Chapter 23: Digestive System Flashcards
Digestive Tract:
o About 9 meters or 30 feet long (in cadaver).
o Accessory organs: Teeth, Tongue, Salivary glands, Liver, Gall bladder, Pancreas.
o Most of “stuff” inside tube has not yet entered body tissues!
Nutrient Disassembly:
o Carbohydrates become monosaccharides (Glucose, Fructose, Galactose).
o Triglycerides become Fatty acids + glycerol, some monoglycerides.
o Proteins become amino acids (few di- and tri- peptides).
o Vitamins stay as vitamins.
o Minerals stay as minerals.
o Water stays as water.
Processes of Digestive System:
o Ingestion. o Mechanical Digestion (mixing). o Chewing = Mastication. o Propulsion: o Deglutition = swallowing. o Peristalsis. o Mass movements. o Secretion (water, mucus, bile, enzymes, hormones). o Chemical Digestion = breaking nutrients down into small pieces. o Absorption (small intestine). o Defecation.
Histology of the Digestive Tract:
o 4 Tunics (Layers): Mucosa, Submucosa, Muscularis Externa, and Serosa.
Mucosa:
o Mucous epithelium: o Many types. o Exocrine cells. o Endocrine cells. o Lamina propria: o Very vascular!! o Lymphatic follicles. o Glands. o Muscularis mucosae.
Submucosa:
o Thick c.t. layer. o Bigger blood and lymphatic vessels. o Glands. o Lymphatic follicles. o Submucosal plexus (Meissner’s plexus).
ENS (Enteric Nervous System):
o Nervous network regulating digestive motility, secretions, and blood flow
o More neurons than spinal cord!
o Definitely influenced by ANS:
o Parasympathetic:
o Enhances gland secretion.
o Enhances motility.
o Sympathetic:
o Inhibits gland secretions.
o Inhibits smooth muscle contraction (exception: some sphincters are excited by sympathetic nerv. system).
o Causes vasoconstriction of blood vessels to the digestive tract.
Regulation of Digestive System:
o Local neuronal control: o Enteric sensory neurons (detect stretch & chemicals). o Enteric motor neurons (activate glands or change motility). o CNS control: o ANS: vagus and sympathetic control. o Conscious sight/smell/taste. o Hormonal control: o Systemic (gastrin, CCK, secretin). o Paracrine (histamine, PGs).
Muscularis Externa:
o Circular layer of smooth muscle. o Can form sphincters! o Myenteric (Auerbach) plexus. o Longitudinal layer of smooth muscle. o Exceptions.
Peristalsis:
o Adjacent segments of alimentary tract organs alternately contract and relax moving food along the tract distally.
Serosa:
o Outermost layer.
o Usually represents visceral peritoneum.
o Sometimes not part of peritoneum = adventitia.
Peritoneum:
o Largest serous membrane of body.
o Visceral peritoneum.
o Peritoneal cavity.
o Parietal peritoneum.
o Mesentery = double layer of peritoneum that stabilizes intestines/keeps them from becoming entangled during digestion.
o Examples: Mesentary “proper”, mesocolons, lesser omentum, greater omentum, and falciform ligament.
Retroperitoneal Organs:
o Intraperitoneal: organ is almost completely surrounded by peritoneum.
o Retroperitoneal: lies against the posterior body wall and is covered by peritoneum only on the anterior side:
o Examples: Duodenum, Pancreas, Ascending and descending colon, Rectum, Kidneys, ureters, urinary bladder and Adrenal glands.
Blood Supply of the Digestive System:
o Arteries: o Celiac trunk o Superior mesenteric a. o Inferior mesenteric a. o Veins from pancreas, stomach, GB, spleen, small and large intestines drain into the HEPATIC PORTAL VEIN. o Hepatic portal system.
Tongue:
o Skeletal muscle. o Lingual papillae: o Filiform. o Fungiform. o Foliate. o Circumvallate. o Lingual tonsils. o Lingual glands: o Mucus and lingual lipase.
Salivary Glands:
o Parotid: below ear/over masseter muscle.
o Submandibular: lower edge of mandible.
o Sublingual: deep to tongue in mouth floor.
o All have ducts emptying into oral cavity.
o Secrete salivary amylase, lysozyme, IgA.
Functions of Saliva:
o Deglutition: Swallowing. o Taste. o Buffer. o Chemical digestion. o Salivary amylase. o Protection: o Lysozyme enzyme. o IgA. o Rinsing action—1 to 1.5 quarts/day!!!
Tooth Composition:
o Enamel: o Calcium phosphate or carbonate. o Hardest substance in the body. o Dentin = calcified c.t. that is harder than bone! o Cementum: o Bone-like. o Attaches root to periodontal ligament.
Dentition:
o Primary = deciduous = baby teeth:
o 20 teeth that start erupting at 6 months.
o Permanent teeth:
o 32 teeth that erupt between 6 to 12 years.
o Differing structures indicate function.
o Incisors for biting.
o Canines for tearing.
o Premolars and molars to crush/grind.
Pharynx:
o Skeletal muscle lined by mucous membrane.
o DEGLUTITION pushes bolus of food into oropharynx.
o Soft palate elevated.
o Larynx lifted as epiglottis closes.
Digestive Processes of Esophagus:
o 1. Buccal Phase: The upper esophageal sphincter is contracted (closed). The tongue presses against the hard palate forcing the food bolus into the oropharynx.
o 2. Pharyngeal-esophageal phase begins: The tongue blocks the mouth. The soft palate and its uvula rise, closing off the nasopharynx. The larynx rises so that the epiglottis blocks the trachea. The upper esophageal sphincter relaxes; food enters the esophagus.
o 3. Pharyngeal-esophageal phase continues: The constrictor muscles of the pharynx contract, forcing food into the esophagus inferiorly. The upper esophageal sphincter contracts after food enters.
o 4. Peristalsis moves food through the esophagus to the stomach.
o 5. The gastroesophageal sphincter surrounding the cardial orifice opens. After the food enters the stomach, the sphincter closes, preventing regurgitation.
Esophageal Disorders:
o Dysphagia: difficult swallowing.
o Esophageal obstructions (tumors, constrictions).
o Impaired peristalsis (neuromuscular disorders).
o Acute esophagitis: ingestion of irritating substances, viral inflammation, intubation.
o Barrett’s esophagus (dysplasia).
o GERD = gastroesophageal reflux disease.
o LES fails to close adequately.
o Stomach contents “reflux”.
o HCl from stomach irritates esophageal lining = heartburn (radiating substernal pain).
Risk Factors for GERD:
o Hiatal hernia
o Recurrent vomiting (bulimia)
o Lying down right after a meal
o Delayed gastric emptying (common in DM)
o Increased abdominal pressure: Pregnancy or obesity, Tight fitting clothing, Large meals.
o Reduced LES muscle tone: Smoking, OCAs, Pregnancy (or even late menstrual cycle stages), Large amounts of dietary fat, Alcohol and caffeine, Carminatives (peppermint and spearmint).
Hiatal Hernia:
o Protrusion of stomach through the esophageal hiatus of the diaphragm.
o 2 types of Hiatal Hernia:
o Sliding hiatal hernia (95 percent); Very common.
o Paraesophageal.
o Most common GI d/o !!!!!
o LES fails to close adequately →stomach acid “refluxes” leads to irritation esophageal mucosa.
o Causes severe esophagitis due to excessive gastric reflux: GERD.