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The Digestive System

Chapter 19

gastrointestinal (GI) tract A continuous tube that extends from the mouth to the anus
accessory digestive organs Teeth,tongue, salivary glands, liver, gallbladder, and pancreas
ingestion This process involves taking foods and liquids into the mouth (Eating)
secretion Each day, cells within the walls of the GI tract and accessory organs secrete a total of about 7 liters of water, acid, buffers, and enzymes into the lumen of the tract
mixing and propulsion alternating contraction and relaxation of smooth muscle in the walls of the GI tract mix food and secretions and propel them toward the anus. (Motility)
digestion Mechanical and chemical processes break down ingested food into small molecules
mechanical digestion the teeth cut and grind food before it is swallowed, and then smooth muscles of the stomach and small intestine churn the food
chemical digestion the large carbohydrate, lipid, protein, and nucleic acid molecules in food are broken down into smaller molecules by digestive enzymes
absorption the entrance of ingested and secreted fluids, ions, and small molecules that are products of digestion into the epithelial cells lining the lumen of the GI tract
defecation wastes, indigestible substances, bacteria, and cells shed from lining of the GI tract, and digested materials that were not absorbed leaved the body through the anus
mucosa, submucosa, muscularis, and serosa four layers of the GI tract
mucosa A layer of epithelium, areolar connective tissue (propia), smooth muscle (lamina muscularis mucosae) that increases surface area for digestion and absorption and protects GI against pathogens
submucosa Areolar connective tissue that binds the mucosa and muscularis
muscularis skeletal muscle that forms the external anal sphincter, mouth, pharynx, and upper esophagus
serosa and peritoneum membrane that secretes a slippery, watery fluid that allows the tract to glide easily against other organs
greater omentum drapes over the transverse colon and small intestine like a "fatty apron"
mesentery A part of the peritoneum that binds the small intestine to the posterior abdominal wall
oral cavity cheeks, hard and soft palates, and tongue
hard palate consists of the maxillae and palatine bones, forms most of the roof of the mouth
soft palate muscles in the mouth
uvula projections of the soft palate, prevents entry of food and liquids into the nasal cavity
lingual frenulum a fold of mucous membrane in the midline of the undersurface of the tongue, limits the movement of the tongue posteriorly
papillae projections on the upper surface and sides of the tongue
parotid, submandibular, sublingual 3 salivary glands
parotid glands located inferior and anterior to the ears between the skin and masseter muscle
submandibular glands found in the floor of the mouth
sublingual glands beneath the tongue and superior to the submandibular glands
saliva 99.5% water, 0.5% solutes. Water helps dissolve foods so they can be tasted and begins digestion. Solutes begin digestion of starches in the mouth
salivary amylase breaks down starch in the mouth
salivation secretion of saliva
mastication mechanical digestion consisting of chewing
bolus end product of mastication
pharynx a funnel-shaped tube that is composed of skeletal muscle and lined by mucous membrane
esophagus a muscular tube lined with stratified squamous epithelium, transports food to the stomach and secretes mucus
upper esophageal sphincter and lower esophageal spincter 2 sphincters at the end of the esophagus
upper esophageal sphincter regulates movement of food from the pharynx into the esophagus
lower esophageal sphincter regulates movement of food from the esophagus to the stomach
voluntary, pharyngeal, and esophageal 3 stages of swallowing
voluntary stage bolus is forced to the back of the mouth cavity and into the oropharynx by the movement of the tongue
pharyngeal stage breathing is temporarily interrupted when the soft palate and uvula move upward to close off the nasopharynx and the epiglottis seals of the larynx
esophageal stage food is pushed through the esophagus by peristalsis
peristalsis muscular contractions along the esophagus
stomach mixing chamber and holding reservoir
rugae large folds of the mucosa
mucous neck cells secrete mucus
chief cells secrete pepsinogen
pepsinogen inactive form of pepsin
parietal cells produce hydrochloric acid which kills microbes and converts pepsinogen into pepsin
gastric juices the secretions of the mucous, chief, and parietal cells
G cells secrete the hormone gastrin
mixing waves gentle, rippling peristaltic movements of the muscularis
chyme bolus mixed with gastric juices
gastric emptying mixing wave forces a small amount of chyme through the the partially closed pyloric sphincter into the duodenum
pancreatic duct secretions pass from the the pancreas to the duodenum; unites the common bile duct from the liver and gallbladder, forming a common duct to the duodenum
acini pancreatic cells arranged in clusters, exocrine
pancreatic juice cells within acini secrete a mixture of fluid and digestive enzymes, contains water, salt, sodium bicarbonate, and enzymes
pancreatic islets 1% of the other pancreatic cells, endocrine. Secrete glucagen, insulin, somastatin, and pancreatic polypeptide
pancreatic amylase breaks down starch in pancreas
trypsin, chymotrypsin, and carboxypeptidase protein-digesting enzymes
pancreatic lipase digests tryglycerides
ribonuclease and deoxyribonuclease digests nucleic acids
enterokinase activated form of trypsin
liver weighs 1.4 kgs and is the second largest organ in the body
gallbladder pear-shaped sac that hangs from the lower front margin of the liver
lobules units of the liver
hepatocytes specialized cells that make up lobules
sinosoids highly permeable capillaries
emuslification the breakdown of large lipid globules into a suspension of small lipid globules, and absorption of lipids following their digestion
bilirubin principal bile pigment
absorptive cells found in the small intestine, contain microvilli and digest and absorb nutrients in small intestinal chyme
s cells, CCK cells, and K cells secrete hormones into the bloodstream such as secretin, cholecystokinin (CCK), and glucose-dependent insulinotropic peptide (GIP)
duodenal glands secrete an alkaline mucus
circular folds permanent ridges of the mucosa and submucosa that enhances absorption by increasing surface area
villi fingerlike projections of the mucosa
lacteal lymphatic capillary
microvilli tiny projections of the plasma membrane
intestinal juice secreted by the intestinal glands, contains mucus, alkaline
segmentations localized contractions that slosh chyme back and forth
maltase splits maltose into two molecules of glucose
sucrase breaks sucrose into a molecule of glucose and a molecule of fructose
lactase digests lactose into a molecule of glucose and a molecule of galactose
peptidases enzymes produced by absorptive cells that line the villi
micelles tiny droplets that include some bile salt molecules along with the long chain fatty acids, monoglycerides, cholesterol, and other dietary lipids
chylomicrons large spherical particles that are coated with proteins
mass peristalsis a strong peristaltic wave that begins in the middle of the colon and drives the colonic contents into the rectum
defecation reflex result of mass peristalsis
cephalic phase smell, sight, sound, or thought of food activates neural centers in the brain, leading to salivation
gastric phase gastrin is released
intestinal phase slows digestion
Created by: pontarelli
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