SESSION 2: THE MOUTH AND PHARYNX 9 In the pig s digestive tract, food flows in only one direction from mouth to anus.this allows for greatly specialized sections that can act independently of each other. It also allows the animal to continue to eat while previously eaten food is still being digested. The mouth opens into the oral cavity. Use scissors to cut through the corners of the mouth to the back of the jaw, so that the mouth opens widely. See figure on the next sheet. Study it during the dissection to be sure you can identify all the structures on your pig. Note the hard palate, which makes up the anterior part of the roof of the mouth. It is made of bone and covered with folds of mucus membrane. The hard palate separates the oral cavity from the nasal cavities. Note that the membranes continue posteriorly, forming the soft palate, which does not contain bone. It lifts during swallowing to keep food from backing up into your nose. Notice the sensory papillae on the surface of the muscular tongue. Taste buds within the papillae are responsible for the sensations associated with food ingestion: salty, sweet, sour, and bitter. In the region of the lower jaw, remove the skin just in front of the ear and locate one of the salivary glands. They are the color and consistency of used chewing gum and quite different from the stringy muscles. See Figure 2 which shows the location of the pig s 3 salivary glands: parotid, sublingual, and submaxillary. You should be able to locate at least 1. At the base of the tongue, the oral cavity ends and the pharynx begins. The pharynx is the common passageway for the digestive and respiratory tracts because both air and food must pass through this structure. You may have to extend the cuts you made earlier to open the mouth wide enough to see the pharynx and associated structures. (A sore throat is really a sore pharynx or pharyngitis.) At the posterior end of the tongue you will find a trough shaped fold of tissue, the epiglottis. You may have to reach deep into the pharynx with your probe to locate the epiglottis and pull it out into view. Dorsal to this is an opening, the glottis, which leads into the larynx, part of the respiratory system. During swallowing the epiglottis forms a kind of lid over the glottis and deflects the food away from the glottis. When the epiglottis fails to do this, the food enters the glottis and choking results. (Food goes down the wrong way. ) Dorsal to the glottis find the second, wider opening into the esophagus. The esophagus is a collapsible muscular tube connecting the pharynx to the stomach. Food enters the esophagus by the reflex swallowing of the
10 pharynx and passes through the esophagus and gut by waves of muscular contractions called peristalsis. Pass the end of your probe into the glottis and then into the esophagus. Be certain that you can tell which is which. Notice that air entering through the nose must cross the pathway of food during swallowing. The air coming into the nose enters the food passageway at the pharynx. The area it goes through from the beginning of the nasal cavity to the pharynx is called the nasopharynx. Study the pictures below. Be sure you understand the anatomy of the mouth and pharynx. Figure 2 shows the location of the pig s 3 salivary glands (sublingual, submaxillary and parotid). You should be able to locate at least one of them.
THE MOUTH AND PHARYNX FUNCTION SHEET 11 Describe the functions of the following structures: 1. Nasopharynx in handout (definition only) 2. Sensory Papillae 3. Salivary glands 4. Pharynx 5. Epiglottis 6. Larynx 7. Esophagus 8. Hard Palate 9. Glottis BODY CAVITIES/ORGANS OF THE NECK FUNCTION SHEET Explain the functions of these structures: 1. Diaphragm 2. Thymus gland 3. Larynx 4. Trachea 5. Thyroid gland 6. Esophagus 7. Coelom 8. Abdominal cavity 9. Thoracic cavity 10. Pleural cavities 11. Pericardial cavity 12. Heart 13. Lungs 14. Peritoneum
12 SESSION 3: BODY CAVITIES/ORGANS OF THE NECK Opening the Body Cavity: Expose the organs in the neck, the thoracic cavity, and the abdominal cavity by making the incisions through the body wall shown in the figure below. * First, make an incision across the neck (incision 4). Then make a medial cut, starting at line 4 and continuing posteriorly to the umbilical cord. Cut all the way through the body wall with a pair of scissors but lift the body wall toward you as you do so, to prevent cutting any internal organs. * Continue posteriorly by making a pair of incisions, each lateral to the umbilical cord and posterior to the mammary papillae (incision 2). The midventral strip of tissue lying between this pair of incisions contains the umbilical arteries, urinary bladder, and in the male, the penis. It can be turned back, by parting incision 1 and cutting the umbilical vein that extends anteriorly from the umbilical cord to the liver. Cut the vein in such a way that you will be able to find it again. * Look in the abdominal cavity and notice the muscular diaphragm that forms a more or less transverse partition between the abdominal cavity and the thoracic cavity. * Make lateral incisions through the body wall (incision 3) just posterior to the attachment of the diaphragm. Follow the attachment of the diaphragm to the rib cage all the way to the back muscles. * Next cut through the diaphragm peripherally where it attaches to the rib cage. Do this on both sides of the body. * Cut through the rib cage carefully. * Finally, carefully cut through the membranes that bind the thoracic organs to the ventral wall of the thorax. You can now bend back the flaps of the rib cage, clean out the cavity (if necessary) and get a good view of the internal organs. Organs of the Neck: * Notice a large, gland-like mass on each side of the neck, the thymus, which develops from pharyngeal pouches (gill slits). It is relatively large in the fetus and infant, but becomes smaller with age. It is important in the development of the body s defense mechanisms, because it contains a specific type of white blood cell that produces antibodies when exposed to foreign invaders. * The larynx can be seen as a hard, whitish swelling in the throat region. The larynx houses the vocal cord. Extending posteriorly from the larynx is the trachea, or windpipe. It is a whitish tube characterized by rings of cartilage.
13 * Trace the trachea posteriorly. A short distance posterior to the larynx, you will see that it is covered by a small, dark, compacted glandular mass -- the thyroid gland. This gland produces the hormone, thyroxin, which is involved in maintaining a high metabolic rate. * Dorsal to the trachea is the esophagus, a collapsible muscular tube connecting the pharynx to the stomach. Carefully use your probe to move the trachea aside and make the esophagus visible. * The Coelom: The coelom (pronounced seelum ) is the term referring to the body cavity in which the thoracic and abdominal organs are located. * Notice the dark, muscular partition posterior to the lungs and anterior to the liver. This is the diaphragm which separates the thorax and the abdomen. The thorax is divided into three parts: The spaces around the lungs are referred to as the left and right pleural cavities. * Between the two pleural cavities is the pericardial cavity which contains the heart. * Carefully remove the remains of the transparent membranes which surround these organs to fully expose the heart and lungs. * The abdominal cavity is located posterior to the diaphragm. Most of the digestive, excretory, and reproductive organs are found here. The transparent membrane that covers the abdominal organs is called the peritoneum. 4