Esophagus

Esophagus — This muscular tube is located dorsal to the trachea. Food is pushed forward in the esophagus by the rhythmic contractions of its walls in a process known as peristalsis.

The esophagus extends posteriorly and dorsally within the thorax, then passes through the diaphragm into the abdominal cavity where it ends at the stomach

In order to find the esophagus use a probe to move the diaphragm away from the heart towards the abdominal cavity. Then with a pair of scissors, cut the left and right edges of the diaphragm slightly, just enough for you to completely pull it away from heart. Then gently use your probe to left the heart slightly to expose the esophagus underneath.

To view it from the abdominal cavity, locate the stomach and move the diaphragm up towards the heart. Then to the left corner of the stomach towards the liver and up against the diaphragm, you should be able to view the connection point of the esophagus to the stomach.

Urinary Bladder

Urinary Bladder — in the fetal pig the urinary bladder is an elongated sac in the lower ventral abdominal cavity. It lies between the prominent umbilical arteries and is seen when the portion of the body wall supporting the umbilical cord is folded down. You can use your probe to separate it out from the umbilical cord by sticking it underneath the point of connection and breaking through the connective tissue to free it from the skin of the umbilical cord.

Large Intestine

Large Intestine: the large intestine is joined at the bottom of the small intestine. Follow the coils of the small intestine. The end of the ileum enters the large intestine. At this juncture the cecum, a short blind sac about 2 cm. long, is formed. This organ takes about sixteen hours to finish the process of the digestive system. Food is no longer broken down at this stage of the GI tract. The colon absorbs vitamins such as K, B12, thiamine and riboflavin. The large intestine also compacts feces and stores fecal matter in the rectum until it can be released by the anus in defecation.

      · Cecum: the cecum connects the ileum with the ascending colon of the large intestine.

      · Ileocecal Valve: the ileocecal valve is situated at the junction of the small intestine (ileum) and the large     intestine. This passage limits the reflux of the colonic contents into the ileum.

      · Ascending Colon: the ascending colon is the first section of the large intestine. The main function of this section is to remove the water and other nutrients from waste material and recycle it back into the body by the blood stream. The waste material is then moved upwards towards the transverse section of the colon by peristalus (muscle contraction).

      · Transverse Colon: the transverse colon is the second section of the large intestine and connects the ascending colon to the descending colon. The transverse colon expulses the left over water and nutrients that came from the ascending colon into the blood stream and uses peristalus (muscle contraction) and carries the waste to the descending colon.

      · Descending Colon: the descending colon is the third section of the large intestine and is connected to the transverse colon and the sigmoid colon. The descending colon expulses of any left over water and nutrients into the blood stream and is moved to the sigmoid colon by peristalus (muscle contraction).

      · Sigmoid Colon: the sigmoid colon is the fourth section of the large intestine that is connected in between the descending colon and the rectum. The sigmoid colon also absorbs water and nutrients into the blood stream for recycling.

      · Rectum: the rectum is the fifth and final section of the large intestine that is connected between the sigmoid colon and the anus. It is the posterior dorsal portion of the large intestine and descends along the midline through the pelvic girdle to the onus, the intestinal opening to the exterior. The rectum, just like the rest of the large intestine, is a temporary storage place for fecal matter. When it becomes full the pressure from the fecal matter forces the anal canal apart making the fecal matter enter the canal and uses peristalic waves (muscle contraction) to propel the fecal matter out of the rectum forcing the anal muscles up.  

  · Anus: the anus is the intestinal opening to the exterior of the body. It is found underneath the pig's tail and expels the feces (waste) out of the body using peristalus (muscle contraction).

The spiral colon is a compact coiled mass clearly visible upon the left ventral surface. It is shorter, darker, and thicker than the small intestine. It is the major portion of the large intestine.

Anus

Liver

Liver — This dark brown organ dominates the upper abdomen. The falciform ligament, a ventral peritoneal membrane attaches the liver to the diaphragm and to the ventral body wall. The coronary ligament attaches the dorsal portion of the liver to the central tendon of the diaphragm.

The falciform ligament lies in a cleft of the liver which divides it into right and left halves. Five lobes can be differentiated. The four principal lobes may be seen from the ventral aspect, they are the right lateral, right central, left central and left lateral. A very small lobe, the caudate lobe, may be seen when the intestinal coils are moved to the left. It is attached to the posterior surface of the right lateral lobe.

Gall Bladder — Lift the right central lobe of the liver and expose the gall bladder embedded within a depression in its dorsal surface. This sac-like structure stores bile secreted by the liver and releases it into the duodenum. Bile is transported by the cystic duct from the gall bladder. It is joined by the hepatic duct from the liver to form the common bile duct which enters the duodenum.

Pancreas

Pancreas — Lift the main portion of the small intestine. Expose the stomach and duodenum. Observe the pancreas, a lobulated glandular structure lighter in color than the neighboring intestines. Its main portion lies in the loop of the duodenum. An elongated portion may be observed extending to the left, toward the stomach and spleen. Parts of the gland may also be seen along the dorsal body wall extending to the right of the duodenum and along the dorsal midline. The pancreatic duct enters the duodenum. It is small and difficult to find since it is embedded in glandular material.

Spleen

Spleen — this dark-colored elongated organ can readily be seen in the left side of the abdominal cavity without moving any other organs. It lies to the left of the stomach, along its greater curvature, and extends toward the right. It is tied to the stomach by a portion of the greater omentum, a specialized fold of the peritoneum, known as the gastrosplenic ligament.

Kidneys

Kidneys — this reddish-brown bean-shaped organ lays embedded retroperitoneal, or behind the parietal peritoneum, in the dorsal body wall, one on each side. To locate them you must lift the small and large intestines to reveal the dorsal body underneath, and then use your probe to break through the mesentery cover them in order to view them completely. You will be able to identify where they are by seeing an oval shaped lump through the mesenteries on both the left and right sides of the dorsal body.

Small Intestine

Small Intestines: the small intestines are located under the liver and the stomach. The small intestines contain millions of villi which contains microvilli so that the nutrients from the stomach and duodenum can be absorbed efficiently with such a large surface area.

Duodenum: the first portion of the small intestine is the duodenum. It is a continuation of the pyloric end of the stomach. It is a short “U” shaped tube, approximately 1 cm. long. The common bile duct and the pancreatic duct open into the duodenum. It uses enzymes to break down food in the small intestine and regulates the rate of which the stomach empties with hormonal pathways. Secretin and chloecytokinin are released from the cells in the duocanal epithelium in response to acidic and fatty stimuli when the pyloris opens and releases gastric chyme into the duodenum for further digestion.

Jejunum: The second section of the small intestine is the jejunum, which makes up about half the length of this organ. The jejunum lies between the duodenum and the ileum. The jejunum is specialized in the absorption of carbohydrates and proteins. What is left over from the stomach and the duodenum is soaked into the villi of the jejunum and is carried into the blood stream.

Ileum: the ileum is the final part of the small intestine and is connected to the jejunum and is separated from the cecum by the ileocecal valve. The ileum mainly absorbs vitamin B12 and bile salts as well as other digestion products that were not absorbed by the jejunum with the villi and microvilli that are a part of the folds in the ileum's inner wall.

The coils of the small intestine are held in place by a fine peritoneal membrane, the mesentery. It may be observed when lifting a coil of the small intestine and stretching the two ends. A fine, thin membrane, the mesentery, will be visible. It is responsible for the coiling observed.

Stomach

Stomach — This muscular pouch lies on the left side in the upper abdomen. It is the continuation of the esophagus. Find the esophagus and locate where it pierces the diaphragm to join the stomach. This is the cardiac end of the stomach. The fundus is the dilated anterior portion; the body is the main portion, while the pyloric region is the most posterior. This end joins the duodenum.

The cardiac sphincter controls the entrance of food into the stomach from the esophagus. The pyloric sphincter at the posterior end regulates the release of partially digested food (chyme) into the duodenum. Look along the inner walls of the stomach and note the rugae, or folds which help to churn and mix the food with digestive juices.

Mesenteries

The Mesenteries: make up the double layer extensions of the pericardium, they support most of the organs in the abdominal cavity. To locate the mesenteries, look for a layer of tissue that is lining the abdominal cavity. Some parts of the mesentery are attached to the organs to hold them in place.

Salivary Glands

To find the salivary glands, you must turn the fetal pig on its side first to get a better view of its cheeks. Then carefully cut through the skin along the side of the head between the ear and the mouth. Separate the skin from the underlying tissues and remove it to expose more of what is underneath. The platysma and other muscles associated with the skin are also removed to expose the salivary glands and ducts. This is to be don’t very carefully since the structure to be examined lie directly below the skin.

Parotid Gland — This is the largest of the salivary glands. It lies ventral to the pinna (external ear) and is recognized by its triangular shape and lobular texture. The parotid duct, can be seen emerging from the anterio-ventral edge of the gland by several roots. It then crosses the lower portion of the masseter muscle of the cheek, following the course of the prominent external maxillary vein. It continues to the mouth and opens opposite the upper fourth molar. You can find the opening by looking inside the cheek and tugging lightly on the duct with forceps.

Submandibular Gland — Most of this gland lies beneath and ventral to the parotid gland just posterior to the angle of the jaw. It is small and oval in shape. Separate the two glands. Its duct is hard to trace since it passes amongst some of the jaw muscles. It extends to the angle of the jaw, passes to the floor of the mouth, to the anterio-ventral connection of the tongue. At this point it opens into the mouth.

Sublingual Gland — This is the third salivary gland. It is flat and narrow and lies along the duct of the submandibular gland. Its duct parallels that of the submandibular and both open under the tongue, along its side.

The Digestive System

To examine the digestive system of the fetal pig, we cut down the center of the fetal pig, and around the umbilical cord. We made several horizontal cuts to make it easier to fold back the flaps of skin, to make the digestive system more accessible. Scissors are helpful when cutting through the ribs. Make sure to cut carefully and not too deeply, to avoid damaging the organs in the thoracic and abdominal cavity. 

Pull away the flaps of skin and muscle to expose the organs of the digestive system.

Video - Dissection Overview

Lets Take a Closer Look- this video shows an overview of the entire abdominal dissection pointing out the major parts included in it.