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 Pig (Sus scrofa)

Texy by Lazaro Gonzales, Jr.

Digestive System:

The pig is an omnivore, which means it consumes both meat and plants.  The jaw and facial musculature involved in the beginning of the digestive process are discussed in the “Fetal Pig – Jaw and Facial Musculature” lab.  This lab concentrates more on the digestive organs of the abdominal cavity.  These organs are the liver, stomach, large intestine, small intestine, caecum, gall bladder, and pancreas [1,2,3,4,5].  The digestive organs reflect the diet of the animal.  The liver plays a large role in fetal development and is also responsible for the removal of toxins in the blood; it converts some toxins to bile [1,2,3].  Inferior to the liver lays the gall bladder.  This organ is involved in bile storage and is connected to the liver via the common bile duct.  The function of the stomach is to store food for further digestion and also releases enzymes and acid to break down food.  The small intestine then breaks the food down slowly and absorbs nutrients from it.  The next storage organ is the large intestine, which holds the food long enough to absorb the remaining water and nutrients [1].  The pancreas is an important gland that secretes digestive enzymes to break down any type of food [1].

The esophagus pierces the diaphragm and connects to the stomach.  Continuing caudally the small intestine (duodenum, jejunum, and ileum) attaches to the stomach at the pyloric sphincter.  This leads into the large intestine (colon) and goes into the rectum, which terminates in the anal opening [2]. 

General Dissection:

I opened the abdominal cavity by starting an incision at the top of the abdominal cavity and cutting caudally around the umbilicus to the end of the trunk.  I made sure the cut was shallow so as to not cut any organs in the abdominal cavity.  When I reached the caudal end of the trunk I cut deeply through the pubic symphysis to observe the urogenital and digestive organs to the pubic symphysis.  The pubic symphysis was not very difficult to cut through because of its cartilaginous state in the fetal pig.

The liver was the largest organ in the abdominal cavity and is located at the cranial end of the abdominal cavity.  Caudal to the right lobe of the liver is the gall bladder.  The stomach is located on the left side of the abdominal cavity.  The diaphragm caused the most problems in the removal of the digestive tract from the body.  I used the scissors to cut away as much of it as possible then used the scalpel to cut just above the cranial end of the stomach.  I severed the caudal end of the digestive tract approximately an inch from the anal opening near the rectum.  The large intestine was coiled and connected with mesentery.  It took much meticulous work to separate the large intestine from itself.  I used sharp pointed scissors to scrape away the mesentery.

Comparative Anatomy:

The rabbit’s digestive system differed from the fetal pig’s in that it had a longer large intestine and an extremely large caecum.  This type of digestive tract is common among hindgut-fermenting herbivorous mammals.  It was also true of the beaver, which mostly eats wood.  I noticed the organs in the abdominal cavity were located more caudally than they would be in the adult.  Once they develop more they will shift more cranially.  The liver was very large in proportion to body size compared to other mammals.  The liver develops earlier than the gut tube.  Also, the liver was visible well-vascularized, and the hepatic portal system showed with blue latex.  The cat was pregnant with kittens and each fetus also had a proportionally large liver.

References:

1. Field, H.E.  1944.  The Fetal Pig: An Introduction to Mammalian Anatomy.  Stanford University Press, CA.

2. Odlaug, T.O.  1980.  Laboratory Anatomy of the Fetal Pig.  Wm. C. Brown Company Publishers, Dubuque, Iowa.

3. Walker, W.F.  1980.  Dissection of the Fetal Pig.  W.H. Freeman and Company, San Francisco, CA.

4. Smith, D.G.  1998.  A Dissection Guide and Atlas to the Fetal Pig.  Morton Publishing Company, Englewood, CO.

5. Holstad, G.E.  1959.  The Fetal Pig: An Introduction to the Anatomy of the Fetal Pig.  Burgess Publishing Company, Minneapolis, MN.