The Chemical Level of Organization, Chapter 3. Mucosa - 2. He was the son of Henry Barlow Carter, a well-known artist and it is possible that he honed his natural talents with his father. Additionally, it serves as a conduit for a dense branching network of nerves, the submucosal plexus, which functions as described below. then you must include on every physical page the following attribution: If you are redistributing all or part of this book in a digital format, The hard palate, a bony structure, forms the roof of the mouth. It also joins the mucosa to the bulk of underlying smooth muscle (fibers running circularly within layer of longitudinal muscle). Digestive mucosa is made up of three sublayers: (1) a lining epithelium, (2) a lamina propria, and (3) a musclularis mucosae. Explain the reason. Epithelial cells have a very brief lifespan, averaging from only a couple of days (in the mouth) to about a week (in the gut). Being able to predict the churn rate is the key to success for the telecommunication industry. Each layer has a different function and quality, which makes it unique. Two B. In the stomach and small intestine, the smooth muscle generates folds that increase the absorptive surface area of the mucosa. Removing #book# Name the layers of the small intestine from superficial to deep. From the inside out they are called the mucosa, submucosa, muscularis externa, and serosa. This is the . The secretions of the associated glandular organs, such as the salivary glands, pancreas, liver, and gall bladder, aid the GI tract in accomplishing these functions. The digestive tract, from the esophagus to the anus, is characterized by a wall with four layers, or tunics. the epithelium is simple columnar, and is organized into gastric pits and glands to deal with secretion. The smooth muscle is responsible for movement of food by peristalsis and mechanical digestion by segmentation. Since the mucosa is the innermost layer within the GI tract, it surrounds an open space known as the lumen. The GI tract is composed of four layers. It is composed of epithelium cells and a thin connective tissue. The mucosa is a mucous membrane that lines the inside of the digestive tract from mouth to anus. Each hematocrit specimen was spiked to obtain four glucose concentrations (50-500 mg/dL). Rather, this blood is diverted to the liver where its nutrients are off-loaded for processing before blood completes its circuit back to the heart. Along the way, note how the food changes consistency and form. Additionally, it serves as a conduit for a dense branching network of nerves, the submucosal plexus, which functions as described below. Explain how the enteric nervous system supports the digestive system. The serosa is the portion of the alimentary canal superficial to the muscularis. Aggressive surgery, improvements in anesthesia safety, the advance of critical care expertise, and antibiotics have greatly improved the mortality rate from this condition. General structure of the gut wall: This cross section shows the mucosa in relation to the interior space, or lumen. CliffsNotes study guides are written by real teachers and professors, so no matter what you're studying, CliffsNotes can ease your homework headaches and help you score high on exams. Within these folds are blood vessels, lymphatic vessels, and nerves that innervate the organs with which they are in contact, supplying their adjacent organs. citation tool such as, Authors: J. Gordon Betts, Kelly A. For example, when an ulcer perforates the stomach wall, gastric juices spill into the peritoneal cavity. The blood vessels second function is to supply the organs of the alimentary canal with the nutrients and oxygen needed to drive their cellular processes. The main function of the organs of the alimentary canal is to nourish the body by digesting food and absorbing released nutrients. What are the layers of mucosa? Name the major functions of the large intestine. Intrinsic innervation of much of the alimentary canal is provided by the enteric nervous system, which runs from the esophagus to the anus, and contains approximately 100 million motor, sensory, and interneurons (unique to this system compared to all other parts of the peripheral nervous system). Support/stabilize the organs of the abdominopelvic cavity and route for blood. Even after development is complete, they maintain a connection to the gut by way of ducts. A broad layer of dense connective tissue, it connects the overlying mucosa to the underlying muscularis. In general, sympathetic activation (the fight-or-flight response) restricts the activity of enteric neurons, thereby decreasing GI secretion and motility. Left, right, caudate, and quadrate lobes. { "22.5A:_Mucosa" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", "22.5B:_Submucosa" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", "22.5C:_Muscularis" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", "22.5D:_Serosa" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()" }, { "00:_Front_Matter" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", "22.01:_Overview_of_the_Digestive_System" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", "22.02:_Nervous_System_of_the_Digestive_System" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", "22.03:_The_Peritoneum" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", "22.04:_The_Alimentary_Canal" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", "22.05:_Layers_of_the_Alimentary_Canal" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", "22.07:_The_Liver" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", "22.08:_The_Gallbladder" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", "22.09:_The_Pancreas" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", "22.10:_The_Small_Intestine" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", "22.11:_The_Large_Intestine" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", "22.12:_Chemical_Digestion" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", "22.13:_Absorption" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", "22.14:_Phases_of_Digestion" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", "22.6:_The_Stomach" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", "zz:_Back_Matter" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()" }, [ "article:topic", "license:ccbysa", "showtoc:no" ], https://med.libretexts.org/@app/auth/3/login?returnto=https%3A%2F%2Fmed.libretexts.org%2FBookshelves%2FAnatomy_and_Physiology%2FAnatomy_and_Physiology_(Boundless)%2F22%253A_Digestive_System%2F22.05%253A_Layers_of_the_Alimentary_Canal%2F22.5A%253A_Mucosa, \( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}}}\) \( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash{#1}}} \)\(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\) \(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\)\(\newcommand{\AA}{\unicode[.8,0]{x212B}}\), status page at https://status.libretexts.org, Describe the structure and function of the mucosa of the GI tract. 2. In the small intestine, the epithelium (particularly the ileum) is specialized for absorption, with villi and microvilli increasing surface area. Lipids are absorbed via lacteals, tiny structures of the lymphatic system. Hormones secreted by several endocrine glands, as well as endocrine cells of the pancreas, the stomach, and the small intestine, contribute to the control of digestion and nutrient metabolism. The digestive organs within the abdominal cavity are held in place by the peritoneum, a broad serous membranous sac made up of squamous epithelial tissue surrounded by connective tissue. Incisors, cuspids (canines), bicuspids (premolars), and molars. Lecture 6: Anatomy of the Body Wall Learning Objectives 1. 22.5A: Mucosa is shared under a CC BY-SA license and was authored, remixed, and/or curated by LibreTexts. Inflammation of the peritoneum is called peritonitis. The Immune System and Other Body Defenses, Chemical Reactions in Metabolic Processes, Quiz: Chemical Reactions in Metabolic Processes, Connective Tissue Associated with Muscle Tissue, Quiz: Connective Tissue Associated with Muscle Tissue, Quiz: Structure of Cardiac and Smooth Muscle, Muscle Size and Arrangement of Muscle Fascicles, Quiz: Muscle Size and Arrangement of Muscle Fascicles, Quiz: The Ventricles and Cerebrospinal Fluid, Quiz: The Hypothalamus and Pituitary Glands, Quiz: Functions of the Cardiovascular System, Quiz: Specific Defense (The Immune System), Humoral and Cell-Mediated Immune Responses, Quiz: Humoral and Cell-Mediated Immune Responses, Quiz: Structure of the Respiratory System, Quiz: Structure of the Digestive Tract Wall, Online Quizzes for CliffsNotes Anatomy and Physiology QuickReview, 2nd Edition. It is the absorptive and secretory layer of the GI tract. What roles do exons have? A&P: Chapter 38 Section: Organization of the Digestive System Awarded 25 points out of 25 possible points. What are some possible roles introns might have? The mucosa consists of the epitheliumitself and also the supporting loose connective tissue, called lamina propria, immediately beneath the epithelium. Since it lacks sarcomeres, it is nonstriated. This venous network takes the blood into the liver where the nutrients are either processed or stored for later use. Contains the submucosal enteric neural plexus that controls GI secretions and localized blood flow, David N. Shier, Jackie L. Butler, Ricki Lewis, Charles Welsh, Cynthia Prentice-Craver, David Shier, Jackie Butler, Ricki Lewis, Hole's Essentials of Human Anatomy and Physiology, David Shier, Jackie Butler, John Hole, Ricki Lewis. The mucosa is the innermost layer. (d) The shells are then connected to each other by a metal wire. It has four parts- cardiac, fundus, body and pyloric portion. Anatomy & Physiology by Lindsay M. Biga, Sierra Dawson, Amy Harwell, Robin Hopkins, Joel Kaufmann, Mike LeMaster, Philip Matern, Katie Morrison-Graham, Devon Quick & Jon Runyeon is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License, except where otherwise noted. Name the four major regions of the stomach in order from its connection with the esophagus to the small intestine. Chapter 1. Also called the gastrointestinal (GI) tract or gut, the alimentary canal (aliment- = "to nourish") is a one-way tube about 7.62 meters (25 feet) in length during life and closer to 10.67 meters (35 feet) in length when measured after death, once smooth muscle tone is lost. The muscularis in the small intestine is made up of a double layer of smooth muscle: an inner circular layer and an outer longitudinal layer. The LibreTexts libraries arePowered by NICE CXone Expertand are supported by the Department of Education Open Textbook Pilot Project, the UC Davis Office of the Provost, the UC Davis Library, the California State University Affordable Learning Solutions Program, and Merlot. The oral cavity is lined by which type of epithelium? As soon as food enters the mouth, it is detected by receptors that send impulses along the sensory neurons of cranial nerves. secretory and absorptive functions in small intestine and large intestine. Wise, Eddie Johnson, Brandon Poe, Dean H. Kruse, Oksana Korol, Jody E. Johnson, Mark Womble, Peter DeSaix. The serosa is the portion of the alimentary canal superficial to the muscularis. Each layer has different tissues and functions. From the inside out they are called: mucosa, submucosa, muscularis, and serosa. Both the mouth and anus are open to the external environment; thus, food and wastes within the alimentary canal are technically considered to be outside the body. Within these folds are blood vessels, lymphatic vessels, and nerves that innervate the organs with which they are in contact, supplying their adjacent organs. In electrostatic equilibrium, what is the charge on (a) the outer surface of the inner shell, (b) the inner surface of the outer shell, and (c) the outer surface of the outer shell? As its name implies, the submucosa lies immediately beneath the mucosa. If $V$ equals a constant throughout a given region of space what can you say about $\mathrm{E}$ in that region? 2. Arteries supply the digestive organs with oxygen and processed nutrients, and veins drain the digestive tract. Inflammation of the peritoneum is called peritonitis. Here's how these organs work together in your digestive system. Describe the formation and structures of the 'generalised' body wall 2. Stratified Squamous epithelium for protection against friction and abrasion. Note that during fetal development, certain digestive structures, including the first portion of the small intestine (called the duodenum), the pancreas, and portions of the large intestine (the ascending and descending colon, and the rectum) remain completely or partially posterior to the peritoneum. The computer governs all system modules and gives instruction according to real-time analysis of feedback. Thus, the location of these organs is described as retroperitoneal. Legal. describe the four layers of the gi tract There are 4 layers in gastrointestinal tract: from inside to outside these are mucosa, submucosa, muscular layer and serosa. When you consider that the alimentary canal is exposed to foodborne bacteria and other foreign matter, it is not hard to appreciate why the immune system has evolved a means of defending against the pathogens encountered within it. While the colon has two layers like the small intestine, its longitudinal layer is segregated into three narrow parallel bands, the tenia coli, which make it look like a series of pouches rather than a simple tube. The four layers of the alimentary or digestive tract are listed as: Serosa: It is formed of the mesothelium and is found at the exterior part of the canal. Accessory digestive organs, despite their name, are critical to the function of the digestive system. In general, the GI tract is composed of. lamina propria. Muscularis mucosaThis thin layer of smooth muscle is in a constant state of tension, pulling the mucosa of the stomach and small intestine into undulating folds. . Three C. Four Correct D. Five The tissue layers that compose the walls of the GI tract are: mucosa, submucosa, muscularis, and serosa. Two concentric spherical metal shells are insulated from each other and from the surroundings. Table 23.1 gives a quick glimpse at how these other systems contribute to the functioning of the digestive system. Mucosa It is part of the digestive tract, located between the esophagus and the duodenum. Describe the orientation of smooth muscle fibers in the muscularis externa of the digestive tract. The breakdown of lipid droplets by bile salts. The contractions of these layers promote mechanical digestion, expose more of the food to digestive chemicals, and move the food along the canal. If you are redistributing all or part of this book in a print format, A cross-section of the abdomen shows the relationship between abdominal organs and the peritoneum (darker lines). The most variation is seen in the epithelium tissue layer of the mucosa. The layers are discussed below, from the inside lining of the tract to the outside lining: The mucosa is a mucous membrane that lines the inside of the digestive tract from mouth to anus. The third layer of the alimentary canal is the muscularis (also called the muscularis externa). Once food products enter the small intestine, the gallbladder, liver, and pancreas release secretionssuch as bile and enzymesessential for digestion to continue. Describe the four layers of the gastrointestinal tract walls, including locations. The stomach can perform these roles due to the layers of the stomach wall. are licensed under a, Structural Organization of the Human Body, Elements and Atoms: The Building Blocks of Matter, Inorganic Compounds Essential to Human Functioning, Organic Compounds Essential to Human Functioning, Nervous Tissue Mediates Perception and Response, Diseases, Disorders, and Injuries of the Integumentary System, Exercise, Nutrition, Hormones, and Bone Tissue, Calcium Homeostasis: Interactions of the Skeletal System and Other Organ Systems, Embryonic Development of the Axial Skeleton, Development and Regeneration of Muscle Tissue, Interactions of Skeletal Muscles, Their Fascicle Arrangement, and Their Lever Systems, Axial Muscles of the Head, Neck, and Back, Axial Muscles of the Abdominal Wall, and Thorax, Muscles of the Pectoral Girdle and Upper Limbs, Appendicular Muscles of the Pelvic Girdle and Lower Limbs, Basic Structure and Function of the Nervous System, Circulation and the Central Nervous System, Divisions of the Autonomic Nervous System, Organs with Secondary Endocrine Functions, Development and Aging of the Endocrine System, The Cardiovascular System: Blood Vessels and Circulation, Blood Flow, Blood Pressure, and Resistance, Homeostatic Regulation of the Vascular System, Development of Blood Vessels and Fetal Circulation, Anatomy of the Lymphatic and Immune Systems, Barrier Defenses and the Innate Immune Response, The Adaptive Immune Response: T lymphocytes and Their Functional Types, The Adaptive Immune Response: B-lymphocytes and Antibodies, Diseases Associated with Depressed or Overactive Immune Responses, Energy, Maintenance, and Environmental Exchange, Organs and Structures of the Respiratory System, Embryonic Development of the Respiratory System, Digestive System Processes and Regulation, Accessory Organs in Digestion: The Liver, Pancreas, and Gallbladder, Chemical Digestion and Absorption: A Closer Look, Regulation of Fluid Volume and Composition, Fluid, Electrolyte, and Acid-Base Balance, Human Development and the Continuity of Life, Anatomy and Physiology of the Testicular Reproductive System, Anatomy and Physiology of the Ovarian Reproductive System, Development of the Male and Female Reproductive Systems, Changes During Pregnancy, Labor, and Birth, Adjustments of the Infant at Birth and Postnatal Stages. They transport the protein and carbohydrate nutrients absorbed by mucosal cells after food is digested in the lumen. Specifically, the more anterior parts of the alimentary canal are supplied with blood by arteries branching off the aortic arch and thoracic aorta. Submucosal- nerve network between the mucosa and submucosa. Also called the gastrointestinal (GI) tract or gut, the alimentary canal (aliment- = to nourish) is a one-way tube about 7.62 meters (25 feet) in length during life and closer to 10.67 meters (35 feet) in length when measured after death, once smooth muscle tone is lost. Organs of the Alimentary Canal The Mouth and Oral cavity. https://openstax.org/books/anatomy-and-physiology-2e/pages/1-introduction, https://openstax.org/books/anatomy-and-physiology-2e/pages/23-1-overview-of-the-digestive-system, Creative Commons Attribution 4.0 International License, Blood supplies digestive organs with oxygen and processed nutrients, Endocrine hormones help regulate secretion in digestive glands and accessory organs, Skin helps protect digestive organs and synthesizes vitamin D for calcium absorption, Mucosa-associated lymphoid tissue and other lymphatic tissue defend against entry of pathogens; lacteals absorb lipids; and lymphatic vessels transport lipids to bloodstream, Skeletal muscles support and protect abdominal organs, Sensory and motor neurons help regulate secretions and muscle contractions in the digestive tract, Respiratory organs provide oxygen and remove carbon dioxide, Bones help protect and support digestive organs, Kidneys convert vitamin D into its active form, allowing calcium absorption in the small intestine, Apron-like structure that lies superficial to the small intestine and transverse colon; a site of fat deposition in people who are overweight, Anchors the liver to the anterior abdominal wall and inferior border of the diaphragm, Suspends the stomach from the inferior border of the liver; provides a pathway for structures connecting to the liver, Vertical band of tissue anterior to the lumbar vertebrae and anchoring all of the small intestine except the initial portion (the duodenum), Attaches two portions of the large intestine (the transverse and sigmoid colon) to the posterior abdominal wall, Identify the organs of the alimentary canal from proximal to distal, and briefly state their function, Identify the accessory digestive organs and briefly state their function, Describe the four fundamental tissue layers of the alimentary canal, Contrast the contributions of the enteric and autonomic nervous systems to digestive system functioning, Explain how the peritoneum anchors the digestive organs. From the inside out they are called: mucosa, submucosa, muscularis, and serosa. As soon as food enters the mouth, it is detected by receptors that send impulses along the sensory neurons of cranial nerves. The longitudinal, circular, and oblique orientations of muscle fibers. The mucosa is the innermost layer of the GI tract. To appreciate just how demanding the digestive process is on the cardiovascular system, consider that while you are resting and digesting, about one-fourth of the blood pumped with each heartbeat enters arteries serving the intestines. 1. Answer and Explanation: 1. Walls of the digestive tract have four concentric layers. Notice that the epithelium is in direct contact with the lumen, the space inside the alimentary canal. describe the four layers of the gi tract. The alimentary canal is the part of the digestive system that food actually passes through (the. Despite the fact that people use it on a daily basis, most people only have a basic understanding of what it is and how it works. Thus, the challenge is to predict the churn percentage of customers with higher accuracy without comprising the profit. What layer of the alimentary canal tissue is capable of helping to protect the body against disease, and through what mechanism? The four major layers of the GI tract are: the innermost layer is the mucosa, next to it is the submucosa, then comes the muscular View the full answer Transcribed image text: Describe the four major layers of the GI tract that are found from esophagus to anus. A sheet of mesentery that is remnant of the ventral mesentery, between the liver and the anterior wall of the peritoneal cavity. These tissues serve to hold the alimentary canal in place near the ventral surface of the vertebral column. EpitheliumIn the mouth, pharynx, esophagus, and anal canal, the epithelium is primarily a non-keratinized, stratified squamous epithelium. The space shared between the digestive and respiratory tracts. are not subject to the Creative Commons license and may not be reproduced without the prior and express written A. The membrane consists of epithelium, which is in direct contact with ingested food, and the lamina propria, a layer of connective tissue analogous to the dermis. The celiac trunk services the liver, stomach, and duodenum, whereas the superior and inferior mesenteric arteries supply blood to the remaining small and large intestines. Food enters the mouth, is digested, and used for energy and nutrients; what cannot be used is expelled from the body. These folds dramatically increase the surface area available for digestion and absorption. Chemical peritonitis can develop any time the wall of the alimentary canal is breached, allowing the contents of the lumen entry into the peritoneal cavity. wall of tubular gastrointestinal tract consists of 4 concentric layers: mucosa. bookmarked pages associated with this title. Mucosa. The digestive tract, from the esophagus to the anus, is characterized by a wall with four layers, or tunics. The small intestine has four tissue layers: The serosa is the outermost layer of the intestine. An important one of these folds is the mesentery which attaches the small intestine to the body wall allowing for blood vessels, nerves, and lymphatic vessels to have a secure structure to travel through on their way to and from the small intestine. Previous It is rounded and hollow, and located near the diaphragm in the left part of your abdomen. The membrane consists of epithelium, which is in direct contact with ingested food, and the lamina propria, a layer of connective tissue analogous to the dermis. Even more severe peritonitis is associated with bacterial infections seen with appendicitis, colonic diverticulitis, and pelvic inflammatory disease (infection of uterine tubes, usually by sexually transmitted bacteria). Hemorrhagic peritonitis occurs after a ruptured tubal pregnancy or traumatic injury to the liver or spleen fills the peritoneal cavity with blood. Contribution of Other Body Systems to the Digestive System. Thus, the location of these organs is described as retroperitoneal. Mucous membrane: It is also known as mucosa. Mucosa - Circular muscle layer and longitudinal muscle layer are the two sublayers. The veins that collect nutrient-rich blood from the small intestine (where most absorption occurs) empty into the hepatic portal system. The gustatory system or sense of taste is the sensory system that is partially responsible for the perception of taste (flavor). The digestive system includes the organs of the alimentary canal and accessory structures. (5 Points) Serosa - The outer layer allows fluids to escape, keeping the outer surface wet and allowing organs to slide past one another during digestion and movement. All rights reserved. Want to cite, share, or modify this book? Epithelial cells have a very brief lifespan, averaging from only a couple of days (in the mouth) to about a week (in the gut). There are four layers making up our atmosphere: The troposphere, stratosphere, mesosphere and thermosphere.