2Chapter 26 OutlineGeneral Structure and Functions of the Digestive SystemOral CavityPharynxGeneral Arrangement of Abdominal GI OrgansEsophagusThe Swallowing ProcessStomachSmall IntestineLarge IntestineAccessory Digestive OrgansAging and the Digestive SystemDevelopment of the Digestive System
3Introduction The digestive system includes organs that: ingest the foodtransport the ingested materialdigest the material into smaller usable componentsabsorb the necessary digested nutrients into the bloodstreamexpel waste products from the body
4IntroductionThe digestive system is composed of two separate categories of organs:Digestive organscollectively make up the gastrointestinal (GI) tract, also called the digestive tract or the alimentary canalAccessory digestive organs
6GI Tract Organs The GI tract organs are as follows: oral cavity pharynxesophagusstomachsmall intestinelarge intestine
7Accessory Digestive Organs The accessory digestive organs are not part of the long GI tube, but often develop as outgrowths of that tube. They are as follows:……….. teeth……….. tongue……….. salivary glands………. liver……….. gall bladder……….. pancreas
8Digestive System Functions IngestionDigestionPropulsionSecretionAbsorptionElimination of wastes
9Peristalsis and Segmentation Propulsion of food along the GI tube involves two types of movement:peristalsissegmentationPeristalsis is the ripple-like wave of muscular contraction that forces material to move further along the GI tract.Segmentation is the churning and mixing of material helping to disperse the material and mix it and combine it with digestive organ secretions.
11Oral Cavity Contains the following structural features: cheeks, lips, and palatetonguesalivary glandsteeth
12Cheeks, Lips, and PalateCheeks form the lateral wall of the oral cavity and are comprised mainly of the buccinator muscles.The cheeks end anteriorly as the lips.The gingivae (gums) cover the alveolar processes of the teeth.The internal surface of the upper and lower lips are attached to the gingivae by a thin, midline mucosa fold called the labial frenulum.
13Cheeks, Lips, and Palate The palate forms the roof of the oral cavity. The anterior two-thirds of the palate is called the hard palate because it is comprised of bone. The posterior one-third of the palate is soft and muscular and is called the soft palate.Extending from the soft palate posteriorly is the uvula, which elevates during swallowing and closes off the posterior entrance to the nasopharynx.
15Cheeks, Lips, and PalateThe fauces represent the opening from the oral cavity to the oropharynx.The fauces are bounded laterally by paired muscular folds:palatoglossal archpalatopharyngeal archThe palatine tonsils (see Chapter 24) are housed between the two arches.
16TongueThe tongue manipulates and mixes ingested materials during chewing and helps compress the partially digested materials into a bolus.A bolus is a globular mass of ingested materials that can be more easily swallowed.The inferior surface of the tongue attaches to the floor of the oral cavity by a thin, midline mucous membrane called the lingual frenulum.
18Salivary GlandsSalivary glands produce and secrete saliva into the oral cavity.Saliva serves the following functions:moistens ingested materials to become a slick bolusmoistens, cleanses, and lubricates the structures of the oral cavitychemical digestion of ingested materialsantibacterial actiondissolves materials so that taste receptors on the tongue can be stimulated
19Salivary GlandsThree pairs of salivary glands are located external to the oral cavity:parotid glandssubmandibular glandssublingual glands
21Parotid Salivary Glands Largest of the three salivary glandsLocated anterior and inferior to the ear. Lateral side of face, under earsSecrete 25–30% of total salivaParotid duct runs parallel to the zygomatic arch and pierces the buccinator muscle just opposite the second upper molarAlso secrete amylase
23Submandibular Salivary Glands Reside inferior/lateral to the body of the mandibleProduce the majority of the saliva (60–70%)A submandibular duct transports saliva from each gland through a papilla in the floor of the mouth on the lateral sides of the lingual frenulum
25Sublingual Salivary Glands Inferior/anterior to the tongueEach gland extends multiple tiny sublingual ducts that open onto the inferior surface of the oral cavity just posterior to the submandibular duct papillaContribute only 3–5% of total saliva
27Salivary Gland Secretion Two types of secretory cells are found in salivary glands:Mucous cells—secrete mucin, which forms mucus upon hydrationSerous cells—secrete a watery fluidcontaining ions, lysozyme, and salivary amylase
30Teeth The teeth are collectively known as the dentition. A tooth has an exposed crown, a constricted neck, and one or more roots that fit into dental alveoli.Dentin forms the primary mass of the tooth. It is harder than bone.Each root is covered with cementum.The external surface of the dentin is covered with a layer of enamel that forms the crown of the tooth.
31TeethThe center of the tooth is a pulp cavity that contains connective tissue called pulp.A root canal opens into the connective tissue through an opening called the apical foramen. Blood vessels and nerves pass through this opening and are housed in the pulp.
33Surfaces of the Teeth Teeth have several surfaces: mesial surface distal surfacebuccal surfacelabial surfacelingual surfaceocclusal surface
34Teeth Two sets of teeth develop and erupt in a normal lifetime: deciduous teeth—erupt between 6–30 months, 20 in number, and are oftencalled milk teethpermanent teeth—replace thedeciduous teeth and are 32 innumber
36Permanent TeethIncisors—most anteriorly placed, shaped like chisels, and have a single rootCanines—posterolateral to the incisors, pointed tips for puncturing and tearingPremolars—posterolateral to canines, have flat crowns with prominent ridges called cusps for crushing and grindingMolars—thickest and most posterior teeth, also adapted for crushing and grinding of ingested materials
38Pharynx Shared by the respiratory and digestive systems Three skeletal muscle pairs of pharyngeal constrictors (superior, middle, and inferior) form the wall of the pharynx and participate in swallowingCN X innervates most pharyngeal musclesBranches of external carotid arteries supply the pharynxInternal jugular veins drain the pharynx
39PeritoneumAbdominopelvic cavity is covered with moist serous membranes:parietal peritoneum—lines the insidesurface of the body wallvisceral peritoneum—covers the surfaceof internal organs within the cavity
40PeritoneumOrgans that are completely surrounded by visceral peritoneum are called intraperitoneal organs. They include the stomach and most of the small intestines.Organs that lie in direct contact with the posterior abdominal and pelvic walls and are only covered on their anterolateral surfaces with visceral peritoneum are called retroperitoneal organs. Examples are the pancreas, ascending and descending colon of the large intestines, and the rectum.
42MesenteriesFolds of peritoneum that support and stabilize intraperitoneal GI tract organsBlood vessels, lymphatic vessels, and nerves are sandwiched between the two folds and supply the digestive organs
44MesenteriesThe greater omentum extends inferiorly like an apron from the greater curvature of the stomach and covers most of the abdominal organs.The lesser omentum connects the lesser curvature of the stomach and the proximal end of the duodenum to the liver.The mesentery proper suspends most of the small intestines from the posterior abdominal wall.The mesocolon is a peritoneal fold that attaches parts of the large intestine to the posterior abdominal wall.
47The Wall of the Abdominal GI Tract The wall of the GI tract from the esophagus to the large intestine is composed of four concentric layers called tunics. From deep (in contact with ingested materials) to superficial (the external covering) they are:mucosasubmucosamuscularisadventitia or serosa