The Gastrointestinal System
In this lab you will be learning about the gastrointestinal system.
Begin by clicking on the following:
The gastrointestinal system (GI system) can be thought of as a long tube called the ailimentary canal that begins in the mouth and continues to the anus. There are also some accessory organs attached to the canal.
Begin by locating the parotid gland right and left and the submandibular glands right and left. These are 2 of the 3 salivary glands. Not only do these glands secrete saliva but they also secrete a digestive enzyme called salivary amylase that begins the chemical breakdown of carbohydrates. There is a 3rd set of salivary glands called the sublingual glands located under the tongue.
Rotate the image 90 degrees to the right.
Dissect away the following structures:
Parotid gland right
Submandibular gland right
Styloglossus right
Hyoglossus right
Locate the 3rd salivary gland called the sublingual gland located just under the tongue.
Locate the superior constrictor right and inferior constrictor right. These are 2 muscles that are activated when swallowing. They are smooth muscles under involuntary control and innervated by cranial nerves. Thus swallowing problems are commonly linked to cranial nerve or brainstem injuries.
Use your text to view the areas of the pharynx.
Click on the following to reorient the image:
Locate the esophagus (muscular layer of the esophagus) and the stomach. Also locate the left and right lobes of the liver. Notice how close the stomach is to the liver.
Rotate the image 180 degrees.
Observe the connection point between the stomach and esophagus. The esophagus connects to the stomach at an area called the cardiac region of the stomach. There is a small circular muscle called the cardiac or esophageal sphincter. This muscle normally remains closed until something is swallowed. In some people part of the cardiac region of the stomach pushed superiorly through the diaphragm. This is called a hiatl hernia and can cause gastric reflux. The sphincter cannot remain closed so the contents of the stomach move up into the esophagus. This can wear away the lining of the esophagus which can be a serious problem.
Dissect away the right and left lobes of the liver.
Locate the pancreas just inferior to the stomach. The pancreas is a member of 2 systems; the GI and endocrine systems. It's primary role in the GI system is to secrete digestive enzymes.
Dissect away the pancreas.
Observe the stomach again. The stomach is divided into a number of regions. Besides the cardiac region mentioned above there is the body, fundus and pyloric regions of the stomach. The inside of the stomach contains folds or rugae which help to mix food. There are also convex and concave curves of the stomach called the greater and lesser curvatures.
Locate the pyloric orifice. This area of the stomach contains a sphincter muscle called the pyloric sphincter. This muscle works to regulate the emptying of the contents of the stomach.
Locate the duodenum.
The duodenum is the first part of the small intestines. The pancreas secretes its substances into the duodenum via a duct called the pancreatic duct. The gallbladder also secretes bile into the duodenum via the common bile duct. Bile is made in the liver. The gallbladder is a storage area for bile. When fatty food enters the duodenum the gallbladder contracts and pushes the bile into the duodenum. The bile works to break up fats by a process called emulsification.
Locate the right and left hepatic ducts and the bile duct (common bile duct).
Locate the pancreatic duct.
The next part of the ailimentary canal is called the jejunum. You can see the connection point between duodenum and jejunum by dissecting away the following:
Second segment of the jejunum
Here you will see the duodenaljejunal flexure.
Dissect away the third and fourth segments of the jejunum.
You should now see the proximal jejunum.
Locate the proximal ileum. The ileum is the last section of the small intestine. Locate the terminal ileum. This is the last segment of the ileum and ends at the cecum. Locate the cecum. This is where the large intestine begins.
Rotate the image back to 0 degrees.
Locate the following:
Ascending colon
Transverse colon
Descending colon
Sigmoid colon
Longitudinal layer of the muscular layer of the rectum
These represent the large intestine. Notice the difference between the large and small intestines. The large intestine is divided into large sections containing pouch-like structures called haustra. The structure reflects the function of each portion of the intestines. The small intestine has a large surface area because it absorbs the nutrients. The large intestine does very little absorption of nutrients. It mainly absorbs water and electrolytes and moves the material through.
Accessory organs of digestion.
Reorient the image by clicking on the following:
Locate the right and left lobes of the liver as well as the falciform ligament. The falciform ligament separates the right and left lobes. Locate the round ligament of the liver. This ligament is a remnant of fetal circulation and connects to the umbilicus.
Locate the gallbladder. Notice how it is located in an inferior-posterior position.
Dissect away the left lobe of the liver to better see the gallbladder.
There are 2 other lobes not seen in this dissection. They are the caudate and quadrate lobes. Use your text to locate these.
This concludes the lab