Biol 111 Comparative & Human Anatomy Lab 5: Digestive, Respiratory, and Urogenital Systems of the Shark Spring 2014

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1 Biol 111 Comparative & Human Anatomy Lab 5: Digestive, Respiratory, and Urogenital Systems of the Shark Spring 2014 Philip J. Bergmann Lab Objectives 1. To learn the component parts of the shark digestive, respiratory, and urogenital systems. 2. To study how the organs are suspended in the coelomic cavity. 3. To gain an appreciation for the integration of the digestive and respiratory systems. 4. To understand how the function of the digestive organs is related to their morphology, location, and sequence. 5. To be able to determine the sex of a shark based on external and internal anatomy. 6. To gain an appreciation for the integration of the excretory and reproductive systems. Material to Learn 1. Shark digestive and respiratory system Figures 3.22, 3.24 to 3.26 Associated text: pp (supplementary) OMIT: Figure Any labeled blood vessels in the figures or text. 2. Shark urogenital system Figures 3.33, 3.34 Associated text: pp (supplementary) OMIT: Any labeled blood vessels in the figures or text; these will be covered in a future lab. Term list Digestive & Respiratory Branchial arches Cloaca Colon Digitiform gland Duodenum Esophagus Falciform ligament Gall bladder Gastrohepatoduodenal ligament Gastrosplenic ligament Gill raker Greater curvature of the stomach Hemibranch Holobranch Internal pharyngeal slit Lamellae Liver Right lobe Median lobe Left lobe Mesentery Mesogaster Mesorectum Oral cavity Pancreas Ventral lobe Isthmus Dorsal lobe Papillae Parietal peritoneum Pharynx Primary tongue Pyloric sphincter 1 Rectum Rugae Spiracle Spiral valve Spleen Stomach Body Pylorus Valvular intestine Visceral peritoneum Urogenital Accessory urinary duct Archinephric duct Clasper Cloaca Epididymis Kidney

2 Leydig's gland Mesorchium Mesotubarium Mesovarium Nidamental gland Ostium tubae Ovary Oviduct Siphon Testis Urinary Papilla Urogenital papilla Uterus Other terms Coelom Coelomate Pericardial cavity Peritoneal cavity Background & Instructions During today s lab you will explore the digestive, respiratory, excretory, and reproductive systems of the shark. The digestive and respiratory systems are closely integrated, as are the excretory and reproductive systems. The dissections are much easier and less time consuming than those of the muscles, so these systems are combined in a single lab. 1. Dissecting instructions 1. Revealing the anterior end of the gastrointestinal tract is the most involved part of today's dissection. Use your large scissors to cut through the branchial arches of the shark on one side. To do this, insert the blunt blade of the scissors into the angle of the mouth and make a frontal cut through the middle of the branchial arches, proceeding posteriorly until you cut through the last one and cut through the scapular process of the pectoral girdle. Where to make this cut will be drawn on the whiteboard. 2. Now you can fold open the ventral jaw and pharyngeal wall to get a view much like that seen in figure Note, however, that you should NOT make other cuts that you see in that figure only the one cut through the gills. Some of the cartilaginous elements on the uncut side may snap as you fold open and this is okay. You can use probes to pin the animal open for ease of examination. Put one probe through the spiracle on the cut side, and put the other probe through the thin tissue anterolateral to the primary tongue on the cut side. 3. The sharks will have an incision through the body wall into the body cavity that was used to inject the blood vessels. The incision may be closed with a staple. If it is, remove the staple carefully. Then use the large scissors to extend the incision anteriorly and posteriorly. Make your cut slightly off the ventral midline to avoid cutting medial structures. When you cut with the large scissors always have the blunt blade in and try to tilt it up toward you to minimize your chance of cutting through structures that you need to study. Cut anteriorly until you reach the anterior extent of the abdominal cavity (near the anterior of the liver). 4. Cut posteriorly all the way to the cloaca you will have to cut through the puboischiadic bar to do so. Finally, cut laterally on each side of your ventromedial cut, anterior to the cloaca and again posterior to the pectoral fins. This will create two large flaps of body wall, giving you access to the abdominal cavity, which contains the majority of the GI tract and all of the reproductive and excretory structures. 5. Very little further dissection of the digestive system is needed, with two exceptions. First, you should cut open the stomach to observe its internal morphology. Check to see if there is any undigested food inside the stomach. It is not uncommon to find whole fish in the stomach. 2

3 Second, you should carefully cut away part of the wall of the valvular intestine to reveal the spiral valve inside. 6. In examining the excretory and reproductive systems, you will need to uncover the kidney. Kidneys are retroperitoneal in position, meaning that instead of being suspended in the peritoneal cavity by a mesentery, like other organs, they are plastered against the body wall. You can find the kidney of the shark (and the cat next week) under a thin layer of connective tissue, along the dorsal body wall. Gently tear through the connective tissue using curved forceps to expose the kidney and associated ducts. 7. Since the reproductive system differs between sexes, make sure that you also examine a shark of the opposite sex of the one you are working on. 2. Digestive and respiratory integration The digestive and respiratory systems share certain structures due to the common passage of water through them anteriorly. The respiratory system of the shark is restricted to the pharyngeal region, while the digestive system continues independently posterior to the pharyngeal region. During feeding and respiration, the shark will lower the floor of the mouth to create negative pressure inside, allowing for efficient movement of water into the pharyngeal cavity when the mouth is opened. When the mouth is closed, raising the buccal floor increases pressure, forcing water over the gill lamellae and out through the gill slits. What parts of the gastrointestinal tract are shared with the respiratory system? What is one muscle that is used to open the jaw? What is a muscle that would be used to decrease volume of the buccal cavity, forcing water over the gills an out of the pharyngeal cavity? What is the difference between a holobranch and a hemibranch branchial septum? How many of each does the shark have? 3

4 3. Body cavities and digestive system Trace the digestive system posteriorly all the way to the cloaca, identifying and examining structures as you go. Tracing the digestive system in the same order as food passes through it is helpful for learning the order of the structures and how they work together. Before looking at the organs themselves, consider the cavity that they are in and how they are suspended in that cavity. Vertebrates are coelomate organisms, meaning that they have a body cavity, or coelom. In the shark, the coelom is subdivided into a small cavity containing the heart, called the pericardial cavity (you will examine this in a future lab), and the large peritoneal cavity, which contains all of the main organs. Each cavity has a thin connective tissue lining. The part of the lining that is adhered to the body wall is the parietal peritoneum, while the lining that covers the organs is the visceral peritoneum. You cannot see these linings because they are thin and closely connected to underlying tissue, but you should know where they are. Organs are suspended in the peritoneum by mesenteries. These are thin connective tissue sheets that connect the organs to the body walls and allow the blood supply to cross from the body wall to the organs. Mesenteries are either simply called mesenteries or have the prefix meso~, or else they are called ligaments, not to be confused with ligaments that connect two bones together. Often the name of a mesentery tells you what it connects. For example, the mesorectum connects the rectum to the dorsal body wall, while the gastrosplenic ligament connects the stomach and the spleen. Mesentery is both a general term for all of these structures AND a specific term for the mesentery that connects the intestine to the dorsal body wall - pay close attention to how this term is used. Name four mesenteries? What is each one connected to? How can you tell that they are mesenteries from their names? Now trace the digestive system anterior to posterior. Cut open the stomach and esophagus. It is difficult to distinguish these two structures because the shark esophagus is short and broad, but the internal structure differs. The stomach has a single curve and can be divided into the anterior and large body and the posterior and narrower pylorus, which is the section after the curve. The muscular pyloric sphincter feels hard to the touch and separates the stomach from the duodenum and intestine. The intestine then flows into the rectum and to the cloaca. Also note the accessory glands that secrete digestive enzymes that are deposited into the gastrointestinal tract: the liver and gallbladder, and the pancreas. You should also learn to recognize the spleen, although this is not a digestive gland, but involved in hemopoesis, or the production of blood. 4

5 How can you distinguish the esophagus and stomach? Explain what the spiral valve is for and how it functions. How does the GI tract of the shark differ from what you saw in the lamprey? Why? Sharks lack a swim bladder to maintain neutral buoyancy. As you dissect the shark, can you tell how the shark is able to maintain buoyancy? (Hint What does the shark have a lot of inside?) Pretend that you are a small fish that the shark consumes. Trace and write down all of the structures that you pass through as you are digested and turned to wastes that are then returned back to the ocean. Mouth buccal cavity 5

6 4. Urogenital systems The excretory and reproductive systems of the shark (as with most vertebrates) are closely integrated because they share some structures. The excretory system refers to the structures involved in the production of nitrogenous wastes such as urine, which differs from the production of feces (which is the purview of the gastrointestinal system). The excretory system consists of a kidney, which filters blood to remove nitrogenous wastes, and ducts to expel urine from the body. In some forms, there is a storage chamber for urine, the urinary bladder, but fishes, including the shark, are not among them (wait for the cat, next week). Urine exits the body via the urinary papilla in the female or the urogenital papilla in the male. In the female, the kidney is drained by the archinephric duct, a duct that served the anterior, non-functional, part of the kidney during development. In the male, a new duct, the accessory urinary duct, drains the kidney. These two ducts are quite narrow and hard to find. The reproductive system consists of ovaries or testes and associated structures. In a female, the oviduct leads from the ovary to the uterus, where young develop. The dogfish shark is viviparous, so has placenta-like structures allowing for gas exchange, and nutrient and waste exchange with the mother. The uterus then opens to the cloaca. The nidamental gland is a swelling of the oviduct in its anterior third that secretes a thin membrane over developing ova, post fertilization. Finally, the ostium tubae is the opening of the oviduct by the ovary. The oviduct itself projects anteriorly and loops around the liver from its dorsal to its ventral sides. You can find the ostium tubae by exploring with a blunt probe by the falciform ligament. The mesentery that connects the ovary is the mesovarium and that which connects to the oviduct is the mesotubarium. In the male, the testis is suspended in the body cavity by the mesorchium, and is drained by efferent ductules (microscopic) that run through the mesorchium to the epididymis, which is a small tangle of ducts. The epididymis then runs into the archinephric duct, which takes sperm to the wider seminal vesicle. Sperm can be stored in the sperm sac, from which it can enter a groove in the clasper. What does ostium tubae mean in Latin? What is the name of the duct that drains the following? Kidney: Testis: Ovary: 6

7 Describe how insemination occurs in sharks. Trace all the structures that a sperm would travel through to go from the testis in the male to the oviduct in the female, where fertilization occurs. Testis efferent ductules 7

Student Guide to the Frog Dissection

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