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11 Name: Date: Period: The Dissection 1. Place your specimen dorsal side down. Make your incisions following the diagram below. Make sure to make shallow cuts with the scissors. DO NOT CUT TOO DEEP! You will damage the internal organs! It may be beneficial to use the forceps (or your fingers) to pull up on the skin as you cut. 2. As you open the flaps of skin you will see a thin layer of tissue. Use the scalpel or scissors to cut through the tissue to get it out of the way. Be careful not to puncture or accidentally remove any of the internal organs. 3. The Digestive System: Using the descriptions below and the packet of diagrams provided, identify all of the structures listed below. a. Rectal gland The rectal gland excretes salts from the body. It is connected to the colon through a small duct. b. Ileum The ileum is the second portion of the small intestine and has a ringed appearance. This is due to the spiral valve inside the ileum, which increases the surface area available for digestion and enzymatic action. c. Pancreas (ventral lobe) the ventral pancreas lies on top of the duodenum (the first portion of the small intestine). The pancreas is the major gland of the digestive system in vertebrates. This structure is white or cream in color and lumpy in texture. The pancreas secretes pancreatic (digestive) juices into the duodenum. Pancreatic juice is a combination of water, electrolytes, and enzymes. The pancreas also produces hormones that are important in the regulation of sugar levels and the metabolism of fats and carbohydrates. d. Pancreas (dorsal lobes) The dorsal region of the pancreas is most easily seen by lifting and turning the stomach and duodenum. e. Hepatic portal vein The hepatic vein runs parallel to the bile duct. It is part of the hepatic portal system that transports blood from the body back to the heart. f. Bile duct The bile delivers secretions from the gall bladder to the duodenum. g. Liver The liver of the shark consists of 3 lobes: the right lateral lobe, the left lateral lobe and the medial lobe. The vertebrate liver is the most prominent organ in the body cavity and has many functions. It metabolizes carbohydrates and fats and produces bile and bile salts that emulsify fats in the duodenum. In the duodenum, bile functions in the emulsification, digestion, and absorption

12 Name: Date: Period: of fats. The alkaline nature of the bile helps to neutralize the acids in the stomach. The shark liver has some unique characteristics. It is highly rich in oil and provides some buoyancy as the shark swims (the oil is less dense than the surrounding water). The other function of the oil is the storage of energy (other vertebrates store energy as fat). h. Gall bladder The gall bladder stores and concentrates bile secreted by the liver and delivers it to the duodenum through the bile duct. The gall bladder is a round pea green structure on the under surface of the medial lobe of the liver. i. Heart The heart consists of two main chambers: the atrium and the ventricle. The ventricle is the muscular portion of the heart responsible for pumping blood. The atrium is relatively nonmuscular and receives blood from the sinus venosus. j. Stomach The stomach is a large J shaped pouch located in proximity to the left lateral lobe of the liver. Inside the stomach lining is the rugae, which increases surface area available for digestion of food. **Cut open the stomach. What do you see? Is there any food in there? Record this in your packet. k. Kidneys The kidneys are organs that run along either side of the midline within the body cavity and are divided laterally by a strip of connective tissue called the caudal ligament. The ki9denys are responsible for the excretion of hydrophilic substances such as ions, water, and other nitrogenous wastes. l. Duodenum the duodenum is the first portion of the small intestine and is U shaped. m. Spleen The spleen is a dark triangular organ near the stomach. The cells inside the spleen engulf and digest foreign cells and dead cells in a process known as phagocytosis. The spleen also recycles old red blood cells and platelets by removing the iron and other useful components. The spleen is also processes and removes bacteria. It also plays a role in immune function. n. Colon The colon is the narrowed portion of the ileum that leads to the cloaca. In general, the colon digests bacteria, reabsorbs water, and forms feces. Waste is expelled from the colon through the short section of the rectum and out to the external environment through the cloaca. o. Cloaca The cloaca is a single excretory opening that receives nitrogenous waste from the kidneys, solid wastes from the rectum, and fluids from the reproductive organs and transfers them out to the external environment. 4. The Urogenital System: The urogenital system consists of the excretory and reproductive systems, which differ between the male and female. In order to see the reproductive structures, you will need to remove the liver and other digestive organs. Identify the following structures on your specimen. Male Urogenital Structures a. Seminal Vesicle The seminal vesicle is an enlarged extension of the vas deferens. It is in the seminal vesicle that secretions are added to the sperm to create the seminal fluid, which creates a medium for sperm to swim within. b. Vas deferens The vas deferens transports mature sperm from the epididymis to the seminal vesicle. c. Epididymis The epididymis functions to store sperm. While in the epididymis, the sperm matures.

13 Name: Date: Period: d. Testes The testes are the site where the sperm are created. Hormones, such as testosterone are produced here as well. e. Sperm Sac The paired sperm sacs receive seminal fluid from the seminal vesicles. They join together and form the urogenital sinuses, which extend through the urogenital papilla. f. Cloaca and urogenital papilla The cloaca is the common opening for solid and liquid wastes and reproductive fluids. The urogenital papilla is a conical shaped structure within the cloaca. In males, it is larger than in females and is curved. Urine and seminal fluids pass through the urogenital papilla. Female Urogenital Structures a. Uterus The uterus is where the fertilized egg implants and grows. b. Oviduct The oviduct is a channel that transports eggs from the ovary to the uterus. c. Ovary The ovary is the site of oogenesis (creation of eggs) and production of sex hormones. Depending on when your shark was harvested, there may or may not be eggs present within the ovary. d. Yolk Sac The yolk sac nourishes the developing embryo. This structure is only present in sharks that are ovoviviparous (like the dogfish). e. Embryos The embryos of the spiny dogfish remain in the uterus for up to 2 years. When they are born, they are exact miniatures of the adult. f. Cloaca and urogenital papilla The cloaca is the common opening for solid and liquid wastes and reproductive fluids. The urogenital papilla is a conical shaped structure within the cloaca. In females, it is smaller than in males and is not curved. Urine passes through the urogenital papilla. 5. If there is time and you have completed everything above, you may do the following: a. Locate and remove the brain (Extra Credit) b. Remove some scales and look at them under a dissecting scope. c. Remove the lens from the eye.