CLASS SET – DO NOT REMOVE!

DISSECTING A MAMMAL – THE RAT Objectives: 1. Examine the external anatomy of the rat. 2. Dissect the digestive, respiratory, circulatory, excretory, and reproductive systems of the rat and relate each structure to its function. Materials: Preserved Rat Goggles

Scissors Markers/Pins

Pins Scalpel Apron Dissecting Tray Probe Hand Lens

Grading: Grading Your grade on this laboratory will be assessed according to the following criteria:  Class Participation (serious approach, proper cleanup and lab safety)  Lab Checklist  Lab Practical Exam (at the end of lab)

INTRODUCTION (Answer question #1 on your pre-lab sheet.) For the next several days, you will be studying the anatomy of the rat as a means of understanding the body plan of vertebrates, particularly mammals. Although at first glance the anatomy of the rat appears to be quite different from that of a human, these differences are mainly in size and proportion. Therefore, by studying the anatomy of the rat, you gain a better understanding of human anatomy. Rats are vertebrates or backboned animals and also mammals. Mammals share many common characteristics such as body hair, mammary glands and specialized teeth. Some internal features common to all mammals are diaphragm, a fourchambered heart and similar specialized systems. By observing the internal and external anatomy of the rat, you will be able to learn more about these common traits shared by mammals. CLASSIFICATION (Answer questions #2 on your pre-lab sheet.) Taxonomy, the science of classification, helps to organize and relate species to one another. New information is constantly being discovered through molecular analysis, fossil finds and comparative anatomical studies, which can cause taxonomists to modify classifications as the new information emerges. The classification of the white rat is as follows… Kingdom Animalia Phylum Chordata Subphylum Vertebrata Class Mammalia Order Rodentia Family Muridae Genus Rattus Species rattus DISSECTION TERMINOLOGY (Answer question #3 on your pre-lab sheet.) 1. Anterior –toward the head 2. Posterior – toward the tail 3. Dorsal – toward the backbone 4. Ventral – toward the belly 5. Lateral – toward the side

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6. Medial – toward the midline 7. Proximal – lying near the point of reference 8. Distal – lying further away from the point of reference

IDENTIFYING EXTERNAL ANATOMY Parts and Function (Answer questions #4 - 9 on your pre-lab sheet.) 1. Nostrils – allows air into the trachea, found at the anterior of the rat’s body 2. Teeth – 2 incisors for biting and tearing and 6 molars for chewing 3. Eyelid – one upper and one lower to protect the eyeball 4. Nictitating Membrane – a third lid-like transparent membrane that covers the eyeball 5. Vibrissae – whiskers that are extremely sensitive to touch and possibly changes in air pressure 6. Pinnae – external ears used to sense sound 7. Forelimbs – front legs used for grasping and holding 8. Hind-limbs – back legs used for running, climbing and jumping; are more powerful than forelimbs 9. Digits – finger-like projections on limbs 10. Digital Pads – swollen, thickened skin located on tips and bases of digits 11. Foot Pads – swollen, thickened skin on the sole of each foot 12. Urethral Aperture (female only) – opening for release of urine in females 13. Vaginal Aperture (female only) – female genital opening 14. Anus – posterior opening located at base of tail for excretion of solid waste 15. Urogenital Aperture (male only) – opening of the penis; discharges urine and sperm 16. Scrotum (male only) – a double pouch that contains two testes 17. Mammary Papillae – 12 nipples used for nursing young 18. Tail – covered in bristles and scales approximately ¾ the length of the rat; used for balance

EXTERNAL Procedure 1. Obtain a rat and ziplock bag for storage. Line your tray with a paper towel. Rinse you rat with tap water if necessary to remove excess preservative. Label your ziplock bag with your group names and class period (set aside). 2. Note that the body is divided into a head and trunk, separated by the neck region. On the head region, locate and be able to identify on the rat each of the external features listed above. To examine the teeth, you will have to make an incision / cut through each cheek with your scissors and pry open the mouth with your probe. 3. On the ventral surface of the trunk region are two rows of mammary papillae, which extend from the armpit region to the groin region on either side of the midline. In rats there are usually 12 pairs which are most prominent in pregnant or lactating females. Also, visible on the ventral surface is the anus just beneath the base of the tail. Slightly anterior to the anus are the urogenital openings. In females there are two separate openings: the anterior urethral aperture leading from the urinary system and the more posterior vaginal aperture leading from the reproductive tract. In males the urinary and reproductive systems share a single opening (urogenital aperture) at the tip of the penis which is hidden in a fold of skin located between the prominent scrotum. 4. Examine all of these features on your rat. Determine the sex of your rat and then examine another student’s rat of the opposite sex. 5. The tail is sparsely covered with hair and bears reptile-like scales of epidermal origin. There are two pairs of appendages attached to the trunk, the hind limbs arising from the pelvic region and the forelimbs arising from the shoulder region. On each of these feet, are the digits, digital pads, and the foot pads. 2

IDENTYFYING INTERNAL ANATOMY It is not easy to study the internal organs of a human. However, anatomy of the human systems can be studied by examining the systems of the rat, an animal similar to a human. A rat resembles a human both internally and externally in many ways. Your rat is to be used to observe many systems in the investigations to come. Therefore, it is important that directions for dissections be followed exactly. Do not remove any organ or structure unless you are directed to do so. It is important to remember that dissecting does NOT mean “cut up”; in fact, it means “to expose to view”. Careful dissection techniques will be needed to observe all the structures and their connections to other structures. You will not need to use a scalpel as it is not the best tool for dissection. Scissors serve better because the point of the scissors can be pointed upwards to prevent damaging organs underneath. ALWAYS raise structures to be cut with you forceps before cutting, so that you can see exactly what is underneath and where the incision should be made. Never cut more than is absolutely necessary to expose a part.

The Muscular and Skeletal System of the Rat (Answers 10-16 on your pre-lab sheet) 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. The movement caused by the contraction of the muscle is called the action. Muscles can be easily identified from one another by their shape and overlap.

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. STOP! HAVE YOUR TEACHER SIGN YOUR CHECKLIST! Try to identify 3 of the following muscles (you choose which 3). Place a pin to mark the muscles you are naming: 1. Biceps brachii - located on the anterior surface of the humerus. Action: flexes lower arm 2. Triceps brachii - located on the sides and back of the upper arm. Action: extends lower arm 3. Spinotrapezius - located across the dorsal thoracic region of the rat. Action: moves scapula up and backward 4. Latissimus dorsi - located posterior (and partially covered) by the spinotrapezius. | Action: moves the humerus 5. Biceps femoris - located on the side of the thigh, in two bundles. Action: flexes the lower leg 6. Tibialis Anterior - located on the front of the leg. Action: flexes foot

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7. Gastrocnemius - located on lower leg, bulk of the calf muscle. Attaches to heel by the Achilles Tendon. Action: extends the foot 8. External Oblique - located on the sides of the abdomen.Action: flexes body wall. 9. Gluteus Maximus - located on the lower back and rear. Action: extends the thigh at the hip 10. Pectoralis Major/Minor - located in chest area. Action: adducts arm (draws it forward)

STOP! HAVE YOUR TEACHER SIGN YOUR CHECKLIST!

Procedure: Exposing the bones of the leg. Carefully tease away the biceps femoris and gastrocnemius to expose the 3 leg bones: Tibia, Fibula, and Femur and the small patella (kneecap). You can also see the ligaments around the knee that attach the bones of the lower leg to the femur and the achilles tendon which attaches the the gastrocnemius to the ankle. Note that the joint of the hip is called a ball and socket joint. Examine how the bones fit into the pelvis. STOP! HAVE YOUR TEACHER SIGN YOUR CHECKLIST!

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PREPARING FOR THE CAVITY DISSECTION 1. Place the rat on its back in the dissecting tray which has been lined with paper towel. Obtain several dissecting pins from the teacher if you do not already have some. Like all tetrapods (four limbs or feet), your rat has two “cavities” in its body. The abdominal cavity, containing the gut and its associated organs, and the thoracic cavity (chest), containing the heart and lungs. The two cavities are separated by the diaphragm, or breathing muscle. Before you begin to open these cavities, remember one thing:

YOUR GOAL IS TO OPEN BOTH BODY CAVITIES WITHOUT SPOILING OR CUTTING THE INTERNAL ORGANS!!

ABDOMINAL CAVITY PROCEDURE (Answers questions 17-18 on your pre-lab sheet) 2. Use tweezers or your fingers to pull the skin and underlying tissue away from the body to loosen it before you begin cutting. Then, as you are making your incision, pull up with the scissors as you go. 3. Follow the dotted lines on the external anatomy drawing of your answer sheet. Make a cut at the base of the abdomen on the ventral side of your rat. Cut through the skin and abdominal muscles exposing the internal organs. As you continue anteriorly, toward the thoracic region, you will encounter the diaphragm separating the abdomen and chest. 4. DO NOT cut through the diaphragm or ribs at this time. We will open the thoracic cavity in a later step. 5. Make lateral cuts at each limb so that you can easily fold back the ‘flaps’ like a book. DO NOT REMOVE THE FLAPS. Open the flaps and pin them down. They will be placed back over the cavities each day when you are finished so that the internal organs will not dry out over night. 6. Identify the diaphragm, a thin sheet of muscle that separates the abdominal and thoracic (chest) cavities. 7. Now look at the large organs within the abdominal cavity. Locate the large, dark brown, multi-lobed liver, posterior to the diaphragm. Just under the liver, find the sack like stomach with the small intestine-the thin, coiled tubeextending out posterior from it. The coiled mass of thicker tubing below the small intestine is the large intestine.

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DIGESTIVE SYSTEM (Answers questions 19-28 on your pre-lab sheet) Parts and Function (Answer questions #11-19 on your student answer sheet.) 1. Esophagus – muscular tube that is next to the trachea; used to pass food from mouth to the stomach 2. Tongue – elongated muscular structure visible on the floor of the mouth 3. Liver (ancillary organ) – dark brown organ located under the dome of the diaphragm; consists of 4 lobes; regulates blood glucose, blood cholesterol, hormones and makes bile 4. Stomach – large, muscular pouch that lies below the liver; mixes food with digestive juices 5. Small Intestine – 6 times the length of the rats body; carries out most of the digestion of food 6. Large Intestine – shorter and wider than small intestine; removes water from undigested food 7. Mesentery – fine, thin, membranous tissue that holds organs in place 8. Pancreas (ancillary organ) – secretes the hormone insulin into the bloodstream; releases digestive enzymes into the small intestine DIGESTIVE Procedure 1. Pry open the mouth. Insert your scissors into one of the corners of the mouth and cut through the skin, muscles, and bones. Repeat this procedure with the other corner of the rat’s mouth. Do not cut too deep or remove the bottom jaw completely. You should be able to easily examine the inside of the mouth. 2. Notice the tongue on the floor of the mouth or lower jaw. Rub your finger along the surface of the rat’s upper jaw between the teeth. Notice the ridges on the hard palate on the roof of the mouth. Food is rolled against this hard surface and formed into a ball that is easily swallowed. Behind the hard palate is the soft palate. 3. Locate the following digestive organs. You may have to carefully move some organs side to side to see others. They are listed in the order that food moves through them. Do NO additional cutting in this part of the dissection unless directed to do so. 4. The esophagus can be viewed at the back of the mouth or in the throat region if the incision through the skin also cut through the muscle in the neck. Do this and examine it. The esophagus can also be viewed when you open the chest cavity later. It is the only digestive organ found in the thoracic cavity. 5. Continue your study by examining the abdominal cavity in more detail. The esophagus leads to a large, slack Jshaped stomach on the left side of the rat’s body. Lift up the lobes of the liver to locate it. Enzyme’s secreted by glands in the stomach aid in protein digestion. On the left side of the stomach is a long, slender, brown, flat organ that stores and filters blood. This is the spleen. At the lower end of the stomach is a muscular constriction called the pyloric sphincter which regulates the movement of food from the stomach into the small intestine. 6. Notice that the coiled narrow small intestine leads from the posterior end of the stomach. Digestion is completed in the small intestine. The liver contributes bile, a greenish liquid that breaks large fat droplets into smaller droplets. This bile is carried from the liver to the small intestine through a thin tube called the bile duct-locate this duct. Rats

do not possess a gall bladder so they cannot store bile. 7. Find the mesentery-the fine, thin membrane that holds the intestines in place. Find the light colored pancreas, which is located in the mesentery between the stomach and the small intestine. This glandular organ secretes digestive enzymes into the top portion of the small intestine. 8. The small intestine leads to the thicker, tightly coiled large intestine. This is where the process of concentrating feces by reabsorbing water and electrolytes from the intestinal contents. Notice how the large intestine spirals through the abdominal cavity, loops through the upper portion of the small intestine, and then forms a straight tube, the rectum. The rectum leads to the anus, the outside opening of the rat’s body. 9. Examine the stomach in more detail by making a longitudinal slit in the wall of the stomach. Notice the folds of the inner walls of the stomach. These surfaces unfold allowing the stomach to stretch and expand when it is full of food. Examine the small intestine in more detail by carefully making a small slit in a small portion of the intestine. Examine the internal surface with your finger. Notice the hair like structures called villi which increase the surface area of the small intestine for more efficient absorption of nutrients.

STOP! HAVE YOUR TEACHER SIGN YOUR CHECKLIST!!

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UROGENITAL SYSTEM (Excretory and Reproductive Systems) (Answers questions 29-36 on your pre-lab

sheet) Parts and Function 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.

Kidneys – bean-shaped organs surrounded by fat; removes waste from blood Ureters – transport urine from kidney to bladder Urinary Bladder – temporary storage of urine Urethra – transports urine from bladder out of body Ovaries – female gonads (sex organs) that produce female gametes (eggs) and female sex hormones Oviducts – also called fallopian tubes; egg travels from ovary through oviducts to uterus Fat bodies – provides protection for ovaries Uterus – site of rat embryo development Testes – male gonads that produce sperm and male sex hormones; located in scrotum Penis – copulatory organ of males; contains the urethra which discharges sperm and urine Scrotum- protects and houses the testes Prostate Gland- produces semen

UROGENITAL Procedure 1. Push the intestines to the side and locate the dark red, bean-shaped kidneys along the opposite sides of the dorsal body wall. The kidneys filter wastes from the blood. 2. Each kidney connects to a ureter-a white tube that carries urine from the kidney to the urinary bladder. Locate a ureter on the concave side of one of the kidneys just below the renal artery and vein. Trace the ureters to the urinary bladder. Urine leaves the bladder through the urethra. To locate the urethra, spread the hind legs as far apart as you can. Then use your scissors to make a small incision in the tissue a little to one side of the mid-ventral line. Probe with your fingers until you find the cartilage and expose the urethra. The urethra leads to the urogenital opening through which urine passes out of the body. 3. Select one of the kidneys and carefully bisect it (cut it in half). Do not remove the kidney or cut all the way through it. Identify the medulla and the cortex of the kidney.

REPRODUCTION - FEMALE RAT Procedure 1. Posterior to the kidneys, locate the off white, almond-shaped ovaries. 2. Use a probe to locate the thin, threadlike oviducts or fallopian tubes, that loop behind the ovaries. In a mature female rat, eggs break through the ovary walls and pass into the oviduct. Tiny cilia line this passage, sweeping the egg through the coiled tube. If fertilization occurs, it usually takes place in one of the oviducts. 3. Trace the oviducts as they lead into the wider tubes called the uterine horns. Multiple births are common in rats. The uterine horns allow multiple fetuses to spread out along the abdominal cavity walls. Where the uterine horns unite forms the body of the uterus. This narrowing marks the location of the cervix. 4. Notice how the urethra merges with the vagina (where sperm enter the rat) near the urogenital opening. This common tube is called the urogenital sinus. REPRODUCTION - MALE RAT Procedure 1. Locate the scrotum on either side of the anus. Carefully, cut through the lining of the scrotum pull back the skin on one side exposing the testes. A male has two testes-small oval masses where sperm is produced. 2. Along the side of the testes, find the coiled mass of tiny tubes-the epididymis-that store the sperm. Sperm travel from the epididymis through the vas deferens to the urethra near the entrance to the urinary bladder. From this point the excretory and reproductive system share the same passageway, the urethra. 3. Just above the bladder is the prostate gland which produces semen.

STOP!! HAVE YOUR TEACHER SIGN YOUR CHECKLIST! 7

THORACIC CAVITY PROCEDURE 1. It is now time to dissect the thoracic (chest) cavity. Use the scissors to cut through the ribs, lateral to the sternum (both sides). NOTE: Keep the lower edge of your scissors tightly pressed against the inner sides of the bones to avoid puncturing the delicate lung and heart tissues and other structures just under the ribs. 2. Remove the two sides of the rib cage exposing the thoracic cavity.

CIRCULATORY SYSTEM Parts and Function (Answer questions 37-42 on your pre-lab sheet.) 1. Heart – major organ that consists of 4 chambers (atria and ventricles) 2. Aorta – largest artery in the body that takes oxygenated blood from left ventricle out into the body 3. Pulmonary Artery – artery that takes deoxygenated blood to the lungs 4. Right Atrium – deoxygenated blood from body enters heart here 5. Left Atrium – receives oxygenated blood returning from lungs 6. Right Ventricle – pumps deoxygenated blood to the lungs 7. Left Ventricle – pumps oxygenated blood to the body 8. Spleen – recycles red blood cells; maturation center for white blood cells Procedure 1. Free the diaphragm from the body wall by clipping the diaphragm around the edges where it joins the ribcage. Pull the diaphragm down so it covers the liver. 2. Locate the heart in the middle of the chest cavity between the lungs. Note that the heart is enclosed in a transparent membrane, the pericardium. 3. Mammalian hearts are divided into four chambers. The top chambers, the atria, collect blood as it comes into the heart. The bottom chambers, the ventricles, pump blood to the lungs and body. Notice the coronary blood vessels that run down the central surface of the heart. 4. Notice the blood vessels leading to and from the heart. The anterior and posterior venae cavae enter the right atrium. Lift the heart and rotate it to your right to locate these blood vessels. Find the pulmonary artery that leads from the right ventricle to the lungs. The pulmonary veins lead from the lungs into the left atrium. The aorta (with the curved aortic arch), located underneath the pulmonary artery, carries the blood from the left ventricle to the rest of the body. 5. Finally, again, locate the spleen which is to the left of the stomach in the abdomen. It is a reservoir for blood and helps make white blood cells. STOP!! HAVE YOUR TEACHER SIGN YOUR CHECKLIST!

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RESPIRATORY SYSTEM Parts and Function (Answer questions 43-46 on your pre-lab sheet.) 1. Diaphragm – muscular wall that moves to fill and empty lungs of air; separates thoracic and abdominal cavity 2. Trachea – windpipe that leads from nasal cavity to lungs; held open by cartilaginous rings 3. Larynx – voice box located at top of trachea 4. Lungs – organs used for exchange of gases from bloodstream 5. Pleura – membrane that surrounds and protects the lungs Procedure 1. Trace the path air would follow through the respiratory system of your rat. Use the following instructions as your guide. Open the mouth of your rat. 2. Using the probe, follow the pathway down the throat, past the pharynx into the glottis, or opening into the trachea or windpipe. Notice how the respiratory tract passes in front of the esophagus of the digestive tract. Use your probe to bend the epiglottis forward. Note how it covers the entrance of the glottis, preventing food from entering the lungs. 3. Remove your probe. Observe the upper chest cavity. Locate the trachea. Locate the reddish thyroid gland that lies over the trachea. 4. Find the enlarged region of the respiratory tract just posterior to the glottis. This region is the larynx, or voice box, which contains the rat’s vocal cords. The larynx is hard because it is covered with a cartilage shield. 5. Notice the rings of cartilage attached to the trachea below the larynx. Cartilage rings support the trachea, preventing it from collapsing when the rat respires. Follow the path of the trachea as it divides into two tubes, the bronchi, that enter the lungs. You may need to lift or move the lungs to the side to observe the entrance of the bronchi. 6. Notice the outer linings of the lungs, the pleura. These membranes protect the surfaces of the delicate lung tissue as the lungs expand and contract. Notice that the lungs are divided into lobes. 7. Feel the texture of the lungs. The hardness and compactness of the lung tissue is due to preservatives. In a living rat, the lung tissues are made up of tiny resilient air sacs called alveoli. Gas exchange occurs in the alveoli. 8. Before you clipped the diaphragm from the body cavity, it formed an airtight seal between the chest cavity and the abdominal cavity. The movement of the diaphragm causes air to flow in and out of the lungs.

STOP!! HAVE YOUR TEACHER SIGN YOUR CHECKLIST!

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