Introduction to the Digestive System Dr. Munguti J.K

Outline The digestion process Divisions of the digestive system General structure of the hollow GIT Accessory GI glands

Digestive Processes Ingestion Propulsion Mechanical digestion Chemical digestion Absorption Defecation

Divisions: Alimentary canal Accessory Digestive Organs Continuous, muscular digestive tube winding throughout the body Digests and absorbs food particles Consists: Oral cavity, Pharynx, Esophagus, Stomach, Small and Large Intestines Accessory Digestive Organs Contains the following organs: Teeth, Tongue, Gallbladder, Salivary Glands, Liver, and Pancreas

General Structure Four basic layers: Mucosa Submucosa Lining epithelium Mucosal glands Lamina propria Muscularis mucosa Submucosa Muscularis externa Serosa/adventitia

Oral Cavity Two components Roof: Contains Oral cavity proper Vestibule Hard and soft palates Contains Tongue Teeth Accessory salivary glands

Tongue Roughened dorsal surface Functions Filiform papillae Foliate papillae Fungiform papillae Circumvallate papillae Functions Sensory organ Cleaning of the oral cavity Deglutition Help in mechanical digestion

Salivary Glands Main salivary glands Accessory salivary glands Parotid Submandibular Sublingual Accessory salivary glands Functions Moisten food Clean the oral cavity Chemical digestion Dissolve chemical substances Lubrication

Teeth Deciduous Permanent Incisors- cutting and shredding Canines- piercing and tearing Molars- grinding Premolars- grinding and crushing

Oesophagus Muscular tube Has regional constrictions/ blood supply Skeletal muscles (upper 1/3) Smooth muscle (lower 1/3) Has regional constrictions/ blood supply Regional changes in mucosal epithelium

Stomach Parts Greater and lesser curvatures Mucosal folds: rugae Cardiac Fundus Body Pylorus Greater and lesser curvatures Mucosal folds: rugae 3 – layered muscular layer Longitudinal Circular Oblique

Stomach Cells types? Functions Chemical digestion Physical digestion Temporary “storage” of food Disinfection Absorption of alcohol Production of intrinsic factor Production of hormones

Small Intestines Major site for digestion and absorption Cell types? Duodenum Jejunum Ileum Cell types? Receives the pancreatic juice And bile

Duodenum Four parts 25 – 30 cm long Secretes intestinal fluid Superior Descending Transverse Ascending 25 – 30 cm long Secretes intestinal fluid Receives the: CBD Pancreatic duct

Jejunum and Ileum Proximal 2/5 Left upper quadrant Larger diameter Thicker walled Less prominent arterial arcades Longer vasa recti More mesenteric fat Distal 3/5

Appendix Has lymphoid tissues in its walls Suspended by mesoappendix Varied location Retrocecal Retrocolic Pelvic Subcecal Preileal Postileal

Rectum Continuation of sigmoid colon 3 lateral flexures Rectosigmoint junction 3 lateral flexures Superior/ intermediate/ inferior Terminal segment – ampulla Lacks Taenia coli, Haustra Omental appendices

Anal Canal Extraperitoneal Demarcated from rectum by 3 – 5 cm long Anorectal ring/ flexure 3 – 5 cm long Contains the anal sphincters

Salivary Glands Main glands Accessory glands Produce saliva Parotid Submandibular Sublingual Accessory glands Produce saliva Functions

Liver and Gallbladder In the right hypogastrium & epigastrium Two main surfaces Diaphragmatic Visceral

Liver – Functions & Relations Secretory Excretory Energy metabolism Storage functions Immune?

Pancreas Mainly retroperitoneal Several parts Two components Head Uncinate process Neck Body Tail Two components Exocrine Endocrine

Review The digestion process Divisions of the digestive system General structure of the hollow GIT Accessory GI glands