Digestive Physiology Lab Homework SU23 Answer Key PDF

Lab 9: Digestive Anatomy Introduction The digestive system is composed of the alimentary canal, which is essentially a long tube that is open to the outside at both ends, and accessory organs that aid in digestion of foodstuffs but are not directly part of the digestive tract. The accessory organs c...

Lab 9: Digestive Anatomy Introduction The digestive system is composed of the alimentary canal, which is essentially a long tube that is open to the outside at both ends, and accessory organs that aid in digestion of foodstuffs but are not directly part of the digestive tract. The accessory organs contribute secretions or provide other functions that serve to enhance the ability of the digestive tract to break down large complex molecules in foodstuffs into smaller molecules that cells can readily use. In this lab, we will study the structure of the organs of the digestive system and the histology of selected organs. Learning Objectives By the end of this lesson you will be able to: Describe the overall function of the digestive system Describe the functions of the individual organs and structures of the digestive system Identify the organs of the alimentary canal on a model Identify the accessory organs of digestion on a model Describe the histologic structure of the alimentary canal, and the specific components (layers) that comprise it Identify the histologic structure of the esophagus, stomach, small and large intestine, and liver Overview of the Digestive System The function of the digestive system is to break down the foods we eat, release their nutrients, and absorb those nutrients into the body. Breaking down large molecules into smaller molecules – a process called digestion – can occur by mechanical digestion (crushing, tearing, mixing) and by chemical digestion (hydrolysis). The smaller molecules can pass through the epithelial cells lining the digestive tract and into the blood – a process called absorption. The alimentary canal (or gastrointestinal tract) is a group of organs that form a long tube to conduct food from the mouth to the anus. Organs of the alimentary canal include the mouth, pharynx, esophagus, stomach, and small and large intestine (see Fig. 9.1a). The accessory organs of the digestive system assist in mechanical or chemical digestion of food, working together to break complex molecules into simple substances that can be taken into cells efficiently and readily used. Accessory organs include the teeth, tongue, salivary glands, liver, gallbladder, and pancreas. 1  (b) (a) (c) Figure 9.1 – Organs and membranes of the digestive system. (a) Organs of the alimentary canal and accessory organs, (b) transverse view of peritoneal membranes, and (c) sagittal view of peritoneal membranes. Image Credit: (a&b) OpenStax. CC by 4.0. (c) “Midsagittal View of Peritoneum" by KL Nguyen is a derivative from the original work of Daniel Donnelly is licensed under CC BY 4.0. Membranes of the Digestive System: Peritoneum Much of the digestive system is enclosed in a thin serous membrane called the peritoneum. The parietal peritoneum is fused to the abdominal wall, while the visceral peritoneum adheres to the organs (see Fig. 9.1b). The mesentery is a double fold of the peritoneum that wraps around the small intestine and other abdominal organs, anchoring them to the posterior abdominal wall. The mesentery provides a passageway for blood vessels, lymphatic vessels, and nerves to reach these organs. The greater omentum is formed by a long drape of the visceral peritoneum descending from the stomach and covering much of the small intestine that doubles back on itself to end at the transverse colon. This forms an apron-like structure that lies anterior to the other organs in the abdominal cavity and often contains considerable adipose deposits. 2 Histology of the Alimentary Canal The organs of the gastrointestinal tract, from the lower esophagus to the anal canal, have a common arrangement of four layers. These four layers are the mucosa, the submucosa, the muscularis externa, and the serosa (sometimes called adventitia). Variations are seen in this basic histological plan that correlate to the function of each organ. As one example, the stomach has an extra layer of smooth muscle tissue to promote churning /mechanical digestion. Figure 9.2 – Structure of the alimentary canal wall. Image Credit: OpenStax. CC by 4.0. From deep to superficial, the characteristics of the four layers are as follows: The mucosa is comprised of three tissues: epithelium that is in contact with the contents in the lumen, underlying connective tissue called the lamina propria, and a thin layer of smooth muscle called the muscularis mucosae. The submucosa is areolar connective tissue, and is where blood vessels, glands, nerves / nerve plexi and lymphatic tissue are found. The muscularis externa (sometimes called simply the muscularis) generally consists of two layers of smooth muscle. The fibers of the innermost layer are arranged circularly, while the fibers in the superficial layer are longitudinal (running parallel to the axis of the organ). The serosa surrounds all the digestive organs that are suspended in the abdominal cavity. As the name implies, the serosa is a serous membrane: two layers separated by a 3  thin space filled with serous fluid. Each layer of the serosa is composed of a thin layer of connective tissue overlying simple squamous epithelium. In the abdominal cavity, the serosa is also called the visceral peritoneum. Organs located outside the abdominal cavity, such as the esophagus, have only a single-layered membrane here called the adventitia. ACTIVITY 1: IDENTIFY DIGESTIVE SYSTEM ORGANS The pathway of food as it progresses along the alimentary canal is described in the following sections. Use the Structures to Know section of the lab manual to identify all digestive system structures on the torso model, head plate model, and skull. Organs of the Alimentary Canal, from Mouth to Anus Mouth (Oral Cavity) Mechanical and chemical digestion begins in the oral cavity, where foodstuffs are ingested. Structures and glands (such as the teeth and salivary glands) in the mouth contribute to the digestive functions there, and will be described in more detail with the accessory structures. The mouth is bounded superiorly by the palate, divided into the hard palate (which is a bony plate of the maxilla), and the soft palate, the muscular region at the back of the mouth that ends in a finger-like extension called the uvula. Pharynx The mouth leads to the pharynx, a funnel-shaped region that allows access to both the esophagus of the digestive system and the larynx/trachea of the respiratory system. A bolus of foodstuffs will move through the oropharynx and the laryngopharynx when it is swallowed. Figure 9.3 – The mouth and pharynx. Image Credit: OpenStax. CC by 4.0. 4 Esophagus The pharynx leads to the esophagus, a long muscular tube located posterior to the trachea. Wavelike contractions of smooth muscle (peristalsis) in the esophagus propel the bolus of food toward the stomach. The esophagus is separated from the stomach by a ring of smooth muscle tissue called the gastroesophageal sphincter (or cardiac sphincter). This ring of smooth muscle tissue regulates the movement of food between the esophagus and the stomach so that food moves in one direction only. It also prevents the contents of the stomach from splashing or re- entering the esophagus where they can do damage to those tissues. The esophagus has no digestive or absorptive function. The mucosa of the esophagus is composed of non-keratinized stratified squamous epithelium, which protects against the wear and tear associated with potentially abrasive food particles that are propelled through the esophagus to the stomach. Stomach The stomach is a muscular, sac-like organ shaped vaguely like a backwards C, located in the upper left quadrant of the abdominopelvic cavity. The dome-shaped fundus extends superiorly, while the pylorus extends laterally toward the small intestine like the tail of the letter C. The cardia is the region located near the entrance of the esophagus, and the large midportion is the body of the stomach. The inside part of the C-shaped organ is called the lesser curvature while the outer part is called the greater curvature. Gastric folds inside the stomach are called rugae and allow for expansion of the stomach as food enters. In the pylorus, there is another band of smooth muscle called the pyloric sphincter, which serves the same function as the gastroesophageal sphincter – to ensure that there is one-way movement of foodstuffs through the alimentary canal. The stomach is a temporary storage region for food and is also the site of mechanical and chemical digestion. The stomach contains a third (innermost) layer of muscularis that is arranged obliquely, and aids in the churning function of the stomach. Gastric glands located within gastric pits in the mucosa secrete hydrochloric acid (HCl) and a variety of enzymes that aid in chemical digestion. After food is processed in the stomach it forms a creamy mass called chyme. Figure 9.4 – Stomach. The major regions of the stomach include the cardia, fundus, body, and pylorus. Image Credit: OpenStax. CC by 4.0. 5  ACTIVITY 2: EXAMINE THE HISTOLOGY OF THE ESOPHAGUS AND STOMACH Examine the slide of the gastroesophageal junction and distinguish the esophagus from the stomach tissue. Try to distinguish the four layers of the alimentary canal wall. Note the stratified squamous epithelia of the esophagus. Note the simple columnar epithelia and the gastric pits and goblet cells of the stomach. Stomach Esophagus (a) (b) Figure 9.5 – Microanatomy of the stomach. (a) Microanatomy of the stomach wall. (b) Histology of the gastroesophageal junction. Image Credit: (a) OpenStax. CC by 4.0. (b) Histologyguide.org Small Intestine Once chyme passes through the pyloric sphincter, it enters the small intestine, a long tube about 20 feet long in a cadaver, but only about 6 feet long in a living person due to muscle tone. The three subdivisions of the small intestine are the duodenum (~10 inches), the jejunum (~8 feet), and the ileum (~12 feet). The ileum joins the large intestine at the ileocecal valve, which regulates movement of chyme into the cecum of the large intestine. The amount of lymphoid tissue in the submucosa of the small intestine increases along its length, and the Peyer’s patches are patches of MALT located in the ileum. The small intestine is the main site of nutrient absorption in the alimentary canal. Enzymes in the duodenum help complete the digestive process. Brush border enzymes are located on the columnar epithelial cells of the mucosa, and other enzymes enter the duodenum from the pancreas through the main pancreatic duct. The wall of the small intestine contains three structural modifications that increase the surface area of the mucosa for absorption: 1. Microvilli line the simple columnar epithelium of the mucosa. 2. Villi are fingerlike extensions of the mucosa and give the intestinal wall a ridge-like appearance. 6  3. Circular folds are deep folds of the mucosa and submucosa that force chyme to move in a spiral through the small intestine, further mixing chyme and slowing its progress, thereby increasing absorption. (a) (b) Figure 9.6 – The small intestine. (a) The three regions of the small intestine are the duodenum, jejunum, and ileum. (b) The greater omentum covering the small intestines. Image Credit: (a) OpenStax. CC by 4.0. (b) Dr. Johannes Sobotta from Atlas and Text-book of Human Anatomy Volume III. Figure 9.7 – Histology of the small intestine (a) The absorptive surface of the small intestine is enlarged by the presence of circular folds, villi, and microvilli. (b) Micrograph of the circular folds. (c) Micrograph of the villi. (d) Electron micrograph of the microvilli. Image Credit: OpenStax. CC by 4.0. Micrograph provided by the Regents of University of Michigan Medical School © 2012. 7 ACTIVITY 3: EXAMINE THE HISTOLOGY OF THE DUODENUM AND ILEUM Examine the slides of the duodenum and ileum, and be able to distinguish between them. Note the villi and goblet cells in the mucosa of both regions. Try to distinguish the four layers of the alimentary canal wall. Note the Peyer’s patches (dark purple) in the ileum. Peyer’s patches (a) (b) Figure 9.8 – Histology of the small intestine. (a) Micrograph of the duodenum. (b) Micrograph of the ileum. Image Credit: Histologyguide.org Large Intestine The large intestine (so named for its larger diameter than the small intestine) extends from the ileocecal valve to the anus. The large intestine has 4 main regions: the cecum (a bulbous blind- ended pouch from which the vermiform appendix extends), the colon, composed of ascending, transverse, descending, and sigmoid colon, the rectum, and the anal canal, which opens to the body exterior. The anal canal is closed by two sphincters: an internal (involuntary) anal sphincter composed of smooth muscle and an external (voluntary) anal sphincter composed of skeletal muscle. In the large intestine, the muscularis layer is reduced to a band of muscle called the teniae coli. The teniae coli bunch up the colon into a succession of pouches called haustra (singular = haustrum). Fat-filled sacs of visceral peritoneum called epiploic appendages hang from the colon’s surface. The major function of the large intestine is to finish absorption of nutrients and water, synthesize certain vitamins, and eliminate feces from the body. Figure 9.9 – The large intestine. Image Credit: OpenStax. CC by 4.0. 8 ACTIVITY 4: EXAMINE THE HISTOLOGY OF THE COLON Examine the slide of the colon. Try to distinguish the four layers of the alimentary canal wall. Note the abundant goblet cells lining the mucosa of the colon. Figure 9.10 – Histology of the large intestine. (a) The large intestine has numerous goblet cells that secrete a protective mucus lining. (b) Micrograph showing the colon’s simple columnar epithelium and goblet cells. Image Credit: OpenStax. CC by 4.0. Micrograph provided by the Regents of University of Michigan Medical School © 2012. 9 Accessory Organs of the Digestive System Teeth and Tongue The teeth start the process of mechanical digestion by tearing, grinding and crushing large foodstuffs into smaller particles. This increases the surface area of the food that is exposed to the action of enzymes and digestive juices. The tongue has many functions, including taste, speech, manipulation of food in the mouth and swallowing. The rough surface of the tongue aids in the breakdown of food there. The 20 deciduous teeth, or baby teeth, first begin to appear at about 6 months of age. Between approximately age 6 and 12, these teeth are replaced by 32 permanent teeth. Salivary glands There are 3 major pairs of salivary glands in the mouth: the parotid salivary glands, found outside the mouth and superficial to masseter on both sides; the submandibular salivary glands, located just below the jaw; and the sublingual salivary glands, located under the tongue. All three pairs of salivary glands are exocrine glands, meaning they secrete saliva through ducts into the oral cavity. Saliva is a watery fluid that contains antibacterial compounds, enzymes, and mucus. Saliva is important in lubricating foodstuffs in the mouth so they pass smoothly through the esophagus to the stomach. The enzymes in saliva ensure that chemical digestion begins in the mouth. (a) (b) Figure 9.11 – The teeth and salivary glands. (a) The lower deciduous teeth for a child (top picture) and lower permanent teeth for an adult (bottom picture). (b) The three salivary glands. Image Credit: OpenStax. CC by 4.0. 10  Liver and Gallbladder The liver is responsible for numerous functions: synthesizing and releasing bile, detoxification of exogenous substances in the blood, synthesis of plasma proteins, and storage of certain nutrients. It can be divided into 4 lobes: the large right lobe and smaller left lobe (separated by the falciform ligament, an incursion of the mesentery) and the smaller quadrate lobe and caudate lobe, which can be seen in a posterior view. The liver tissue is organized into units called lobules. In each lobule, hepatocytes (liver cells) surround a central vein that drains deoxygenated blood from the liver. The unique microanatomy of the liver begins with the functional unit called the lobule, a rough six-sided arrangement of hepatocytes (liver cells), blood vessels and bile canaliculi. At the corners of each lobule three vessels are found together that form a portal triad: a branch of the hepatic portal vein, a branch of the hepatic artery, and a bile duct. Oxygenated blood in the hepatic artery and deoxygenated blood in the hepatic portal vein leave those vessels and mix in the broad, leaky capillaries called sinusoids, which deliver blood to the central vein in the center of the lobule. From the central vein, blood then travels to the hepatic vein, and then to the inferior vena cava. Bile that is synthesized in the hepatocytes travels toward the bile ducts at the corners of the lobule. The gallbladder, a greenish sac-like structure, is tucked up inferiorly under the lobes of the liver. Its greenish hue comes in part from the bile that is stored within. Bile is made in the liver, and excess bile is stored in the gallbladder. Bile that is made in the liver travels through small ducts until it reaches the common hepatic duct. Some bile will travel to the gallbladder through the cystic duct, where it is stored. When stimulated (by food reaching the duodenum), the gallbladder will contract and force bile through the cystic duct to the common bile duct, and then to the duodenum where it aids in the emulsification and digestion of fats. (a) (b) Figure 9.12 – Liver. (a) Posterior of the liver showing the four lobes and the gallbladder. (b) Gallbladder and associated ducts. Image Credit: (a) Dr. Johannes Sobotta – Sobotta’s Atlas and Textbook of Human Anatomy 1906, Public Doman. https://commons.wikimedia.org/w/index.php?curid=29901575 (b) OpenStax. CC by 4.0. 11  ACTIVITY 5: EXAMINE THE HISTOLOGY OF THE LIVER Examine the slide of the liver. Try to distinguish the individual lobules surrounding the central veins. Portal triad Central vein Figure 9.13 –Microscopic anatomy of the liver. The liver receives oxygenated blood from the hepatic artery and nutrient-rich deoxygenated blood from the hepatic portal vein. Image Credit: Histologyguide.org Pancreas The pancreas is a comma-shaped, somewhat spongy gland that is nestled into the curve of the duodenum, posterior to the stomach. It has both exocrine and endocrine function. The exocrine portion is composed of clusters of acinar cells that synthesize and release digestive enzymes, bicarbonate and other substances that are important for digestion. Collectively, the digestive substances synthesized by the acinar cells is called pancreatic juice. The pancreatic juice is secreted into the pancreatic duct and travels to the duodenum to aid in digestion. The endocrine portion is composed of discrete structures called pancreatic islets, which synthesize and release the hormones insulin and glucagon. Figure 9.14 – Pancreas. Image Credit: OpenStax. CC by 4.0. Micrograph provided by the Regents of University of Michigan Medical School © 2012. 12 Structures to Know DIGESTIVE SLIDES □ Gastroesophageal junction o Esophagus o Stomach □ Duodenum □ Ileum □ Colon □ Liver HEAD PLATE MODEL – SAGITTAL VIEW □ Hard palate □ Soft palate □ Uvula □ Tongue □ Esophagus □ Pharyngeal tonsil □ Palatine tonsil □ Lingual tonsil HEAD PLATE MODEL – FRONTAL VIEW □ Hard palate □ Oral Cavity □ Sublingual Salivary Gland □ Molars 13 TORSO MODEL □ Hard palate □ Soft palate □ Tongue □ Sublingual salivary gland □ Submandibular salivary gland □ Parotid salivary gland □ Esophagus □ Pancreas STOMACH o Cardial part (cardia) o Fundus o Body o Pylorus o Pyloric sphincter o Lesser curvature o Greater curvature o Gastric folds (rugae) SMALL INTESTINES o Duodenum (on large intestine model) o Jejunum o Ileum 14 LARGE INTESTINES o Ileocecal valve o Cecum o Appendix o Haustrum o Tenia coli o Ascending colon o Right colic flexure o Transverse colon o Left colic flexure o Descending colon o Sigmoid colon o Rectum o Anal canal o Anus LIVER o Falciform ligament o Left lobe o Right lobe o Caudate lobe o Quadrate lobe o Hepatic portal vein o Hepatic artery o Common hepatic duct o Gallbladder 15  o Cystic duct o Common bile duct o Hepatic vein o Inferior vena cava SKULL □ Central incisor □ Lateral incisor □ Canine □ First premolar (bicuspid) □ Second premolar (bicuspid) □ First molar □ Second molar □ Third molar 16 Terms to Know □ Digestion □ Absorption □ Bolus □ Chyme □ Peristalsis □ Alimentary canal (gastrointestinal tract) □ Mucosa □ Submucosa □ Muscularis □ Serosa □ Gastric pit □ Microvilli □ Villi □ Circular folds □ Peyer’s patches □ Parietal / visceral peritoneum □ Greater omentum □ Mesentery □ Deciduous teeth □ Permanent teeth □ Pancreatic juice 17 Lab 9: Digestive System Review Worksheet 1. Name the four layers of the alimentary canal wall, from the lumen outward: ________________________________________________________________________ 2. Fill in the table below with the functions of the alimentary canal / digestive system organs. Organ Function(s) Mouth Esophagus Stomach Small Intestine Large Intestine Liver Gallbladder Pancreas 18 3. Match the structures on the left with the correct description on the right. Passage of digested products from the intestinal A. Mesentery K lumen into the bloodstream. Projections of the plasma membrane that increase B. Mucosa F the surface area of intestinal cells for absorption. C. Submucosa B Innermost lining of the alimentary canal. Layer of connective tissue in the alimentary canal D. Bolus C wall between mucosa and muscularis. Liquid created when food is mixed with digestive E. Greater omentum H juices in the stomach. F. Villi D Mass of chewed food produced in the mouth. Finger-like projection of the mucosa of the small G. Microvilli G intestine. Breaking down large molecules into smaller H. Chyme J molecules. Long drape of the visceral peritoneum that covers I. Peristalsis E much of the small intestine. Double fold of the peritoneum that anchors viscera J. Digestion A to the abdominal wall. Muscular contractions and relaxations that propel K. Absorption I food through the GI tract. 19 4. For each organ of the alimentary canal, identify / classify the epithelial tissue that is present in the mucosa. Give at least one other modification of the basic histological plan of the alimentary canal that is seen in each organ, and describe how this modification contributes to the function of that organ. Organ Epithelium? Another modification of the histological plan, and how this modification contributes to the function of the organ Stratified There is a thick layer of longitudinally arranged smooth Esophagus Squamous muscle fibers from the muscularis mucosae. This aids the stratified squamous epithelial in its protective function. Simple There are gastric glands located within gastric pits in the Stomach Columnar mucosa that secrete hydrochloric acid (HCl) and a variety of enzymes that aid in chemical digestion. Simple Small Intestine Columnar Presence of Peyer’s patches that are collections of lymphoid tissue that respond to specific antigens and pathogens. Simple Large Intestine Columnar The large intestine has numerous goblet cells that secrete a protective mucus lining. 20 5. Identifying anatomical structures of the stomach: Fill in the table on the right with the name of the digestive system structure, region, feature, or organ that corresponds to each label on the model at the left. Label Structure, region, feature or organ A Gastroesophageal Sphincter B Fundus C Rugae/ Gastric Folds D Pyloris E Body F Lesser Curvature G Greater Curvature H Pyloric Sphincter I Esophagus J Cardiac Region 21 6. Identifying anatomical structures of the gastrointestinal tract: Fill in the table on the right with the name of the digestive system structure, region, feature, or organ that corresponds to each label on the model at the left. Label Structure, region, feature or organ A stomach B Pancreas/Pancreatic duct Duodenum C D Ascending Colon E Transverse Colon F Jejunum G Descending Color H Ileum I Appendix J Ileocecal Valve K Cecum L Rectum 22 7. Identifying anatomical structures of the liver: Fill in the table on the right with the name of the digestive system structure, region, feature, or organ that corresponds to each label on the model at the left. (NOTE – the model is shown in the inferior view.) Label Structure, region, or feature A Left Lobe B Caudate Lobe C Inferior Vena Cava D Hepatic Vein E Hepatic Artery F Hepatic Portal Vein G Cystic Duct H Round Ligament of Liver Quadrate Lobe I Gallbladder J K Right Lobe 23 8. Label the structures / regions of the digestive system. 24 9. Label the structures / regions of the digestive system. Then use the figure to help you answer the following questions. a. Mechanical digestion begins in the _______mouth/oral cavity______________. b. Chemical digestion begins in the _____mouth/oral cavity__________________. c. Propulsion of the bolus down the esophagus into the stomach through rhythmic contractions of smooth muscle is called ____peristalsis__________. d. Most absorption of nutrients occurs in the ____small intestines___________. e. Chyme travels through the _____large intestines___________, where water and specific vitamins are absorbed and the remaining waste materials pass to the rectum. 25