Rat Dissection External Anatomy

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2 Rat Dissection External Anatomy 1. Note the hairy coat that covers the rat and the sensory hairs (whiskers) located on the rat's face, called vibrissae. 2. The mouth has a large cleft in the upper lip which exposes large front incisors. Rats are gnawing mammals, and these incisors will continue to grow for as long as the rat lives. 3. Note the eyes with the large pupil and the nictitating membrane found at the inside corner of the eye. This membrane can be drawn across the eye for protection. The eyelids are similar to those found in humans. 4. The ears are composed of the external part, called the pinna, and the auditory meatus, the ear canal. 5. Locate the teats on the ventral surface of the rat. Check a rat of another sex and determine whether both sexes have teats. 6. Examine the tail, the tails of rats do not have hair. Though some rodents, like gerbils, have hair on their tails. 7. Locate the anus, which is ventral to the base of the tale. 8. On female rats, just posterior to the last pair of teats, you will find the urinary aperture and behind that the vaginal orifice which is in a small depression called the vulva. 9. On males, you will find a large pair of of scrotal sacs which contain testes. Just anterior to the scrotal sacs is the prepuce, which is a bulge of skin surrounding the penis. The end of the penis has a urogenital orifice, where both urine and sperm exit. Procedure: Skinning the Rat You will carefully remove the skin of the rat to expose the muscles below. This task is best accomplished with scissors and forceps where the skin is gently lifted and snipped away from the muscles. You can start at the incision point where the latex was injected and continue toward the tail. Use the lines on the diagram to cut a similar pattern, avoiding the genital area. Gently peel the skin from the muscles, using scissors and a probe to tease away muscles that stick to the skin. Muscles are attached to bones by connective tissue called tendons that adhere to spines, knobs, and ridges on bones. You will need to refer to the rat skeleton to determine where the muscles are attached to bones. The end attached to the bone that does not move during contraction is called the origin. The end of the muscle that attaches to the bone that does move is called the insertion. Rat Anatomy Organs of the Head and Neck 2

3 Head, Thoracic, and Abdominal Organs 1. Locate the salivary glands, which on the sides of the neck, between muscles. Carefully remove the skin of the neck and face to reveal these glands. Salivary glands are soft spongy tissue that secrete saliva and amylase (an enzyme that helps break down food). There are three salivary glands - the sublingual, submaxillary, and parotid. 2. Find the lymph glands which lie anterior to the salivary glands. Lymph glands are circular and are pressed against the jaw muscles. 3. After you have located the submaxillary glands, remove them to find the underlying structures. 4. The thyroid gland is a gray or brown swelling on either side of the trachea. To locate the trachea you will need to carefully remove the sternohyoid muscles of the neck. The trachea is identifiable by its ringed cartilage which provides support. The esophagus lies underneath the trachea, though it is easier to locate in the abdominal cavity where it enters the stomach. Procedure: Pin the structures of the head and neck. The Thoracic Organs Procedure: Cut through the abdominal wall of the rat following the incision marks in the picture. Be careful not to cut too deeply and keep the tip of your scissors pointed upwards. Do not damage the underlying structures. Once you have opened the body cavity, you will need to rinse it in the sink. 1. Locate the diaphragm, which is a thin layer of muscle that separates the thoracic cavity from the abdominal cavity. 2. The heart is centrally located in the thoracic cavity. The two dark colored chambers at the top are the atria (single: atrium), and the bottom chambers are the ventricles. The heart is covered by a thin membrane called the pericardium. (We will come back to the heart later.) 3. Locate the thymus gland, which lies directly over the upper part of the heart. The thymus functions in the development of the immune system and is much larger in young rats than it is in older rats. 4. The bronchial tubes branch from the trachea and enter the lungs on either side. The lungs are large spongy tissue that take up a large amount of the thoracic cavity. Bronchial tubes may be difficult to locate because they are embedded in the lungs. 3

4 The Abdominal Organs 1. The coelom is the body cavity within which the viscera (internal organs) are located. The cavity is covered by a membrane called the peritoneum, which covers four region visceral peritoneum - covers the internal organs mesenteries - attach the internal organs to the dorsal body wall omentia - connect organ to organ 2. Locate the liver, which is a dark colored organ suspended just under the diaphragm. The liver has many functions, one of which is to produce bile which aids in digesting fat. The liver also stores glycogen and transforms wastes into less harmful substances. Rats do not have a gall bladder which is used for storing bile in other animals. There are four parts to the liver: 3. The oesophagus pierces the diaphragm and moves food from the mouth to the stomach. Is is distinguished from the trachea by its lack of cartilage rings. 4. Locate the stomach on the left side just under the diaphragm. The functions of the stomach include food storage, physical breakdown of food, and the digestion of protein. The opening between the oesophagus and the stomach is called the cardiac sphincter. 5. Slit the stomach lengthwise and notice the ridges, called rugae. The attachment between the stomach and the intestine is called the pyloric sphincter. 6. The spleen is about the same color as the liver and is attached to the greater curvature of the stomach. It is associated with the circulatory system and functions in the destruction of blood cells and blood storage. A person can live without a spleen, but they're more likely to get sick as it helps the immune system function. 7. The pancreas is a brownish, flattened gland found in the tissue between the stomach and small intestine. The pancreas produces digestive enzymes that are sent to the intestine via small ducts (the pancreatic duct). The pancreas also secretes insulin which is important in the regulation of glucose metabolism. The greater omentum is the membranous curtain of tissue that hangs from the stomach and contains lymph nodes, blood vessels, and fat. Find the pancreas by looking for a thin, almost membrane looking structure that has the consistency of cottage cheese. 8. The small intestine is a slender coiled tube that receives partially digested food from the stomach (via the pyloric sphincter). It consists of three sections: duodenum, ileum, and jejunum. 9. Use your scissors to cut the mesentery of the small intestine, but do not remove it from its attachment to the stomach and rectum. If you are careful you will be able to stretch it out and untangle it so that you can see the relative lengths of the large and the small intestine. 10. Locate the colon, which is the large greenish tube that extends from the small intestine and leads to the anus. The colon is also known as the large intestine. The colon is where the finals stages of digestion and water absorption occurs and it contains a variety of bacteria to aid in digestion. The colon consists of five sections: 11. Locate the cecum - a large sac in the lower thrid of the abdominal cavity, it is a dead-end pouch and is similar to the appendix in humans. It also is the point at which the small intestine becomes the large intestine. 4

5 12. Locate the rectum - the short, terminal section of the colon between the descending colon and the anus. The rectum temporarily stores feces before they are expelled from the body. Urogenital System The excretory and reprodutive systems of vertebrates are closely integrated and are usually studied together as the urogenital system. However, they do have different functions: the excretory system removes wastes and the reproductive system produces gametes (sperm & eggs). The reproductive system also provides an environment for the developing embryo and regulates hormones related to sexual development. Excretory Organs 1. The primary organs of the excretory system are the kidneys. These organs are large bean shaped structures located toward the back of the abdominal cavity on either side of the spine. Renal arteries and veins supply the kidneys with blood. 2. Locate the delicate ureters that attach to the kidney and lead to the bladder. Wiggle the kidneys to help locate these tiny tubes. Procedure: Remove a single kidney (without damaging the other organs) and dissect it by cutting it longitudinally. Locate the cortex (the area) and the medulla (the inner area). 3. The urethra carries urine from the bladder to the urethral orifice (this orifice is found in different areas depending on whether you have a male female rat). outer or 4. The small yellowish glands embedded in the fat atop the kidneys are the adrenal glands. The Reproductive Organs of the Male Rat 1. The major reproductive organs of the male rat are the testes (singular: testis) which are located in the scrotal sac. Cut through the sac carefully to reveal the testis. On the surface of the testis is a coiled tube called the epididymus, which collects and stores sperm cells. The tubular vas deferens moves sperm from the epididymus to the urethra, which carries sperm though the penis and out the body. 2. The lumpy brown glands located to the left and right of the urinary bladder are the seminal vesicles. The gland below the bladder is the prostate gland and it is partially wrapped around the penis. The seminal vesicles and the prostate gland secrete materials that form the seminal fluid (semen). The Reproductive Organs of the Female Rat 1. The short gray tube lying dorsal to the urinary bladder is the vagina. The vagina divides into two uterine horns that extend toward the kidneys. This duplex uterus is common in some animals and will accomodate multiple embryos (a litter). In contrast, a simple uterus, like the kind found in humans has a single chamber for the development of a single embryo. 5

6 2. At the tips of the uterine horns are small lumpy glands called ovaries, which are connected to the uterine horns via oviducts. Oviducts are extremely tiny and may be difficult to find without a dissecting scope. Procedure: Pin the organs of the urogenital system. 6

7 Investigation 9 - Dissection and anatomical study of the rat (Rattus norvegicus) Aims: 1. To dissect and identify organs in thoracic cavity, abdominal cavity and urino- genital system 2. To note the similarities and differences between the rat and human digestive system, excretory system and reproductive system. Theoretical background: Dissection is a technique used to study the internal organs of a dead animal. It shows the internal structure of the animal, how the tissues look and feel, and how they are interrelated. Since the rat is a vertebrate and a mammal, many aspects of its structural organization are common with all other vertebrates, including man. In a way, studying the rat is like studying a human. Dissecting tools will be used to open the body cavity of the rat and observe the structures. Keep in mind that dissecting means "to expose to view. Since rats are herbivorous, they have 4 long, sharp incisors for gnawing and 12 molars for chewing but have no canines and premolars. The toothless space between the incisors and molars is called the diastema. This gap allows manipulation of the vegetable matter in the mouth by the tongue, thus ensuring a better chewing action. Rat s digestive system is similar to ours except that they have longer small intestine and a large caecum to digest cellulose. They have no gall bladder. There are no differences between human and rat excretory systems. The female rats have a V-shaped uterus that can hold many fetuses where as human uterus is smaller and usually holds only one fetus at a time. Materials: A preserved rat Forceps Drawing pins Methanol A scalpel Dissecting board Small ruler Detergent solution in a large container Dissecting scissors Disposable gloves Newspaper. Model of a human torso, Dissecting probe Cotton string A hand lens Medium sized plastic bag Lab coat Video on rat Charts on rat Disposable gloves dissection dissection Method: 1. Wrap the dissecting board with several thicknesses of newspaper. Get the necessary dissecting equipment, dissecting board, string, drawing pins, a ruler and obtain a preserved rat specimen for your group. 2. Wear surgical gloves and place the rat on its back in the middle of the dissecting board and pin the paws with drawing pins to the board. 3. Tie a length of string around each leg (near the foot), spread the legs wide to each side and secure the loose string ends around the board. (Your teacher will show you how to do this). 7

8 First incision 2 nd and 3 rd incisions Fig 9.1-External structure of the rat Fig Internal structure of the rat New illustrations draw diagrams similar to these ones When doing dissection, wear a lab coat and disposable gloves. The rat is stored in a chemical that can be painful and harmful if you get it in your eyes, nose, or mouth, so be careful. The tools of dissection are very dangerous. Make sure you are not distracted when you perform the dissection Digestive system: a) Mouth and teeth Fig 9.3- The mouth cavity and teeth of the rat New illustration Draw a diagram similar to this one 1. Use the closed scissors to pry the mouth open gently. You may have to dislocate the jaw-bone to do this. Observe the shape and size of the teeth and the empty space between incisors and molars called diastema. Check the number of incisors canines, premolars and molars. (refer to figure 9.3) The dental formula for the rat is as follows: Incissors Canines Premolars Molars Total teeth Upper jaw Lower jaw A. Draw a labeled sketch of the teeth in the upper and lower jaw and comment on the degree of tooth specialization. Compare the rat s teeth with those of a human. 8

9 b) Abdominal cavity Liver Diaphragm Bile duct Stomach Pancreas Spleen Large intestine Mesentery Caecum Small intestine Appendi x Rectum Anus Fig 9.4 Digestive system of the rat New illustration draw a diagram similar to this one 2. Use your forceps to pinch of skin in the middle of the abdomen and pull the skin upwards. 3. Use the scissors to make a small V-shaped incision. Stick the blunt blade of the scissors into the incision and cut upwards along the mid-line up to the throat and then back towards the tail, taking care to lift the skin upwards before cutting it. (refer to figure 9.1) 4. Insert the blunt end of the closed scissors under the cut and start separating (peeling back) the skin from the underlying muscle tissue. Peel the skin back to either side as mush as you can and pin it to the board. You may have to make more cuts. 5. Pinch the abdominal muscle in the centre of the abdomen and cut an incision large enough to take the blunt blade of the scissors. 6. Carefully cut in a straight line up towards the chest as far as you can. Continue cutting towards the tail. 7. Now cut the line left and right at the tail end of the incision and at the chest end. Point the blunt end of the scissors towards the rat to avoid damaging the underlying organs. To avoid damage to the internal organs be sure to lift the muscles as you cut. 8. You should have two flaps of tissue that can be folded back and pinned to the board. The abdominal cavity is now exposed. Now you will be able to see the chest cavity containing the heart, lungs and esophagus and the abdominal cavity containing the digestive system, excretory system and reproductive system. The chest cavity is separated from the abdominal cavity by a thin muscular membrane called the diaphragm. (refer to figure 9.2) Note: If this is a fresh rat, pour some methanol over the organs in the cavity. B. Make a labeled sketch of the undisturbed abdominal cavity. Which appears to be the largest organ that you can see? 9

10 9. Use your blunt probe to move organs about carefully and investigate without dislocating them. 10. In the abdominal cavity, pick up the esophagus as it comes through the diaphragm and note where the esophagus enters the stomach. 11. Over the stomach you will see a reddish brown liver which is divided into five lobes. The rat has no gall bladder. 12. Note the spleen which is a flattened, reddish organ lying just below the stomach. 13. A glandular organ called the pancreas is found near the stomach. 14. Now follow the small intestine all the way along until it becomes the large intestine. 15. At the junction between the small and large intestines, there is a blind pouch called the caecum which is important in cellulose digestion. Humans do not have a caecum. 16. At the end of the large intestine there is an expanded portion called the rectum, which opens to the exterior through the anus. C. Based upon what you can observe, what is the function of the mesentery membrane? 17. Follow the small intestine until it widens into a bag like structure called caecum and colon. The colon leads to the rectum which contains pellet shaped faeces. The rectum terminates as the anus. 18. Carefully stretch the intestines and examine the thin mesentery membrane attached to the small intestine which holds the intestine together. (refer to figure 9.4) 19. Separate the intestines from the thin membrane using your fingers taking care not to break the intestines. 20. Cut through the oesophagus and as close to the anus as possible, remove the alimentary canal and stretch it out on the dissecting board. Measure and record the length and diameter of the following organs: ( i)esophagus ( ii) stomach iii) liver ( iv) small intestine ( v) large intestine and (vi) caecum D. Enter your measurements in table9.1 E. Draw alabelled diagram of the digestive system on a separate sheet of paper. 19. Cut the alimentary canal just above and below the stomach and remove the stomach. Cut and remove 3 cm long from the small intestine and large intestine. Use a scalpel to cut down the length of each carefully so their contents can be examined. F. Observe, compare and comment on the consistency of food in the stomach, in the intestine and in the large intestine. 20. Wash the food out from all three sections and study the structure of the internal lining of each. G. Compare and comment on the internal lining of the stomach, the small intestine and the large intestine. Results: Table 9.1- Measurements and appearance of digestive organs-enter your measurements and observations of the digestive organs in the table given below: Organ measured Diameter (cm) Length (cm) Appearance of the food and lining Esophagus Stomach Liver Small intestine Large intestine Caecum Whole digestive system 10

11 Thoracic cavity: Trachea Right atrium Lungs Aorta Heart Left ventricle Fig 9.5- Thoracic cavity of the rat New illustration- draw a diagram similar to this 1. Locate the diaphragm which is a thin layer that separates the thoracic cavity from the abdominal cavity. 2. Use your scissors to cut a line up through the rib-cage (lifting as you cut) towards the throat and then cut left and right. Fold back or remove the ribs. The chest cavity is now exposed. 3. Spread the ribs apart and examine the heart which is centrally located. The two dark coloured chambers at the top are the atria and the bottom chambers are ventricles. The apex of the heart is formed by the large, muscular, left ventricle. The right ventricle is not clearly distinguished externally from the left, but is smaller and has thinner walls. The heart is covered by a thin membrane called the pericardium. 4. Open the pericardium and examine the surface of the heart and the large blood vessel, aorta, connected to it. 5. On either side of the heart are the large, spongy lungs that take up a large amount of space of the thoracic cavity. 6. Find the trachea which leads to the lungs by dividing into two bronchi. Immediately under the trachea is the gullet leading to the stomach. (refer to figure 9.5) 6. Remove the lungs and the heart and place them aside on a news paper. H. Sketch and label the organs in the chest cavity (left lung, right lung, trachea, bronchi and the heart. Urino-genital system a) Excretory system 1. Carefully remove the digestive system, place them in a beaker and cover them with methanol... Wash the abdominal cavity with water and note the colour and size of the kidneys located on either side of the backbone. 2. Locate the ureter leading from the kidney to the urinary bladder which expels urine via the (refer to figure 9.6) urethra Fig 9.6- Excretory system of a rat New illustration draw a diagram similar to this one I. Sketch and label the excretory system 11

12 b) Reproductive system: Figure 9.7- Male urino-genital system New illustrations draw diagrams to similar to these ones i) Male reproductive system- The testes are located in the scrotal sac. On the surface the testes is a coiled tube called the epididymus which collects and stores sperm cells. The vasdeferens is a tube which carries the sperm to the urethra, which carries sperm through the penis and out of the body. The gland below the bladder is the prostate gland which secretes the seminal fluid (semen) 1. Examine the genital area of your rat. Locate the male's scrotum and cut longitudinally through the skin to locate the testes. 2. Separate the skin from the testes and continue the cut up to the abdominal cavity. Notice the epididymus lying around each testis. 3. Find the vas deferens that leads from each testis to the urethra. 4. On either side of the bladder you will find two sets of glands. The smaller, round, posterior ones are the prostate glands. The larger pair of glands are the seminal vesicles. 5. Follow the urethra as it goes through the penis. In males the bladder and the testes both empty to the outside through the urethra. J. Sketch and label the male reproductive system ii) Female reproductive System- The short gray tube lying dorsal to the urinary bladder is the vagina which divides into two uterine horns that extend toward the kidneys. This duplex uterus accommodates multiple embryos. In contrast, a simple uterus, like the kind found in humans has a single chamber for the development of a single embryo. At the tips of the uterine horns are small glands called ovaries which are connected to the uterine horns via oviducts. Oviducts are extremely tiny and may be difficult to find without a dissecting scope. 12

13 Oviduct Vagina Figure 9.8- Female urino-genital system Fig 9.9-V shaped rat uterus with six embryos html New illustration- draw a diagram similar to this one 1. If your specimen is a female rat, observe the following organs: 2. In the female you will find two uterine horns 3. The two uteri join and open into the vagina. 4. At the anterior end of each uterus there is a short oviduct which opens into a transparent pocket around the small, round ovary. 5. Some female rats may be pregnant and have several small embryos in the uteri. If your rat is pregnant, cut longitudinally along the uteri and observe the embryos. 6. On the exterior, just ventral to the tail, you will find the anus, the vaginal opening and the urethral opening. 7. Observe the reproductive organs of a male rat/female rat dissected by other groups and note the differences. H. Sketch and label female reproductive system Disposal of dissected rat 1. After finishing the dissection, place your dissecting instruments in a container of detergent solution, wash, dry and pack them in the boxes provided. 2. Drain the methanol from the beaker with the discarded intestines and other organs and place them back into the rat s cavity. 3. Remove the drawing pins from the board, wrap the rat in the news paper and place in a plastic bag for disposal. Make sure no organs are left in the sink. 4. Dispose of your gloves in the bag provided, wash your hands and finger nails thoroughly in detergent solution, rinse and dry them Results: 1. Draw and label the diagrams of the mouth, digestive system, thoracic cavity, male and female urino-genital systems of the rat on a separate sheet of paper and submit your diagrams to your teacher. Discussion: Digestive system: 1. Describe the type of teeth possessed by the rat. 2. What are the functions of incisors and molars? 3. What can you infer about the rat s diet from its teeth? 4. How are rat s teeth different from human teeth? 5. Describe the shape and structure of the stomach? 6. Which organ is the largest? How much of the abdominal cavity did it occupy? 5. What differences did you notice between the small intestine and the large intestine? 6. What is the advantage of having a long, small intestine? 13

14 7. Where is the caecum situated? The caecum contains microorganisms which digest cellulose. How do these microbes help in the process of digestion for a rat? 8. What is the function of the mesentery? 9. What would be the functions of the liver, spleen and pancreas? 10. Compare human digestive system to that of a rat. Chest cavity: 11. Which organs were seen in the chest cavity? 12. Name the membrane that separates the chest cavity from the abdominal cavity/ Excretory system: 13. Describe the shape and position of the kidneys? 14. What are the functions of the following organs: a) ureters b) urinary bladder c) urethra? Reproductive system: 12. What are the functions of the following reproductive organs: a) Penis: b)testes: c) Ovaries: d) Uterus: 13. What is the difference between human uterus and rat uterus? 14. How many fetuses did you notice in the rat? Conclusion: Describe the similarities and differences between the rat and human digestive system, excretory system and reproductive system. (refer to the human torso) ****************** EX 1- Dissection of a rat Time: 2 x 45 minute lessons Background knowledge: Dissection is a technique used to study the internal organs of a dead animal. It shows students the internal structure of the animal, how the tissues look and feel, and how they are interrelated. All mammals possess similar type of organs and systems whether they are small or large in size. To understand the structure and functions of our systems, it is helpful to dissect smaller mammals such as rats. Since rats are herbivorous, they have 4 long, sharp incisors for gnawing and 12 molars for chewing but have no canines and premolars. The toothless space between the incisors and molars is called the diastem. Their digestive system is similar to ours except that they have longer small intestine and a large caecum to digest cellulose. They have no gall bladder. There are no differences between human and rat excretory systems. The female rats have a V-shaped uterus that can hold many fetuses where as human uterus is smaller and usually holds only one fetus at a time. Learning outcome: After completing this dissection, students will become proficient in dissecting and become familiar with the structure and functions of various organs and systems of the rat and also note the differences between human and rat systems. Aim: To dissect and note the structures and functions of various organs and systems in the rat. Equipment: a preserved rat, scalpel, sharp scissors, dissecting probe, forceps, dissecting needle, dissecting board, surgical gloves, long string, drawing pins, small ruler, model of a human torso, charts and videos on rat dissection and an old newspaper. Method: Resource an external diagram similar to this 14

15 Resource: Core Biology Practical p 3.28 Figure 1-External diagram Figure 2-Internal diagram 4. Get the necessary dissecting equipment, dissecting board, string, drawing pins, a ruler and a news paper. Obtain a preserved rat specimen for your group. 5. Wear surgical gloves and lay the rat down on its back on the dissecting board and pin the paws to the dissecting board. 6. Secure the rat firmly to the dissecting board with a string. (Your teacher will show you how to do this). 7. Grab a pinch of skin between the hind legs and make a V-shaped cut with a pair of sharp scissors. Hold the skin with forceps and continue to cut upwards along the mid-line up to the throat. (See figure 1) 8. Cut across both the front legs and back legs taking care not to cut the underlying muscles. 9. Peel the skin off the rat and pin the skin to the dissecting board. 10. To avoid damage to the internal organs, be sure to lift the muscles as you cut. Note: point the blunt end of the scissors towards the rat to avoid damaging the underlying organs 11. Pin down the muscles to the board securely. Now you will be able to see the chest cavity containing the heart, lungs and esophagus and the abdominal cavity containing the digestive system, excretory system and reproductive system. The chest cavity is separated from the abdominal cavity by a thin muscular membrane called the diaphragm. (See figure 2) Chest cavity: 15

16 Trachea Aorta Lungs Heart Left ventricle Figure 3- Chest cavity 1. Open the chest cavity by cutting through the center of the ribs. Carefully extend the cut into the hollow of the throat between the bottom jaws. 2. Observe the lungs and the heart located in the chest cavity. 3. Trace the trachea as it divides and goes into the lungs. 4. The heart is covered by a membrane known as the pericardium. The apex of the heart is formed by the large, muscular, left ventricle. The right ventricle is not clearly distinguished externally from the left, but is smaller and has thinner walls. 5. Remove the lungs and the heart and place them aside on a news paper. a) Digestive system Figure 4- Rat s skull and teeth 16

17 Mouth and teeth: 2. Open the mouth of the rat and observe the shape and size of the teeth and the empty space between incisors and molars. Check the number of incisors and molars. Abdominal cavity 3. In the abdominal cavity, pick up the esophagus as it comes through the diaphragm and note where the esophagus enters the stomach. Liver Diaphragm Bile duct Stomach Pancreas Spleen Large intestine Mesentery Caecum Small intestine Appendix Rectum Anus Resource: Core biology practical p 3.28 Figure 5- Rat s digestive system 4. Over the stomach you will see a reddish brown liver which is divided into five lobes. The rat has no gall bladder. 5. Note the spleen which is a flattened, reddish organ lying just to the left and posterior to the stomach. 6. A glandular organ called the pancreas is found near the stomach. 7. Now follow the small intestine all the way along until it becomes the large intestine. 17

18 8. At the junction between the small and large intestines, there is a blind pouch called the caecum which is important in cellulose digestion. Humans do not have a caecum. 9. At the end of the large intestine there is an expanded portion called the rectum, which opens to the exterior through the anus. 10. Carefully stretch the intestines and examine the thin mesentery membrane attached to the small intestine which holds the intestine together. 11. Separate the intestines from the thin membrane using your fingers and pin it to one side on the dissecting board. 12. Measure the diameter and length of the whole digestive system and the following organs: a. Esophagus b) stomach c) liver d) small intestine e) large intestine and f) caecum 13. Enter your measurements in the table given under results. 14. Draw and label the diagram of the digestive system on a separate sheet of paper. b) Urino-genital system i) Excretory system 1. Wash the abdominal cavity with water and note the colour and size of the kidneys located on either side of the backbone. 2. Trace the ureters leading from the kidney to the urinary bladder which expels urine via the urethra. ii) Reproductive system: Kidney Kidneys Seminal gland Ureter Ovary Coagulating gland Prostate gland Bladder Uterus Penis Testes Scrotum Figure 6- Male urino-genital system Resources: Core Biology practical p 3.28 i) Male reproductive system Anus Urethra Figure 7- Female urino-genital system 6. Examine the genital area of your rat. If your rat is a male rat, observe the following organs: 7. Locate the male's scrotum and cut longitudinally through the skin to locate the testes. 18

19 8. Separate the skin from the testes and continue the cut up to the abdominal cavity. Notice the epididymis lying around each testis. 9. Find the vas deferens that leads from each testis to the urethra. Note: You will probably have to cut through some muscles in the pelvis area to locate some of these structures. Be careful as you do so. 10. To either side of the bladder you will find two sets of glands. The smaller, round, more posterior ones are the prostate glands. The larger pair of glands are the seminal vesicles, which are actually two different glands the vesicular glands and the coagulating glands. 11. Follow the urethra as it goes through the penis. In males the bladder and the testes both empty to the outside through the urethra. ii) Female reproductive System 8. If your rat is a female rat, observe the following organs: In the female you will find two V shaped uteri. 9. The two uteri join and open into the vagina. 10. At the anterior end of each uterus there is a short, convoluted oviduct, which opens into a transparent pocket around the small, round ovary. 11. Some female rats may be pregnant and have small embryos in the uteri. If your rat is pregnant, cut longitudinally along the uteri and observe the embryos. 12. On the exterior, just ventral to the tail, you will find the anus, the vaginal opening and the urethral opening. 13. Observe the reproductive organs of a male rat/female rat dissected by other groups and note the differences. 14. After finishing the dissection, wrap the rat and the organs in a newspaper and place it in a bag provided for disposal. Make sure no organs are left in the sink. 15. Clean you dissecting board and instruments with a detergent and pack up. 16. Dispose of your gloves in the bag provided, and wash your hands thoroughly with soap. Results: 1. Draw and label the diagrams of the digestive system and the male and female urinogenital systems of the rat on a separate sheet of paper and submit your diagrams to your teacher. 2. Enter your measurements of the digestive organs in the table given below: Organ measured Diameter (cm) Length (cm) Esophagus Stomach Liver Small intestine 19

20 Large intestine Caecum Whole digestive system Analysis of results: Chest cavity: 7. Which organs did you see in the chest cavity? 8. What separated the chest cavity from the abdominal cavity? Digestive system: 9. Describe the type of teeth possessed by the rat. 10. Describe the shape and structure of the stomach? 15. Which organ is the largest? How much of the abdominal cavity did it occupy? What differences did you notice between the small intestine and the large intestine? 16. Where is the caecum situated? What is its purpose? Excretory system: 17. Describe the shape and position of the kidneys? 18. What are the functions of the ureters, urinary bladder and urethra? Reproductive system: 10. What are the functions of the following reproductive organs: b) Penis: b)testes: c) Ovaries: d) Uterus: 11. What is the difference between human uterus and rat uterus? 12. How many fetuses did you notice in the rat? Conclusion: Look at the model of a human torso and describe the differences between the rat and human digestive system, excretory system and reproductive system. Safety rules: When doing dissection, wear a lab coat and surgical gloves. The rat is stored in a chemical that can be painful and harmful if you get it in your eyes, nose, or mouth, so be careful. The tools of dissection are very dangerous. Make sure you are prepared and not distracted when you perform dissection. Dispose of the dissected rat by wrapping it in a newspaper and put it in a bag provided. Don t discard any organs in the sink. Clean the sink with a disinfectant. Dispose your gloves in the rubbish bin and wash your hands with a disinfectant. Suggestions for teachers: Students should have background knowledge of the various systems of the human body so that they can identify and compare with the systems in the rat. Show some charts and videos on dissecting a rat. 20

21 A demonstration of the dissection would be helpful before students begin their dissection. Order few male rats, few pregnant and few non-pregnant female rats. Provide detergent, soap and a bag to dispose off the rats after dissection. Make the students aware of the websites they can use. Websites: Suggested answers for EX 5- Dissection of a rat Results: Diagrams of digestive system and excretory system Liver Diaphragm Bile duct Stomach Pancreas Spleen Large intestine Mesentery Caecum Small intestine Appendi x Rectum Anus Digestive system 21

22 Kidney Kidneys Seminal gland Ureter Ovary Coagulating gland Prostate gland Bladder Uterus Penis Testes Scrotum Male urino-genital system Anus Urethra Female urino-genital system 2. Measurements of the digestive organs in the table given below: results will vary Organ measured Diameter (cm) Length (cm) Esophagus Stomach Liver Small intestine Large intestine Caecum Whole digestive system Analysis of results: a) Chest cavity: 11. Lungs, heart, trachea and esophagus were seen in the chest cavity. 12. The diaphragm separated the chest cavity from the abdominal cavity. b) Digestive system: 13. A rat has 4 sharp incisors to gnaw at food and 12 molars for grinding food. Canines and premolars are absent. There is an empty space between the incisors and molars called diastem 14. The stomach is J shaped and is muscular. 19. The liver is the largest organ and it occupies 1/3 rd of the abdominal cavity. 20. The small intestine is narrower in diameter and longer in length than the large intestine. 21. The caecum is situated at the junction of small intestine and large intestine. It contains microbes, which help in digesting cellulose. c) Urino-genital system i) Excretory system 22. Kidneys are reddish brown, bean shaped organs situated on either side of the backbone. 23. Ureters carry urine from the kidneys to the urinary bladder for storage. Urine is expelled via the urethra. ii) Reproductive system: 10. Functions of the reproductive organs: c) Penis: Expels sperm and urine. d) Testes: Produce and store sperm. e) Ovaries: Produce ova. f) Uterus: Fetuses develop in the uterus. 11. Rats have V shaped uterus with 2 branches where as humans have only one small, un-branched uterus. 12. Rat s uteri contain many fetuses. Answers may vary 22

23 Conclusion: The main differences between the rat and human systems are: Rats have only incisors and molars. Humans have incisors, canines, premolars and molars. Rats have large caecum but humans have small appendix. Rats have longer small intestine compared to human s small intestine. Female rats have V-shaped and branched uterus that holds many fetuses. Human uterus is un-branched and usually holds one fetus. Rats have common urino-genital openings and humans have separate urinary and genital openings. 23