Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Male external structures Skinning cuts—do NOT cut the organs underneath First become familiar with the external anatomy of the rat that is given in the diagrams. Any bold-face term is a hint that that structure is something you will need to know. Each person is responsible for knowing the anatomy of both genders of rat. Following the center dotted line in the diagram cut through the skin and muscles only and 2 cm laterally from the incision line. There may be an incision near the neck where the circulatory system was injected. Sometimes this is a useful starting point for inserting the scissors for the cut and then pulls the skin away from the body. 1 If the specimens came in a bucket of preservative, the body cavities may have excess fluid in them due to diffusion. (it isn’t water so osmosis is out) You may have to dump the excess fluid into the sink when you cut into the abdominal cavity. each testis is large and housed in a pouch (scrotum) located between the penis and anus. Mouth Structures: You will need the bone cutter for this part and it will make noise. This bothers some people. Cut the jaws apart at the mandibular joint and identify the following structures: soft palate, hard palate molars, and tongue. Anatomical Terms for External Anatomy Pinna (not pictured)-The flaplike, external ear that directs sound into the ear opening (external auditory meatus). Three groups need to do the next part, and everyone will need to observe these structures while intact and when excised. To easily see the trachea and esophagus, cut into the throat area. Move the muscles to the side with the probe or dissecting needle until you come to a structure that looks like a white vacuum cleaner hose. There will be a large swelling in this tube. Remove the swelling by cutting the tube ½ cm below the swelling and directly above the swelling. You should find the following structures: Vibrissae-long, stiff hairs located on the face that have a sensory (tactile0function; the “whiskers” Nares-Paired openings leading into the nose; the nostrils. Anus-The opening to the digestive tract, located under the base of the tail. Female urogenital structures-In female rats, there are two openings, close together, in front of the anus, whereas male have only one. The most anterior opening of the female is the urethral orifice, and it leads to the urinary system. The vaginal orifice is the external opening of the reproductive system, and it lies posterior to the urethral orifice. Mammary papillae (nipples)-Present in females only. There generally are six on each side, three in the chest area and three in the abdominal area. Trachea: The white tube that looks like it has rings in it. This is also known as the wind pipe as it carries air to the lungs. Esophagus-A thin-walled, unsupported tube for food transport that lies dorsal to the larynx and trachea. Its connection to the stomach is described in abdominal section. Sometimes people inadvertently cut this when they cut out the trachea, please make sure you are only cutting the trachea. Larynx-This structure is also known as the voice box and you should see the vocal cords on the top of the large part of the trachea. Male urogenital structures -In males, reproductive products and urine exit the body at the tip of the penis. The penis is usually hidden inside a fold of skin and will be described in more detail in urinary and reproductive section. In males in breeding condition, 2 Abdominal Cavity and Digestive System (Fig 8) constriction. There are three parts to the small intestines based on microscopic structures: the duodenum, jejunum and ileum. Using scissors carefully open the abdominal cavity by cutting through the abdominal muscles, along the ventral midline, from the urogenital area to the sternum. Be sure to lift the muscles as you cut to avoid damage to the internal organs. If necessary, cut laterally from the sternum, along the posterior boundary of the rib cage, and again laterally from the urogenital area, toward the backbone, in front of the legs. This will leave you with a flap of tissue on each side that may be pinned to the tray, allowing an unobstructed view of the organs. Mesenteries-Translucent membranes attaching to and holding the internal organs in place. Fat bodies often appear within the mesenteries and blood vessels travel along them to various organs. Liver-Large brown organ dominating the anterior of the cavity. It consists of four sections or lobes. The median lobe is most superficial, and it is divided by a long notch near the ventral midline. A small caudate lobe is hidden under the left lobe. Among other things, the liver manufactures bile to aid fat digestion. Each lobe is drained by tubes that eventually combine to form a bile duct that carries bile to the small intestine. Unlike humans, a rat lacks a storage organ (gall bladder) for bile. Stomach-Curved baglike structure under the left side of the liver. The greater omentum is a prominent mesentery that is attached to the outer curve of the stomach and contains multiple fat deposits. Three groups will cut open the stomach and look for undigested food particles. Small Intestines-Long coiled tube that leaves the stomach. The junction between the stomach and small intestine has a distinct 3 Colon-Is shorter and wider than the small intestine. The cecum is a sacklike bulge near the junction with the small intestine that is near the appendix which is a projection from the intestine that doesn’t go anywhere. Pancreas-Gland that is light tan and has a bumpy appearance. Usually found near the mesentery nearest the stomach and duodenum. Produces insulin to regulate blood sugar. Spleen-Dark colored long gland near the left of the stomach. It is not related to the digestive system, it is part of the immune system. Figure 2 Thoracic Cavity: Respiratory and Circulatory Systems Respiratory System To observe the organs of the thoracic cavity, one needs to cut laterally to the sternum through the cartilage of the ribs. To make the flaps lie flat one may need to cut through the clavicle. The 4 muscle and bone can then be bent back to that the rib cage can be folded over like a book. Bronchus- Dorsal to the heart, the trachea splits into a right and left bronchus that travels to the lungs. Their dorsal location means that they are not visible in the ventral view shown. Lung- Spongy structures located in the thoracic cavity. The right lung consists of four lobes, whereas the left has only one; what may appear to be a second left lobe, in reality, is a lobe that extends from the right side. The surface of the lung is covered by visceral pleura, and the walls of the thoracic cavity are covered by parietal pleura. The pleura are homologous to the peritoneum of the abdominal cavity. Diaphragm- A thin muscular sheet, seen earlier, that separates the abdominal and thoracic cavities. Its action draws air into the lungs. Heart and Associated Structures Pericardium- the tough membrane forming a sac around the heart. Cut through it to expose the structures inside. Atria- Portions of the outer walls of the right and left atria are extremely visible as dark flaps on top of the heart. Blood vessels entering the right atrium are the vena cava (two anterior and one posterior) that return oxygen-poor blood from the body. Pulmonary veins (4) leave the lungs and enter the left atrium with oxygen-rich blood; their dorsal location means that they are not visible in the ventral view shown. Ventricles-The major pumping chambers of the heart. Right and left ventricles can be distinguished by pushing on them with the blunt probe. Someone in the class will be responsible for cutting the 5 heart so one can see the thickness of the different chambers. A pulmonary artery exits the right ventricle from the lungs. The aorta leaves the left ventricle, sends major branches forward, and makes a prominent turn to the left before disappearing dorsal to the heart. Arteries Our specimens are not injected with paint to differentiate the arteries from the veins. Aorta- The major artery leaving the dorsal part of the heart and immediately curving to the animal’s left. Urinary and Reproductive Structures You will be responsible for structures on BOTH genders so make sure you get a chance to study whatever you don't have. Also make sure you see what the pregnant uterine horns look like. Depending on length of gestation, that group may be able to remove a fetus with the placenta intact. Urinary Structures Kidney- Located against the dorsal body wall and surrounded by fat. You will have to move most of the intestines to the side or even completely out of the abdominal cavity. Note its beanlike shape. This indentation along the medial surface, where the arteries and veins connect, is the hilus. Slice one kidney horizontally into two halves using a scalpel. On the inside, you can readily distinguish two regions—an outer renal cortex, where the blood is filtered, and an inner renal medulla, where the urine is concentrated and collected. Also embedded in fat, just anterior to the kidney, is the smaller adrenal gland, an organ of the endocrine system; it appears dark compared to the surrounding fat. Ureter- A whitish tube that leaves each hilus and passes caudally to the urinary bladder. The ureters are surrounded by fat of the same color; use forceps to remove the fat, but go slowly to avoid tearing the ureter. Urinary bladder- A small sack for temporary storage of urine. It is about the size of a pea when empty. Female Genital Structures Ovary-A small nodule, usually buried in fat, posterior and lateral to each kidney, A tiny, coiled tube (oviduct) leads from the ovary to the uterus, but it is not readily seen without magnification. Uterus-Unlike its human counterpart, the uterus of a rat consists of a pair of elongated structures called the uterine horns. These may be greatly expanded in a pregnant female; if so, open one horn and look for embryos. 6 Vagina- The horns open into a single vagina that lies dorsal to the urethra. The vagina exits the body at the vaginal orifice seen earlier. Male Genital Structures Testis-Open the scrotum and associated tissues on one side, and observe the testis. Epididymis-A highly coiled tube attached to the surface of the testis. It acts as a storage site for mature spermatozoa. Penis-The intromittent organ that allows internal fertilization of the female. 7