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Welcome to the Rat Lab! I know you have all be anxiously awaiting this wonderful lab! Here are some things to know about the changes in this lab. First of all there is an addendum that needs to be handed out to students. I wasn’t satisfied with the urogenital or the circulation parts so I added some more info. Also before you begin, make sure to spend a few minutes going over some basic anatomy terms like frontal plane, medial, lateral, ventral, etc. If you have questions just ask! The students need to get all sections signed before they move onto the next one! We need to make sure they have actually did the dissections and laid all the parts out to get as much as they possibly can out of the rat. We don’t want their deaths to be in vain! I have generated a list of questions to ask students before you sign their papers. Each section has their own set. You don’t need to ask all of them to each student, just as long as they know what they’re talking about. These questions will not be the write up rather they will aid in their knowledge of anatomy to assist them in their write up. This lab will take the entire time. When students ask in the beginning of lab, just let them know that they will get out in 2 hours and 50 minutes. I want them to learn as much as possible so it should take awhile to go through everything in detail. Questions to ask before you sign out students: Digestive(c) How do you tell the difference between the trachea and the esophagus? The trachea is a striated structure located on top of the esophagus, which is smoother. (d) If you were designing an organism why might you have one opening which leads to two separate compartments? Answers will vary. They may not design it this way. Anything is acceptable as long as they’re thinking. (e) What did you notice about the inside of the stomach? Very rough with many folds. What function might account for this anatomy? The stomach needs to digest all the foods we eat. Therefore, the low pH leads to high rate of turnover in the stomach, which accounts for the roughness. The many folds increase the thickness of the stomach wall so you don’t degrade through it. Ulcers occur when the stomach lining gets too thin. (f) What was the length of the small and large intestine? Varies. How do you think the length relates to function? The small intestine is much longer so it can absorb many more nutrients. Practically all absorption of nutrients takes place in the small intestine. You also see a lot of folds to increase the surface area to increase absorption. The large intestine is much shorter than the small. The large intestine does not need to absorb much more than water. The function is to form feces from the things the small intestine could not use. You really don’t want all the rejects hanging out in your bowels that long so it is shorter to allow the absorption of water and then it leaves the body. Uro-genital1) What is the difference between the length of the urethra between the sexes? The female urethra is much shorter than the males. In the male you have three sections: membranous urethra- middle portion, spongy- extends through the length of the penis allowing the urine to leave through the urogenital orifice. 2) Why are the kidneys behind the dorsal wall? For protection. The organism needs to protect the kidneys so don’t want them to get tangled up in the peritoneal cavity. If an animal was to suffer a blow to the stomach the kidneys will not be damaged if they are in the retroperitoneal cavity. 3) How does the lining of the uterus differ from the lining of the stomach? Why is this so? The uterus is much smoother than the stomach was. The uterus needs to be protective and gentle to any developing embryo. You do not need low pH so it doesn’t need to be that thick and rough. 4) How did the reproductive tract of the opposite sex function? Make sure they have checked out another rat and they have switched explanations. Heart1) Find both the Atria and both ventricles. How do you tell the left from the right chambers? The right chambers will be on the rat’s right side. Make sure they know where the septum that divides the two. 2) What functional difference accounts for the difference in anatomy between the left and right ventricle? The left ventricle has to pump blood to the entire body so it must be much thicker because it has more work to do. The right just pumps blood into the lungs. 3) What is the difference between arteries and veins? Arteries carry blood away from the heart. Veins carry blood to the heart. Why isn’t the pulmonary vein what people typically think of when they think of veins? The pulmonary vein returns oxygenated blood from the lungs to the heart. People typically think the difference between veins and arteries is in how much O2 they contain. Not so! 2. Uro-genital system a) After removing the intestines, you will see one of the two kidneys embedded in the dorsal body wall. From these, ureters lead to the urinary bladder. The ureters are small white tubes and are often difficult to find. The urinary bladder empties to the outside through the urethra. Be sure you can locate the urethral opening on both male and female rats. After examining the tubes, return back to kidneys. Carefully remove one of the two. Make a frontal planar cut so you can see the inside of the organ. Locate the following features: Hilus: depression near the center of the medial border. The renal artery and vein, lymphatic vessels, and nerves enter and exit through here. Pelvis: located in the center of each kidney, the pelvis contains cuplike extensions called calyces. These collect newly formed urine and channel it out of the kidney. Cortex: The outer region of each kidney. Renal corpuscles, which function in blood filtration, are found here. Medulla: The inner region of the kidney b) The reproductive system of the female rat is relatively simple. In the female, the prominent uterine horns pass dorsally to the bladder and ureters. Where the horns join, dorsal to the urethra, is the vagina, which opens to the exterior through the vaginal opening. On the exterior, the anus is just ventral to the tail, the vaginal opening is ventral to the anus, and the urethral opening is ventral to the vagina. At the anterior end of each uterine horn is a short, convoluted oviduct, which opens into a transparent pocket around the small, round ovary. Often the ovary is hard to find. Feel the fat at the end of the uterus for a small, hard, round body. Some female rates may be pregnant and have small embryos in the uterine horns. Cut longitudinally along the uterine horns. If your rat was pregnant, you may observe embryos. How does the interior surface of the uterus differ from the interior surface of the stomach? Why might you expect to find a difference in the two tissues? c) The male reproductive system is more complicated than that of the female. Locate the male’s scrotum. Cut longitudinally through just the skin to locate the testes. Separate the skin from the testes and continue the cut up to the abdominal cavity. Notice the epididymis lying around each testes. Find the vas deferens that leads from each testes to the urethra. You will probably have to cut through some muscles in the pelvic area to locate some of these structures; be careful as you cut. Two sets of glands are located on either side of the bladder, the smaller, round more posterior ones are the prostate glands. The larger pair of glands is the seminal vesicles, which are actually two separate glands – the vesicular glands and the coagulating glands. Follow the urethra as it goes through the penis. In males the bladder and the testes both empty to the outside through the urethra. Q1. The kidneys are found lying in between the mesenteries and the dorsal body wall. However, the remaining organs of the urinary tract, the ureters and the urinary bladder, are found inside the peritoneum (the coelom, or body cavity). What does this tell you about the developmental origins of these structures? (Hint: see Chapter 47) Q2. Find a group that has dissected an animal of the opposite sex from your own. Explain to them the reproductive tract of your animal. How do the reproductive tracts of the two animals differ? Uro-genitary tract T.A. Signature______________________________ 3. Circulatory System The circulatory system consists of three basic components. The heart is a pump that imparts pressure to the blood to establish the pressure gradient needed for blood to flow to the tissues. The blood vessels serves as the passageways through which blood is directed and distributed from the heart to all parts of the body and then returned back to the heart. The blood serves as the transport medium within which materials being transported are dissolved or suspended. (a) Return to the heart in the thoracic cavity. The heart lies in the posterior center of the thoracic cavity and is surrounded by membranes that together make up the pericardial cavity. The heart consists of 4 chambers: the right atrium, the left atrium, the right ventricle and the left ventricle. In general, the atria are receiving chambers, while the ventricles are discharging chambers. The major mass of the heart, which you see immediately upon opening the cavity, is in the ventricles. (b) Circulation from the body to lungs: blood returns to the heart from the systemic circulation through the systemic veins. These veins, which enter the heart from the anterior part of the body, are the vena cava. Blood entering the right atrium is pumped through the tricuspid valve into the right ventricle. Blood leaves the right ventricle through the pulmonary semilunar valve into the pulmonary artery, which goes to the lungs. This is the only time in which an artery will carry deoxygenated blood. Once the blood travels through the lungs, it becomes oxygenated. (c) Circulation from lungs to heart to body: oxygenated blood returns to the heart through the pulmonary vein. Most people are confused by the name, but the pulmonary vein is actually a vein. Why all the confusion? The oxygenated blood enters the heart through the left atrium and then the blood passes through the bicuspid valve into the left ventricle. The heavy walled ventricle pumps blood though the aortic semilunar valve into the aorta. The aorta delivers oxygenated blood to the body through the body's major arteries. (d) Other feature of the heart: besides the main chambers of the heart, there are many other features in the heart that should be noticed. Notice that the heart is divided by a muscular partition (the septum). This separation is very important because the right half of the heart is receiving and pumping low-oxygenated blood while the left side of the heart receives and pumps high-oxygenated blood. Be sure to notice the three types of tissues that make up the heart. The endocardium is a thin layer of endothelium and is a unique type of epithelial tissue that lines the entire circulatory system. The myocardium is composed of cardiac muscle and makes up the bulk of the heart wall. The epicardium is the thin external membrane covering the heart. For your dissection, carefully remove the heart from the thoracic cavity and lay it on the lab bench. Make a planar cut so you can see the four chambers. Find both atria and both ventricles. Locate the septum dividing the heart into left and right portions. This muscular partition separates the low O2 blood from the blood with high O2 content. Notice the wall of the ventricle is much thicker than the wall of the right ventricle. What functional difference accounts for the difference in anatomy? Q1. How do nutrients from the digestive system find their way to the kidneys? Q2. What is the difference between arteries and veins? Circulatory System T.A. Signature______________________________ Ten -point Write-up Individual Exercise; Due ???? A. Animal Use 1. Rats provide an excellent model for many human processes that cannot ethically be explored. For example, the mechanisms of many neurobiological processes are similar between the two animals. Do you think it's OK to use rats for experiments in which knowledge is gained that might possibly benefit humans? What might be some alternative ways to gain the same knowledge without using live animals for experimentation? B. The Dissection 1. What do rats eat? Follow a bolus of rat food from its mouth to its anus. At each step of the journey, comment on the digestive processes that are occurring (physiology) and the morphological features of each organ (brain, mouth, esophagus, stomach, small intestine, large intestine, rectum) that are involved in digestion. 2. What feature of the kidneys allows mammals to be well adapted to a terrestrial environment? Why is this such an important advancement in evolution? 3. Choose one aspect from each of the female and male reproductive systems and describe its function and importance. 4. Make a schematic diagram of the circulatory system. Label the following: Right Ventricle, Pulmonary arteries, capillary beds (in lungs), Left Atrium, Left Ventricle, Aorta, Capillary beds (head and arms, as well as abdominal organs and legs), Anterior Vena Cava, posterior Vena Cava, and Right Atrium. Be sure to include the oxygen content at each step. C. Learning Goals 1. Now that you have successfully completed the dissection of the rat, how do you think this lab is important to you? In your study of biology? In your understanding of the material of this class?