Physiology H Digestive

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Introduction

• Provides processes to break down molecules into a state easily used by cells - A disassembly line: Starts at the mouth and ends Digestive System at the anus • Digestive functions are initiated by the parasympathetic division Chapter 29 - Digestion occurs during periods of low activity - Produces more energy than it uses

Anatomy The Digestive System

• Oral cavity • Pharynx • Esophagus • Stomach • Small intestine and large intestine • Accessory organs: Pancreas, liver, and gallbladder

From Herlihy B: The human body in health and illness, ed 4, St. Louis, 2011, Saunders.

Physiology Gastrointestinal Tract

• Ingestion: Taking materials into mouth by • Muscular tube throughout digestive system eating/drinking • Accessory organs and glands secrete • Digestion: Breaking down food into molecules substance to aid in digestion that can be used by the body • GI tract wall has four layers: - Includes mechanical and enzymatic action - Mucosa • Absorption: Simple molecules from the - Submucosa gastrointestinal (GI) tract move into the - Muscle layer: Responsible for peristalsis bloodstream or lymph vessels and then into - Serosa body cells • Defecation: Eliminating indigestible or unabsorbed material from the body Copyright © 2016 by Elsevier Inc. All rights reserved. 5 Copyright © 2016 by Elsevier Inc. All rights reserved. 6

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Peristalsis Oral Cavity

• First portion of GI tract • Contains: - Teeth - Tongue - Openings for salivary glands

From Thibodeau GA, Patton KT: Anatomy & physiology, ed 6, St. Louis, 2007, Mosby.

Oral Cavity Teeth

• Where food is chewed (masticated) with help • Used to bite off and break up larger pieces of of the teeth and tongue food into smaller ones • Chewed food becomes a soft mass of food • Adults: 32 secondary teeth (bolus) • Children: 20 primary teeth • Food is then swallowed and propelled toward - Usually shed between 6 and 12 years of age the stomach via peristalsis • Medical term for swallowing is deglutition

Teeth Tongue

• Classified according to shape and function • Large, strong muscle that: - Incisors - Mixes food with saliva - Cuspids: Canines - Directs bolus toward back of throat - Bicuspids: Premolars - Multicuspids: Molars • Third molars are called wisdom teeth

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Salivary Glands Salivary Gland Secretions

• Three pairs: • Saliva: Clear, watery fluid that keeps mucosa - Submandibular moist and lubricates food - Sublingual • Salivary amylase - Parotid - Digestive enzyme found in saliva • Largest - Breaks down carbohydrates • Lingual lipase - Breaks down lipids

Pharynx Esophagus

• Transports the bolus and liquids during • Muscular tube from pharynx to stomach swallowing • Secretes mucus to aid in transport of food • Passageway for digestive and respiratory • Contains two valves (sphincters) system - Upper esophageal sphincter: Keeps air from the stomach during breathing - Lower esophageal sphincter (LES): Trigger for relaxation is food travelling down esophagus and approaching the stomach

Stomach The Stomach

• J-shaped, saclike organ • Enlargement of GI tract bound at both ends by sphincters - Serves as an expandable food storage tank • Rugae: Folds in stomach lining that allow it to enlarge • Three regions: Fundus, body, and pylorus - Also contains a greater curvature and lesser curvature

From Herlihy B: The human body in health and illness, ed 4, St. Louis, 2011, Saunders.

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Stomach Stomach Secretions

• Gastric juice: Blend of enzymes and acids • Hydrochloric acid: - Eventually becomes chyme - Produced by parietal cells • Chyme passes through the pyloric sphincter - Breaks down protein and activates many gastric • Body maintains energy needs with only two enzymes or three meals per day • Instrinsic factor: - Produced by parietal cells

- Binds to B12; temporarily protected from deactivation

Small Intestine Small Intestine

• Coiled tube bound at both ends by sphincters • Villi - Pyloric sphincter: Where digestive materials enter - Fingerlike projections that house blood and lymph small intestine capillaries - Ileocecal sphincter: Where digestive materials • Lacteals leave small intestine - Blood vessels and lymphatic vessels contained in • Three sections: each villus - Duodenum: Contains ducts from liver, gallbladder, • Microvilli: Give the small intestine a brush and pancreas border - Jejunum: Continues from duodenum (7 to 8 feet) - Ileum: Longest section (about 12 feet)

Small Intestine Wall Absorption Sites

From Herlihy B: The human body in health and illness, ed 4, St. Louis, 2011, Saunders. Copyright © 2016 by Elsevier Inc. All rights reserved. 23 Copyright © 2016 by Elsevier Inc. All rights reserved. 24

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Large Intestine Large Intestine Sections

• Digestive materials enter and pass through • Cecum the ileocecal sphincter - Small saclike structure located in right lower • Three sections: quadrant - Vermiform appendix hangs from cecum - Cecum • Contains lymphatic tissue - Colon • Ascending colon: From cecum to hepatic - Rectum (right colic) flexure • Transverse colon: From hepatic flexure to splenic (left colic) flexure

Large Intestine Sections Large Intestine

• Descending colon - From splenic flexure to sigmoid flexure • Sigmoid colon - From sigmoid flexure to rectum • Rectum - Stores feces; terminal section is the anal canal • Anus: Contains anal sphincter

From Thibodeau GA, Patton KT: Anatomy & physiology, ed 6, St. Louis, 2007, Mosby.

Defecation Peritoneum

• Rectum fills with feces • Large serous membrane that envelops • Anal sphincter distends, causing defecation abdominal cavity reflex • Layers • Feces is eliminated - Parietal peritoneum: Lies against abdominal cavity - Feces = stool wall - Visceral peritoneum: Surrounds each abdominal organ • Peritoneal cavity lies between the two layers and contains serous fluid

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Mesenteries Peritoneum

• Mesenteries: Connect all divisions of small intestine to each other • Contain: - Greater omentum: From stomach and duodenum to transverse colon - Lesser omentum: From stomach and duodenum to the liver

From Thibodeau GA, Patton KT: Anatomy & physiology, ed 6, St. Louis, 2007, Mosby.

Accessory Organs Accessory Organs

• Consists of the: - Liver - Gallbladder - Pancreas • Produce substances that aid digestion

Liver Liver Functions

• Largest internal organ • Metabolizes carbohydrates, proteins, and fats • Lies beneath diaphragm • Produces blood cells during fetal • Most complex internal organ development • Performs many important functions • Produces plasma proteins and antibodies • Stores many nutrients • Detoxifies blood by removing toxic wastes, drugs, and hormones • Destroys old red blood cells and platelets • Produces bile

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Liver Secretions Gallbladder

• Bile • Pear-shaped sac that lies on inferior surface - Breaks apart large fat globules into smaller ones of the liver - This creates a larger surface area for fat-digesting • Stores and concentrates bile produced by enzymes liver - Gives urine and stool their colors • Rugae enable gallbladder to expand as it fills with bile - Gallbladder sometimes contracts and moves bile into duodenum

Pancreas Pancreas Secretions

• Shaped like a fish • Trypsinogen • Pancreatic duct runs length of pancreas and - Becomes trypsin when it enters duodenum empties into the duodenum • Chymotrypsin and carboxypeptidase • Secretes enzymes that break down all - Break down proteins categories of digestible foods • Pancreatic amylase - Converts polysaccharides into disaccharides • Pancreatic islets contain alpha and beta cells • - Secrete glucagon and insulin Pancreatic lipase helps convert fats into fatty acids

Pancreatic Cells

Modified from Patton KT: Anatomy & Physiology, ed 8, St. Louis, 2013, Mosby.