Chapter 24 Digestive System I. Anatomy of the Digestive System: a. The digestive tract is also called the alimentary tract or canal 1. gastrointestinal tract technically only refers to the stomach & intestines b. regions of the digestive tract include: 1. mouth or oral cavity with accessory organs, salivary gland & tonsils 2. pharynx (throat) with tubular mucus glands 3. esophagus with tubular mucus glands 4. stomach 5. small intestines – consists of: a. duodenum b. jejunum c. ileum d. liver e. gallbladder accessory organs f. pancreas 6. large intestines – consists of: a. cecum b. colon c. rectum d. anal canal 7. anus II. Functions of the Digestive System: 1. ingestion 2. mastication (chewing) 3. propulsion – movement from one end to the other of the digestive tract a. usually 24-36 hours b. deglutination – swallowing moves food & liquids (bolus) from the oral cavity into the esophagus c. Peristalsis – is responsible for moving material through most of the digestive tract. i. Muscular contractions occur in peristaltic waves. ii. Some parts of large intestine move material by mass movement, which all contractions that extend over much larger parts of the digestive tract. 4. Mixing – mix with digestive secretions to help break it into smaller parts. i. Segmental contractions – are mixing contractions that occur in the small intestine. 5. Secretion – secretions are added to lubricate, liquefy, and digest the food. i. Mucus – secreted the entire length of the digestive tract ii. Secretions also contain large amounts of water, which liquefies the food. iii. Enzymes – secreted by the oral cavity, stomach, intestines, & pancreas break large food molecules down. 6. digestion – is the breakdown of large organic molecules into: i. carbohydrates into monosaccharides ii. proteins into amino acids iii. triglycerides into fatty acids & glycerol a. consists of mechanical digestion (mastication & mixing of food), and chemical digestion (enzymes) 7. Absorption – is the movement of molecules out of the digestive tract & into the circulation or into the lymphatic system. a. molecules pass out of the digestion tract by: i. simple diffusion ii. facilitated diffusion iii. active transport iv. cotransport 8. elimination – is the process by which the waste products are removed from the body a. Feces – semi solid waste products that are eliminated from digestive tract by defecation. III. Histology of the Digestive Tract: a. Figure 24.4 b. Digestive tract consists of 4 major layers or tunics c. 3 major types of glands are associated with the intestinal tract: 1. unicellular mucus glands 2. multicellular glands (accessory glands outside the digestive tract 2 3. multicellular glands in the mucosa & submucosa A. Mucosa: a. Innermost tunic – consists of 3 layers i. Inner – mucous epithelium in the mouth, oropharynx, esophagus and anal canal. ii. Loose C.T. (lamina propria) iii. Pouter thin smooth muscle layer (muscularis mucosa) B. Submucosa: a. Thick C.T. layer containing nerves, blood vessels & small glands. b. The nerve plexus of nerve cells form the submucosal plexus (Meissner’s plexus) C. Muscularis: a. Consists of an inner layer of circular smooth muscle & an outer layer of longitudinal smooth muscle. 1. 2 exceptions: i. upper esophagus- mm striated ii. Stomach- 3 layers of smooth muscle. b. Myenteric plexus (Auerbach’s plexus) - is between the 2 muscle layers. c. Submucosal and myenteric plexus constitute the enteric plexus or intramural plexus. i. Important in the control of movement & secretion D. Serosa or adventitia: a. 4th layer of digestive tract is a C.T layer called serosa or adventitia. b. Serosa is called the visceral IV. Regulation of the digestive system: A. Nervous Regulation of the Digestive System: 1. local neuronal control of the digestive tract occurs with in the enteric nervous system (ENS) 2. 3 major types of enteric neurons: i. Enteric sensory neurons detect changes in the chemical compositions or detect mechanical changes. ii. Enteric motor neurons stimulate or inhibit smooth muscle contraction & glandular secretion. iii. Enteric interneurons connect enteric sensory & motor neurons. 3. ENS coordinates peristalsis & regulates local refluxes. Which control activities within specific, short regions. B. Chemical Regulation of the Digestive System: a. Digestive tract produces a number of hormones (gastrin, secretin) which are secreted by endocrine cells. b. Histamine are released locally with in the digestive tract. 3 I. Peritoneum: 1. The serous membrane that covers the organs is the visceral peritoneum, & the one that covers the interior surface of the body wall is the parietal peritoneum. a. Peritonitis – is the inflammation of the peritoneal membranes; may result from chemical irritation or from infection. i. Ascites- accumulation of excess serous fluid in the peritoneal cavity; may accompany peritonitis, starvation, alcoholism or liver cancer. 2. Mesenteries- hold many of the organs in place within the abdominal cavity; 2 layers of serous membranes. 3. Retroperitoneal – abdominal organs that lie against the abdominal wall, have no mesenteries, and include the duodenum, pancreas, ascending colon, descending colon, rectum, kidneys, adrenal glands & the urinary bladder. 4. Lesser omentum – is the mesentery connecting the lesser curvature of the stomach & the proximal end of the duodenum to the liver & diaphragm. (AKA membrane of the bowels). 5. Greater omentum – the mesentery extending as a fold from the greater curvature & then to the transverse colon. a. Omental bursa- a cavity or pocket between both layers of mesentery. b. Fatty apron – large amount of fat that accumulates in the greater omental. 6. Coronary ligament attaches the liver to the diaphragm. 7. Falciform ligament attaches the liver to the anterior abdominal wall. 8. Mesentery proper- refers to the mesentery associated with the small intestine. 9. Transverse mesocolon – mesenteries of parts of the colon which extend from the transverse colon to the posterior body wall. 10. Mesoappendix is also known as the vermiform appendix. 11. Figure 24.5 4 II. Oral Cavity: (mouth) a. Part of the digestive tract bounded by the lips anteriorly, the fauces (throat) posteriorly, the cheeks laterally, the palate superiorly, and a muscular floor inferiorly. b. It is divided into 2 regions: 1. vestibule 2. oral cavity proper A. Lips & Cheeks: a. The lips (labia) are muscular structures formed mostly by the orbicularis oris muscle b. Figure 24.6 5 c. One or more frenula (bridle) which are mucosal folds (upper & lower). d. The cheeks form the lateral walls of the oral cavity. 1. The substance of the cheek includes the buccinator muscle, which flattens the cheek against the teeth, & the buccal fat pad, which rounds out the profile on the side of the face. e. Lips & cheeks are important in the processes of mastication and speech. i. They help manipulate food with in the mouth & hold it while teeth crush it. ii. Also helps form words. B. Palate & Palatine Tonsils: a. Palate consists of 2 parts: 1. hard palate (anteriorly) 2. soft palate (posterior, non-boney) b. Uvula (grape) – is the projection from the posterior edge of the soft palate. c. Palatine tonsils are located in the lateral wall of the fauces. C. Tongue: a. Frenulum – the anterior part of the tongue is relatively free & is attached to the floor of the mouth by this thin fold of tissue. b. The muscles associated with the tongue are divided into 2 categories: 1. intrinsic muscles – with in the tongue itself 2. extrinsic muscles – are outside the tongue but attached to it. i. Protrude & retract the tongue ii. Move the tongue side-to-side iii. They change its shape c. terminal sulcus – a groove on the tongue i. lingual tonsil (lymphoid tissue) on the posterior 1/3 of the tongue: 1. moves food in the mouth 6 2. holds food in place during mastication 3. major role in the mechanism of swallowing 4. major sensory organ for taste 5. one of the primary organs of speech D. Teeth: a. 32 teeth, in 2 dental arches (maxillary arch & mandibular arch) b. teeth in each quadrant include: 1. one central & one lateral incisor 2. one canine 3. 1st & 2nd premolars 4. 1st, 2nd & 3rd molars i. 3rd molars are called wisdom teeth because they usually appear in late teens or early twenties. c. Figure 24.7 d. teeth of the adult mouth are permanent or secondary teeth; most are replacements for primary or deciduous teeth (milk teeth) e. Each tooth consists of a crown with one or more cusps (points), a neck, & a root. i. Figure 24.8 7 f. the clinical crown is that part of the tooth exposed in the oral cavity 1. anatomical crown is the entire enamel – covered part of the tooth g. Pulp cavity – center of the tooth, filled with blood vessels, nerves, & C.T. called pulp. h. Root canal – pulp cavity with in the root 1. Apical foramen – a hole at the point of each root where nerves & blood vessel enter & exit i. Dentin – is living, cellular, & calcified tissue with in the pulp cavity. 1. Enamel – covers the tooth crown, which protects the tooth against abrasion & acids produced by bacteria in the mouth. 2. Cementum – covers the surface of the dentin in the root, which helps anchor the tooth in the jaw. j. teeth are set in alveoli (sockets) 1. gingiva – cover the alveolar processes 2. periodontal ligaments secure the teeth in the alveoli k. play a role in mastication & speech l. dental diseases: 8 E. Mastication: 1. Anterior teeth, incisors & canines primarily cut & tear food; premolars & molars crush and grind food. 2. 4 pairs of muscles move the mandible during mastication: i. temporalis ii. masseter closes the jaw iii. medial pterygoid iv. lateral pterygoid – opens the jaw 3. Medial & lateral pterygoid & the masseter accomplish protraction and lateral & medial excursion of the jaw. 4. temporalis retracts the jaws F. Salivary glands: a. 3 pair of large multicellular glands exist: 1. parotid 2.