Digestive System PDF

Dr. Rhoel  The digestive system is continually at work, yet people seldom appreciate the complex tasks it performs in a choreographed biological symphony Consider what happens when you eat an apple. Of course, you enjoy the apple’s taste as you chew it, but in the following hours, yo...

Dr. Rhoel  The digestive system is continually at work, yet people seldom appreciate the complex tasks it performs in a choreographed biological symphony Consider what happens when you eat an apple. Of course, you enjoy the apple’s taste as you chew it, but in the following hours, you don’t notice that your digestive system is working unless something goes amiss and you get a stomachache. You may be taking a walk or studying or sleeping, having forgotten all about the apple, and yet your stomach and intestines are busy digesting it and absorbing its vitamins and other nutrients. By the time any waste material is excreted, the body has appropriated all it can use from the apple. In short, whether you pay attention or not, the organs of the digestive system perform their specific functions, allowing you to use the food you eat to keep you going. The human digestive tract is a long, coiled, muscular tube that stretches from the mouth to the anus. From the mouth to the anus, the human food tube or the digestive tract is about nine meters long.  Two phases of digestion: Mechanical phase – involves the breaking up of food into small pieces, pushing the food down the food tube, and mixing with it digestive juices Chemical phase – involves the further breaking up of the larger molecules of food into smaller molecules by the action of digestive enzymes Lips Muscularstructures, formed mostly by the Orbicularis Oris Muscle The Keratinized Stratified Epithelium of the skin becomes thin at the margin of the lips  Oral Cavity From Lips – Pharynx Responsible for the initial phase of digestion and absorption Primarily carbohydrates, specifically starch due to the presence of salivary amylase Waldeyer’s Ring Vermillion border – Transitional line/junction between mucous membrane of lips and skin Oral Vestibule Oral Cavity Proper Oral Cavity Tongue A mass of striated muscle covered by mucosa Majorsensory organ for taste and one of the major organs of speech Keratinized dorsal surface Non-keratinized ventral Surface  Tongue Papillae & Taste Receptors Most numerous; Cone Shaped Only Papillae WITHOUT Taste FILIFORM PAPILLAE Buds Avascular Tip and Sides of the Tongue FUNGIFORM PAPILLAE Mushroom or Fungus Shape Lightly keratinized Found Postero-Laterally of the FOLIATE PAPILLAE Tongue Parallel Ridges Found in V-shape @ Terminal Sulcus Largest CIRCUMVALLATE PAPILLAE Least Numerous Serous Minor Salivary Gland – Von Ebner’s Gland  Tongue Papillae & Taste Receptors Most numerous; Cone Shaped Only Papillae WITHOUT Taste FILIFORM PAPILLAE Buds Avascular Tip and Sides of the Tongue FUNGIFORM PAPILLAE Mushroom or Fungus Shape Lightly keratinized Found Postero-Laterally of the FOLIATE PAPILLAE Tongue Parallel Ridges Found in V-shape @ Terminal Sulcus Largest CIRCUMVALLATE PAPILLAE Least Numerous Serous Minor Salivary Gland – Von Ebner’s Gland  Tongue Papillae & Taste Receptors Most numerous; Cone Shaped Only Papillae WITHOUT Taste FILIFORM PAPILLAE Buds Avascular Tip and Sides of the Tongue FUNGIFORM PAPILLAE Mushroom or Fungus Shape Lightly keratinized Found Postero-Laterally of the FOLIATE PAPILLAE Tongue Parallel Ridges Found in V-shape @ Terminal Sulcus Largest CIRCUMVALLATE PAPILLAE Least Numerous Serous Minor Salivary Gland – Von Ebner’s Gland  Esophagus It is a muscular tube, about 25cm long in adults Mucosa has non-keratinized stratified squamous epithelium, and the submucosa contains small mucus-secreting glands, the esophageal glands, which lubricate and protect the mucosa Upper & Lower (Cardiac) Esophageal Sphincter  Regulate the movement of materials into and out of the esophagus Upper 1/3 = Skeletal Muscles Middle 2/3 = Both Skeletal and Smooth Muscles Lower 3/3 = Smooth Muscles Deglutition – Act of swallowing – Most common in the Peristalsis Esophagus; Long movements of the Chyme Chyme – Food mixed with Saliva Segmentation – Most common in intestines; short movements of chyme; chops chyme CardiacSphincter – Terminal end of the Esophagus; Z-line  Stomach J-shaped organ Storage of food Lined by Simple Columnar Epithelium 2nd phase of Digestion with Micro-Villi (+) Rugae – longitudinal folds Cells Secretion Function Surface Mucous Cell Mucous (Alkaline) Primarily lines the Gastric Mucosa “Foveolar Cells” Mucous Neck Cells Mucous (Acid) Protection to Acid  Gastric Acid / Hydrochloric Acid  Digestion and Activation of  Gastroferrin – Binding site of Iron Parietal or Oxyntic Cells Pepsinogen  Intrinsic Factor – Important for Vit.  Absorption of Vit. B12 B12 Inactive form of Pepsin (Digests Chief Cells Pepsinogen Proteins) G-Cell Gastrin – Goes to Parietal Cells Production of Gastric Acid “Enteroendocrine Cell”  Liver Albumin Synthesis  Helps keep fluid from leaking out of your blood vessels into other tissues  Osmotic Pressure Bile Production  Emulsification / Breakdown Fats  Carry away waste Cholesterol Metabolism Detoxification of Drug & Alcohol Excretion Factors for Clotting Glycogen Storage Hormone production  Betatrophin – Regulate metabolism by increasing insulin production via an increase in β cell mass  Angiotensinogen – Inactive form of Angiotensin  Thrombopoietin – A glycoprotein hormone produced by the liver and kidney which regulates the production of platelets  Heparin – an Anti-Coagulant  Hepatocytes Liver  Most Versatile Cell (Flexible) Parts of the Liver:  Functional Unit of the Liver 2 Major Lobes  Protein Synthesis & Detoxification of Right Toxins Left  Drug (Microsomal Cytochrome P450) 2 Minor Lobes & Alcohol Metabolism Caudate (Tail)  Lipid Synthesis Quadrate  Bile Production Porta (Hilum) Hepatic Duct (Right & Left) Kupffer Cells Hepatic Portal Vein  Macrophage Hepatic Artery Ito Cells “HSC” / “Perisinusoidal”  Adipocytes in the Space of Disse; Store Vit. A  Hepatocytes Liver  Most Versatile Cell (Flexible) Parts of the Liver:  Functional Unit of the Liver 2 Major Lobes  Protein Synthesis & Detoxification of Right Toxins Left  Drug (Microsomal Cytochrome P450) 2 Minor Lobes & Alcohol Metabolism Caudate (Tail)  Lipid Synthesis Quadrate  Bile Production Porta (Hilum) Hepatic Duct (Right & Left) Kupffer Cells Hepatic Portal Vein  Macrophage Hepatic Artery Ito Cells “HSC” / “Perisinusoidal”  Adipocytes in the Space of Disse; Store Vit. A  Gallbladder Lined by Simple Columnar Epithelium with Microvilli Stores & Concentrates Bile Common Bile Duct formed by:  Cystic Duct (from Gallbladder)  Hepatic Duct (from Liver) Common Bile Duct empties into the duodenum. Rokitansky-Aschoff Sinuses  Deep Diverticula of the Gallbladder Mucosa The Gallbladder does not contain a submucosa (the stomach, small, and large intestines do!) Glands of Luschka – Developmental abnormality; microscopic small bile ducts found in the subhepatic or subserosal connective tissue. Gallbladder  Pancreas Lobulated Gland  Head (Exocrine)  Body  Tail Ducts:  Wirsung (Main Pancreatic Duct)  Santorini (Accessory Pancreatic Duct) Exocrine Part:  Produces digestive Enzyme Precursors = Proenzyme  Components: Pancreatic Acini  Cell type: Centroacinar Cells Sphincter of Oddi  Small Intestine Site where the Digestive Processes are completed and where nutrients are absorbed 3 Segments:  Duodenum – Brunner’s Gland in Submucosal Layer = Secretes Alkaline Mucus  Jejunum  Ileum Its lining shows a series of permanent circular or semilunar folds (Plicae Circulares) (+) Villi Cell Types in the Small Intestine:  Enterocytes  Goblet Cells  Paneth Cells (Immune Cells) – secretes Lysozyme = Digests bacterial cell wall  Enteroendocrine Cells (APUD) - @ Crypts of Lieberkühn “Intestinal Gland”  M (Microfolds) Cells Small Intestine  Large Intestine “Bowel” Absorbs water & electrolytes Forms indigestible material into feces Parts:  Cecum  Colon (Ascending, Transverse, Descending)  Rectum Colonocytes – Columnar Absorptive Cells Teniae Coli – 3 Longitudinal Bands of muscle used for peristalsis Haustra – Individual segments that allow for independent contraction  General Structure The GI tract is a hollow tube with a lumen of variable diameter and a wall made up of 4 main layers: Mucosa Submucosa Muscularis Serosa  Mucosa (Mucous Membrane) Consist of viz: An epithelial lining; An underlying lamina propria of loose connective tissue Thin layer of smooth muscle “Muscularis Mucosae”  Submucosa Contains denser connective Tissue with larger blood and Lymph Vessels and the Submucosal Plexus “Meissner Plexus” of ANS Brunner’s Gland (+) in Duodenum  Muscularis (Muscularis Externa) Composed of smooth muscle cells organized as 2 or more sub-layers Internal Sublayer (Closer to the Lumen), the fiber orientation is generally circular External sublayer is longitudinal Myenteric Plexus “Auerbach’s Plexus” = Contractions for Peristalsis  Serosa Thin layer of loose connective tissue, rich in blood vessels, lymphatics, and adipose tissue, with Mesothelium  simple squamous covering epithelium Inthe abdominal cavity, the serosa is continuous with mesenteries covered by mesothelium on both sides that support the intestines  Serosa Thin layer of loose connective tissue, rich in blood vessels, lymphatics, and adipose tissue, with Mesothelium  simple squamous covering epithelium Inthe abdominal cavity, the serosa is continuous with mesenteries covered by mesothelium on both sides that support the intestines  Divided by Segments: Foregut i. Esophagus ii. Stomach iii. 1st part of the Duodenum iv. Biliary System (Liver, Gallbladder, Pancreas)  Celiac Trunk = Blood Supply Midgut v. 2nd – 4th part of the Duodenum, vi. Jejunum vii. Ileum viii. Appendix ix. Ascending Colon x. Transverse colon (Proximal 2/3) to Splenic Flexure  Superior Mesenteric = Blood Supply  Divided by Segments: Foregut i. Esophagus ii. Stomach iii. 1st part of the Duodenum iv. Biliary System (Liver, Gallbladder, Pancreas)  Celiac Trunk = Blood Supply Midgut v. 2nd – 4th part of the Duodenum, vi. Jejunum vii. Ileum viii. Appendix ix. Ascending Colon x. Transverse colon (Proximal 2/3) to Splenic Flexure  Superior Mesenteric = Blood Supply  Divided by Segments: Hindgut xi. Transverse Colon (Distal 1/3) xii. Descending Colon xiii. Sigmoid Colon xiv. Rectum Inferior Mesenteric = Blood Supply