Metazoa III: Reductionism

Transcription

1 Lab 5 Metazoa III: Reductionism Lab Outline Inquiry Question Lab Preparation Questions Virtual Pig Dissection Activity 1: Basic Histology Activity 2: Anatomy of Major Organ Systems You work for the company Fetal Pig Dissection Research in Motion, the Sheep Brain proud makers of the BlackBerry wireless communication tools. Questions to Explore Your boss just handed you an iphone and said, How can we compete with this? Figure out how it works and give me a full report tomorrow morning. How will you figure out how the iphone works? Should you decide to disassemble it, what would you learn? How does it receive a wireless signal? What type of computer does it have? How is information stored? How does the touch screen work? Or instead, you work for UPS; one afternoon while you are making a rural delivery on the north fork of Long Island, your truck dies. There is no help in sight, and of course, you forgot your cell phone. Can you figure out what caused your truck to stop running? Are you out of gas? Is there water in the intake, a dead alternator, or a blown head gasket? Both the iphone and UPS truck are complex machines with multiple, highly complex, internal systems. So too is the human body. So how do scientists study this complex biological machine? Many of the early investigations of the human body involved dissection. One type of dissection was called trepanation, in which the physicians or scientists of a given society would drill holes into the skull. Evidence dating as far back as the Neolithic period shows that these holes were partially healed, which suggests that the subjects were alive for a period of time after the dissection. In this lab, you will investigate major organ systems of the fetal pig as a representative model of mammals. Almost all of the structures that you will see during lab are also found in humans. By studying the anatomy of each system separately, you will learn how it contributes to the physiological function of the entire mammalian machine. Proficient use of the compound microscope Identify basic cellular morphology Identify and distinguish the four major tissue types Dissect the major organ systems of the fetal pig 73

2 BIO 204 Fundamentals of Scientific Inquiry in the Biological Sciences I Trace the path of blood through the fetal and adult mammalian cardiovascular system Trace the path of air from mouth to alveoli Trace the path of food from mouth to anus Trace the path of urine from kidneys to urethra Briefly describe the function of the cardiovascular, pulmonary, gastrointestinal, urinary, nervous, skeletal, muscular, and reproductive systems Distinguish histological samples of epithelial tissue, connective tissue, nervous tissue, skeletal muscle, smooth muscle, cardiac muscle, artery, vein, lung tissue, bronchiole, intestine, adipose, bone, cartilage, simple vs. stratified cells, and squamous vs. cubiodal vs. columnar cells Write the answers to the following questions in your laboratory notebook. 1. Read Campbell, pp What are the morphological and functional differences between epithelial, connective, nervous and muscle tissue? Based on Table 40.1 on p. 827, what organ systems do you think are involved in regulating ph? Why? 2. Based on Figure 42.4 on p. 870, what advantages might the four chambered heart of a mammal have over the two chambered heart of a fish? What disadvantages might it have? 3. Based on Figure 42.9 on p. 875, what are the main differences between arteries and veins? 4. Based on Figure 42.1 on p. 875, why does sitting in a chair for a long time result blood pooling in the veins of your legs? 5. Using the following terms, draw two cardiovascular system diagrams, one of the human fetus just before birth, and one of the human adult. Show the direction of blood. Include: left atrium, right atrium, left ventricle, right ventricle, pulmonary artery, pulmonary vein, lungs, body, vena cava, aorta, placenta, umbilical vein, umbilical arteries, hepatic portal vein, ductus arteriosis, and foramen ovale. 6. What are three primary functions of the renal system? 7. Based on Figure 48.2 on p. 1012, which nervous system is most like humans? Why? 8. What is the physiological difference between the thymus and the thyroid? Where is each located? 74

3 Metazoa III: Reductionism Lab 5 adipose collagen columnar coronal plane cuboidal dorsal vs. ventral epithelium fibroblast fibrous macrophage medial vs. lateral proximal vs. distal pseudostratified rostral vs. caudal sagittal plane secretory squamous standard anatomical position stratified superior vs. inferior transverse plane Either search for fetal pig dissection on the web, or visit one of the sites below, and perform an online pig dissection. Make sure to identify all of the major organ systems including digestive, cardiovascular, respiratory, renal (some sites refer to it as excretory which is not precise because many other tissues in the mammal are excretory), reproductive (external & internal), and nervous (click General Biology II, then click fetal pig)

4 BIO 204 Fundamentals of Scientific Inquiry in the Biological Sciences I Materials Dissection kits (required-must be purchased by the student) and latex gloves (optional) Fetal pigs: one for every two students; preferably one male and one female per lab group Compound microscopes (two per group) Slides: Epithelia: simple squamous epithelium, simple cuboidal epithelium, simple columnar epithelium, pseudostratified columnar epithelium, stratified epithelium Connective: adipose, bone, and blood smear Nervous: spinal cord Muscle: skeletal muscle Tissue: artery and vein cross section, lung and bronchiole, intestine Models of human heart, human circulatory system, and human digestive system Paper towels, string, and anti-bacterial soap NOTE: Text terms in italics are to be identified in either the fetal pig, on slides under the light microscope, on photographs, or on micrographs. Questions that are italicized should be answered in your lab notebook. Get a microscope (one for every two people) from the cabinet and the slides listed below. In the space provided, sketch each cell or tissue type. Record magnification and label important features on each diagram. All of these slides are stained. The most common histological stain is Hematoxylin and Eosin (H&E) in which hematoxylin stains basophilic structures blue (such as nuclei) and eosin stains acidophilic structures red (such as cytoplasm and some proteins). 1. Compare simple, stratified, and pseudostratified epithelium. 2. Compare squamous, cuboidal, and columnar epithelium. 3. View a blood smear stained with Wright s Stain. The light pink cells are red blood cells and the purple containing cells are white blood cells. What is the ratio of red to white blood cells? Go on Wikipedia, search for white blood cells, and use this guide to find a neutrophil on your blood smear. 4. Compare adipose tissue with lung tissue. What is the difference? Hint: which structure stains purple with an H&E stain? 5. Sketch bone tissue. 76

5 Metazoa III: Reductionism Lab 5 6. View skeletal muscle. The muscle is pink with purple nuclei. What structures are responsible for the many striations? 7. On the spinal cord slide, what is the hole in the middle of the tissue? Distinguish between the gray and white matter. Do you see the light purple soma (neuronal cell bodies) in the gray matter? 8. What distinguishes the intestine tissue from any of the other tissue that you have viewed today? Get two dissection pans and two pigs per group, preferably one male and one female. Make sure you know how to identify sexes in the fetal pig from the external anatomy. 1. Before cutting, identify the following: head, tail, nares, mammary papilla, scrotum, urogenital opening, anus, and umbilical cord. 2. Following the dashed lines on the adjacent diaphragm (Figure 5.1), make one shallow incision directly down the midline of the pig from the chin to the umbilical cord. Organs lie just below the skin, muscle, and ribcage, so be careful to avoid puncturing these organs. Figure From the point directly above the cord, make two additional incisions (#2) forming a horseshoe towards the legs of the pig. The umbilical vein carries blood from the placenta to the heart. Tie it off so you can find it later, cut it distally, and then fold back the skin caudally. 4. In cutting through the skin in the thoracic region (incision #1), you will have to cut through the sternum (breastbone). Do so now using the scissors, but BE CAREFUL. Just beneath the rostral end (towards the nose) of the sternum are the major blood vessels that enter and exit the heart. When making this and other cuts with scissors, remember to lift the tips of the blades up as far as possible to prevent damage to the structures underneath it. 5. Remove the membrane of connective tissue surrounding the organ cavities and pry back the ribs so you can see the internal organs. Make two additional lateral incisions (incision #3) under the forelegs of the pig, if necessary, to make this easier. 6. Identify the italicized structures in the following steps. Remember to answer the questions in your lab notebook. 77

6 BIO 204 Fundamentals of Scientific Inquiry in the Biological Sciences I Throat Region Clear away the connective tissue in the throat region to see the thymus and the thyroid glands. The thymus gland is large in young animals and can be found both in this region and also in the thoracic cavity, surrounding the heart. You may remove this material, but note the characteristically grainy texture that helps identify it as gland rather than connective tissue. The thyroid is the small, dark, symmetrical organ in the midline of the pig s neck. Directly dorsal to the thyroid is the trachea. Without removing the thyroid, note the ringed cartilage that prevents collapse of the trachea during inspiration (it resembles the hose of a vacuum cleaner). Trace the trachea rostrally to the larynx. Gently push the thyroid and the trachea to one side and locate the esophagus, which is dorsal to the trachea. The large vessels near the surface of the neck are the jugular veins. Dorsal, and slightly medial to these veins, and lateral to the trachea, are the internal and external carotid arteries. Immediately adjacent to the carotid arteries is the vagus nerve, the tenth cranial nerve (X). Note that the jugular veins, carotid arteries and vagi are all bilateral structures. thymus & thyroid trachea larynx esophagus jugular vein, internal/ external carotid artery, vagus nerve What differences do you see between the esophagus and the trachea? How does this relate to function? Examine the artery & vein cross section slide. Then, cut a small piece of both the carotid artery and jugular vein from your pig. Describe the similarities and differences between each in your lab notebook. Thoracic and Abdominal Cavities Tissues throughout the body metabolize glucose and oxygen (O 2 ) and produce carbon dioxide (CO 2 ) as waste. Large, multicellular organisms require a cardiovascular system which delivers O 2 and glucose to the tissues via arteries and removes CO 2 via veins. This is why highly metabolic tissues, such as muscle and nervous tissue are highly vacularized. Name one tissue in the human body that does not have blood vessels directly associated with it (avascular tissue)? How does this tissue survive? 78

7 Metazoa III: Reductionism Lab 5 Cardiovascular System The mammalian cardiovascular system consists of the heart and two circuits of blood vessels: (1) the pulmonary circuit includes the blood vessels that carry blood to and from the lungs and (2) the systemic circuit includes the blood vessels that carry blood to and from the rest of the body. Find the heart in the thorax. From the outside it appears to have two parts: a top part with blood vessels and a bottom triangular part. The dark flaps on the top, and on either side of the pulmonary artery and aorta, are the left and right atria; the bottom part contains the left and right ventricles. Note: whenever we describe a left and right, we are referring to the pig s left and right. If your pig is on its back (as it should be), then the left atrium and left ventricle will be on the right side of the heart, etc. heart left atrium, right atrium left ventricle, right ventricle Examine the model of the heart and trace the flow of blood from the vena cava through the right side of the heart to the pulmonary artery. Then trace the blood from the pulmonary vein to the left side of the heart to the aorta. Note the valves that prevent the backflow of blood in the heart. Dorsal to the heart, find the vena cava that carries oxygen poor blood from the tissues to the right atrium. Then blood goes to the right ventricle, the pulmonary artery, and the lungs where it is oxygenated. Locate the aorta that curves rostrally, dorsally, and then caudally toward the abdomen. It is often said that this vessel looks like a bagpipe. Follow the aorta down into the abdomen, noting the arteries that branch off from it to the major abdominal organs, including the celiac, mesenteric, and renal arteries. Nestled between the aorta and the vena cava on the dorsal side of the heart (the side closest to the spine) are the branch points from the pulmonary artery and vein. The large dark purple structure on the dorsal side of the heart is the merger of the cranial and caudal vena cava. The pulmonary artery and vein are dorsal to this structure. Because this is a fetal pig and not an adult, there are important cardiovascular differences that you should be aware of. The ductus arteriosus, present only in the fetus, is a small blood vessel that shunts blood from the pulmonary artery directly to the aorta. The foramen ovale is a shunt from the right to the left atrium. vena cava aorta celiac, mesenteric, & renal arteries What organs do these three arteries eventually supply? Why are these structures present in the fetal pig and not the adult pig? 79

8 BIO 204 Fundamentals of Scientific Inquiry in the Biological Sciences I Pulmonary System As you were dissecting the throat region, you identified the trachea (commonly called the windpipe). Open the fetal pig s mouth and try to locate the opening to the trachea. It is probably blocked by a small flap of skin called the epiglottis. Surrounding the heart on either side are lobes of the lungs. The developing fetal lungs are filled with fluid and not air and therefore do not participate in gas exchange. Rather, the mother breathes for the fetus in the gas exchange that occurs across the placenta. In the adult, gas exchange between the body and the outside world occurs in the lungs. Aquatic vertebrates, like fish, have gills that serve the same purpose. Both systems allow the body to release CO 2 that has been generated by the cells as a by-product of metabolism and to absorb O 2, needed for aerobic metabolism. Locate the muscular wall that divides the thorax from the abdomen. This is the diaphragm, which is skeletal muscle. A pig breathes much like you do. During inspiration, or breathing in, the diaphragm contracts; this increases the internal volume of the thorax and pushes the chest wall outward. This increase of volume results in a decrease of pressure (compared to the outside of the body). Air passively moves from higher pressure (outside of the body) to lower pressure (inside of the lungs) and a gas pressure equilibrium is reached UNTIL the diaphragm relaxes. Then the chest wall recoils into its original resting position (before you took a breath) and now the pressure on the inside of the lungs is greater than the outside the body. So air moves passively from higher pressure (inside of the lungs) to lower pressure (outside of body) and equilibrium occurs until you want to breathe again! trachea epiglottis Based on the anatomical position of the epiglottis, what is its function? lungs diaphragm During exercise, how does inspiration differ from this explanation? Examine the slide of lung tissue. The many open spaces are the alveoli where gas exchange occurs. Locate the small capillaries and blood vessels in the lung tissue. Also, in most slides of the lung, you will be able to locate a bronchiole, which is the last branch of the lung airway before the alveoli. A bronchiole is surrounded by smooth muscle but does not have cartilage. 80

9 Metazoa III: Reductionism Lab 5 Gastrointestinal (GI) Tract Unlike plants which are autotrophic, animals must ingest food in order to survive. After ingestion, the GI tract must digest macromolecules, absorb nutrients, and egest (eliminate unused food). The GI tract is a long assembly line of processes that normally involve the secretion of special enzymes by glands such as the salivary glands, stomach, pancreas, etc. In this portion of the laboratory, you will examine the structure of the digestive system and learn its anatomy. The GI tract is a tube that begins in the mouth and ends at the anus. The inside of the GI tract is, in effect, the outside of the body? So, all materials absorbed from food and liquids must pass through the wall of the tract to enter the body. Food in the mammalian tract is digested mechanically and chemically. Chewing by the teeth in the mouth is purely mechanical and breaks the food into smaller particles, which increase the surface area on which digestive enzymes can act. Masticated food forms a bolus that the tongue helps you swallow. As the bolus passes through the pharynx, the epiglottis folds over the trachea so that the bolus can pass into the esophagus. The food moves caudally within the esophagus into the stomach. Notice that the esophagus passes through the diaphragm and thus is an organ that is found in both the thoracic and abdominal cavities. Now that we have reached the abdominal cavity, it may be necessary to remove part of the large dark purple structure that is taking up most of the space in the rostral abdomen, the liver. The liver must be lifted out of the way so that you can see the stomach. As you do this, notice another dark purple organ in this region on the left side the stomach, the spleen. The stomach has a muscular wall and contraction of this wall mixes the food and enzymes. Epithelial cells in the stomach secrete hydrochloric acid (HCl), which lowers the ph (acid) of the stomach contents. HCl also stimulates the release of pepsinogen, a zymogen (an inactive proenzyme) that is converted to the active enzyme, pepsin. Pepsin is a protease that digests protein. The stomach then empties into the first section of the small intestine, called the duodenum. mouth anus teeth tongue epiglottis esophagus stomach liver spleen small intestine 81

10 BIO 204 Fundamentals of Scientific Inquiry in the Biological Sciences I Accessory glands of the duodenum release digestive fluids and enzymes which mix with the food. The liver produces bile salts, which are stored in the gallbladder. The cystic duct carries the bile to the common duct where it joins with pancreatic enzymes and ultimately is excreted into the duodenum where it mixes with food. Sometimes, bile salts precipitate and form stonelike objects called gallstones which cause painful irritations and affect one s ability to digest fats. Locate the pancreas in the bend of the duodenum caudal to the stomach. The pancreas is an exocrine gland that releases digestive enzymes into the GI tract ( outside of the body ). The pancreas is also an endocrine gland which releases hormones such as insulin and glucagon into the cardiovascular system. The small intestine is long (if you have time at the end of lab, pull it out and try to measure its length). This is where the majority of nutrient and water absorption takes place. Look at a slide of the small intestine under the microscope. Note that the lining has many folds. This folding increases the surface area for greater food absorption. Also notice that the intestines are surrounded by mesentery, a clear sheet of tissue that attaches them to the dorsal wall of the abdomen. Mesentery is a two layered membrane of mesothelium and connective tissue that support the blood vessels, lymphatic vessels and nervous tissue of the intestines. Find where the small intestine empties into the colon. (The colon is much shorter than the small intestine, but is larger in diameter, which is why it is often called the large intestine.) At this junction, the food must make a hairpin curve through a cul-de-sac like structure that is called a cecum. In many herbivores, this sac is large and contains organisms that secrete the enzyme cellulase, which then digests cellulose. In humans, our appendix is the vestigial remnant of this structure. The colon is responsible for the absorption of water left after digestion and food absorption in the stomach and small intestine. It is also used for storage of the waste material. The colon ends at the anus. Note the sphincter that prevents the emptying of the colon except during the process of defecation. duodenum gallbladder common bile duct pancreas mesentery colon cecum How is the pancreas affected by Type I diabetes mellitus? What is the difference between an endocrine and an exocrine gland? What types of muscle would you expect to find in the intestines? sphincter 82

11 Metazoa III: Reductionism Lab 5 Renal and Reproductive Systems Sometimes called the excretory system, the renal system is responsible for the removal of metabolic waste. The kidneys are the primary organ of this system and they filter the blood to form urine, which contains excess water, ions such as sodium, and waste products like urea. The renal system also maintains a homeostatic balance of proteins, sugars, and some hormones. Push the intestines to one side so you can see the paired kidneys, and carefully cut away some of the connective tissue so you can trace the ureters which carry urine from the kidneys to the bladder, located ventrally between the umbilical arteries. Urine is stored here, and then released through the urethra to the outside in the female, or through the urethra and penis to the outside in the male. Find the renal artery and renal vein. Very carefully dissect away some of this connective tissue to find the adrenal gland attached to the rostromedial surface of the kidney. Use special care, because it is easy to discard the very small pink gland with the connective tissue. Female The ovaries in the female are small kidney-shaped organs within the abdominal cavity just caudal to the kidneys. They are closely associated with tubes called the horns of the uterus (the equivalent of the fallopian tubes in humans). These tubes join centrally at the body of the uterus. Follow the uterus down to the vagina (you must cut the ventral pubic bone), where it joins the urethra and exits the body, just ventral to the colon and anus. (Note that in humans, the vagina and the urethra do not join, but have separate openings to the body surface, between the labia.) Make a longitudinal cut through the uterus and vagina, and note the glans clitoris on the ventral surface of the genital papilla. kidneys Kidney failure rapidly leads to death. Explain ureters bladder What is the advantage of having a bladder? renal artery, renal vein adrenal gland Is the adrenal gland part of the renal or reproductive systems? ovary horns of the uterus uterus, vagina glans clitoris genital papilla Male In males, note the scrotal sacs on the exterior. In order to find the testes, you will have to locate the two ductus deferens: tubes which join just dorsally to the caudal end of the bladder, which you can trace back to the abdominal wall. scrotal sacs ductus deferens 83

12 BIO 204 Fundamentals of Scientific Inquiry in the Biological Sciences I The inguinal canal is a small tunnel in the abdominal wall that was formed by the descent of the testes, through which the spermatic cord, which also carries the spermatic artery and nerve, descend to the scrotum. Note: in very immature fetal pigs, the testes may not have yet descended to the scrotal sac, and may be located in the abdominal cavity instead. Cut through the abdominal wall in this area on one side only, and continue to cut through the skin of the scrotal sacs until you find the testis. Note the gubernaculum, which attaches the testes to the scrotal sac, and the epididymis, which runs along the side of the testis to the ductus deferens. Sperm are formed in the seminiferous tubules within the testis, and then move to the epididymis, where they mature and are stored until ejaculation through the ductus deferens. Follow the ductus deferens back rostrally to the urethra. Just dorsally, where they enter the urethra, are small paired glands, the seminal vesicles. The prostate gland is located between the seminal vesicles, but in the pig it is quite small it is extremely difficult to find. Now trace the urethra caudally towards the anus. Located on either side are the paired bulbourethral glands (Cowper s glands, in humans). All these glands secrete the liquid, called seminal fluid, which carries the sperm. Nervous System Return to the thoracic cavity and locate the descending aorta and esophagus dorsal to the heart. The smaller whitish nerve running along between them is the vagus nerve. Dissect this nerve trunk. Now turn the pig dorsal side up. Make a cut through the skin directly over the vertebral column. In the small of the back, make a cross sectional cut through the vertebra. Note the characteristic shape of the vertebra, and find the spinal nerve cord running through the central hollow section, the vertebral canal. inguinal canal spermatic cord testis and gubernaculum epididymis seminal vesicles prostate gland bulbourethral glands Is Is the vagus nerve one structure, or a bundle of of smaller structures? vertebra spinal cord vertebral canal Observe the cross section of the spinal cord. Find the dura matter, the white matter and the gray matter. Where do you see most of the neuronal cell bodies, in the white or grey matter? 84

13 Metazoa III: Reductionism Lab 5 Sheep Brain Observe major parts of sheep brain, finding the following parts of the CNS: brain, cerebral hemispheres, longitudinal fissure or sulcus, olfactory bulb, cerebellum, medulla oblongata, spinal cord, optic nerve, optic chiasma, and pons. Be sure to observe both the dorsal and ventral sides of the sheep brain. Note the major parts of the brain: the cerebrum, the cerebellum and the medulla oblongata. Note that there are two cerebral hemispheres separated by the longitudinal fissure. Turn the brain to the ventral side, and note the paired olfactory lobes, immediately on either side of the central fissure. Slightly posterior to these, locate the optic chiasma. This is where the optic nerves cross, forming the -shape. Try to locate the hypothalamus and pituitary gland. Place slides back into the cabinet. Properly dispose of your fetal pig and all tissues according to your TA s instructions. 85

14 BIO 204 Fundamentals of Scientific Inquiry in the Biological Sciences I 1. Many structures in the mammalian body are bilateral structures. Why do you think this is so? What evolutionary event might this represent? 2. Why is there a relationship between surface area and amount of absorption in the GI tract? 3. In Figure 5.2, what pattern do you see in the fetal pig s nervous system? How does this pattern relate to the skeletal vertebra? How is this pattern similar to an earthworm? 4. What major organ systems are involved in regulating ph in the fetal pig? 5. Describe the path of food from mouth to anus. 6. Describe the path of air from mouth to alveoli. 7. Describe the path of blood from the right atrium to the vena cava in an adult cardiovascular system. How does this pathway differ in fetal circulation? Figure