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24 Digestive

Digestive System

gastrointestinal (GI) tract (alimentary canal) mouth, most of pharynx, esophagus, stomach, small intestine, and large intestine
accessory digestive organs teeth, tongue, salivary glands, liver, gallbladder, and pancreas
digestive process ingestion, secretion, mixing and propulsion, digestion, absorption, and defecation
secretion water, acid, buffers, and enzymes into lumen from GI tract cells
mixing and propulsion alternating contractions and relaxations of smooth muscle in the walls of the GI tract, known as motility
digestion mechanical digestion churns food; chemical digestion – hydrolysis
components of the wall of GI tract mucosa, submucosa, muscularis, and serosa
mucosa's 3 layers epithelium, lamina propria, and muscularis mucosae
lamina propria connective tissue with blood and lymphatic vessels and mucosa-associated lymphatic tissue (MALT) that contain immune system cells
muscularis mucosae thin layer of smooth muscle making folds to increase surface area
submucosa connective tissue binding mucosa to muscularis; contains many blood and lymphatic vessels; submucosal plexus (neurons)
muscularis voluntary skeletal muscle (mouth, pharynx, esohpagus, and anal sphincter) and involuntary; arranged in circular fibers and outer longitudinal fibers; myenteric plexus
enteric nervous system (ENS) extends from esophagus to anus; myenteric plexus and submucosal plexus; motor neurons, interneurons, and sensory neurons
myenteric plexus (plexus of Auerbach) located between circular and longitudinal smooth muscle layers; controls GI tract motility
submucosal plexus (plexus of Meissner) located within the submucosa; controls secretions
ANS influence parasympathetic stimulation increases secretions and motility by stimulating the ENS; sympathetic stimulation inhibits ENS
peritoneum largest serous membrane in the body; parietal peritoneum, peritoneal cavity, and visceral peritoneum
ascites accumulation of liters of fluid in the peritoneal cavity
parietal peritoneum lines the wall of the abdominopelvic cavity
visceral peritoneum covers some of the organs in the cavity
retroperitoneal kidneys, ascending and descending colons, duodenum, and pancreas (located behind the peritoneum)
major peritoneal folds (5) greater omentum, falciform ligament, lesser omentum, mesentery, and mesocolon
greater omentum the largest peritoneal fold that drapes over the transverse colon and small intestine like a “fatty apron”
falciform ligament attaches the liver to the anterior abdominal wall and diaphragm
lesser omentum suspends the stomach and duodenum from the liver
mesentery binds the jejunum and ileum of the small intestine to the posterior abdominal wall
mesocolon binds the transverse colon and sigmoid colon to the posterior abdominal wall
structure of the mouth cheeks, hard and soft palates, and tongue
uvula a conical muscular process hanging from the soft palate; drawn superiorly during swallowing to prevent food from entering the nasal cavity
function of salivary glands when food enters the mouth, secretion increases to lubricate, dissolve, and begins chemical digestion
3 pairs of salivary glands parotid, submandibular, and sublingual
parotid glands located between the skin and masseter muscle; secrete saliva via a parotid duct
submandibular glands found in the floor of the mouth; submandibular ducts
sublingual glands Found beneath the tongue; lesser sublingual ducts
saliva 99.5% water and 0.5% solutes;ions, dissolved gases, urea, uric acid, mucus, IgA, lysozyme, and salivary amylase
urea and uric acid in saliva helps remove waste molecules
IgA in saliva prevents attachment of microbes
tongue structure skeletal muscle covered with mucous membrane; attached to the hyoid bone; extrinsic muscles (hyoglossus, genioglossus, and styloglossus); intrinsic muscles; lingual frenulum (fold of mucous membrane on the bottom of the tongue)
tongue function maneuvers food for chewing, shapes mass, and forces food back for swallowing
lingual glands secrete salivary lipase (fats and oils)
ankyloglossia abnormally short or rigid lingual frenulum resulting in an impairment of speech
major regions of a tooth (3) crown, root, and neck
layers of a tooth (5) enamel, dentin, cementum, pulp, and root canals
dentitions sets of teeth
deciduous dentitions primary teeth, milk teeth, or baby teeth; 20 teeth (no molars)
permanent dentitions deciduous teeth replaced somewhere between the ages of 6-12; 32 teeth
pharynx food passes into the oropharynx and laryngopharynx; the muscular contractions in those areas help propel food into the esophagus to the stomach
histology of the esophagus mucosa, submucosa, muscularis, sphincters, and adventitia (attaches to the surroundings)
function of the esophagus secretes mucus and transports food
upper esophageal sphincter (UES) regulates movement into the esophagus
lower esophageal sphincter (LES) regulates movement into the stomach
deglutition swallowing; involving mouth, pharynx, and esophagus
3 stages of deglutition voluntary, pharyngeal, and esophageal
peristalsis progression of coordinated contractions and relaxations to push a bolus forward; occurs in the esophageal stage
pharyngeal stage when bolus enters the oropharynx it sends impulses to the deglutition center in the medulla; returning impulse tells the uvula to ascend and the epiglottis to close
four main regions of the stomach cardia, fundus, body, and pylorus
pylorus (2) pyloric antrum, connects to the body of the stomach; pyloric canal, connects into the duodenum
histology of the stomach mucosa, submucosa, muscularis, and serosa
mucosa of the stomach gastric glands open into gastric pits; mucous neck cells, parietal cells, chief cells, and G-cells
mucous neck cells secrete mucus
parietal cells produce intrinsic factor (for absorption of B12) and hydrochloric acid
chief cells secrete pepsinogen and gastric lipase
G-cells endocrine cell that secrete gastrin
gastrin stimulates gastric activity
muscularis of the stomach has an additional 3rd inner oblique layer
serosa of the stomach part of the visceral peritoneum
rugae folds of the stomach when it is empty
mechanical digestion in the stomach mixing waves (produces chyme) and gastric emptying (forces 3 mL of chyme into the duodenum)
chemical digestion in the stomach salivary amylase (digestion of starch continues until inactivated by gastric juice), lingual lipase (gastric juice activates it), and HCl (secreted by parietal cells; the proton pumps powered by H+/K+ ATPases)
pepsin secreted by chief cells in its inactive form pepsinogen, becomes active when in contact with HCl; helps breakdown proteins
why is pepsin secreted in an inactive form? it would breakdown the chief cells that produce it; the stomach is protected by a 1-3mm thick alkaline mucus
gastric lipase breaks triglycerides into fatty acids and monoglycerides
location of the pancreas retroperitoneal, lies posterior to the greater curvature of the stomach
anatomy of the pancreas head, body, tail, and two ducts
pancreatic duct (duct of Wirsung) (larger duct) joins the common bile duct from the liver and gallbladder and enters the duodenum at the hepatopancreatic ampulla
sphincter of hepatopancreatic ampulla (sphincter of Oddi) regulates pancreatic juice and bile into the small intestine
accessory duct (duct of Santorini) leads from the pancreas into the duodenum, just above the hepatopancreatic ampulla
pancreatic acini 99% of the epithelial clusters; constitute the exocrine portion; secrete a mix of fluid and digestive enzymes (pancreatic juice)
pancreatic islets (islets of Langerhans) 1% endocrine portion; secrete glucagon, insulin,somatostatin, and pancreatic polypeptide
pancreatic juice (5) neutral pH, somewhat alkaline; sodium bicarbonate, pancreatic amylase, proteolytic enzymes, pancreatic lipase, and deoxy/ribonuclease
sodium bicarbonate in pancreatic juice buffers chyme, stops pepsin from the stomach, and creates the proper pH for enzymes in the small intestine
proteolytic enzymes trypsin activates enzymes
liver anatomy two lobes joined by the falciform ligament, inferior quadrate lobe, and posterior caudate lobe; coronary ligament suspends the liver from the diaphragm
ligamentum teres (round ligament) remnant of the umbilical vein of the fetus
histology of the liver hepatocytes, bile canaliculi, hepatic sinusoids, and Kupffer cells
hepatocytes major functional cells of the liver; secretes bile
bile canaliculi ducts between hepatocytes that collect bile; exit liver as common hepatic duct and joins the cystic duct from the gallbladder to form common bile duct
hepatic sinusoids receives oxygenated blood form hepatic artery and deoxygenated nutrient-rich blood from hepatic portal vein
stellate reticuloendothelial (Kupffer) cells destroy worn-out RBCs, WBCs, and bacteria from the GI tract
portal triad bile duct, hepatic artery, and hepatic vein
bile properties yellow, brownish liquid; pH 7.6-7.8; water bile salts, cholesterol, lecithin, bile pigments and ions
bile function partial excretory product and partial digestive secretion; bile salts play a role in emulsification and providing a large surface area for pancreatic lipase
emulsification breakdown of a large lipid globule into smaller lipid globules
liver functions bile synthesis and secretion; carbohydrate metabolism; lipid metabolism; protein metabolism; processing drugs and hormones; excretion of bilirubin; storage for vitamins; phagocytosis; and activation of Vit-D
small intestine regions (3) duodenum, jejunum, and ileum
small intestine histology mucosa, submucosa, muscularis, and serosa
small intestine mucosa absorptive cells, goblet cells (mucus), intestinal glands (intestinal juice), paneth cells (lysozyme), enteroendocrine cells, and MALT
small intestine serosa completely surrounds the organ except for a major part of the duodenum
circular folds (plicae circulares) ridges of mucosa and submucosa cause chyme to spiral (increased surface area for absorption)
villi finger-like projections of the mucosa; contain an arteriole, venule, blood capillary and lacteal
microvilli projections of apical (free) membrane of absorptive cells; brush border with brush border enzymes
intestinal juice water and mucus; slightly alkaline; 1-2L; provides liquid medium aiding in absorption
brush border enzymes produced by absorptive cells and inserted into plasma membrane by microvilli; carbs, proteins, and nucleic acids
mechanical digestion in the small intestine controlled by myenteric plexus; segmentations, mixing contractions to bring chyme in contact with mucosa; migrating motility complexes (MMC)
carbohydrate digestion in the small intestine pancreatic amylase, α-dextrinase, sucrase, lactase, and maltase break them to monosaccharides which can be absorbed
protein digestion in the small intestine trypsin, chymotrypsin, carboxypeptidase, and elastase from pancreas; completed by aminopeptidase and dipeptidase in brush border
lipid digestion in the small intestine pancreatic lipase and emulsification by bile salts
nucleic acid digestion in the small intestine ribonuclease and deoxyribonuclease in pancreatic juice; nucleosidases and phosphatases in brush border.
absorption in the small intestine occurs by facilitated diffusion into blood (monosaccharides, amino acids, dipeptides, and tripeptides); lipids absorbed by simple diffusion
micelles formed by bile salts and ferry chains of fatty acids and monoglycerides for absorption
chylomicrons formed within a cell it is recreated from triglycerides
lacteals used to transport lipids into blood with a chylomicron protein coat
electrolyte absorption sodium ions reclaimed by active transport along with some other ions
vitamin absorption fat-soluble absorbed by simple diffusion
water absorption 9.3L ingested, 7.0L in GI secretions; occur by osmosis
daily volume 9.3L ingested/secreted, 0.1L excreted,; total absorbed 9.2L
large intestine regions (5) cecum, appendix, colon, rectum, and anal canal
ileocecal sphincter regulates passage of chyme between the small intestine and large intestine
colon divisions (4) ascending, transverse, descending, and sigmoid
internal anal sphincter smooth muscle
external anal sphincter skeletal muscle
histology of large intestine mucosa, submucosa, muscularis, and serosa
large intestine mucosa no circular folds or villi; does have microvilli on absorptive cells
large intestine muscularis longitudinal muscle modified to form teniae coli also forms haustra (pouches, segments seen)
mechanical digestion by the large intestine haustral churning, peristalsis, mass peristalsis (pushes contents toward the rectum)
chemical digestion by the large intestine final stage by bacterial action; ferment carbs; produces some vitamins B and K; mucus but no enzymes
phases of digestion (3) cephalic phase, gastric phase,and intestinal phase
cephalic phase smell, sight, thought or initial taste of food activates neural centers; prepares mouth and stomach for food to be eaten
gastric phase neural regulation by stretch receptors and chemorecptors; hormonal mechanisms (gastrin from G-cells); promotes gastric secretion and motility
intestinal phase begins when food enters small intesting; slows exit of chyme from the stomach
cholecystokinin (CCK) stimulates flow of bile and pancreatic juice; from CCK cells in the small intestinal crypts in response to chyme containing amino acids
secretin stimulates flow of pancreatic juice that is rich in bicarbonate (HCO3-) ions to buffer the acidic chyme; produced by S cells of the small intestinal crypts
Created by: sibuxiang



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