Download Digestive System—This system consists of several organs that work

DIGESTIVE SYSTEM OF THE CAT
The Digestive System consists of a number of organs that work together to accomplish the physical and
chemical activities associated with the digestion process. Vertebrates ingest large particles of food that
contain proteins, fats & oils, carbohydrates, and nucleic acids. The digestive system, with its muscles
and numerous enzymes, physically and biochemically breaks down food substances into small molecules
such as amino acids, fat components, glucose, fructose, galactose, and nucleotides that can be readily
absorbed into the bloodstream through the small intestinal lining. Most of these molecules are small,
water-soluble molecules that are easily transported in the vertebrate blood since it is a water-based
medium. Some of the small fat components have to be packaged and absorbed a special way in order to
make it into the body.
The Digestive System consists of the alimentary canal and some accessory organs. The alimentary
canal is a continual tube beginning at the mouth and terminating at the anus. There are also several
accessory organs associated with the alimentary canal. The bulk of the digestive organs are situated in
the abdominal cavity, but there are several digestive structures associated with the head as well. You
will examine the organs of this system from an anterior to posterior direction.
Part A – Abdominal region
Prior to the identification of these structures, the abdominal cavity must be opened. Make a cut as
shown below.
1. Greater omentum—The first thing you will probably see when you
open up the abdominal cavity is the greater omentum. Find the
stomach and identify the greater omentum that connects to the greater
curvature of the stomach. The greater omentum contains adipose and
lymph nodes that help fight infection within the abdominal cavity.
(Do not remove this yet.)
2. Parietal peritoneum—With the abdominal cavity open, identify the
parietal peritoneum of the abdominal cavity.
Q1: What organs are located behind the
parietal peritoneum against the dorsal wall?
3. Visceral peritoneum—Identify a visceral peritoneum. This is also known as the outer
serosa layer of an organ.
4. Mesentery/Mesocolon—The
mesentery/mesocolon looks like “cobwebs”
connecting the organs to other organs and the
abdominal wall. Identify the mesentery and
mesocolon.
5. Lesser Omentum—Identify the lesser curvature
of the stomach and its associated lesser omentum.
6. Liver—This vital organ is the largest gland in the vertebrate body weighing three-four
pounds in the adult human. It consists of five lobes in the cat but only four in the human.
Identify the right and left medial lobes, right and left lateral lobes, and the single caudal
lobe. The liver lobules filter a tremendous blood volume from the hepatic portal system,
removing some substances from the blood while adding others.
a. The falciform ligament is a fold of the peritoneum that is located between the left
and right lobes of the liver. Its function is to connect the ventral side of the liver
to the abdominal wall. Identify the falciform ligament on the cat’s liver.
Q2: Blood received by the liver through the hepatic portal system is loaded with
glucose shortly after a meal. Explain what the liver does with the excessive blood
sugar with the help of the pancreas.
Q3: During times of fasting, the blood sugar level drops. Explain what the liver
does with the help of the pancreas to raise the blood sugar level.
Q4: The liver also stores fat or adipose tissue. What does this have to do with
vitamins A, D, E, and K?
Q5: Bacteria in the intestines and many body cells produce toxic ammonia (NH3)
that gets into the bloodstream. What does the liver do with this biochemical
hazard and other toxins?
Q6: The spleen, red bone marrow, lymph nodes and the liver are all capable of
destroying old worn-out erythrocytes. Hemoglobin is broken down into a
chemical pigment called bilirubin and placed into the bloodstream. What does
the liver do with bilirubin?
7. Spleen—The spleen is a long slender dark-colored organ that is situated laterally to the
stomach and extends towards the ventral side of the cat. The spleen is not part of the
digestive system, but instead . Locate this structure.
8. Gall bladder—Locate the gall bladder embedded ventrally in the right medial lobe of the
liver. Then see if you can find and identify the following structures:
a. Hepatic ducts—Identify the common hepatic duct before it joins with the cystic
duct.
b. Cystic duct—Locate this structure that connects to the gall bladder.
c. Common bile duct— This is actually very difficult to locate. Locate where the
pancreas comes in close contact with the duodenum and see if you can find the
duct.
9. Pancreas—This organ is not as easy to spot but has a ventral lobe suspended in the
duodenal mesentery and a dorsal lobe found dorsal to the greater curvature of the
stomach. Locate both lobes and leave the pancreas intact, but separate the pancreas from
the small intestine and stomach.
Q7: This gland functions both as an exocrine and an endocrine gland. Acinar
cells border minute ducts that lead to the major pancreatic duct. These cells
secrete the pancreatic juice that act upon specific food substances when they
reach the duodenum. This is an exocrine function. What does exocrine mean?
Q8: Little groups of pancreatic cells called “Islets of Langerhans” secrete
insulin and glucagon to help control blood sugar. This is an endocrine function.
What does endocrine mean?
Q9: Describe the influence on sugar metabolism provided by the pancreatic
hormones listed below.
 Insulin
 Glucagon
Leave behind:
Liver
Gall Bladder
Pancreas
Spleen
10. Stomach—In order to study the gastrointestinal tract more easily, you will now
remove the entire GI tract as one unit. On the posterior end of the esophagus,
make your first cut, and at the posterior end of the rectum, make your second cut.
Carefully lift the entire GI tract out of the abdomen, cutting mesentery where
necessary and taking care not to destroy the other organs you are leaving behind.
In particular, be careful when separating the duodenum from the pancreas, leaving
the connection between the duodenum and the common bile duct intact. (Cut the
common bile duct above this point.)
a. Cardiac sphincter—
Identify the location of
the cardiac or
gastroesophageal
sphincter where the
esophagus joins the
anterior end of the
stomach.
Q10: What is
regurgitation?
b. Slice the stomach open lengthwise and remove any contents. Throw contents in
trash and rinse stomach out if necessary. Locate the rugae if possible. If not,
observe another group’s cat that has rugae.
Q11: Did your cat’s stomach contain chyme?
c. The stomach wall has four layers of tissue. Cut into the ventral stomach wall and
remove a ¼ square inch from it with you scalpel. Use the dissecting scope try to
identify the four layers from inside out.
Mucosa  Submucosa Muscularis  Serosa
d. Pyloric sphincter—This involuntary, circular muscle provides a valve between
the stomach and the duodenum at the gastro-duodenal junction. Locate this
structure.
11. Small Intestine—Duodenum
a. This is the very first portion of the small intestine just medial to the pyloric
sphincter. Identify it in the cat where it is about two inches long. In the human, it
is about ten inches long. This portion of the intestine receives the common bile
duct into which the cystic, hepatic, and pancreatic ducts drain.
b. Sphincter of Oddi—Within the duodenum, chyme is mixed with bile and
pancreatic enzymes. Carefully slice the duodenum open lengthwise and look for
the Sphincter of Oddi. If visible, it would be a small opening near the pyloric
sphincter.
12. Small Intestine—Jejunum
This is the second part of the small intestine measuring about three feet long in
the human and comprises about 2/5 of the small intestinal length in most
vertebrates. This tube receives the partially digested food mass from the
duodenum and secretes several enzymes to complete chemical digestion. Some
absorption of digested food molecules does take place through its wall into the
blood.
a. Remove the mesentery of the small intestine to stretch it out. Carefully slice a
portion of the jejunum and ileum open lengthwise. Using a dissecting scope
examine the cut edge of its walls and also an internal surface view of its mucosa.
Q12: Does the jejunum of the cat contain plicae circulares?
b. Identify the villi under a dissecting scope.
Q13: Explain why each villus has an arteriale and a venule.
Q14: What are lacteals and why are they needed?
c. Now look at a prepared microscope slide containing a section of the jejunum.
Identify the microvilli, which are sometimes called the brush border, and the
goblet cells which make mucus.
13. Small Intestine—Ileum.
This last portion of the small intestine is about six to seven feet long in a human
and constitutes about 3/5 of the small intestinal length in most vertebrates. The
ileum absorbs digested food molecules into the bloodstream.
Q15: Peristaltic muscular action occurs about eleven times per minute moving
the food through the intestinal tract at about three inches per minute. The circular
muscles of the intestinal muscularis also cause segmental action. How does
segmentation facilitate digestion in the jejunum and absorption in the ileum?
Q16: Simple passive transport is sometimes responsible for the absorption of
digestive food molecules into the bloodstream. Explain what this means.
Q17: Active transport is the most common method of absorption of intestinal
nutrients into the blood. Explain what this means.
Ileocaecal valve—Locate this valve as a constriction at the junction of the ileum
and the beginning of the colon. This junction is normally found in the lower right
quarter of the abdominal cavity.
14. Large Intestine—Caecum
The caecum is a holding area for the food that needs to pass through the large
intestine. In humans, this is also the location of the vermiform appendix. Identify
the caecum on the large intestine side of the ileocaecal valve.
Q18: Does the cat have an appendix like the human does?
15. Large Intestine—Colon—This tubular structure has a greater diameter but a lesser
length than the small intestine. Identify its ascending, transverse, and descending
portions. It receives a liquid mass from the ileum. The cat lacks a sigmoid colon.
Q19: Does the cat’s colon have haustra like the human colon does?
16. Large Intestine—Rectum—Identify the last tubular portion of the digestive tract.
Q20: What is its function?
17. Large Intestine—Anus—This is the opening of egestion or defecation. Identify this
structure.
Part B – Head region
1. Parotid salivary glands—This pair is one of three major pairs of salivary glands in the
cat or human. The parotids are the largest salivary glands situated ventral to the base of
the ear and posterior to the masseter muscle. These glands are the ones infected when the
mumps virus attacks a human. Remove the skin from this area. Clean the superficial
fascia and adipose tissue from this area either on the left or right side of the face. Locate
this structure.
2. Parotid duct— Within the parotid gland, cells line minute ducts and empty a secretion
called saliva into ducts that drain it to a single major duct on each side of the head. This
parotid duct that drains the parotid gland to the oral cavity. The parotid duct is a
transparent tube that passes across the masseter muscle. If possible, locate this structure.
3. Submandibular (Submaxillary) salivary glands—Try to locate one of these glands.
This gland is smaller than the parotid and is found ventral and posterior to it. (The
Sublingual salivary gland will not be located in this lab. You would find this gland
deeper within the neck.)
Part C – Mouth region
You will now open the mouth cavity. Do not destroy the exposed parotid duct in the process. The
cheek tissue should be bisected (cut in half) starting at the corners of the mouth and working towards the
mandibular joint. The coronoid process of the mandible will need severed from the rest of the mandible
on both sides.
4. Oral cavity. Locate this structure.
5. Hard palate—This forms the anterior part of the roof of the mouth. Locate this
structure.
6. Soft palate—This forms the posterior part of the roof of the mouth. Locate this
structure.
Q21: Does the cat have a uvula like the human?
7. Tongue
a. Lingual frenulum. Locate this structure.
b. Bisect the end of the tongue into right and left halves. Examine the musculature
of the tongue.
Q22: Do all the muscle fibers travel in the same direction? Why or Why not?
c. Remove a part of the tongue and look at it under the stereoscope. There are
several kinds of papillae found on the human tongue. See if you can identify the
papillae that your cat has. Filiform papillae are short threadlike elevations
covering most of the tongue surface. In cats and cattle they are heavily cornified
to give a rasping tongue. These papillae are mainly to help us grasp food.
Fungiform papillae are knob-like projections of the tongue scattered among the
filiform papillae. Circumvallate or vallate papillae are 8 to 12 large circular
papillae arranged in a V near the base of the tongue. Both the fungiform and the
circumvallate papillae have taste buds associated with them.
Filiform Papillae
Circumvallate Papillae
Fungiform Papillae
8. Epiglottis & Pharynx—Look past the oral cavity and deep into the larygnopharynx and
find the opening to the epiglottis.
Part D – Neck region
9. Esophagus—On the ventral side of the neck, nudge the trachea to the cat’s right. This
should reveal a portion of the esophagus. Follow the esophagus down as far as possible.
If we opened the chest, you would be able to follow the esophagus pass posterior to the
heart and lungs and see it pass through the diaphragm. (We will do this at a later date.)
Part E – Disorders of the digestive system.
(Look in your textbook or online to find this information.)
a. What is gastritis?
b. What is a peptic ulcer?
c. What is a duodenal ulcer?
d. What is gastroenteritis?
e. Describe diabetes and what causes it?
f. What is jaundice?
g. What is hepatitis?
h. What are hemorrhoids?
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