Digestive System PPT PDF

Digestive System __________ Ms. Daisy R. Sucaldito CASE – Biology Department  Topic Learning Outcomes List the major functions of the digestive system. Describe the general histology of the digestive tract. Describe the parts and the major functions of each of the p...

Digestive System __________ Ms. Daisy R. Sucaldito CASE – Biology Department  Topic Learning Outcomes List the major functions of the digestive system. Describe the general histology of the digestive tract. Describe the parts and the major functions of each of the parts of the digestive tract. Describe the anatomy, physiology, histology and ducts of the liver and pancreas. Describe the digestion, absorption and transport of carbohydrates, lipids, and proteins. Discuss water movement into and out of the digestive tract. Describe the effects of aging on the digestive system. Digestion and the Digestive System Digestion is the breakdown of large organic molecules into smaller molecules that can be absorbed. The digestive system performs the task of digestion. Food is taken into the digestive system, where it is enzymatically broken down into smaller and smaller particles for absorption.  Digestive System Functions 1. Ingestion of and mastication solids and liquids. 2. Propulsion and mixing. 3. Digestion and secretion. 4. Absorption 5. Elimination Digestive System  Digestive System The digestive system consists of the digestive tract, plus specific associated organs. The digestive tract is also referred to as the GI (gastrointestinal tract). The tract is one long tube from the mouth to the anus.  Digestive Tract Components Oral cavity (mouth) Pharynx Esophagus Stomach Small intestines Large intestines Rectum Anus  Associated Organs The digestive system includes some associated organs not directly in the digestive tract but have ducts that lead into the tract. These associated organs are the: Salivary glands Liver Gallbladder Pancreas Digestive System  Layers of Digestive Tract Wall The layers of the tract wall are also termed tunics. 1. Mucosa – innermost layer; secretes mucus. 2. Submucosa – above mucosa; contains blood vessels, nerves, small glands. 3. Muscularis – above submucosa; longitudinal, circular, and oblique muscles 4. Serosa/adventitia – outermost layer When covered with peritoneum, it is called serosa. Regions of digestive tract not covered by peritoneum is called adventitia. Digestive Tract Histology Peritoneum – layer of smooth epithelial tissue. (serous membranes: visceral and parietal peritoneum) Mesenteries – connective tissue of organs in abdominal cavity. Specific Mesenteries: Lesser Omentum – mesentery connecting lesser curvature of stomach to liver and diaphragm. Greater Omentum – mesentery connecting greater curvature of stomach to transverse colon and posterior body wall. Peritoneum and Mesenteries  Oral Cavity First part of digestive system. Contains stratified squamous epithelia. Salivary glands – produce saliva which contains enzymes to breakdown carbohydrates into glucose. - Cleanse mouth. - Dissolve and moisten food.  Oral Cavity Amylase – salivary enzyme that breaks down carbohydrates. Lysozyme – salivary enzymes that are active against bacteria. Tongue – house taste buds and mucus. Oral Cavity  Teeth 32 teeth in normal adult. Incisors, canine, premolars, molars, wisdom. 20 primary teeth (baby teeth).  Teeth Each tooth has crown, cusp, neck, root. Center of tooth is pulp cavity. Enamel is hard covering protects against abrasions. Cavities are breakdown of enamel by acids from bacteria. Molar Tooth in Place in the Alveolar Bone  Palate Palate roof of oral cavity Two (2) Parts: Hard Palate - anterior part Soft Palate - posterior part  Salivary Glands Salivary Glands Includes parotid, submandibular, and sublingual. They produce saliva (a mixture of serous and mucous fluids) containing enzymes to breakdown food. *Parotid glands (beside the ear) are serous glands and the largest gland among all the 3 *Submandibular glands produce more serous than mucus secretions. *Sublingual glands is the smallest among all 3 and produce primarily mucous secretions. Mumps is inflammation of parotid gland. Salivary Glands  Secretions of Oral Cavity Saliva is secreted approximately 0.5L to 1.5L per day. Salivary amylase – a starch-splitting enzymes; and other polysaccharides to produce disaccharides maltose and isomaltose (sweet taste). Humans, however, lack the necessary enzymes to digest cellulose. Mastication – food taken into the mouth are chewed and masticated by teeth breaking large food particles into many small ones.  Pharynx Throat Connects the mouth to the esophagus. It has three parts: Nasopharynx Oropharynx Laryngopharynx  Esophagus Tube that connects the pharynx to the stomach. Transports food to the stomach. Heartburn Occurs when gastric juices regurgitate into esophagus. Caused by caffeine, smoking, or eating or drinking in excess.  Swallowing Voluntary Phase Bolus (mass of food) formed in mouth and pushed into oropharynx. Pharyngeal Phase Swallowing reflex initiated when bolus stimulates receptors in oropharynx. Esophageal Phase Moves food from pharynx to stomach. Peristalsis Wave-like contractions moves food through digestive tract. Peristalsis  Stomach Located in abdomen. Storage tank for food. Can hold up to 2 liters of food. Produces mucus, hydrochloric acid, protein digesting enzymes. Contains a thick mucus layer that lubricates and protects epithelial cells on stomach wall from acidic pH (3).  Stomach 3 Muscular Layers Outer longitudinal, middle circular, and inner oblique to produce churning action. Rugae Large folds that allow stomach to stretch. Chyme Paste-like substance that forms when food begins to be broken down.  Stomach Pyloric Opening opening between stomach and small intestine. Pyloric Sphincter thick, ring of smooth muscle around pyloric opening. Hunger Pangs stomach is stimulated to contract by low blood glucose levels usually 12-24 hours after a meal. Anatomy and Histology of the Stomach (c) ©Victor Eroschenko  Secretions of the Stomach As food enters the stomach, it is mixed & become a semifluid mixture called chyme. Stomach secretions from the gastric glands include mucus (by mucous neck cells), HCl and intrinsic factor (by parietal cells) , pepsinogen (by chief cells), and gastrin (by stomach; a hormone responsible for the regulation of secretions in stomach). A thick layer of mucus lubricates and protects the epithelial cells of the stomach wall from the damaging effect of the acidic chyme and pepsin. Hydrochloric acid produces a pH of about 2.0 in the stomach.  Secretions of the Stomach Pepsinogen is secreted by the stomach wall and is converted by HCL to activate the enzyme pepsin which breaks the peptide covalent bonds of proteins. Low pH kill microorganisms. Intrinsic factor bind with vitamin B12 (important in the synthesis of DNA and red blood cell production) and makes it more readily absorbed in the small intestine. Gastrin is a hormone that helps regulate the stomach secretions. Regulation of Stomach Secretions Three (3) Phases: Cephalic Phase 1st phase Stomach secretions are initiated by sight, smell, taste, or food thought. Regulation of Stomach Secretions Gastric phase 2nd phase Partially digested proteins and distention of stomach promote secretion. Intestinal phase: 3rd phase Acidic chyme stimulates neuronal reflexes and secretions of hormones that inhibit gastric secretions by negative feedback loops.  Movement in the Stomach Mixing Waves Weak contraction Thoroughly mix food to form chyme. Peristaltic Waves Stronger contraction Force chyme toward and through pyloric sphincter. Hormonal and neural mechanisms stimulate stomach secretions. Stomach empties every 4 hours after regular meal, and 6 to 8 hours after high fatty meal. Movement in the Stomach  Small Intestine Measures 6 meters in length. Major absorptive organ. Chyme takes 3 to 5 hours to pass through. Contains enzymes to further breakdown food. Contains secretions for protection against the acidity of chyme.  Parts of Small Intestine Duodenum first part ; 25 cm long Contains absorptive cells, goblet cells, granular cells, endocrine cells. Contains microvilli and many folds. Contains bile and pancreatic ducts. Jejunum second part ; 2.5 meters long and absorbs nutrients. Ileum third part ; 3.5 meters long. Small Intestine  Mucosa of the Small Intestine The mucosa of the small intestine is simple columnar epithelium with four major cell types. 1. Absorptive cells, which have microvilli, produce digestive enzymes, and absorb digested food. 2. Goblet cells, which produce a protective mucus. 3. Granular cells, which may help protect the intestinal epithelium from bacteria; and 4. Endocrine cells, which produce regulatory hormones.  Mucosa of the Small Intestine The epithelial cells are located within tubular glands of the mucosa, called intestinal glands or crypts of Lieberkühn, at the base of the villi. Granular and endocrine cells are located in the bottom of the glands. The submucosa of the duodenum contains mucous glands, called duodenal glands, which open into the base of the intestinal glands. Anatomy and Histology of the Duodenum (d) ©Steve Gschmeissner/Science Source RF Secretions of the Small Intestine Secretions of small intestine mainly contain mucus, ions, and water. The epithelial cells in the walls of the small intestine have enzymes bound to their free surfaces. Peptidases enzymatically breakdown proteins into amino acids for absorption. Disaccharidases enzymatically breakdown disaccharides into monosaccharides for absorption. Movement in the Small Intestine Mixing and propulsion of chyme are the primary mechanical events that occur in the small intestine. Peristaltic contractions proceed along the length of the intestine for variable distances and cause the chyme to move along the small intestine. Segmental contractions are propagated for only short distances and mix intestinal contents. Movement in the Small Intestine The ileocecal sphincter at the juncture of the ileum and the large intestine remains mildly contracted most of the time. Peristaltic contractions reaching the ileocecal sphincter from the small intestine cause the sphincter to relax and allow chyme to move from the small intestine into the cecum. The ileocecal valve prevents movement from the large intestine back into the ileum. Segmental Contractions in the Small Intestine Liver Anatomy  Liver Ducts Hepatic Duct Transport bile out of liver. Common Hepatic Duct Formed from left and right hepatic duct. Cystic Duct Joins common hepatic duct. From gallbladder. Common Bile Duct Formed from common hepatic duct and cystic duct. Bile and Pancreatic Secretions  Functions of the Liver Digestive and excretory functions. Stores and processes nutrients. Detoxifies harmful chemicals. Synthesizes new molecules. Secretes 700 milliliters of bile each day. Bile dilutes and neutralizes stomach acid and breaks down fats. Control of Bile Secretion and Release  Pancreas Located posterior to stomach in inferior part of left upper quadrant. Head near midline of body. Tail extends to left and touches spleen. Endocrine tissues have pancreatic islets that produce insulin and glucagon. Insulin – protein hormone that increases the uptake of glucose and AA by most tissues. Glucagon – acts primarily on the liver to release glucose into the circulatory system. Exocrine tissues produce digestive enzymes that travel through ducts.  Pancreatic Secretions The major protein-digesting enzymes are: 1. Trypsin 2. Chymotrypsin 3. Carboxypeptidase  Pancreatic Secretions Pancreatic amylase continues the polysaccharide digestion that began in the oral cavity. The pancreatic enzyme lipase is a lipid- digesting enzyme. The pancreatic nuclease enzymes degrade DNA and RNA to their component nucleotides. Duodenum and Pancreas Control of Pancreatic Secretions  Large Intestine Function is to absorb water from indigestible food. Contains cecum, colon, rectum, anal canal. Cecum Joins small intestine at ileocecal junction. Has appendix attached which is a 9 cm structure that is often removed.  Large Intestine Colon 1.5 meters long ; contains ascending, transverse, descending, sigmoid regions. Rectum Straight tube that begins at sigmoid and ends at anal canal. Anal Canal last 2 to 3 cm of digestive tract.  Food takes 18-24 hours to pass through. Feces is product of water, indigestible food, and microbes. Microbes synthesize vitamin K. Large Intestine (b) ©CNRI/SPL/Science Source  Note: The following slides and/or the remaining few subtopics are for your independent study.  Digestive Process 1. Digestion – breakdown of food occurs in stomach and mouth. 2. Propulsion – moves food through digestive tract includes swallowing and peristalsis. 3. Absorption – primarily in duodenum and jejunum of small intestine. 4. Defecation – elimination of waste in the form of feces. Digestion Digestion of Carbohydrates, Lipids, and Proteins  Carbohydrate Digestion Polysaccharides split into disaccharides by salivary and pancreatic amylases Disaccharides are broken down into monosaccharides by disaccharidases on the surface of intestinal epithelium Glucose is absorbed by cotransport with Na+ into the intestinal epithelium Glucose is carried by the hepatic portal vein to the liver and enters most cells by facilitated diffusion. Transport of Glucose Across the Intestinal Epithelium  Lipid Digestion Lipase breaks down triglycerides into fatty acids and monoglycerides. Bile salts surround fatty acids and monoglycerides to form micelles. Micelles attach to the plasma membranes of intestinal epithelial cells, and the fatty acids and monoglycerides pass by simple diffusion into the intestinal epithelial cells.  Lipid Digestion Within the intestinal epithelial cell, the fatty acids and monoglycerides are converted to triglycerides. Proteins coat the triglycerides to form chylomicrons, which move out of the intestinal epithelial cells by exocytosis. The chylomicrons enter the lacteals of the intestinal villi and are carried through the lymphatic system to the blood. Transport of Lipids Across the Intestinal Epithelium  Lipoproteins Lipids are packaged into lipoproteins to allow transport in the lymph and blood. Lipoproteins are molecules that are partly water soluble and partly lipid soluble. Since lymph and blood contain water and lipids are not water soluble, lipoproteins are necessary for transport. Lipoproteins include chylomicrons, low-density lipoproteins (LDL), and high-density lipoproteins (HDL). Lipoproteins  Protein Digestion Pepsin is a protein-digesting enzyme secreted by the stomach. The pancreas secretes trypsin, chymotrypsin, and carboxypeptidase into the small intestine in an inactive state. In the small intestines these enzymes are activated.  Protein Digestion In the small intestine, other enzymes termed peptidases, bound to the microvilli of the intestinal epithelium further break down small peptides into tripeptides. Absorption of tripeptides, dipeptides, or individual amino acids occurs through the intestinal epithelial cells by various cotransport mechanisms. Transport of Amino Acids Across the Intestinal Epithelium  Water and Minerals Water can move across the intestinal wall in either direction. The movement depends on osmotic pressures. 99% of water entering intestine is absorbed. Minerals are actively transported across wall of small intestine. Fluid Volumes in the Digestive Tract QUESTIONS? THANK YOU!