Digestive System- Part I Ch. 23
Functions of the Digestive System 1. Take in food (ingestion) 2. Break down food into nutrient molecules (digestion) 3. Absorb molecules into blood (absorption) 4. Expel indigestible remains (defecation)
Digestive System: early observations • “Gastric experiments” starring: - Alexis St. Martin - the fistulated man - William Beaumont -“The Father of Gastric Physiology” • Experiments and Observations on the Gastric Juice, and the Physiology of Digestion published in 1838.
Cool facts about digestive system • Length of the GI tract: 9 m (30 ft), 6m of it the SI • Surface area: as large as a studio apartment!
Two main divisions 1. Alimentary Canal (GI tract) • Mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum 2. Accessory Organs • Teeth, tongue, salivary glands, gall bladder, liver, pancreas Pharynx
Mouth (oral cavity) Teeth Tongue Esophagus Liver Gallbladder Anus Duodenum Jejunum Ileum Small intestine Parotid gland Sublingual gland Submandibular gland Salivary glands Pharynx Stomach Pancreas (Spleen) Transverse colon Descending colon Ascending colon Cecum Sigmoid colon Rectum Vermiform appendix Anal canal Large intestine Gastrointestinal tract Accessory organs • Mechanically & chemically breakdown food • Connect to GI tract via ducts
Digestive System Processes 1. Ingestion – taking in solids & liquids via oral cavity 2. Propulsion – movement of food thru GI tract (24-36 hrs) a) Deglutition (swallowing) - to move from oral cavity to esophagus b) Peristalsis - wave-like alternation of contraction & relaxation of smooth muscles to move food thru GI tract 3. Mechanical digestion a) Mastication (chewing) – increases surface area & mixes food with saliva b) Churning – in stomach to mix food with gastric juices c) Segmentation – rhythmic constriction of small intestines to mix food and expose all surfaces for absorption
Digestive System Processes 4. Chemical digestion – enzymes to break down complex food molecules into their building blocks 5. Absorption – passage of digested food (+ vitamins, minerals, and water) from GI tract into blood and lymph (mostly occurs in small intestines) 6. Defecation – elimination of indigestible substances from body via feces
Food Ingestion Propulsion Esophagus Stomach Pharynx Mechanical digestion Chemical digestion • Chewing (mouth) • Churning (stomach) • Segmentation (small intestine) Small intestine Large intestine Defecation Anus Feces Blood vessel Lymph vessel Absorption • Swallowing (oropharynx) • Peristalsis (esophagus, stomach, small intestine, large intestine) Mainly H 2 O Peristaltic contraction moves food down Segmental contraction mixes food
Serous Membranes of Digestive System • Parietal peritoneum • Visceral peritoneum • Mesentery – double layer of serous membranes extending from body wall to digestive organs • Provides pathway for blood vessels, lymphatic vessels, & nerves • Holds organs in place • Stores fat • Omentum is an ex.
serosa muscularis externa submucosa mucosa muscularis externa submucosa mucosa adventitia
You've reached the end of your free preview.
Want to read all 56 pages?