The Digestive System: Introduction, Mouth, Esophagus and Deglutition PDF

Anatomy and Physiology I. Pharmacy The Digestive System: Introduction, Mouth, Esophagus and Deglutition Dr. Teresa Olivar Department of Biomedical Sciences Digestive system Two groups of organs: The gastrointestinal tract: fr...

Anatomy and Physiology I. Pharmacy The Digestive System: Introduction, Mouth, Esophagus and Deglutition Dr. Teresa Olivar Department of Biomedical Sciences Digestive system Two groups of organs: The gastrointestinal tract: from the mouth to the anus through the thoracic and abdominopelvic cavities. Mouth, most of the pharynx, esophagus, stomach, small intestine and large intestine. Lenght: 5-7 meters in a living person. The accesory digestive organs: teeth, tongue, salivary glands, liver, gallbladder, and pancreas. Dr. Teresa Olivar 2  Functions (I) 1. Ingestion: taking food and liquids into the mouth (eating) 2. Secretion: Cells within the walls of the GI tract and accessory digestive organs secrete water, acid, buffers and enzymes into the lumen of the tract (7l/day) 3. Mixing and propulsion: Motility: capability of the GI tract to mix and move material along its length. Alternating contractions and relaxations of smooth muscle in the walls of the GI tract mix food and secretions and propel them toward the anus. Dr. Teresa Olivar 3  Functions (II) 4. Digestion: Mechanical digestion The teeth cut and grind the food before it is swallowed, and then smooth muscles of the stomach and small intestine churn the food. Food molecules become dissolved and thoroughly mixed with digestive enzymes Chemical digestion Large carbohydrate, lipid, protein and nucleic acid molecules in food are split into smaller molecules by hydrolysis. Digestive enzymes catalyze these catabolic reactions. Some substances can be absorbed without chemical digestion: vitamins, ions, cholesterol and water. Dr. Teresa Olivar 4 Function (III) Absorption The entrance of ingested and secreted fluids ions, and the products of digestion into the epithelial cells lining the lumen of the GI tract. The absorbed substances pass into blood or lymph and circulate to cells throughout the body. Defecation Wastes, indigestible substances, bacteria, cells sloughed from the lining of the GI tract, and digestive materials that were not absorbed. The eliminated material is termed feces. Dr. Teresa Olivar 5 Layers of the GI tract The wall of the GI tract from lower esophagus to the anal canal has the same four-layered arrangement of tissues. From deep to superficial: Mucosa Submucosa Muscularis Serosa Dr. Teresa Olivar 6  Layers of the GI tract Four layers: Food - Lumen 1.Mucosa Mucosa 2.Submucosa Submucosa 3.Muscularis Muscularis 4.Serosa Serosa Dr. Teresa Olivar 7 Dr. Teresa Olivar 8  Mucosa: epithelium, lamina propia, muscularis mucosae It’s the inner lining of the GI tract. Epithelium, lamina propia and muscularis mucosae. EPITHELIUM In the mouth, pharynx, esophagus and anal canal: protective function In the stomach and intestines: protective, secretion and absorption function. The rate of renewal of GI tract epithelial cells is rapid: every 5 to 7 days they slough off and are replaced by new cells. Located among the epithelial cells are exocrine cells (mucus, fluid) and several types of endocrine cells (enteroendocrine cells- hormones) Dr. Teresa Olivar 9 Mucosa: epithelium, lamina propia, muscularis mucosae Lamina propia It contains many blood and lymphatic vessels for the absortion of nutrientes It contains the majority of the cells of the mucosa-associated lymphatic tissue (MALT). It contains inmuno system cells that protect against disease. MALT is present along the GI tract, especially in the tonsils, small intestine and large intestine. Muscularis musosae It’s a thin layer of smooth muscle fibers. It presents many folds to increase the surface area of digestion and absorption Movements of this layer ensure that all absorptive cells are fully exposed to the contents of the GI tracts. Dr. Teresa Olivar 10 Dr. Teresa Olivar 11 Submucosa It contains many blood and lymphatic vessels that receive absorbed food molecules. There is an extensive network of neurons known as the submucosal plexus. Dr. Teresa Olivar 12 Muscularis Skeletal muscle: in the mouth, pharynx, superior and middle parts of esophagus  voluntary swallowing Skeletal muscle: external anal sphincter  voluntary control of defecation. Smooth muscle: rest of the GI tract  two layers: Inner sheet of circular fibers Outer sheet of longitudinal fibers Involuntary contractions of the smooth muscle: Help break down food Mix food and digestive secretions Propel it along the tract. Dr. Teresa Olivar 13  Serosa It’s the outer layer of the GI tract. In the esophagus: Adventicia In the portions of the GI tract that are suspended in the abdominopelvic cavity: Visceral Peritoneo PERITONEUM Parietal peritoneum: It lines the wall of the abdominopelvic cavity Visceral peritoneum: It covers some of the organs in the cavity and is their serosa Peritoneal cavity: It’s the slim space containing lubricating serous fluid that is between the parietal and visceral portions. Dr. Teresa Olivar 14 Dr. Teresa Olivar 15 Regulation of the GI tract Autonomic regulation is extrinsic to the GI track. It’s superimposed on “intrinsic” modes of regulation. The GI tract contains intrinsic sensory neurons: Enteric nervous system They have their cell bodies within the gut wall They are not part of the autonomic system. Local regulation of the GI tract Paracrine regulation Hormonal regulation (hormones secrete by the mucosa) Dr. Teresa Olivar 16 Regulation of the GI tract. Autonomic nervous system It’s innervated by the sympathetic and parasympathetic divisions of the autonomic nervous system. Parasympathetic nerves stimulates motility and secretions Vagus nerve: it’s the source of parasympathetic activity in the esophagus, stomach, pancreas, gallbladder, small intestine and upper portion of the large intestine. The lower portion of the large intestine receives parasympathetic innervation from spinal nerves in the sacral region. Sympathetic nerves reduces peristalsis and secretory activity and stimulate the contraction of sphincter muscles along the GI tracts. Dr. Teresa Olivar 17 From mouth to stomach Mastication Digestion Mechanical Saliva Chemical Deglutition Dr. Teresa Olivar 18 Teeth They are accessory digestive organs located in sockets of the alveolar processes of the mandible and maxillae. The alveolar processes are covered by the gingivae or gums. The sockets are lined by the periodontal ligament or membrane, which consists of dense fibrous connective tissue that anchors the teeth to the socket walls. There are three major external regions: the crown, root and neck. 19 Dr. Teresa Olivar 20 Internally, Dentin consists of a calcified connective tissue that gives the tooth its basic shape and rigidity. It’s harder than bone because of its higher content of calcium salts (70% of dry weight) Dentin is covered by enamel (calcium phospate and calcium carbonate - 95% of dry weight). It’s the hardest substance in the body. Enamel protects the tooth from the wear and tear of chewing, and against the acid that can dissolve de dentin. Dr. Teresa Olivar 21 Internally, The dentin of the root is covered by cementum, another bonelike substance, which attaches the root to the periodontal ligament. The dentin encloses a space: the pulp cavity. The pulp cavity is filled with pulp. Pulp: blood vessels, nerves and lymphatic vessels. Root canals, with an opening at its base: the apical foramen Dr. Teresa Olivar 22 Dentitions: deciduous and permanent teeth Deciduous = primary teeth, milk teeth or baby teeth They begin to erupt at about 6 mooths of age and approximately two teeth appear each month thereafter, until all 20 are present. The deciduous teeth are lost between ages 6 to 12 years. They are replaced by the permanent teeth. Permanent dentition contains 32 teeth that erupts between age 6 to adulthood. Dr. Teresa Olivar 23  20 teeth 32 teeth Dr. Teresa Olivar 24 Dr. Teresa Olivar 25 Types of teeth: Central and lateral incisors for cutting into food. The cuspids (canines), which have a pinted surface called a cusp, to tear food. First, second and third molars (wisdom teeth). They crush food to prepare it for swallowing. Dr. Teresa Olivar 26  Salivary glands They secrete saliva into the oral cavity. Without stimulation: enough saliva is secreted to keep the mucous membranes of the mouth and pharynx moist and to clean the mouth and teeth. When they are stimulated, they increase the secretion of saliva and it lubricates, disolves and begins the chemical breakdown of the food. The mucous membrane of the mouth and tongue contains many small salivary glands that open directly, or indirectly via short ducts, to the oral cavity. Labial, buccal and palatal glands (lips, cheeks ans palate) Lingual glands (tongue) Dr. Teresa Olivar 27  Major salivary glands They lie beyond the oral mucosa, into ducts that lead to the oral cavity. THREE PAIRS OF MAJOR SALIVARY GLANDS The Parotid glands They are localted inferior and anterior to the ears. Parotid duct The submandibular glands They are in the floor of the mouth. The submandibular ducts The sublingual glands They are beneath the tongue and superior to the submandibular glands. The lesser sublingual duct Dr. Teresa Olivar 28 Dr. Teresa Olivar 29 Composition of saliva 99.5% Water Ions: sodium, potassium, choloride, bicarbonate and phosphate. Urea, uric acid Mucus Inmunoglobulin A Lysozyme: a bacteriolytic enzyme Salivary amylase (breaksdown starch) Dr. Teresa Olivar 30 Not all salivary glands supply the same ingredients The parotids glands secrete a watery liquid containing salivary amylase. Submandibular glands contain also mucous cells, therefore they secrete a fluid that contains amylase but is thickened with mucus. Sublingual glands contain mostly mucous cells, so they secrete a much thicker fluid (high amount of mucus and a very small quantity of salivary amylase). Dr. Teresa Olivar 31 Functions of saliva Water: dissolves foods so that they can be tasted by gustatory receptors and so that digestive reactions can begin. Chloride ions activate salivary amylase to start the breakdown of starch. Bicarbonate and phosphate ions buffer acidic foods that enter the mouth (Saliva is only slightly acid). Salivary glands help remove waste molecules from the body (eg. Urea and uric acid) Protection Mucus lubricates food and the movements of the tongue and lips and keeps the mucous membranes moist. IgA prevents attachment of microbes so they cannot penetrate the epithelium Lysozyme kills bacteria. Dr. Teresa Olivar 32 Salivation It’s controlled by the Autonomic Nervous System Average of daily secreted saliva: 1-1,5l Most components of saliva are reabsorbed, which prevents fluid loss. Parasympathetic stimulation promotes continuous secretion of saliva. Sympathetic stimulation inhibits salivation. It dominates during stress, resulting in dryness of the mouth. If the body becomes dehydrated, the salivary glands stop secreting saliva to conserve water  dryness of the mouth  sensation of thirst. Dr. Teresa Olivar 33 Salivation - Regulation The smell, sight, sound and thought of food Parasympathetic division Cortex Olfactory area Stimulates salivation Visual area - + Glossopharyngeal Parotid glands nerve (IX) Salivary nuclei Sensory information (brain stem) Feel and taste of food Tongue Facial nerve (VII) Sublingual Submandibular glands Dr. Teresa Olivar 34 Salivation - Regulation Sympathetic division Inhibitis salivation Dr. Teresa Olivar 35 Mechanical digestion: Mouth Chewing or mastication: food is manipulated by the tongue, ground by the teeth, and mixed with saliva. Food is reduced to a soft, flexible, easily swallowed mass called bolus. Chemical digestion: Salivary amylase Initiates the breakdown of carbohydrates (starch)  disaccharides, trisaccharide, short-chain glucose polymers  monosaccharides Lingual lipase Dietary triglycerides  fatty acids and diglycerides. It’s activated in the acidic environment of the stomach and thus start to work after food is swallowed. Dr. Teresa Olivar 36 Deglutition The movement of food from the mouth into the stomach. It’s facilitated by the secretion of saliva and mucus and involves the mouth, pharynx, and esophagus. Dr. Teresa Olivar 37 Pharynx Three parts: the nasopharynx (functions only in respiration), the oropharynx and the laryngopharynx (both have digestive as well as respiratory functions). Swallowed food passes from the mouth into the oropharynx and laryngopharynx. The muscular contractions of these areas help propel food into the esophagus and then into the stomach. Dr. Teresa Olivar 38 Esophagus It is a collapsible muscular tube, about 25 cm long. It lies posterior to the trachea. It begins at the inferior end of the laryngopharynx. It pierces the diaphragm through an opening called the esophageal hiatus and ends in the superior portion of the stomach. The muscularis of the superior third of the esophagus is skeletal muscle, the intermediate third is skeletal and smooth muscle and the inferior third is smooth muscle. Dr. Teresa Olivar 39 Esophagus At each end of the esophagus, the muscularis forms two sphincters: the upper esophageal sphincter (UES)- skeletal muscle, and the lower esophageal sphincter (LES) – smooth muscle The UES regulates the movement of food from the pharynx into the esophagus. The LES regulates the movement of food from the esophagus into the stomach. Dr. Teresa Olivar 40 Deglutition The movement of food from the mouth into the stomach. It’s facilitated by the secretion of saliva and mucus and involves the mouth, phariynx, and esophagus. Three stages: The voluntary stage: The bolus is passed into the oropharynx. The involuntary stages: The pharyngeal stage: passage of the bolus through the pharynx into the esophagus. The esophageal stage: passage of the bolus through the esophagus into the stomach. Dr. Teresa Olivar 41 1. The bolus is forced to the back of the oral cavity and into the oropharynx by the tongue (voluntary stage) 2. The bolus stimulates receptors in the oropharynx, which send impulses to the deglutition centre. 3. The uvula moves upward to close off the nasopharynx. 4. The epiglottis closes off the opening to the larynx (protection of the respiratory tract) 5. The bolus moves through the oropharynx and the laryngopharynx. 42 Dr. Teresa Olivar 6. The UES relaxes and the bolus moves into the esophagus. 7. Peristalsis (progession of coordinated contractions and relaxations of the circular and longitudinal layers of the muscularis), pushes the bolus onward. 8. As the bolus approaches the end of the esophagus, the lower esophageal sphincter relaxes and the bolus moves into the stomach. Dr. Teresa Olivar 43 Dr. Teresa Olivar 44