Biology 3B Comparative Anatomy III – Cardiovascular & Respiratory Systems Page 1 of 10 Biology 3B Cardiovascular, Respiratory and Digestive systems of vertebrates: shark/fish, mudpuppy and rat. Objectives • To locate and identify the organs for the cardiovascular, respiratory and digestive systems of various vertebrates (dogfish or perch, mudpuppy and rat) • To understand the functions of the organs in aforementioned systems. • To be able to trace homologies between the different species • To understand blood flow though 2-4 chambered hearts. • To recognize changes from fetal circulation to adult circulation. BODY CAVITIES Vertebrates have a coelomic body cavity. This coelomic space is divided anteriorly into a pericardial (heart) cavity and a posterior pleuroperitoneal cavity by the transverse septum, a tough, white membrane. This is the situation in the dogfish and Necturus. In mammals, the thoracic cavity is subdivided into a central pericardial cavity and paired lateral pleural cavities around the lungs. The esophagus runs through this cavity, but we will be looking primarily at the posterior cavity, the abdominal cavity in this lab. These cavities are separated by a muscular diaphragm in mammals. The posterior pleuroperitoneal, visceral or abdominal cavity, houses the liver, digestive tract, and gonads. This body cavity has muscular walls (mesoderm). The visceral cavity is lined on the inside with a transparent parietal (somatic) peritoneum. It is attached to the muscles of the body wall but it also overlies the urogenital system, which is retroperitoneal. The parietal peritoneum from each side meet dorsally and ventrally to form a double walled mesentery. This splits to line the digestive tract and other organs as the splanchnic (visceral) peritoneum. The peritoneum is serous (wet). The fluid serves as a lubricant to allow frictionless movement of the organs. The primary mesenteries are dorsal and ventral, although the dorsal mesentery is often interrupted and moved to one side or the other with the organs and the ventral mesentery is reduced to the membranes of the liver and bladder. Mesenteries running from organ to organ are usually called ligaments. Dogfish or Perch Respiratory System In the shark (perch), the circulatory and respiratory systems is one as the heart pumps unoxygenated blood to the gills for oxygenation and from their oxygenated blood is distributed to the body. Gas exchange also takes place in the skin, but primarily in the gills. Look at the diagrams and follow in your shark the passage of water in the mouth and spiracles (which have a one way valve) and through the five gill slits (NOTE: There are no spiracles or gill slits present in the perch). The gill slits close and the pharyngeal chamber expands to suck in water. When the pharynx is filled, the mouth closes and the gill chambers expand and fill with water. Then the gill slits open and the chambers constrict to flush out the water. If you look down the gill slits, on each side you will see one half of the gill, a demibranch. The internal septum, blood vessels, nerves, muscles and two demibranchs make up each holobranch. At their base are gill rakers, which project into the mouth and protect the gills from mechanical injury. The demibranchs have primary lamellae, which can be easily seen, and secondary lamellae, which can be seen if you remove aBiology 3B Comparative Anatomy III – Cardiovascular & Respiratory Systems Page 2 of 10 portion of the gill and examine it closely. The oxygen rich water flows in a countercurrent pattern to the blood and allows efficient oxygen and carbon dioxide exchange to take place. Dogfish Heart and Aortic Arches To expose the blood vessels, first skin the roof of the mouth where the efferent (e=from) branchial arteries are located. They are pink and usually well injected. Make a shallow cut just inside the teeth and peel the skin off by flaying it. You will have to go well down the pharynx to the place where the arteries meet. If the dogfish is not injected well, dissect a perch to locate the efferent branchial arteries. To do so, you must cut reflect the operculum back as you cut anteriorly. Make sure that you do not cut the ventral aorta. The floor of the mouth, under the attached tongue, has the afferent (a=to) branchial arteries and posteriorly the heart. There will not be any blue latex, so the vessels are not injected and are delicate. They are colorless or brown with blood. Remove only the skin with a scalpel. Expose the heart by removing its protective cartilage and identify the sinus venosus, auricle and single ventricle. Trace the ventricle anteriorly into the conus arteriosus, and into the short ventral aorta. Pry off the cartilage on the afferent vessels with forceps and tease it loose with dissecting needles but do not use the scalpel any more in this area. The vessels are almost stuck to the cartilage. Expose all 5 afferent branchial arteries as far as the right gills. Follow one into the gill as far as you can. Expose the efferent arteries on each side of this afferent one and find how the major efferent duct loops up to the proceeding gill. In the region of the gills, skin a pair of gill arches and trace one loop of the efferent branchial arteries around a gill slit. Using your diagrams, trace the pathway of the blood through the afferent branchial arteries, the gills and the efferent branchial arteries. Necturus Respiratory System Much of the respiration in amphibians is through the skin. Up to 75% of the oxygen and 90% of the carbon dioxide is exchanged this way in aquatic forms. In addition, Necturus has three pairs of gills and one pair of lungs. External gills develop before the two gill slits open and can be waved about by branchial muscles. Lungs developed from swim bladders, which sometimes function as lungs in fish that gulp air. Look for the glottis, a longitudinal slit in the pharynx floor, which is the opening to the lungs. The larynx is a pair of cartilages surrounding the glottis and will not be noticed. The trachea is short. The lungs are long, slender and saclike. They run along the dorsal sides of the pleuroperitoneal cavity and are attached to the body wall by the pulmonary ligament on the left side and on the right, the hepatocavopulmonary ligament that also supports the liver. The