Anatomy and Physiology with Integrated Study Guide Third Edition
advertisement
Chapter 15 Lecture Slides Digestive System Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Nutrients are required for normal body function Carbohydrates, proteins, lipids, vitamins, minerals Derived from food Food we eat is too big to be directly passed into blood Goals of digestive system Digest food into smaller molecules Absorb smaller molecules into the blood Digestive system consists of: Alimentary canal Long tube food passes through Accessory organs 15.1 Digestion: An Overview Digestion involves Mechanical digestion Physical breakdown of food into smaller pieces Forms a greater surface area for contact with digestive enzymes Chemical Splitting digestion of complex, non-absorbable food molecules into small, absorbable nutrient molecules by hydrolysis Enzymes speed up the reaction and enables digestion to occur 15.2 Alimentary Canal: General Characteristics Muscular tube about 9m in length Extends from mouth to the anus Portions are specialized to perform different digestive functions Lumen is the hollow space within the canal in which food moves Alimentary Canal • • • • • • Mouth Pharynx Esophagus Stomach Small intestine Large intestine Structures of the Wall Serosa Outermost layer Formed of visceral peritoneum, continuous with parietal peritoneum Secretes serous fluid onto the outer surface of the canal Muscular layer Under the serosa Two layers of smooth muscle that differ in fiber orientation Purposes: Mix food with digestive secretions Move food along the canal Submucosa Between muscular layer and mucosa Has nerves, lymphatic vessels, blood vessels, loose connective tissue Mucosa Surface of highly folded, simple columnar epithelium Functions of epithelium Secrete digestive enzymes and mucus Folds increase surface area of canal Movements Smooth muscle layers produce two types of movement Mixing movements (segmentation) Alternating rhythmic contractions in short segments of the tube Mix food with secretions Peristalsis Propels food along the canal Circular muscle fibers produce ring-like constrictions that move along tube in wavelike manner 15.3 Mouth Functions Intake of food Mechanical breaking food into small pieces Mixing it with saliva Swallowing it Surrounded by cheeks, palate, and tongue Cheeks Lateral walls of the mouth Lips Surrounds mouth opening Forms anterior surface Palate Separates the oral cavity from the nasal cavity Hard palate Anterior portion supported by bone Soft palate Posterior portion lacking bony support Uvula on posterior edge is sensitive to touch stimuli Assists with swallowing and gag reflex Tongue Floor of oral cavity Lingual frenulum Limits Papillae Give posterior movement of the tongue rough texture to tongue that aids in food manipulation Taste buds Other tongue functions Moves food during chewing Mixes food with saliva Pushes food into pharynx Teeth Accessory structures involved in mastication (chewing) Humans form two sets of teeth Deciduous First set of teeth, “baby teeth” Permanent teeth teeth Second set of teeth, adult teeth 32 permanent teeth total form Four types of permanent teeth Incisors Biting off food Cuspids Grasp and tear food Bicuspids & Molars Both bicuspids and molars crush and grind food Tooth anatomy Crown Portion above gingiva Root Embedded in socket in alveolar bone of jaw Attachment of root to jaw Cementum Periodontal membrane Composition of a tooth Dentin Bulk of tooth Bone-like Enamel Hardest substance of the body Resists abrasion caused by chewing Pulp cavity Central portion Blood vessels, and nerves enter cavity through root canal Salivary Glands Secrete saliva into the mouth Activated by the presence of food in the mouth or thoughts of food Functions Bind food particles Dissolve food Cleanse and lubricate mouth Start carbohydrate digestion Aid in the sense of taste Salivary Glands Parotid glands In front of each ear over masseter muscle Submandibular Located in floor of mouth Sublingual Located glands glands in floor of mouth under tongue Saliva composition 99.5% water Helps dissolve substances Mucus Binds food during chewing and swallowing Salivary amylase Enzyme that speeds digestion of starch and glycogen into maltose Lysozyme Enzyme that kills certain bacteria Digestion in the Mouth Mechanical digestion Mastication Increases surface area of food particles Mixes food with saliva Chemical Digestion digestion of starch and glycogen into maltase by salivary amylase 15.4 Pharynx and Esophagus Pharynx Passageway connecting nasal and oral cavities with esophagus and larynx Transports food from mouth to esophagus during swallowing Esophagus Muscular tube extending from pharynx to stomach Uses peristalsis to move food into the stomach Esophageal mucosa produces mucus for lubrication and ease in food passage Lower esophageal sphincter Guards junction of stomach and esophagus Constricted to prevent regurgitation of stomach contents Opens only to allow food into the stomach 15.5 Stomach J-shaped pouch Lies in the upper left abdominal quadrant Basic functions of Stomach Temporary food storage Mixing food with gastric juice Starting protein digestion Structure Subdivisions Cardia Fundus Body Pylorus Pyloric sphincter At junction of stomach and duodenum Constricted to close stomach outlet Relaxes to allow food pass into duodenum Stomach is lined by a thick mucus membrane Stomach is organized into rugae Allow mucosa to stretch as stomach fills with food Mucosa contains gastric glands that open at gastric pits Gastric Juice Secretion of the gastric glands Cells near opening secrete mucus Protects mucosa from actions of digestive secretions Chief cells At bottom of glands Secrete digestive enzymes Parietal cells At mid-portion of glands Secrete hydrochloric acid Gastric juice converts food into chyme Released sphincter intermittently into the duodenum by pyloric Control Gastric of Gastric Secretion juice is produced continuously Secretion increases when food is on its way to or in the stomach Includes sight, smell,or thought of food; food in mouth, food in stomach Parasympathetic impulses increase with food stimuli Directly stimulate gastric glands increase secretion Cause stomach cells to produce gastrin hormone Hormone secretion also stimulates gastric gland Parasympathetic impulses decrease in frequency as stomach empties Decreases gastric juice secretion Intestinal mucosa secretes two hormones in response to chyme Cholecystokinin Secretin Both help decrease gastric juice secretion Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer. Digestion and Absorption Hydrocholiric acid (pH 2) Activates enzyme pepsin Denatures proteins, inhibits most bacterial growth Pepsin Breaks proteins into smaller peptides Rennin, an infant enzyme Curdles milk proteins Keeps it in stomach longer Makes proteins more easily digested Intrinsic factor Essential for absorption of vitamin B12 Stomach absorbs water, minerals, some drugs, alcohol 15.6 Pancreas Posterior Digestive to pyloric portion of stomach function (exocrine function) is to secrete pancreatic juice Juice collected by pancreatic duct Pancreatic duct joins the common bile duct, which enters the duodenum Hepatopancreatic sphincter regulates entrance into duodenum Control of Pancreatic Secretion Neural control Parasympathetic impulses stimulate pancreas to secrete pancreatic juice Hormonal control Secretin Released by intestines in response to acid chyme Causes pancreas to produce juice rich in carbonates Neutralize acidity of chyme Cholecystokinin Secreted by intestines in response to fat-laden chyme Stimulates secretions rich in digestive enzymes Digestion by Pancreatic Enzymes Pancreatic amylase Breaks starch and glycogen into maltose Pancreatic lipase Breaks fats into monoglycerides and fatty acids These molecules are absorbable Trypsin Breaks proteins into peptides Activated by intestinal secretions 15.7 Liver Largest gland in the body at 1.4 kg Located in upper right quadrant, protected by ribs Dark, reddish brown color Liver functions Secretion of bile Role in carbohydrate digestion Role in lipid digestion Role in protein digestion Detoxifies poisons and harmful chemicals Removes worn out blood cells Stores fat, glycogen, iron, and several vitamins Synthesis of blood proteins Nutrient inter-converstion Liver is divides into four lobes Liver blood supply Hepatic artery Brings oxygenated blood Hepatic portal vein Brings deoxygenated blood from digestive tract Hepatic vein drains blood into inferior vena cava Bile is collected into the hepatic duct Hepatic duct and cystic duct from gallbladder form the common bile duct Common bile duct carries bile to the duodenum Gallbladder Stores bile between meals Bile Yellowish, green liquid Consists of water, bile salts, bile pigments, cholesterol, minerals Bilirubin is break down product of hemoglobin Bile salts emulsify lipids in chyme Increases surface area of lipid molecules so it could be easily dissolved by enzymes and absorbed into the intestines Release of Bile When intestine is empty, hepatopancreatic sphincter is closed Forces bile into gallbladder In response to fat in chyme, CCK Causes the gallbladder to contract Relaxes hepatopancreatic sphincter 15.8 Small Intestine 2.5cm wide, 6.4m long Begins at the pyloric sphincter and ends at the large intestine Site of most digestion and absorption of nutrients Structure Three segments Duodenum First and shortest section Jejunum Middle section Ileum Last and longest section Suspended by mesentery from body wall Mucosa has numerous intestinal villi Provide a very large surface area Villus anatomy Covered in simple columnar epithelium Have a centrally located lacteal for fat absorption Have a blood capillary network Intestinal glands Secrete mucus and intestinal juice Microvilli further increase the surface area Folds in epithelial cell plasma membranes Intestinal Juice Slightly alkaline with abundant water and mucus Forms appropriate environment for actions of bile salts and pancreatic digestive enzymes Regulation of Intestinal Secretion Mechanical stimulation due to presence of chyme Activates secretion of intestinal juice and enzymes Neural reflex due to intestinal wall stretch Parasympathetic secretions impulses increase the rate of intestinal Digestion and Absorption General events Vigorous contractions mix chyme with bile, pancreatic juice, and intestinal juice Emulsification of fats occurs Digestion of carbohydrates, proteins, and lipids occur due to pancreatic and intestinal enzymes Absorption of nutrients into the blood stream Intestinal enzymes are used to complete the process of digestion Digestion of disaccharides to monosaccharides Maltase Maltose to glucose Sucrase Sucrose to glucose and fructose Lactase Lactose to glucose and galactose Digestion of fats and proteins Intestinal Fats lipase into monoglycerides and fatty acids Peptidase Peptides into amino acids Absorption of carbohydrates Simple sugars (glucose, fructose, galactose) occurs primarily by active transport Absorption of fats Monoglycerides and fatty acids diffuse into epithelial cells Molecules recombine into fats molecules Chylomicrons form Fat molecules, cholesterol, and phospholipids coated in protein Move from epithelial cells and into lacteals Enter the left subclavian vein with lymph Very small fatty acids enter the villi directly without being recombined Absorption of proteins Amino Other absorbed materials Water, acids are actively absorbed into villi capillaries minerals, and vitamins enter villi capillaries Blood leaving intestines flows to the liver via the hepatic portal vein Absorbed materials are processed before blood enters general circulation 15.9 Large Intestine Ileocecal valve regulates movement of chyme from small intestine into large intestine Structure 6.5cm wide, 1.5m long Consists of three segments Cecum Pouch below ileocecal valve Appendix Colon Ascending colon Transverse colon Descending colon Sigmoid colon Rectum Last portion is anal canal with the anus Stores feces Tenia coli, 3 longitudinal bands of muscle, run length of colon Form haustra Large intestine is supported by mesentery Mucosa possesses no villi Epithelium contains numerous goblet cells Produces no digestive enzymes Bacteria decompose non-digested food residues Yield B vitamins and vitamin K Produce flatus Mucosa produces large amounts of mucus Lubrication and protection against abrasion Main function of large intestine is absorption of water, minerals, and vitamins End product is feces Large amounts of bacteria, mucus, water, and nondigested food residues Movements Mixing and propelling movements are sluggish Undergo mass peristalsis 2-4 times per day Usually after a meal Defecation reflex Rectum fills with feces and stretches Stretching triggers contractions that increase pressure If Opens internal anal sphincter (involuntary muscle) external anal sphincter (voluntary muscle) is relaxed, defecation occurs If external anal sphincter stays contracted, defecation is postponed Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer.
