Download 10. Digestive System

Name____________________________________ Section ________________
10
Digestive System
OBJECTIVES
1. Identify and state the function for the organs of the digestive system
2. Describe where these organs are positioned in relation to each other
3. Review “Organs to know”
MATERIALS NEEDED
Double- injected fetal pigs
Dissecting materials
Gloves
Cotton string/twine
PREPARATION
Read Biology a Guide to the Natural World Chapter 28
INTRODUCTION
In this unit we will be examining the anatomy and physiology of a fetal pig, specifically the digestive
system. The digestive system is a convoluted tube that begins at the mouth and ends at the rectum.
Additional organs and glands run along this tube to aid in digestion. Below is a list of the organs in the
digestive system with their functions.
Peritoneum: lines the abdominal wall and consists of epithelium supported by connective tissue.
Mesenteries: Double-layered sheets of peritoneum, called, project from the body wall and support the
organs.
Liver: the largest organ in the abdomen, performs numerous vital functions, including (1) disposing of
worn-out red blood cells, (2) producing bile, (3) storing glycogen, (4) maintaining the blood glucose
level, and (5) producing blood proteins.
Stomach stores food and has numerous gastric glands that secrete gastric juice, which digests protein.
Small intestine: (1) receives secretions from the pancreas and gallbladder, (2) digestion of all
components of food-carbohydrate, protein, and fat, (3) absorbs the products of digestion: glucose, amino
acids, glycerol, and fatty acids.
Large intestine: absorbs water and prepares feces for defecation at the anus.
Gallbladder: stores and releases bile, which aids the digestion of fat.
Pancreas: (1) produces and secretes pancreatic juice, which digests all the components of food in the
small intestine and (2) secretes the hormones insulin and glucagon into the bloodstream. Insulin and
glucagon regulate blood glucose levels.
Duodenum: begininning of small intestine where bile and pancreatic juices are introcuded by way of
ducts. As an endocrine gland, the pancreas
Spleen: a lymphoid organ in the lymphatic system that contains both white and red blood cells. It purifies
blood and disposes of worn-out red blood cells.
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I. Activity
Preparation
1. Place the fetal pig on its back in the dissecting pan.
2. Tie a cord around one forelimb, and then bring the cord around underneath the pan to fasten back the
other forelimb.
3. Spread the hind limbs in the same way.
4. With scissors always pointing up (never down), make the following incisions to expose the thoracic
and abdominal cavities. The incisions are numbered on Figure 1 to correspond with the following steps.
Thoracic and Abdominal Incisions
1. Cut anteriorly up from the diaphragm, a structure that separates the thoracic cavity from the
abdominal cavity, until you reach the hairs in the throat region.
2. Make two lateral cuts, one on each side of the midline incision anterior to the forelimbs, taking extra
care not to damage the blood vessels around the heart.
3. Make two lateral cuts, one on each side of the midline just posterior to the forelimbs and anterior to the
diaphragm, following the ends of the ribs. Pull back the flaps created by these cuts to expose the thoracic
cavity.
4. With scissors pointing up, cut posteriorly from the diaphragm to the umbilical cord.
5. Make a flap containing the umbilical cord by cutting a semicircle around the cord and by cutting
posteriorly to the left and right of the cord.
6. Make two cuts, one on each side of the midline incision posterior to the diaphragm. Examine the
diaphragm, which is attached to the chest wall by radially arranged muscles. The central region of the
diaphragm, called the central tendon, is a membranous area.
7. Make two more cuts, one on each side of the flap containing the umbilical cord and just anterior to the
hind limbs. Pull back the side flaps created by these cuts to expose the abdominal cavity. Lifting the flap
with the umbilical cord requires cutting the umbilical vein.
Anatomically, the diaphragm separates what two cavities? _____________________________________
List the organs you find in the thoracic cavity ________________________________________________
_____________________________________________________________________________________
List the organs you find in the abdominal cavity.______________________________________________
_____________________________________________________________________________________
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Figure 1. Ventral view of the fetal pig indicating incisions. These incisions are to be made
preparatory to dissecting the internal organs. They are numbered here in the order they
should be done.
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Figure 2. Internal anatomy of the fetal pig. The major organs are featured in this drawing.
Note that in the fetal pig, a red color tells you a vessel is an artery, and a blue color tells
you it is a vein. Contrary to this drawing, keep all the flaps on your pig so you can close
the thoracic and abdominal cavities.
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II. Activity: Abdominal Cavity
Liver
Locate the liver, a large brown organ, and note that its anterior surface is smoothly convex and fits snugly
into the concavity of the diaphragm
Name the liver’s functions__________ _____________________________________________________
Stomach and spleen
Identify the stomach, a large sac dorsal to the liver on the left side.
Locate the point near the midline of the body where the esophagus penetrates the diaphragm and joins the
stomach.
Find the spleen, a long, flat reddish organ attached to the stomach by mesentery.
Name the stomach’s function_ ____________________________________________________________
Name the spleen’s function_______________________________________________________________
Small Intestine
Look posteriorly where the stomach makes a curve to the right and narrows to join the anterior end of the
small intestine called the duodenum.
From the duodenum, the small intestine runs posteriorly for a short distance and is then thrown into an
irregular mass of bends and coils held together by a common mesentery.
Name the small intestine’s function________________________________________________________
Gallbladder and Pancreas
Locate the bile duct, which runs in the mesentery stretching between the liver and the duodenum. Find the
gallbladder, embedded in the liver on the underside of the right lobe. It is a small, greenish sac.
Lift the stomach and locate the pancreas, the light-colored, diffuse gland lying in the mesentery between
the stomach and the small intestine. The pancreas has a duct that empties into the duodenum of the small
intestine.
Name the gallbladder’s function________ __________________________________________________
Name the pancreas’s function_____________________________________________________________
Large Intestine
Locate the distal (far) end of the small intestine, which joins the large intestine posteriorly, in the left side
of the abdominal cavity (right side in humans). At this junction, note the cecum, a blind pouch.
Follow the main portion of the large intestine, known as the colon, as it runs from the point of juncture
with the small intestine into a tight coil (spiral colon), then out of the coil anteriorly, then posteriorly
again along the midline of the dorsal wall of the abdominal cavity. In the pelvic region, the rectum is the
last portion of the large intestine. The rectum leads to the anus.
Name the large intestine’s function ______________________________________________________
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Trace the path of food from the mouth to the anus by drawing the organs below and labeling them.
Storage of Pigs
1. Before leaving the laboratory, place your pig in the plastic bag provided.
2. Expel excess air from the bag, and tie it shut.
3. Write your name and section on the tag provided, and attach it to the bag. Your instructor will indicate
where the bags are to be stored until the next laboratory period.
4. Clean the dissecting tray and tools, and return them to their proper location.
5. Wash your hands.
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III. Activity: Human Anatomy
Humans and pigs are both mammals, and their organs are similar. A human torso model shows the exact
location of the organs in human beings (Fig. 3). You should learn to associate each human organ with its
particular system.
Human Torso
Examine a human torso model, and using Figure 3 as a guide, locate the same organs you have just
dissected in the fetal pig.
Do you see any major differences between pig internal anatomy and human internal anatomy?
Describe some of the differences. __________________________________________________
_____________________________________________________________________________
Figure 3. Human Internal organs.
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GLOSSARY:
Anus - an opening located ventral to the tail where feces is excreted
Colon - a compact, rounded mass of intestine tightly bound by mesentery
Diaphragm - dome-shaped muscle that contracts to draw air into the lungs; most important organ in
respiration
Gall bladder - stores bile that is produced by the liver
Large intestine - part of the digestive tract that absorbs water and prepares feces for defecation at the
anus
Liver - performs numerous vital functions, including (1) disposing of worn-out red blood cells, (2)
producing bile, (3) storing glycogen, (4) maintaining the blood glucose level, and (5) producing blood
proteins
Pancreas - a long, whitish, cauliflower-like organ located dorsal to the stomach; produces digestive
enzymes
Peritoneum - membrane consisting of epithelium supported by connective tissue lining organs.
Pyloric sphincter - a hard ring of smooth muscle; creates a boundary between the stomach and the small
intestine
Rectum - tube that transports undigested food from the large intestine out of the body
Small intestine - secretes digestive enzymes; where most absorption of digested nutrients occurs
Spleen - a lymphoid organ in the lymphatic system that contains both white and red blood cells. It
purifies blood and disposes of worn-out red blood cells.
Stomach - stores food and has numerous gastric glands that secrete gastric juice which digests protein.
Small intestine - part of the digestive tract that receives secretions from the pancreas and gallbladder that
functions in digestion of all components of food-carbohydrate, protein, and fat-the small intestine absorbs
the products of digestion: glucose, amino acids, glycerol, and fatty acids.
Umbilical veins - carries deoxygenated blood from the fetus to the placenta
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