Step 6: Thoracic Organs

Procedure: Cut through the abdominal wall of the rat following the incision marks in the picture. Be careful not to cut to deeply and keep the tip of your scissors pointed upwards. Do not damage the underlying structures. Once you have opened the body cavity, you will need to rinse it in the sink.

1. Locate the diaphragm and the heart is centrally located in the thoracic cavity. The thymus gland, may be visible at the upper part of the heart.

2. The lungs are spongy organs that lie on either side of the heart and should take up most of the thoracic cavity. They lie closer to the back of the rat, you will need to push the ribs to the side to find them.

3. A sheet of muscle can be found just under the heart (and above the liver) - this is the diaphragm. This muscle is only found in mammals. (The diaphragm may have been cut when you opened the thoracic cavity.)

rat thoracic

On this image, the heart and thymus are obscured by fatty tissue at the top of the heart. The pericardium is also not easily seen, as it is a clear membranous sack that surrounds the heart.

The Abdominal Organs

1. Locate the liver, which is a dark colored organ suspended just under the diaphragm. It has four lobes:

median or cystic lobe - located at the top, there is an obvious central cleft
left lateral lobe - large and partially covered by the stomach
right lateral lobe - partially divided into an anterior and posterior lobule, hidden from view by the median lobe
caudate lobe - small and folds around the esophagus and the stomach, seen most easily when stomach is raised


caudate lobe

2. Find the stomach, its a curved organ lying just under the liver. At the top of the stomach you can see the esophagus where it pierces the diaphragm and joins the stomach. Lifting the stomach up may reveal a bumpy glandular organ: the pancreas.


rat digestive

3. The spleen is about the same color as the liver and is attached to the greater curvature of the stomach.

4. The small intestine is a slender coiled tube that receives partially digested food from the stomach (via the pyloric sphincter). It consists of three sections: duodenum, jejunum and  ileum, (Listed in order from the stomach to the large intestine.)  The duodenum is recognizable as the first stretch of the intestine leading from the stomach, it is mostly straight.  The jejunum and ileum are both curly parts of the intestine, with the ileum being the last section before the small intestine becomes the large intestine. 

5. Locate the colon, which is the large greenish tube that extends from the small intestine and leads to the anus. The colon is also known as the large intestine and it consists of four sections:

cecum - large flattened sac in the lower third of the abdominal cavity, it is a dead-end pouch and is similar to the appendix in humans.
ascending colon – food travels upward.
transverse colon – a short section that is parallel to the diaphragm
descending colon – the section of the large intestine that travels back down toward the rectum.
rectum - the short, terminal section of the colon that leads to the anus. The rectum temporarily stores feces before they are expelled from the body.


Go to Step 7: Urogenital System