Part 1: Overview of the Digestive System • Two main groups of organs: – Organs forming alimentary canal, also called gastrointestinal (GI) tract or gut ▪ Continuous muscular tube running from mouth to anus ( in cadaver, shorter in living body) ▪ Digests food into small fragments and absorbs them through mucosal lining into blood ▪ Organs: mouth, pharynx, esophagus, stomach, small and large intestine, anus – Accessory digestive organs ▪ Teeth, tongue, gallbladder ▪ Salivary glands, liver, pancreas – Use ducts to secrete digestive fluids into GI tract Alimentary Canal and Related Accessory Digestive Organs Figure 23.1 Alimentary canal and related accessory digestive organs. 23.1 What Major Processes Occur During Digestive System Activity? • Processing of food involves six essential activities: – Ingestion: eating – Propulsion: movement of food through the alimentary canal, includes: ▪ Swallowing: initiated voluntarily ▪ Peristalsis: primary means of propulsion, involves alternating (involuntary) waves of contraction and relaxation – Mechanical breakdown (formerly mechanical digestion): increases surface area of nutrients, prepares food for chemical digestion by enzymes; includes: ▪ Chewing, mixing food with saliva (via tongue), churning food in stomach, and segmentation (local contractions of SI that mix food with digestive fluids) – Digestion (formerly chemical digestion): catabolism via enzymes, breaking down large food molecules into absorbable chemical building blocks – Absorption: passage of nutrients from lumen of GI tract through mucosal epithelium into blood or lymph – Defecation: elimination of indigestible substances in the form of feces Peristalsis and Segmentation Figure 23.3 Peristalsis and segmentation.