Bio 322 Human Anatomy Objectives for the laboratory exercise Digestive System

Transcription

1 Bio 322 Human Anatomy Objectives for the laboratory exercise Digestive System Required reading before beginning this lab: Saladin, KS: Human Anatomy 5 th ed (2017) Chapter 24 For this lab you will use Exercise #26 in your Wise lab manual. Please be sure to read that before coming to lab or you will not be able to finish within the scheduled lab time. Introduction: The digestive system provides the body with the nutrients, water, electrolytes, and other substances essential for health. They enter as large masses of material which must be broken down to small molecules that can be absorbed into the blood, with residual material passing through for elimination. Since the food and liquids we ingest contain bacteria, viruses, toxins, and many other things that are harmful, there are many lymphatic nodules and cells of the immune system in the walls of digestive system organs. The digestive system consists of a hollow tube extending from the mouth to the anus, into which various glands empty their secretions called the alimentary canal or gastrointestinal tract. The organs of the alimentary canal include the mouth, pharynx, esophagus, stomach, small intestine, large intestine, and anus. Digestion results in molecules which are small enough to be absorbed through the wall of the alimentary canal into the blood in adjacent capillaries, by which they are then distributed throughout the body. As this occurs, smooth muscle in the walls of the various organs is propelling the material through the alimentary canal at specific rates to maximize both digestion and absorption. The residue that remains is a mixture of undigestible food, cells which died and were sloughed off from the linings of the intestines, and some waste materials that the body needs to get rid of. These form the feces that are eliminated through the anus. Salivary glands, the liver, the gall bladder, and the pancreas produce and/or store materials to be added to the alimentary canal. These are the accessory organs of digestion. These include mucous to help things pass more easily through the alimentary canal, digestive enzymes to break down larger molecules, bile for the emulsification of fats, and antibodies to help protect the body against organisms and debris which are ingested

2 Objectives: 1) Complete Exercise #26 in your Wise lab manual, although we will not do the Cat Anatomy section at the end of this exercise. a) On the torso models, identify the oral cavity, parotid salivary gland, submandibular salivary gland, sublingual salivary gland, esophagus, stomach, small intestine, large intestine, liver, gall bladder, and pancreas. Although only the nasopharynx shows on most of the torso models, you should be able to identify where the oropharynx and laryngopharynx are located. b) Within the oral cavity of the torso model, identify the labia, teeth, tongue, hard palate, and soft palate. Identify those structures in your lab partner s oral cavity (or do this on your own oral cavity using a mirror), Identify the labial frenulum and lingual frenulum. Confirm on yourself and your lab partner that the tongue is voluntary skeletal muscle. Identify the actions of the temporalis and masseter muscles as you clench your jaw tightly. Identify the actions of the pterygoid muscles as you gently grind your teeth together. c) On Figure 26.3 in your Wise lab manual (we do not have models of a tooth) identify the root, neck, and crown of a tooth. Identify the enamel, dentin, pulp cavity, and root canal. d) On Figure 26.4b of your Wise lab manual identify each of the eight types of teeth present in each quadrant of the mouth. Identify each of those teeth in each quadrant of your lab partner s oral cavity (or do this on your own oral cavity using a mirror). Realize that the 3 rd molar is commonly removed in adolescents and young adults, so these may be missing in your mouth. e) You should understand the peritoneal cavity and layers of the peritoneum, including mesenteries. Identify where they would be on the torso model, even if not shown in isolation. f) You should understand the layers of the wall of the digestive tract. g) On the torso model, identify the greater curvature, lesser curvature, cardiac region, body, fundus, pyloric region, rugae, esophageal sphincter, and pyloric sphincter of the stomach.

3 h) Identify the duodenum on the torso models. Although they are not differentiated, identify where the jejunum and ilium are. Identify the ileocecal junction. i) On torso models, identify the cecum of the large intestine, appendix, ascending colon, transverse colon, descending colon, sigmoid colon, and rectum. Identify the right colic flexure, the left colic flexure, and the haustra. j) On torso models, identify the sublingual, submandibular, and parotid salivary glands. k) On torso models, identify the pancreas, liver, and gall bladder. Note how the posterior surface of the liver wraps around the inferior vena cava. On the inferior surface of the liver, identify the hepatic ducts, hepatic artery, and hepatic portal vein as they enter or leave the liver. Identify the cystic duct as it connects to the gall bladder. l) On figure of your Wise lab manual, observe how the common bile duct and the pancreatic duct merge just before they deliver bile and pancreatic secretions into the duodenum. 2) Complete the following examinations of the histology of the digestive system. Note that the organs of the alimentary canal all share a common arrangement of their layers into a mucosa, submucosa, and muscularis externa as shown in Figure 26.6 of your Wise Lab Manual, surrounded by connective tissue forming a serosa or adventitia. Be sure you understand this basic arrangement before you examine the following slides. a) Examine slides #9 and #28 of the esophagus. Find a slide in which it was cut in cross-section to show the entire wall. Scan it at 40X and find the central lumen. Switch to higher magnification. Surrounding the lumen is a thick layer of stratified squamous epithelium. Note that the upper cells are thin and flattened parallel to the surface (squamous), but many of them still have nuclei. This is called a non-keratinized or non-cornified type of epithelium. Immediately beneath the epithelium is a thin layer of areolar connective tissue called the lamina propria. Surrounding the mucosa of the esophagus is a thicker layer of areolar connective tissue called the submucosa. It may have some multicellular mucous glands in it. Superficial to this, identify the thick layers of skeletal or smooth muscle making up the muscularis externa. In life there is a layer or areolar connective tissue called the adventitia on the outside of the organ, but this is usually missing on the slides in our lab.

4 b) Examine slide #24 of the stomach. Under 40x magnification, identify its mucosa, submucosa, and muscularis externa. As noted for the esophagus, in life there is a layer or areolar connective tissue surrounding organ, but this is usually missing on the slides in our lab. Examine the mucosa at higher magnifications. With the help of Figure 26.8 in your Wise lab manual, understand how the simple columnar epithelium forms many deep gastric pits where the cells are located which secrete mucous, hydrochloric acid, and digestive enzymes. Note the numerous blood vessels in the submucosa. Identify the smooth muscle forming the muscularis externa while it is not shown well on this slide, this muscle is organized into layers which run different direction in the wall of the stomach (Figure 26.7) to allow it to contract in different directions. c) Examine slide #5 of the small intestine with the naked eye and notice that there are three different sections representing the duodenum, jejunum, and ileum. Although there are some differences among these, we will focus on the structure which they all show. Scan this slide at 40X before switching to a higher magnification. Note the mucosa, submucosa, and muscularis externa again, the connective tissue serosa or adventitia surrounding the outside of this organ is usually not included. The epithelium of the mucosa is simple columnar epithelium. Identify the simple columnar epithelium, which contains lighter-staining goblet cells. These are mucus-producing cells. Under the epithelium lies a thin layer of areolar connective tissue called the lamina propria. These two layers make up the mucosa which is folded into many finger-like projections called villi. Although they have collapsed on this slide and cannot be easily located, realize that many blood vessels and lymphatic vessels lie within the lamina propria of the villi (see Figure in your Wise lab manual). The muscularis externa consists of two layers of smooth muscle tissue. The inner layer is thicker and is called the circular layer due to the circular orientation of its fibers around the tube-shaped intestine. The outer muscle layer is much thinner. It is called the longitudinal layer. These cells run longitudinally along the intestine (actually, they form a loose spiral around it). In one or more of the sections on this slide, you may see lymphatic nodules, dense accumulations of lymphocytes and macrophages which secrete antibodies into these tissues and which can attack bacteria, viruses, or other pathogens which get through the epithelium.

5 3) Complete the following examinations of the histology of the salivary glands, liver, and pancreas. Note that these are accessory organs of the digestive system, so they are not organized into a mucosa, submucosa, or muscularis externa. Instead, they are exocrine glands which have groups of secretory cells and ducts that carry their secretions into the organs where they are needed. a) Examine slide #21 of the salivary glands. Start by scanning this at 40X. There are sections of three different salivary glands on this slide. The common structure of the glands, seen at higher magnification, is to have hollow groups of secretory cells (called acini or sometimes alveoli) attached to a system of ducts that carry the saliva into the mouth as shown in Figure of your Wise lab manual. There are two kinds of acini in salivary glands: darker-staining serous acini and lighter-staining mucous acini. One of the glands on the slide has only serous acini, another has only mucous acini, and the third has mixed (both serous and mucous) acini Examine the gland with mixed acini. The mucous acini are lighter-colored groups of cells that produce the thicker mucus in saliva. The serous acini are darker colored clusters, some of which may be arranged in half-moons of cells capping a group of mucous cells as shown in Figure of your Saladin text. They produce a thinner, more watery saliva containing digestive enzymes. Identify one or two salivary ducts that carry saliva toward the mouth. These structures have a large, open lumen (space) in the middle, surrounded by a simple cuboidal or stratified cuboidal epithelial layer. These ducts are often surrounded by a moderate amount of connective tissue. b) Examine slide #23 of the liver. Scan it at 40X to locate the structures then switch to higher magnification to examine them. Look for the thin walled central veins, each of which is surrounded by large capillaries called sinusoids arranged like the spokes of a wheel around it. The cells lining the sinusoids are the hepatocytes, arranged in cords which also radiate like spokes from the central vein. Each central vein with its sinusoids and cords of hepatocytes forms a hepatic lobule (Figure in your Wise lab manual). Remember that the sinusoids represent a second set of capillaries of a portal system. The first set of capillaries were located in the intestines, pancreas, and spleen; blood flows from them into the liver through the hepatic portal vein. At the edge or corners of the lobules you can often identify three structures that sit close together to form a hepatic triad. The first of these is a bile ductule, carrying bile away from the hepatocytes and

6 leading, eventually, to the common bile duct. The arterioles in the triads are branches of the hepatic artery, and the venules are branches of the hepatic portal vein. Both of these vessels deliver blood into the sinusoids, where it flows past the hepatocytes on its way to the central vein and, eventually, out of the liver into the inferior vena cava. c) Examine slide #20 of the pancreas. Although a small part (about 1%) of this organ consists of endocrine cells forming the pancreatic islets, most of the pancreas is an exocrine gland which produces and secretes digestive enzymes which are sent by the pancreatic duct to the duodenum. As always, start off by scanning the slide at 40X, referring to Figure of your Saladin textbook. Look for clusters of lighter staining cells these are the endocrine pancreatic islets (Figure 18.9 of your Saladin text). The rest of the pancreas consists of darker-staining pancreatic acini. It also has a well-developed system of connective tissue partitions that break the gland up into many smaller pieces. Identify the small pancreatic ducts which usually surrounded by a moderate amount of areolar connective tissue or stroma. 4) Examine the cadaver in a face-up, or supine position. a) Identify the esophagus in the thorax - this may be surrounded by what appears to be many strands of connective tissue, but these are really the vagus nerve, which separates into many small strands surrounding the esophagus. You can feel the thick, muscular wall of the esophagus. Note the location of the esophagus relative to the bodies of the vertebra, the heart (you will have to temporarily replace this in the cadaver) and the descending thoracic aorta. Follow it to the diaphragm. b) Just inferior to the diaphragm of the cadaver, identify the stomach and the opening of the esophagus into it. Although the stomach is enlarged in this individual you should be able to identify its greater curvature, lesser curvature, cardiac region, fundus, body, and pyloric region. Note its relationships to the liver and spleen. Lift up the stomach and identify the pancreas posterior to it. c) You can see the beginning of the duodenum at the pyloric sphincter, but most of it is difficult to identify because in life it is retroperitoneal and surrounded by large amounts of connective tissue. You can easily

7 identify the jejunum where it becomes intraperitoneal and follow it distally, although the mesentery has been cut so that the aorta, inferior vena cava, and kidneys can be identified behind it. As you follow the small intestine distally you will, at some point, shift to the ileum but you will have no way of knowing this. Follow the small intestine to the ileocecal junction. d) The different parts of the colon, or large intestine, are out of position on this cadaver. Return the cecum, the ascending colon, the transverse colon, and descending colon to their approximately normal positions. The vermiform appendix can be seen extending from the cecum. Identify the flexures between the ascending, transverse, and descending colons. 4) This will require you to remove clothing, so you should do it at home. a) On yourself (using a mirror) or another person, identify the oral cavity including the teeth, tongue, lingual frenulum, soft and hard palates, and uvula. Notice that your tongue is rough because of many tiny papillae on its surface. b) With your finger, locate the position of the parotid, sublingual, and submandibular salivary glands. c) Use a washable pen to mark the location of your esophagus, stomach, liver, gall bladder, and pancreas. Outline the area where your small intestine is located. Draw where the cecum and the ascending, transverse, and descending colons are located. Identify the opening of the anus, noting that it normally remains closed unless feces are passing through it. Show off your artwork to your roommate, or mother if you wish, then go take a shower to wash it off. Review: After you have completed this lab exercise, be sure you can answer the questions at the end of Exercise #26 in your Wise lab manual. Do this verbally with your lab partners rather than in written form. The purpose of doing this should not be to write down the correct answer, but rather to be sure that everyone in your lab group understands the information presented in the exercise and to identify any areas which you still do not understand. Remember: one of the best ways to learn new information and to be sure you understand it is to discuss it with another

8 person. If you can t easily answer one of the questions, go back to your Saladin textbook and re-read the relevant section(s), It is also an excellent idea for members of a lab group to set up small quizzes for each other. Ask each other to identify structures on diagrams, models, and preserved specimens. Ask each other to explain the functions of those structures. Here are some additional questions and discussions which may help you understand the human digestive system. Remember these are for discussion, not writing. That s the best way to be sure your brain can explain what you have learned. The laryngopharynx is an inferior continuation of which other part of the pharynx? Where does it lie relative to the larynx? The esophagus runs posterior to what other tubular organ? What is the bend (flexure) called where the ascending colon forms the transverse colon? Where is this in relationship to other organs in the abdomen? What is the bend (flexure) called where the transverse colon forms the descending colon? Where is this in relationship to other organs in the abdomen? Blood enters the superior mesenteric and inferior mesenteric arteries from which larger vessel? The superior mesenteric artery supplies which parts of the intestines? The inferior mesenteric artery supplies which parts of the intestines? The superior mesenteric vein drains blood from which parts of the intestines? The inferior mesenteric vein drains blood from which parts of the intestines? Both the superior mesenteric vein and the inferior mesenteric vein (together with the splenic vein) deliver blood to which larger vein? To what organ does this vein deliver the blood? What is the function of bile in digestion? Blood enters the hepatic artery from which branch of the aorta? The esophagus is an inferior continuation of which part of the pharynx? The muscularis externa is composed of what type(s) of tissue in the upper third of the esophagus? in the middle third of the esophagus? in the lower third of the esophagus?