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Essentials of Human Anatomy & Physiology Chapter 38-2 The Digestive System Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Digestive Functions • Ingestion - active process, conscious choice • Mechanical processing - physical manipulation/distortion • Digestion - chemical breakdown of food into organic fragments • Secretion - release of water, acids, enzymes, buffers and salts • Absorption - movement of organic substrates, electrolytes, vitamins and water across the epithelium into the interstital fluid of the digestive tract • Excretion - elimination of waste products – defecation - eliminates feces – Urination - eliminates urine Alimentary Canal & Accessory Organs Gastrointestinal System • Function:physical and chemical breakdown of food • Includes alimentary canal: path of material flow • Accessory organs: salivary glands, tongue, teeth, liver, gallbladder, and pancreas Alimentary Canal & Accessory Organs Alimentary Canal Food Movement • Peristalsis • Segmentation - occurs in most areas of small intestine , some areas of large intestine – churning of contents to mix with secretions Alimentary Canal Oral Cavity • AKA – Buccal Cavity • Functions – – – – mechanical processing lubrication analysis limited digestion of carbohydrates & lipids Alimentary Canal • Mouth: physical and chemical breakdown. • Mastication-the act of chewing • Saliva contains enzyme amylase to break down carbohydrates Alimentary Canal Oral Cavity • Hard palate - palatine process of maxillary bone • Soft palate - posterior to hard palate – uvula- • Tongue - skeletal muscle • Salivary glands - 3 pair - each produces a slightly different type of saliva – Salivary amylase - parotid salivary glands breakdown complex carbohydrates into maltose Alimentary Canal Alimentary Canal Teeth • Deciduous teeth - baby teeth, milk teeth, primary teeth • Secondary dentition - permanent teeth – – – – Incisors Cuspids Bicuspids Molars Alimentary Canal Accessory Organs Alimentary Canal Pharynx and Esophagus • Pharynx - common passageway for food , liquids, and air • Esophagus - muscular tube to carry food and liquids to the stomach – Swallowing - deglutition • Bolus - oval shaped ball of food • Hiatal hernia - abdominal organs are pushed through the esophageal hiatus Alimentary Canal Alimentary Canal • Pharynx- contains opening to trachea as well. Epiglottis covers opening of trachea. • Esophagus:muscular tube dorsal to trachea • Relies on a rhythmic wave-like motion called peristalsis Alimentary Canal Alimentary Canal Esophagus- transverse view Alimentary Canal • Sphincter-a circular muscle that constricts a passage or closes a natural orifice (opening) • Cardiac sphincter • Pyloric sphincter • Food sits in stomach for 1-4 hours. Gastric juices contain hydrochloric acid- activates pepsin, kills bacteria. Alimentary Canal Stomach • Lined with simple columnar epithelium • Major functions– – – – Bulk storage Mechanical breakdown Use of acids and enzymes to break chemical bonds Production of the intrinsic factor - glycoprotein necessary for the absorption of vitamin B12 • Chyme - injested materials mixed with gastric juices Alimentary Canal Alimentary Canal Stomach • 4 Regions of the Stomach – – – – Cardia Fundus Body Pylorus • Pyloric sphincter • Rugae - ridges and folds • Muscles of the Stomach – Circular, longitudinal, oblique Digestive Enzymes • When chyme enters the duodenum, proteins & carbohydrates are only partly digested, & fat digestion needs to be carried out • Enzymes aid in digestive breakdown & absorption of chyme _____________________________________________________________ Bile Salts (Liver & Gallbladder) Pancreatic & Salivary Amylase (Pancreas & Mouth) Fat Fat Droplets Starch + H2O Maltose Bile is a thick digestive fluid secreted by the liver and stored in gallbladder. Facilitates digestion by emulsifying fats into fatty acids, which can be absorbed by the digestive tract Trypsin & Pepsin (Pancreas) Protein + H2O Peptides Lipase (Pancreas) Fat Droplets + H2O Glycerol + Fatty Acids Peptidases (Intestinal Juice) Peptides + H2O Amino Acids Maltase (Intestinal Juice) Maltose + H2O Glucose Alimentary Canal Alimentary Canal Small Intestine • 80%-90% of absorption • Duodenum - closest to the stomach • Jejunum - most of chemical digestion and nutrient absorption occurs here • Ileum – Ileocecal valve - controls flow into large intestine Alimentary Canal • Small intestine: not so small! 20 feet x 1 inch • Duodenum- 1st 10 inches. bile and pancreatic juice enter • Jejunum- next 8 ft. • Ileum- final 12 ft. When food leaves small intestine, digestion is complete Alimentary Canal Alimentary Canal Alimentary Canal Small Intestine Wall • • • • Picae - transverse folds Villi - finger like projections Microvilli - cover each villi Lacteal - terminal lymph - located in each villi – Chylomicrons - protein-lipid packages • to large to enter blood capillaries • travel through lymph system • Intestinal juice- moistens chyme, buffers acids Alimentary Canal Alimentary Canal Accessory Organs • Liver- largest gland in your body • Secretes bile- emulsifies fat, makes them water soluble. • Stores glucose in the form of glycogen • Makes clotting proteins • Detoxifies blood Accessory Organs Liver • Metabolic regulation – Extract absorbed nutrients or toxins – Monitor and adjust circulating levels of organic nutrients – Fat soluble vitamins A,D,E,K are absorbed and stored • Hematological regulation – one of the largest blood reservoir in the body – Synthesize plasma proteins • Bile production - synthesized from cholesterol – Normal digestion and absorption of fats Accessory Organs Liver • Double Blood Supply – Hepatic artery - oxygenated blood – Hepatic portal vein - deoxygenated blood • carries newly absorbed nutrients Accessory Organs Accessory Organs Gall Bladder • Gallbladder– Storage area for bile – Modification of bile • Emulsification - bile salts (assortment of lipids) break apart, large droplets of lipids, then coat them to make it easier for enzymes to attack • Gallstones - stored bile becomes concentrated Gall Stones Accessory Organs • Gall bladder- stores and concentrates bile • Pancreas- produces insulin, pancreatic juices amylase and lipase. Insulin regulates the uptake of glucose by the cells Accessory Organs Pancreas • The Pancreas- endocrine/exocrine organ – Pancreatic islets • Alpha cells • Beta cells – Acinar cells - secrete pancreatic proenzymes Accessory Organs Alimentary Canal Large Intestine • Large Intestine Functions: – Reabsorption of water – Compaction of feces – Absorption of vitamins – Storing of fecal material Alimentary Canal • Large intestine5 feet x 2 inches. Separated from small intestine by ileocecal valve • Final absorption of water, storage of indigestible material, absorption of vitamins B and K by bacteria. • Colon connects to rectumanal canal opens to the anus Fecal material is expelled. Alimentary Canal Large Intestine • Haustra – pouches, giving bubbled appearance • Cecum- from small intestine – Ileocecal valve – Vermiform appendix • Colon – – – – Ascending - up Transverse- across Descending –down Sigmoid-end • Rectum • Anus Alimentary Canal Alimentary Canal Alimentary Canal & Accessory Organs