Shark Respiratory and Circulatory Anatomy
Instruction
Be sure to write about what you are learning in the lab section of your notebook. You will be expected to answer questions about the lab activity during the lab self test and lab quiz. It helps to have your text and coloring books open beside you for support.
| Refer to the Assigned Readings Below: | |
| Marine Biology Textbook | Chapter 8, pages 164 to 166 |
| Marine Biology Coloring Book | Plates 49 to 51 |
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The specimen in the photograph was prepared by cutting across the gill slits from the pectoral girdle to the corner of the mouth. The chin was cut across the ventral musculature to free the lower jaw and peal it to one side. The gills are the respiratory organs of the shark. The gills are located in a series of pharyngeal pouches. They are composed of gill lamellae, blood vessels, and supporting cartilaginous structures. |
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The oral cavity is the area enclosed by the jaws (mandibular arch) and the cartilage of the throat (hyoid arch). The triangular sharp teeth are arranged in several rows beginning at the outer edges of the upper and lower jaws. Behind the functional teeth are additional rows folded downward, ready to replace any that are lost. The tongue of the shark is practically immovable and without muscles. It is supported anteriorly and posteriorly by cartilage. The pharynx is the portion of the alimentary canal posterior to the hyoid arch between the gills. Posteriorly, it narrows to form the esophagus. The spiracles are openings in the anterior roof of the pharynx. The shark can bring water into its pharynx to the gills by way of the spiracle and mouth. |
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The gills are provided with a rich blood supply. Arteries run directly from the nearby heart to the gills, bringing deoxygenated blood into the gill lamellae. Oxygen diffuses from the ventilating water current flowing over the gills into the blood. |
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As you look at the pharynx, you will see five internal gill slits. They lead into cavities called gill pouches, which lead to the outside by external gill slits. The gill slits are supported by cartilaginous gill arches and guarded by small cartilaginous papillae-like gill rakers which act as strainers to prevent food particles from leaving the pharynx through the gill slits. |
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The partitions between gill pouches are referred as branchial bars. The gill lamellae on one side of a branchial bar are called a demibranch, or half gill. The demibranchs on the anterior and posterior surface of a single branchial bar are termed a holobranch, or complete gill. Thus, one holobranch belongs to two different gill pouches; the anterior half (demibranch) to the anterior gill pouch, the posterior gill demibranch to the posterior gill pouch. |
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The gill lamellae are radially folded, highly vascularized tissue attached to the surface of a tough connective tissue, the interbranchial septum. Each septum is attached medially to a portion of the cartilaginous gill arch. The superficial constrictor muscles act as flap-like valves to open and close the external gill slits. |
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The specimen in the photographs was prepared by removing the skin and the ventral musculature over the pericardial cavity. A membrane was removed to expose the heart and some of its major blood vessels. The pericardial cavity is the upper portion of the body cavity. It is much smaller than the lower cavity, which contains the digestive organs. The pericardial cavity is located anterior to the transverse septum and contains the heart and the major blood vessels leading to and from the heart. The pericardium is the membrane lining the inner walls of the pericardial cavity. |
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The ventricle is the thick muscular walled cavity that pumps blood through the conus arteriosus to the gills and the body. The conus arteriosis contains a series of semilunar valves that direct the blood flow. The atrium is thin-walled with two lateral bulging lobes. It pumps blood to the dorsal ventricle. |
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Blood enters the heart through the sinus venosus, which drains into the atrium. The posterior cardinal sinuses receive blood from the posterior parts of the body and drain through the common cardinal veins into the sinus venosus. |
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The specimen in the photographs was prepared by removing the ventral hypobranchial muscles and connective tissues until reaching the lower jaw. The conus arteriosus was traced anteriorly following the major branching blood vessels. The anterior end of the conus arteriosus continues foward as the ventral aorta. It gives off five pairs of afferent branchial arteries which carry deoxygenated blood from the heart to the gills. The afferent branchial arteries pass laterally from the medial ventral aorta carrying deoxygenated blood to the gills. These afferent vessels enter the interbranchial bars and serve the holobranchs of the gill arches. |
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The specimen in the photographs was prepared by removing the mucous membrane from the roof of the mouth and pharynx. The efferent branchial arteries serve to return oxygenated blood from the gills. This blood is then distributed to all parts of the body. Four pairs of arteries may be seen arising from the gills and uniting in the midline to form the median dorsal aorta. The efferent branchial arteries give off many branches. These carry oxygenated blood to the more anterior parts of the shark's body. The four pairs of efferent branchial arteries join at the dorsal midline to form the large dorsal aorta. The dorsal aorta passes posteriorly, bringing oxygenated blood from the gills to virtually every part of the shark's body. |
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The specimen in the photographs was prepared by carefully dissecting to reveal the source of each efferent branchial artery in the gill lamallae of the gill pouches. The efferent collector loops encircle each of the first four gill pouches. |
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Adjacent collector loops are connected to one another by branches which pass through the interbranchial septa. |
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Lab Activity 5.4 Shark Urogenital and Nervous Anatomy