Chapter 15: Digestive System PDF

Human Anatomy and Physiology with Pathophysiology CHAPTER 15: DIGESTIVE SYSTEM OUTLINE 4. Stomach I. Functions of the Digestive System 5. Small intestine II. Anatomy and Histology of the Digest...

Human Anatomy and Physiology with Pathophysiology CHAPTER 15: DIGESTIVE SYSTEM OUTLINE 4. Stomach I. Functions of the Digestive System 5. Small intestine II. Anatomy and Histology of the Digestive System 6. Large intestine III. Oral Cavity, Pharynx, and Esophagus 7. Rectum IV. Stomach 8. Anus V. Small Intestine VI. Liver and Pancreas VII. Large Intestine Accessory organs: VIII. Digestion, Absorption, and Transport A. Carbohydrates Salivary Glands -secrete amylase B. Lipids Liver -produces bile C. Proteins Gallbladder -secretes bile D. Water and Minerals Pancreas -produce lipase IX. Effects of Aging on the Digestive System X. Diseases Four Major Tunics/Layers I. FUNCTIONS OF THE DIGESTIVE SYSTEM 1. Mucosa -secretes mucus; inner tunic consists of three 1. Ingestion layers: 2. Digestion mucous epithelium 3. Absorption loose connective tissue (lamina propria) 4. Elimination thin outer layer of smooth muscle (muscularis mucosae) 2. Submucosa -thick layer of loose connective tissue II. ANATOMY AND HISTOLOGY OF THE DIGESTIVE SYSTEM containing nerves, blood vessels, and small glands; plexus 3. Muscularis -consists of: Digestive tract -aka gastrointestinal tract; series of hollow organs through which food passes inner layer of circular smooth muscle outer layer of longitudinal smooth muscle sometimes has oblique middle layer (stomach) 4. Serosa (adventitia) -most superficial layer; adventitia -no peritoneum; composed of connective tissue serosa -consists of the peritoneum, which is a smooth epithelial layer Order of food passage: 1. Oral cavity (mouth) 2. Pharynx (throat) 3. Esophagus @medtech.files | by MAPB Chapter 15: Digestive System Peritoneum Oral cavity -aka mouth; beginning of the one-way digestive tract; stratified squamous epithelia Lips -muscular structures formed by the orbicularis oris Cheek -forms the lateral walls and is made of buccinator (flatten the cheeks against the teeth) Tongue -large, muscular organ that occupies most of the oral cavity Frenulum -thin fold of tissue anchoring the underside of the tongue to the floor of the mouth 4 types of lingual papillae: Filiform papillae -conical shape contain fingerlike projections; do not contain taste buds; lined by stratified squamous cornified epithelium Fungiform papillae -mushroom shape; constricted base and expanded surface; found mostly at the tip of the Peritoneum -serous membrane that forms the lining of tongue; contain taste buds; lined by stratified squamous the abdominal cavity non cornified epithelium o Parietal peritoneum -lines the wall of abdominal Foliate papillae -leaflike papillae with ridges and cavity rudimentary in man o Visceral peritoneum -covers the organs Circumvallate papillae -large dome shaped; largest of the Mesenteries -connective tissue, holding organs in lingual papillae; contain taste buds abdominal cavity o Lesser omentum -mesentery connecting the lesser curvature of the stomach to the liver and diaphragm Teeth o Greater omentum -mesentery connecting the greater curvature of the stomach to the transverse colon and posterior body wall; abdominal policeman ‣ omental bursa -a cavity, or pocket formed by greater omentum retroperitoneal -behind peritoneum; other abdominal organs that have no mesenteries III. ORAL CAVITY, PHARYNX, AND ESOPHAGUS A. Anatomy of Oral Cavity Permanent teeth or secondary teeth: 32 teeth Deciduous/ Milk / Primary teeth: 20 teeth Central incisor -central cutting Lateral incisor -lateral cutting Canine -tearing food First and second premolars -tearing and cutting; each with 2 cusps or points 1st – 3rd molars -for grinding; with 3 cusps @medtech.files | by MAPB Chapter 15: Digestive System Three regions: Sublingual glands -smallest pair and produce primarily mucous secretions 1. Crown -superior portion; with one or more cusps 2. Neck -narrow portion Mumps -inflammation of parotid glands 3. Root -largest region of the tooth and anchors it in the jawbone B. Saliva Pulp -central space between tooth ‑ a versatile fluid; a mixture of serous (watery) and mucous Dentin -a living, cellular, calcified tissue that surrounds the fluids pulp ‑ keep the oral cavity moist and contains enzymes that Enamel -hard nonliving mineralized substance that covers begin the process of digestion dentin Cementum -helps anchor the tooth in the jaw Salivary amylase -salivary enzyme that breaks down Gingiva -epithelial covering of alveolar ridges carbohydrates/starch Periodontal ligaments -secure the teeth in the alveoli by Lysozyme -salivary enzymes that are active against embedding into the cementum bacteria Dental caries -or tooth decay; result of the breakdown of Mucin -a proteoglycan that gives a lubricating quality to enamel by acids produced by bacteria on the tooth surface the secretions of the salivary glands Periodontal disease -inflammation and degeneration of the periodontal ligaments, gingiva, and alveolar bone C. Pharynx Palate and Tonsils ‑ aka throat; connects mouth to esophagus ‑ 3 parts: Palate -roof of oral cavity Nasopharynx o Hard palate -anterior part contains bone o Soft palate -posterior portion consists of skeletal Oropharynx muscle and connective tissue Laryngopharynx ‣ uvula -posterior extension of the soft palate ‑ posterior walls of oropharynx and laryngopharynx are Tonsils -located in the lateral posterior walls of the oral formed by pharyngeal constrictor muscle cavity, in the nasopharynx, and in the posterior surface of the tongue D. Esophagus ‑ long muscular tube connecting the pharynx to the Salivary Glands stomach ‑ exocrine glands with ducts that empty into the mouth ‑ 25 cm long; transport food to stomach ‑ produce saliva contains enzymes to breakdown food ‑ joins stomach at cardiac opening ‑ stratified squamous non keratinized Upper esophageal sphincter and lower esophageal sphincter -opens and closes to allow passage of food Submucosa -deep esophageal glands T. Muscularis: o upper 1/3 skeletal muscle o middle 1/3 smooth and skeletal muscle o lower 1/3 smooth muscle E. Swallowing Parotid glands -largest pair, anterior to each ear; flows ‑ or deglutition thru the parotid duct ‑ divided into three phases: voluntary, pharyngeal, and Submandibular glands -medial to the angle of the esophageal phase mandible which produces mostly serous fluids empties into the floor of the mouth @medtech.files | by MAPB Chapter 15: Digestive System 3 phases: 5 Groups of Epithelial Cells 1. Voluntary Phase - bolus (mass of food) formed in mouth Surface Mucous Cells -goblet cells which secrete alkaline and pushed into oropharynx mucus to protect itself from acid 2. Pharyngeal Phase - swallowing reflex initiated when bolus Mucous neck cells -goblet cells that secretes acidic fluid stimulates receptors in oropharynx Parietal cells -very pale cells which produce HCl and 3. Esophageal Phase - moves food from pharynx to stomach intrinsic factor (for digestion of vitamin B12) Peristalsis -wave-like contractions moves food through Chief cells -darker staining cells which produce digestive tract pepsinogen, a precursor hormone for pepsin – w/c digests proteins Endocrine cells -produce regulatory chemicals IV. STOMACH G cells -secrete gastrin which triggers HCl production in parietal cells A. Anatomy of the Stomach Stomach Enlarged portion of the digestive tract inferior to the diaphragm at the end of the esophagus Located in abdomen Storage tank and mixing chamber for food Can hold up to 2 liters of food Produces mucus, hydrochloric acid, protein digesting enzymes Contains a thick mucus layer that lubricates and protects epithelial cells on stomach wall form acidic pH (3) Lined by simple columnar epithelium B. Secretions of the Stomach Chyme -paste-like substance that forms when food begins to be broken down; semifluid mixture; food + stomach secretions HCl -produces a pH of about 2.0; kills microorganism Pepsin -active form of pepsinogen; breaks down protein 3 muscular layers: outer longitudinal, middle circular, and Mucus -forms a thick layer; lubricates the the epithelial inner oblique to produce churning action cells Cardiac opening -aka lower esophageal sphincter; cardiac Intrinsic factor -binds to Vitamin B12 region-opening from the esophagus into the stomach region Heartburn -or gastritis; painful or burning sensation in the Body -greater curvature and lesser curvature chest; occurs when gastric juices regurgitate into esophagus; Pyloric opening -opening between stomach and small caused by caffeine, smoking, or eating or drinking in excess intestine Pyloric sphincter -thick, ring of smooth muscle around pyloric opening Fluid Source Function Rugae -large folds of the mucosa that allow stomach to Mouth stretch Saliva (water, Salivary Moistens and lubricates Fundus -upper part of stomach bicarbonate ions, glands food, neutralizes Gastric pits -opening of gastric glands; tubelike found in mucus) bacterial acids, flushes mucosal surface bacteria from oral cavity Salivary amylase Salivary Digests starch glands @medtech.files | by MAPB Chapter 15: Digestive System  Lysozyme Salivary Has weak antibacterial Secretin -released from the duodenum in response to low pH glands action Stomach Cholecystokinin -stimulated when fatty acids and peptides are Hydrochloric acid Gastric Kills bacteria, converts released; inhibits gastric secretion glands pepsinogen to pepsin Pepsin* Gastric Digests protein glands Major Digestive System Hormones Mucus Mucous Protects stomach lining cells Hormone Source Function Intrinsic factor Gastric Binds to vitamin B12, aids Gastrin Gastric -Increases gastric secretions glands in its absorption glands Small Intestine and Associated Glands Secretin Duodenum -Decreases gastric Bile salts Liver Emulsify fats secretions Bicarbonate ions Pancreas Neutralize stomach acid -Increases pancreatic and Trypsin*, Pancreas Digest protein bile secretions high in chymotrypsin*, bicarbonate ions carboxy- -Decreases gastric motility peptidase* Cholecysto- Duodenum -Decreases gastric Pancreatic Pancreas Digests starch kinin secretions amylase -Strongly decreases gastric Lipase Pancreas Digests lipid motility (triglycerides) -Increases gallbladder Nucleases Pancreas Digest nucleic acid (DNA contraction or RNA) -Increases pancreatic Mucus Duodenal Protects duodenum from enzyme secretion glands and stomach acid and goblet cells digestive enzymes D. Movement in Stomach Peptidases** Small Digest polypeptide intestine Mixing waves -weak contraction; thoroughly mix food to Sucrase** Small Digests sucrose form chyme intestine Peristaltic waves -stronger contraction; force chyme Lactase** Small Digests lactose toward and through pyloric sphincter intestine Hormonal and neural mechanisms stimulate stomach Maltase** Small Digests maltose secretions intestine Stomach empties every 4 hours after regular meal, and 6- *These enzymes are secreted as inactive forms, then activated. 8 hours after high fatty meal **These enzymes remain in the microvilli. Distention of the stomach wall -major stimulus to gastric motility & emptying Cholecystokinin -major inhibitor of motility and emptying C. Regulation of Stomach Secretions Hunger pangs -stomach is stimulated to contract by low blood glucose levels usually 12-24 hours after a meal 1. Cephalic phase -1st phase; stomach secretions are initiated by sight, smell, taste, or food thought Parasympathetic stimulation V. SMALL INTESTINE gastrin, histamine increase stomach secretions Gastrin - hormone that enters the blood and is A. Anatomy of the Small Intestine carried back to the stomach; stimulates additional secretory activity Long narrow tubes that folds to fill a large portion of the Histamine -stimulate gastric gland secretion; abdominal cavity stimulates HCl acid production Measures 6 meters in length 2. Gastric phase -2nd phase; partially digested proteins and Major absorptive organ distention of stomach promote secretion Chyme takes 3-5 hours to pass through 3. Intestinal phase -3rd phase; acidic chyme stimulates Contains enzymes to further breakdown food neuronal reflexes and secretions of hormones that inhibit Contains secretions for protection against chyme’s acidity gastric secretions by negative feedback loops Simple Columnar epithelium @medtech.files | by MAPB Chapter 15: Digestive System  Granular cells -protect the intestinal epithelium from bacteria Endocrine cells -produce regulatory hormone intestinal glands -or crypts of Lieberkühn; tubular glands of the mucosa duodenal glands -open into the base of the intestinal glands Ileocecal junction -site where the ileum connects to the large intestine; consist of: ileocecal sphincter -a ring of smooth muscle ileocecal valve -allow the intestinal contents to move from the ileum to the large intestine Peyer patches -clusters of lymphatic nodules in the ileum; protection from microorganisms Parts of Small Intestine Duodenum B. Secretions of the Small Intestine ‑ C-shaped beginning of SI; shortest and receives partial digestive food; for chemical digestion of food Peptidases -digest proteins; they break the peptide bonds ‑ 25 cm long in proteins to form amino acids ‑ contains absorptive cells, goblet cells, granular cells, Disaccharidases -digest small sugars, specifically endocrine cells disaccharides ‑ contains microvilli and many folds ‑ contains bile and pancreatic ducts C. Movement in the Small Intestine Jejunum ‑ middle and longest section; absorption of important Peristaltic contractions -cause the chyme to move along nutrients such as sugars, fatty acids, and amino acids the small intestine ‑ 2.5 meters long Segmental contraction -propagated only for short Ileum distance; mix intestinal content ‑ main function is to absorb vitamin B12, bile salts, and other analytes not absorbed by the jejunum; the wall D. Absorption in the Small Intestine is made up of folds with many tiny finger-like projections known as villi on its surface Most absorption: duodenum and jejunum ‑ meters long Three Modifications That Increase Surface Area VI. LIVER AND PANCREAS circular folds -run perpendicular to the long axis of the A. Anatomy of the Liver digestive tract Processes nutrients and detoxifies harmful substances villi -tiny, fingerlike projections of the mucosa from the blood microvilli - numerous cytoplasmic extensions Large gland in the RUQ that produces bile that is stored in lacteal -a lymphatic capillary; important in transporting the gallbladder and secreted into the duodenum absorbed nutrients Weighs about 3 lbs. Consist of two lobes: right and left lobe falciform ligament -connective tissue septum that 4 Major Cell Types in the Mucosa separates the right and left lobes porta -gate where blood vessels, ducts, nerves enter and Absorptive cells -contain microvilli; produce digestive exit enzymes, and absorb digested food lobules -divisions of liver with portal triads at corners Goblet cells -produces a protective mucus @medtech.files | by MAPB Chapter 15: Digestive System  Portal triad -contain hepatic artery, hepatic portal vein, Synthesizes new molecules hepatic duct Secretes 700ml of bile each day Hepatic artery -delivers oxygenated blood to the liver, o Bile -important for digestion because it neutralizes which supplies liver cells with oxygen acid and dramatically increases fat digestion and Hepatic portal vein -carries nutrient-rich blood from the absorption digestive tract to the liver o Bile salts -emulsify fats, breaking the fat globules into Hepatic veins -where blood exits the liver; empty into the smaller droplets inferior vena cava o Bilirubin -a bile pigment that results from the Hepatic cords -between center margins of each lobule; breakdown of hemoglobin separated by hepatic sinusoids; formed by hepatocytes o Gallstones -may form if the amount of cholesterol (liver cells) secreted by the liver becomes excessive Hepatic sinusoids - blood channels that separates hepatic cords; contain phagocytic cells that remove foreign C. Anatomy of the Pancreas particles from blood Central vein -center of each lobule; where mixed blood Endo and exocrine gland cradled in the duodenum flows towards; forms hepatic veins Produces pancreatic juices which flow through the Bile canaliculus -a cleft like lumen between the cells of pancreatic duct each hepatic cord Located retroperitoneal Head near midline of body Gallbladder Tail extends to left and touches spleen ‑ small sac on inferior surface of liver Endocrine tissues have pancreatic islet or islets of ‑ stores and concentrates bile (30-50ml) Langerhans that produce insulin and glucagon Exocrine tissues produce digestive enzymes Acini -produce digestive enzymes Liver Ducts Pancreatic duct -joins the common bile duct and empties into the duodenum Hepatopancreatic ampulla -bulb-like structure which opens into the duodenum to aid in digestion D. Functions of the Pancreas Hepatic duct -collects bile from the liver and fuse to become the common hepatic duct Exocrine Secretions of Pancreas: Common hepatic duct -joins the cystic duct from the gallbladder to become the common bile duct Bicarbonate ion (HCO3-) -neutralizes chyme Cystic duct -joins common hepatic duct; from gallbladder Trypsin & Chymotrypsin -split whole and partially Common bile duct -carries bile from the gallbladder or digested proteins into peptides liver and brings it to the duodenum Carboxypeptidase -splits peptides into individual amino acids Pancreatic amylase -continues the polysaccharide B. Functions of the Liver digestion Digestive and excretory functions Lipase -lipid digesting enzyme Stores and processes nutrients Nucleases -enzymes that degrade DNA, RNA to Detoxifies harmful chemicals nucleotides @medtech.files | by MAPB Chapter 15: Digestive System  VII. LARGE INTESTINE Defecation reflex A. Anatomy of the Large Intestine Stimulus: fecal distention of rectal wall Mediated by parasympathetic reflexes Effect: peristaltic contractions in the lower colon and rectum VIII. DIGESTION, ABSORPTION, AND TRANSPORT 1. Digestion -breakdown of food to molecules Mechanical Digestion - breaks large food particles into smaller ones Chemical Digestion -breaking of covalent bonds into organic molecules by digestive enzymes 2. Propulsion -moves food through digestive tract includes swallowing and peristalsis 3. Absorption -primarily in duodenum and jejunum of small Cecum -joins small intestine at ileocecal junction; absorbs intestine water and salt residues; on its posterior wall attach is your 4. Defecation -elimination of waste in the form of feces appendix (wormlike blind sac; 9 cm structure that is often removed) A. Carbohydrates Colon -1.5 meters long; reabsorbs fluid and process waste products with 4 parts: ascending, transverse, descending, Carbohydrates consist primarily of starches, cellulose, sucrose and sigmoid (table sugar), and small amounts of fructose (fruit sugar) and 1. Ascending colon -extends superiorly from the cecum lactose (milk sugar). to the right colic flexure, near the liver, where it turns to the left Polysaccharides split into disaccharides by salivary and 2. Transverse colon -extends from the right colic flexure pancreatic amylases to the left colic flexure near the spleen, where the Disaccharides broken down into monosaccharides by colon turns inferiorly disaccharidases on surface of intestinal epithelium 3. Descending colon -extends from the left colic flexure Glucose is absorbed by cotransport with Na+ into to the pelvis, where it becomes the sigmoid colon intestinal epithelium 4. Sigmoid colon -forms an S-shaped tube that extends Glucose is carried by hepatic portal vein to liver and enters medially and then inferiorly into the pelvic cavity and most cells by facilitated diffusion ends at the rectum o crypts -straight, tubular glands in the muscular lining B. Lipids of the colon o teniae coli -three bands in the intestinal wall Lipid molecules are insoluble or only slightly soluble in Rectum -straight tube that begins at sigmoid and ends at water anal canal Triglycerides -or fats, are the most common type of lipid Anal canal -canal that exits to the outside; last 2-3 cm of o Saturated fats -fatty acids have only single bonds dig. tract between carbons o Internal anal sphincter -smooth muscle o Unsaturated fats -fatty acids have double bonds o Externa anal sphincter -skeletal muscle between carbons o Hemorrhoids -enlarged or inflamed rectal, or Emulsification -bile salts transform large lipid droplets hemorrhoidal, veins that supply the anal canal into much smaller lipid droplets Bile salts emulsify lipids Lipase breaks down lipids which form micelles B. Functions of the Large Intestine Micelles are in contact with intestinal epi. and diffuse with Food takes 18-24 hours to pass through the large intestine cells where they are packaged and released into lacteals and 3-5 hours for chyme to move through small intestine Lipids are stored in adipose tissue and liver Feces is product of water, indigestible food, and microbes Microbes synthesize vitamin K @medtech.files | by MAPB Chapter 15: Digestive System C. Proteins Hepatitis C often a chronic disease leading to cirrhosis and possibly cancer of the Proteins are split into polypeptides by enzymes secreted liver by stomach and pancreas Intestine Peptides and amino acids are absorbed into intestinal epi. Inflammatory localized inflammatory degeneration cells bowel disease (IBD) that may occur anywhere along the Amino acids are actively transported into cells (help from digestive tract but most commonly GH and insulin) involves the distal ileum and Amino acids used to build new proteins proximal colon Irritable bowel disorder of unknown cause marked syndrome (IBS) by alternating bouts of constipation D. Water and Minerals and diarrhea Gluten enteropathy malabsorption in the small intestine Water can move across intestinal wall in either direction (celiac disease) due to the effects of gluten, a protein Depends on osmotic conditions in certain grains, especially wheat 99% of water entering intestine is absorbed Constipation slow movement of feces through the Minerals are actively transported across wall of small large intestine, causing the feces to intestine become dry and hard because of increased fluid absorption while being retained Infections of the Digestive Tract IX. EFFECTS OF AGING ON THE DIGESTIVE SYSTEM Food poisoning caused by ingesting bacteria or With advancing age, the layers of the digestive tract thin, toxins, such as Staphylococcus aureus, Salmonella, or Escherichia and the blood supply decreases. coli Mucus secretion and motility also decrease in the Giardiasis caused by a protozoan, Giardia digestive tract. lamblia, that invades the intestine The defenses of the digestive tract decline, leaving it more Intestinal parasites common under conditions of poor sensitive to infection and the effects of toxic agents. sanitation; parasites include Tooth enamel becomes thinner, and the gingiva recede, tapeworms, pinworms, hookworms, exposing dentin, which may become painful and affect and roundworms eating habits. Dysentery severe form of diarrhea with blood or mucus in the feces; can be caused by bacteria, protozoa, or amoebae X. DISEASES Condition Description Stomach Peptic ulcer lesions in the lining of the stomach or duodenum, usually due to infection by the bacterium Helicobacter pylori Liver Cirrhosis characterized by damage to and death of hepatic cells and replacement by connective tissue Hepatitis inflammation of the liver that causes liver cell death and replacement by scar tissue Hepatitis A infectious hepatitis; usually transmitted by poor sanitation practices or from mollusks living in contaminated waters Hepatitis B serum hepatitis; usually transmitted through blood or other body fluids through either sexual contact or contaminated hypodermic needles @medtech.files | by MAPB Chapter 15: Digestive System