Lab 5: Digestive, Respiratory, and Urogenital Systems of the Shark & Cat Lab Objectives 1. To learn the component parts of the shark & cat 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 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, 3.25, 3.26 and associated text. 2. Shark urogenital system • Figures 3.33, 3.34 and associated text. 3. Cat digestive and respiratory system • Figures 7.39, 7.40, 7.42 to 7.50 and associated text: pp. 204-­‐220 4. Cat urogenital system • Figures 7.68, 7.69, 7.71, 7.72 and associated text: pp. 239-­‐244 Shark Term list Shark Digestive & Oral cavity Archinephric duct Pancreas Clasper Respiratory Bile duct Papillae Cloaca Parietal peritoneum Epididymis Branchial arches Pharynx Kidney Cloaca Primary tongue Leydig's gland Duodenum Pyloric s
phincter Ovary Esophagus Rectum Oviduct Gall bladder Rugae Gill raker Seminal vesicle Greater curvature of Spiracle Siphon Sperm sac the stomach Spiral valve Holobranch Testis Spleen Internal pharyngeal Urinary Papilla Stomach Urogenital papilla • Pylorus slit Valvular intestine Lamellae Uterus Liver Visceral peritoneum Other terms • Right lobe Coelom Coelomate • Median lobe Pericardial cavity Shark Urogenital • Left lobe Abdominal Pore Peritoneal cavity
Mesentery Accessory urinary duct Mesogaster During today’s lab you will explore the digestive, respiratory, excretory, and reproductive systems. 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. 2. Now you can fold open the ventral jaw and pharyngeal wall to get a view much like that seen in figure 3.22. Note, however, that you should NOT make other cuts that you see in that figure – only the one cut through the gills. 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. 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 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. 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? 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. 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. 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. How can you distinguish the esophagus and stomach? 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. 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. 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. Cat Term List
Respiratory & Digestive Anus Ascending colon Cecum Common bile duct Descending colon Diaphragm Duodenum Esophagus Gall bladder Ileum Jejunum Kidney Lingual frenulum Liver • Caudate lobe • Right lateral lobe • Right medial lobe • Quadrate lobe • Left medial lobe • Left lateral lobe Lung • Anterior lobe • Middle lobe • Posterior lobe • Accessory lobe Lymph node Mesenteric lymph nodes Mesentery Omental bursa Omentum Oral cavity Pancreas Parietal peritoneum Parietal pleura Parotid gland Rectum Small intestine Spleen Stomach Tongue Trachea Tracheal ring Transverse colon Visceral peritoneum Visceral pleura Urogenital structures Adrenal gland Anal gland Cervix Clitoris (and fossa) Crus of penis Ductus deferens Epididymis External urethral orifice Glans of penis Inguinal canal Ovary Penis Prostate gland Renal capsule Renal cortex Renal medulla Renal papilla Renal pelvis Scrotum Testis Ureter Urethra Urinary bladder Urogenital aperture and sinus Urogenital opening Urogenital sinus Uterine tube Uterus Vagina As in the shark, the digestive and respiratory systems are closely integrated, as are the excretory and reproductive systems. However, pay close attention to how the systems differ and how their integration differs. The fact that the shark does gas exchange with water and the cat with air is extremely important. The dissections are much easier and less time consuming than those of the muscles, but there are more structures to know in the cat than the shark. Treat the cat as building on the material that you learned for the shark. The structures shared by both animals are in similar places and share similar functions. 1. Dissecting instructions 1. Start by examining the salivary glands. You may need to skin a little of the head to expose the large parotid gland. ;Try to observe the ducts and other salivary glands (you do not need to know these by name). You may have to pick away some of the fascia covering the glands, so be gentle because the glands are more delicate than the muscles. 2. Follow the digestive system from the mouth of the cat posteriorly. 3. Since the cat has its coelom subdivided more than the shark (see below), you will need to open its various chambers separately. Start with the thoracic cavity. On the side that you dissected the musculature of the cat, use your finger to locate the anteriormost rib. Use the large scissors (blunt blade in and tilted up) to cut through this rib. Continue to cut posteriorly until you arrive at the diaphragm. Since the mediastinum runs dorsally from the sternum, you need to avoid damaging it as you cut through the ribs. Make your cut about 0.5 cm off the midline. 4. Cut about 0.5 cm anterior to the diaphragm dorsolaterally to make a triangular flap, similar to that pictured at the top of Figure 7.42 of your lab manual. 5. Repeat this on the other side, so that you have a left and right flap. You should have a 1.5 cm strip of tissue running from the throat to the diaphragm midventrally that contains the intact sternum and associated blood vessels. Finally, break the ribs on each side near their articulation with the vertebrae by bending the body wall flap dorsally. You may have to break some of the ribs one by one because they are quite hard. 6. This gives you access to the lungs and heart. If needed, you can cut the midventral strip of tissue just anterior to the diaphragm to gain a better view of the lungs and heart. 7. To open the peritoneal (abdominal) cavity, simply pinch a bit of the body wall between your fingers or with forceps just off the midline of the abdomen. Then make a small snip with scissors through the pinch – this is an easy way to make a clean cut in without damaging organs. Now use your scissors to cut anteriorly to, but not through, the diaphragm, and posteriorly to the pelvis. Then cut laterally and parallel to the diaphragm and laterally a couple centimeters anterior to the pelvis. These cuts will make two rectangular flaps, giving easy access to the peritoneal cavity, containing much of the digestive and excretory systems. 8. Parts of the excretory and reproductive systems are still not visible because they are obscured by the ventral portion of the pelvis. Palpate the bump formed by the two pubis bones, where they meet anteriorly. This is the anterior end of the pubic symphysis. Use the scalpel to shave the muscle tissue from this bump using a frontal cut to reveal the cartilaginous pubic symphysis. 9. Use the scalpel to cut dorsally (down) through the symphysis. Continue posteriorly, until you have cut through the entire symphysis. You will have to cut through some muscles to do this. Be careful to cut perfectly sagittally – cutting at an angle will embed the scalpel in the bone, which is much harder to cut. Also be careful not to cut any of the structures underneath that you want to study. 10. Grasp the cat by the thighs, near the origin of the femora, and bend them dorsally to break the articulation between the sacrum and the innominate bones. This will open up an area for examination of the excretory and reproductive organs. 11. The remainder of this dissection is less involved and mainly involves cleaning fascia in the pelvic region. Clean the fascia sufficiently to clearly view all of the structures. To reveal the testis and associated structures in a male cat, make an incision with the small scissors (or carefully with scalpel) through the scrotum. Trace the vas deference from the testis, into the body cavity and to the urethra. In a female cat, make a sagittal incision ventrally but off the midline through the urogenital sinus and vagina to reveal the structures in figure 7.72 of your lab manual. 12. Finally, to examine the internal morphology of the kidney, remove the fascia and cut through the kidney frontally to reproduce the view in figure 7.68. Do not cut through the kidney completely, so that it remains attached to the rest of the cat via the ureter. 2. Digestive and respiratory integration Although the cat is terrestrial, while the shark is aquatic, integration of the respiratory and digestive systems remains at the anterior end. Since the cat lacks gill slits and the one-­‐way continuous flow of water through the pharynx that they allow, coordination between these two systems is even stronger. Amniotes in general ventilate the lungs using thoracic muscles (body wall muscles or a diaphragm) and ventilation must be coordinated with swallowing when the animal is eating. How do the components of the respiratory system differ between the shark and the cat? In the cat, which structures are shared by the digestive and respiratory systems? What structure is used by a mammal to prevent food and water from entering the trachea? How many lobes does the cat’s lung have? Name them. 3. Body cavities of the cat In mammals the coelom is subdivided into four cavities. The pericardial and peritoneal cavities remain as in the shark. The pleural cavities house the lungs. The left and right pleural cavities are separated by the mediastinum, a thin connective tissue membrane that is dorsal to the sternum and ventral to the heart. The heart and pericardium are within the mediastinum, slightly on the left side. The pericardium is the tough connective tissue sheath surrounding the heart. The lungs are within the pleural cavities, lined by visceral pleura, while the lining of these cavities along the body wall is called the parietal pleura. Likewise, the heart is lined by visceral pericardium and is located inside the pericardial cavity. The abdominal cavity, to be opened next, is the peritoneal cavity, with the visceral peritoneum lining the organs, or viscera, and the parietal peritoneum lining the body wall. 4. Digestive system Again, in studying the digestive system, start at its anterior end and trace it caudally. The esophagus is long and narrow, similar in shape to the trachea, but collapsed, so it may look like a solid band of muscle. In the abdominal cavity you will find the large stomach, found on the left side. Note the connective tissue membrane containing fat and attached to the greater curvature of the stomach and draped over the intestines. This is the omentum and it actually forms a pouch, called the omental bursa. You can gently lift this off of the viscera and reflect it anteriorly. You do not need to tear or snip it off. Continue following the GI tract posteriorly, finding the structures in the lab manual. Note the large liver, taking up a considerable portion of the peritoneal cavity, and the gall bladder. The common bile duct runs from the gall bladder to the duodenum. Near the duodenum, you will also find the diminutive pancreas, which is thin and lobular. What are the three sections of the small intestine called? What order do they go in? How can you distinguish them? Your cat catches and eats a mouse. Trace the path that a mouse food particle from ingestion at the mouth to the litter box. To do this, list all of the structures that the particle passes through and be very specific. 5. Urogenital systems and integration As in the shark, the excretory and reproductive systems are closely integrated because of common developmental origins. The gonads arise from embryonic tissue near the kidney. The ovaries remain in more-­‐or-­‐less their original position, while the testes descend through the inguinal canals to the scrotum. The ductus deferens (vas deferens in humans) drains the testis and runs through the inguinal canal and then to the urethra. In females, oviducts receive mature ova from the ovaries and allow for their passage to the uterus. The uterus is separated from the vagina by the cervix. Both the vagina and urethra exit into the urogenital sinus. In both sexes, ureters drain the kidneys, moving urine to the urinary bladder. From the bladder, urine is voided via the urethra. Why would the male testis be situated outside of the body cavity in the scrotum?