Digestive Lecture 1 PDF

Anatomy & Physiology FT 400/PT700  Chapter 24 DIGESTIVE SYSTEM Part 1 Lecture Outline Functions of the digestive tract Overview of the major organs of the digestive system Layers of the GI tract...

Anatomy & Physiology FT 400/PT700  Chapter 24 DIGESTIVE SYSTEM Part 1 Lecture Outline Functions of the digestive tract Overview of the major organs of the digestive system Layers of the GI tract The peritoneum Neural innervation of the GI tract The GI tract: oral cavity, pharynx, the esophagus Dr. Kevin Tipper, ND Digestive System Anatomy Consists of: 1. Gastrointestinal (GI) Tract muscular tube also called digestive tract or alimentary canal Food passes along length from mouth to anus 2. Accessory organs produce or store secretions that flow into GI tract through ducts © 2018 Pearson Education, Inc. Functions of the Digestive Tract Ingestion Occurs when solid food and liquid enter the oral cavity Mechanical digestion and propulsion Involves crushing and shredding of food in the oral cavity and mixing and churning in the stomach Chemical digestion Chemical and enzymatic breakdown of food into small organic molecules that can be absorbed by the digestive epithelium Secretion The release of water, acids, enzymes, buffers, and salts by the digestive tract epithelium and by accessory digestive organs Absorption Movement of nutrients across the digestive epithelium and into the bloodstream Defecation Indigestible food is compacted into material waste called feces, which are eliminated by defecation © 2018 Pearson Education, Inc. Functions of the Digestive Tract Mechanical Digestion Includes all movements that help digestion: Mastication (chewing) Swallowing Mixing Peristalsis Muscular contractions in the wall of the GI tract physically break down food by churning it and propelling it along the tract and also help dissolve foods by mixing them with fluids secreted into the GI tract Functions of the Digestive Tract Chemical Digestion Enzymes secreted by accessory organs and cells that line the tract break down the food chemically Mainly accomplished by using water to break down chemical bonds (hydrolysis) Fats are broken down into fatty acids and glycerol Carbohydrates are broken down into monosaccharides Proteins are broken down into amino acids Digestive Tract Overview Description and major organs Muscular tube about 10 m (33 ft) long begins with the mouth and ends with the anus Major organs and their functions: Oral cavity (mouth) Mechanical processing (with the teeth and tongue), moistening, mixing with salivary secretions Pharynx Muscular propulsion of food into the esophagus Esophagus Transport of materials to the stomach © 2018 Pearson Education, Inc. Digestive Tract Overview Major organs and their functions continued: Stomach Chemical breakdown and mechanical processing Small intestine Enzymatic digestion and absorption Large intestine Dehydration and compaction of indigestible materials Accessory Organs Overview Accessory digestive organs Salivary glands Produce saliva containing mucins and enzymes Gallbladder Stores and concentrates bile secreted by the liver Pancreas Exocrine cells secrete buffers and digestive enzymes Endocrine cells secrete several hormones Liver Almost 200 known functions © 2018 Pearson Education, Inc. Layers of the GI Tract Four major layers of the digestive tract Samebasic layers from esophagus to anal canal The layers are: 1. Mucosa 2. ​Submucosa 3. Muscular Layer 4. Serosa or adventitia © 2018 Pearson Education, Inc. Layers of the GI Tract Mucosa (inner lining), 3 components 1. Epithelium Epithelium in the mouth, pharynx, esophagus, and anal canal is nonkeratinized, stratified squamous epithelium (for PROTECTION) Epithelium in stomach and intestines is simple columnar epithelium (for SECRETION and ABSORPTION) 2. Lamina propria areolar connective tissue with blood and lymphatic vessels and mucosa- associated lymphatic tissue (MALT) MALT contains immune cells that protect against disease 3. Muscularis mucosae thin layer of smooth muscle making folds to increase surface area specifically in the stomach and the small intestine © 2018 Pearson Education, Inc. Layers of the GI Tract Submucosa Layer of dense irregular connective tissue Contains blood vessels and lymphatic vessels Also contains exocrine glands in some regions Secrete buffers and enzymes into the digestive tract Has a network of neurons called submucosal (Meissner’s) plexus © 2018 Pearson Education, Inc. Layers of the GI Tract Muscular layer Smooth muscle in two layers inner circular layer outer longitudinal layer Involved in mechanical processing and movement along tract Another network of neurons exists here called the myenteric (Auerbach’s) plexus; between muscle layers © 2018 Pearson Education, Inc. Layers of the GI Tract Serosa Outermost covering of organs along the digestive tract in the abdominal cavity Also called the visceral peritoneum along the digestive tract in the abdominal cavity No serosa in oral cavity, pharynx, esophagus, and rectum Covered instead by adventitia (sheath formed from a dense network of collagen fibers) Firmly attaches tract to adjacent structures © 2018 Pearson Education, Inc. Peritoneum Largest serous membrane of the body Divided into Parietal peritoneum Lines the inner surface of the peritoneal cavity Visceral peritoneum covers organs enclosed by the peritoneal cavity also called serosa Space between is peritoneal cavity and contains lubricating serous fluid Peritoneum Serous membrane Continuously secretes peritoneal fluid into peritoneal cavity ~7 liters/day secreted and reabsorbed Volume at any one time is about 50 mL Thin layer separates parietal and visceral surfaces Allows sliding movements without friction or irritation Rate of fluid moving into the cavity is accelerated by liver disease, kidney disease, and heart failure Accumulation of peritoneal fluid can create abdominal swelling (ascites) Peritoneum Some organs are considered retroperitoneal which means the peritoneum only covers their anterior surface (kidneys, ascending and descending colon, duodenum, pancreas, ureters) 3 major peritoneal folds in the peritoneum 1. mesentery 2. omenta 3. falciform ligaments Peritoneal Folds: Mesentery Mesentery Double sheets of peritoneal membrane Areolar tissue lies between mesothelial layers Provides access route for blood vessels, nerves, and lymphatics Stabilizes attached organs Prevents entanglement of intestines Includes the mesocolon © 2018 Pearson Education, Inc. mesentery of the colon Peritoneal Folds: Mesentery Mesentery Peritoneal Folds: Mesentery Mesentery Peritoneal Folds: Omenta There are two omenta in the body, they are continuations of the mesentery: 1. Greater omentum 2. Lesser omentum Greater omentum (omentum, fat) Attached to stomach and transverse colon Forms a large pouch extending inferiorly between anterior body wall and anterior surface of the small intestine Contains adipose tissue that provides padding and protection Also contains blood vessels and lymphatic tissue Peritoneal Folds: Omenta Lesseromentum (omentum, fat) Suspends the stomach and duodenum from the liver Provides an access route for blood vessels and other structures entering/leaving the liver hepatic portal vein hepatic artery common bile duct Peritoneal Folds: Falciform Ligament Falciform ligament Connects the liver to the anterior body wall The liver is the only digestive organ that is attached to the ANTERIOR abdominal wall Remnant of part of the umbilical vein Peritoneal Folds Peritoneal Folds Peritoneal Folds This dissection video has a pretty good view of the greater omentum and the organs of the peritoneal cavity Peritoneal Folds This dissection video has a pretty good view of the mesentery Review: Layers of the GI Tract Neural Innervation of the GI Tract Nerve plexuses Involved in local control of digestive activities Parasympathetic stimulation increases digestive muscle tone and activity Sympathetic stimulation decreases muscle tone and activity 2 major nerve plexuses: 1. Submucosal neural plexus (Meissner’s) 2. Myenteric plexus (Auerbach’s) Submucosal (Meissner’s) neural plexus Located in the submucosal layer Innervates the mucosa and submucosa Contains sensory neurons, autonomic nerve fibers Neural Innervation of the GI Tract Nerve plexuses (continued) Myenteric (Auerbach’s) plexus (mys, muscle + enteron, intestine) Network of sensory neurons and autonomic nerve fibers Located in the muscularis externa between the circular and longitudinal layers Works with the submucosal plexus to coordinate local control of digestive activity Neural Innervation of the GI Tract Enteric Nervous System (ENS) The submucosal and myenteric plexuses make up the ENS Intrinsic set of nerves: the “brain of the gut” Neurons extending from esophagus to anus Quasi autonomous, meaning it can act on it’s own with some input from the autonomic nervous system Neural Innervation of the GI Tract Autonomic Nervous System (ANS) Extrinsic set of nerves Vagus nerve (CN X) supplies parasympathetic fibres to most of the GI tract EXCEPT the last 1/2 of the large intestine which is supplied from the sacral spinal cord Parasympathetic stimulation will increase secretion and motility by increasing activity of ENS neurons Sympathetic nerve supply arises from thoracic and lumbar region of the spinal cord stimulation decreases secretions and activity by inhibiting ENS The Oral Cavity space that contains the tongue, teeth, and gums Lined by oral mucosa (stratified squamous epithelium) Keratinized in areas that are exposed to severe abrasion (superior tongue surface, hard palate) Thin, nonkeratinized lining on cheeks, lips, and inferior tongue surface Thin mucosa inferior to the tongue allows for rapid absorption of lipid-soluble drugs (example: nitroglycerin) Little to no nutrients are absorbed here Digestion of carbohydrates and lipids begins here The Oral Cavity Oral cavity boundaries Superior boundary Hard palate Formed by the palatine processes of the maxillary bones and horizontal plates of the palatine bones Soft palate Muscular region posterior to the hard palate The Oral Cavity Oral cavity boundaries (continued) Anterior and lateral boundary Cheeks Form the lateral walls of the oral cavity Supported by pads of fat and the buccinator muscles Anteriorly, cheek mucosa is continuous with the labia Labia (lips) Form anterior boundary Inferior boundary Body of the tongue Anterior, mobile portion The Oral Cavity Oral cavity boundaries (continued) Posterior boundary Uvula Dangling process extending from the soft palate Helps prevent food from entering pharynx prematurely Swings upward during swallowing to prevent food from entering the nasopharynx Palatine tonsils (one located on either side of the oropharynx) Root of tongue Fixed portion projecting into the oropharynx Marked by a V-shaped line of vallate papillae Lingual tonsils (located in the root of the tongue) The Oral Cavity Oral vestibule The space between the cheeks (or lips) and teeth Frenulum of the upper lip (frenulum, a small bridle) Attaches gums to upper lip Thick mucosa with ridges covering the hard palate Provides traction for compression of food by the tongue Frenulum of the lower lip Attaches gums to lower lip The Oral Cavity Gingivae (gums) Ridges of oral mucosa surrounding the base of each tooth Firmly attached to the periostea of the underlying bone Palatal arches Located on either side of the uvula Palatoglossal arch Extends between soft palate and base of tongue Palatopharyngeal arch Extends from soft palate to pharyngeal wall The Oral Cavity Tongue Accessory digestive organ Skeletal muscle covered by mucous membrane Has extrinsic muscles that move the tongue side to side and in and out to maneuver food for chewing and forcing food to the back of the mouth for swallowing Intrinsic muscles originate in and insert into connective tissue within the tongue Dorsum and lateral surfaces are covered with papillae which contain taste buds and some receptors for touch The Oral Cavity Tongue Surface flushed by secretions of small glands Secretions contain water, mucins, and lingual lipase (an enzyme that starts the digestion of lipids) Attached to the floor of the mouth by the frenulum of the tongue (lingual frenulum) The Oral Cavity Salivary Glands Salivary glands release saliva into the oral cavity Ordinarily, just enough is secreted to keep mouth and pharynx moist and clean When food enters mouth, secretion increases to lubricate, dissolve and begins the chemical digestion of food 3 pairs of major salivary glands secrete most of the saliva 1. Parotid glands 2. Submandibular glands 3. Sublingual glands The Oral Cavity Salivary Glands Parotid Glands: Lie inferior to the zygomatic arch, deep to the skin, covering the mandible secretes saliva via parotid duct that pierces buccinator muscle Produce serous secretion containing large amounts of salivary amylase Provide ~25 percent of total saliva secretion The Oral Cavity Salivary Glands Sublingual Glands: Located beneath the tongue sublingual ducts open into the floor of the mouth Produce a mucous secretion that acts as a buffer and lubricant Provide ~5 percent of total saliva secretion The Oral Cavity Salivary Glands Submandibular Glands: Located medial and inferior to the body of the mandible and the submandibular ducts enter the oral cavity lateral to the lingual frenulum Secrete a mixture of buffers, mucins, salivary amylase Amylase is an enzyme that breaks down starches Cells transport IgA antibodies into the saliva Provides protection against pathogens Provide ~70 percent of total saliva secretion The Oral Cavity Saliva Mostly water 99.5% 0.5% solutes – ions (sodium, potassium, chloride, bicarbonate and phosphate), dissolved gases, urea, uric acid, mucous, immunoglobulin A, lysozyme, and salivary amylase (acts on starch) Salivary glands produce 1.0–1.5 L of saliva each day Functions Constantly flushes oral surfaces Buffers keep pH of mouth near 7.0 and prevent buildup of acids produced by bacteria Contains antibodies (IgA) and lysozyme to help control oral bacteria populations Mixes with food to form a bolus to be easily swallowed Small glands called Ebner’s glands secrete lingual lipase The Oral Cavity Salivation Controlled by autonomic nervous system Parasympathetic stimulation promotes secretion of moderate amount of saliva Sympathetic stimulation decreases salivation The taste and smell of food are potent stimulators of salivary gland secretions (“cephalic phase” of digestion) Teeth Teeth or dentes Accessory digestive organ Dentin forms the majority of the tooth and is harder than bone Covered by enamel, which is even harder 2 dentitions deciduous or primary teeth “baby teeth” permanent or secondary teeth Teeth Components of a tooth in different regions of the jaws vary in size, shape, and function The bulk of each tooth is composed of dentin Mineralized matrix similar to bone but contains no cells Pulp cavity The interior chamber of the tooth Teeth Components of a tooth Occlusal surface Portion of the crown used for crushing, slicing, or chewing Enamel Covers the dentin of the crown Hardest biologically manufactured substance Composed of calcium phosphate Requires calcium, phosphate, and vitamin D for formation and resistance to decay Teeth Components of a tooth Periodontal ligament Creates gomphosis articulation between root dentin and alveolar bone Root canal Narrow tunnel within the root of the tooth Passageway for blood vessels and nerves to the pulp cavity Opening into the root canal is the apical foramen Teeth Regions of a tooth Crown Portion projecting into the oral cavity from the surface of the gums Neck The boundary between the crown and root Root Portion below the gum line Sits in a bony tooth socket called an alveolus Digestion in the Mouth Themouth is the first place where digestion begins, both mechanical and chemical Mechanical digestion in the mouth Chewing or mastication Food is manipulated by tongue, ground by teeth, and mixed with saliva Forms a soft, flexible mass called bolus Digestion in the Mouth Chemical digestion in the mouth Salivary amylase secreted by salivary glands and acts on starches Only monosaccharides can be absorbed into bloodstream Continues to act until inactivated by stomach acid Lingual lipase secreted by lingual glands of tongue acts on triglycerides Active in the mouth, but becomes even more activated in acidic environment of stomach Acts to breakdown dietary triglycerides into fatty acids and diglycerides Pharynx Membrane-lined cavity posterior to the nose and mouth (throat) Skeletal muscle walls of the pharynx play a key role in swallowing (along with esophagus) Continuous with the esophagus Common passageway for solid food, liquids, and air Three regions 1. Nasopharynx (respiration only) 2. Oropharynx 3. Laryngopharynx The Esophagus Function Actively moves food and liquids to the stomach No enzymes produced here, no absorption Structure Hollow, muscular tube ~25 cm (10 in.) long and 2 cm (0.8 in.) wide Narrowest point at the beginning (posterior to cricoid cartilage) Descends posterior to the trachea Enters the abdominopelvic cavity through the esophageal hiatus (opening in the diaphragm) Hiatal hernia: occurs when part of the stomach protrudes above the diaphragm through the esophageal hiatus The Esophagus Histology of the Esophagus Mucosa nonkeratinized stratified squamous epithelium for protection Mucosa and submucosa form large folds extending the length of the esophagus Allow for expansion with passage of a bolus Submucosa Contains areolar connective tissue, blood vessels, and mucous glands Muscularis externa Superior third is composed of skeletal muscle Middle third is a mix of skeletal and smooth muscle Inferior third is composed of smooth muscle only No serosa Adventitia of connective tissue anchors esophagus to posterior body wall The Esophagus Control of movement Upper esophageal sphincter Band of smooth muscle that functions as sphincter Prevents air from entering the esophagus Lower esophageal sphincter (cardiac sphincter) At the inferior end of the esophagus Normally contracted (prevents backflow of stomach contents) The Esophagus Swallowing or Deglutition Initiated voluntarily but proceeds automatically Facilitated by secretions of saliva and mucus Involves mouth, pharynx, and esophagus Three phases of swallowing 1. Buccal Phase 2. Pharyngeal Phase 3. Esophageal Phase 4. ​Buccal phase (or voluntary phase) Begins with compression of bolus against hard palate Tongue forces bolus into the oropharynx Also elevates soft palate (sealing off nasopharynx) Entry into the oropharynx triggers reflex response Swallowing or Deglutition Three phases of swallowing (continued) ​ 2. Pharyngeal phase Begins with stimulation of tactile receptors in uvula and palatine arches Motor commands from the swallowing center (in medulla oblongata) coordinate muscle contraction in pharyngeal muscles Larynx is elevated; epiglottis is folded; uvula and soft palate are elevated Bolus is moved through the pharynx into the esophagus Swallowing or Deglutition Three phases of swallowing (continued) 3. ​Esophageal phase Begins as bolus is forced through the entrance to the esophagus Bolus is pushed toward the stomach by peristalsis Approach of bolus triggers the opening of the lower esophageal sphincter Bolus enters the stomach Typical travel time is 9 seconds Liquids may travel faster A dry (poorly lubricated) bolus may require secondary peristaltic waves Peristalsis Smooth muscle contractions produce motility of the digestive tract Peristalsis Wave of muscle contraction Food enters the digestive tract as a bolus Moist, compact mass of material Bolus is propelled along the tract by contractions of the muscularis externa (peristalsis) Circular muscles contract behind bolus Longitudinal muscles ahead of bolus contract Process repeats GI PATHOLOGY Periodontal Disease Most common cause for loss of teeth Occurs when dental plaque forms between gums and teeth Resulting bacterial activity may cause: Gingivitis (inflammation of the gums) Tooth decay Eventual breakdown of periodontal ligaments and surrounding bone Link to cardiovascular disease? Inflammation and atherosclerosis REVIEW QUESTIONS What are the components of the GI tract?  Continuoustube extending from the mouth to the anus includes: Mouth Esophagus Stomach small and large intestine  What are some accessory digestive organs?  Teeth Tongue salivary glands Liver Gallbladder pancreas  Which is the most innermost layer of the GI tract?  Mucosa (which is surrounded by submucosa, muscularis, and serosa)  Parasympathetic stimulation of the ANS will have what effect on digestion? Will cause an increase in the motility and in GI secretions to the GI tract  What is the first enzyme that will act on carbohydrates in the body? Where does this begin acting? Salivary Amylase In the mouth  Where does lingual lipase come from and what does it act on?  It is secreted by the lingual glands (specifically von Ebner’s glands) in the tongue. Acts to breakdown fats. Is there anything that is secreted in the esophagus? NO! It is a muscular tube that passes bolus along to the stomach (arguably, mucus)