to its body. 

The structure that takes up most of the space in the abdominal cavity is the intestine, which is a long and curvy.  The intestine us usually  divided into the small intestine and the large intestine.  Food that is broken down and reduced to liquid by the stomach enters the small intestine and all essential nutrients such as water, electrolytes, fatty acids and amino acids are absorbed into the blood.  The small intestine is attached to the stomach at the pylorus and the first part of the small intestine is the duodenum, which is about 95 to 100 mm long in the rat.  Jejunum begins at the end of the duodenum, and it is the longest part of the intestine.  Its average length is 900 to 1350 mm in the rat and it fills up right ventral side of the abdomen.  The ileum is the last part of the small intestine and its length is 25 to 35 mm long in the rat.  Then the large intestine begins which can also be segmented into three different structures ; cecum, colon and rectum.  The ileum is connected to cecum by the ileocecal plica and the cecum marks the beginning of the large intestine.  The colon is the longest part of the large intestine, and it is further subdivided into ascending, transverse and descending colon.  The last part of the large intestine is the rectum and it is a straight midline tube that is continues to become the anal canal.  When broken down food material reaches the large intestine, most of its water and electrolytes have been absorbed by the small intestine, but some still remain to be absorbed in the large intestine.  When all the water and electrolytes are absorbed, any remaining food particles are completely dehydrated mixed  with bacteria to be excreted as feces.  The large intestine also contains microbial organisms that help during the digestion process.  Intestines in other mammals in the class were long and curvy like the one in the rat except for the opossum.  The opossum had a very short gut, which was very interesting. 

Reference:

1. Hebel, Rudolf. Stromberg, M.W. Anatomy of the Laboratory rat.  The Williams & Wilkins Company. Baltimore. 1976