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78 Cards in this Set
- Front
- Back
define digestion
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the chemical and mechanical breakdown of foods into smaller units that can be taken across the intestinal epithelium into the body
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define absorption
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the active or passive transfer of substances from the lumen of the GI tract to the extracellular fluid
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define motility
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the movement of material from teh lumen to the GI tract as a result of muscle contraction.
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define secretion
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refers to both the transepithelial transfer of water and ions from the ECF to the digestive tract lumen and the release of substances synthesized by GI epithelial cells.
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what is the GALT and where is it located?
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gut-associated lymphoid tissue, ~80% of all lymphocytes are here in the small intestine
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what are the three pairs of salivary glands?
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sublingual (under the tongue)
submandibular (under the mandible) parotid (lying near the hinge of the jaw) |
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what are the three parts of the stomach?
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the upper fundus, central body, and lower antrum
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what is the opening of the stomach and the small intestine guarded by?
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pyloric valve or pyloris
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what does the small intestine consist of
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the duodenum, jejunum, and ileum respectively
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what are the two accessory glandular organs?
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the pancreas and the liver
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what is the function of the sphincter of oddi?
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to control pancreatic fluid and bile from entering the duodenum
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what are the four layers of the stomach?
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1. inner mucosa
2. submucosa 3. muscularis externa 4. serosa |
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what are the three layers of the mucosa?
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1. single layer of epithelial cells
2. the lamina propria 3. muscularis mucosae |
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lamina propria
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subepithelial connective tissue that holds the epithelium in place
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rugae
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folds in the wall of the stomach
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plicae
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folds in the wall of the small intestine
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villi
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fingerlike extensions in the intestinal mucosae
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gastric glands
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invaginations of the stomach wall
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crypts
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invaginations of the intestinal wall
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submucosal glands
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deepest invaginations from secretory glands that open into the lumen through ducts.
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what is the function of transporting epithelial cells
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they move ions and water inot the lumen and absorb ions, water, and nutrients into the ECF, at the mucosal (apical)surface
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what is the function of secretory cells?
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they release enzymes, mucus, and paracrine molecules into the lumen at the basolateral surface
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why is the interstitial epithelium considered to be leaky?
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because some water and solutes can be absorbed between the cells
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what is the function of GI stem cells?
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they are rapidly dividing, undiffentiated cells that continuously produce new epithelium in the crypts and gastric glands
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lamina propria
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is subepithelial connective tissue that contains nerve fibers and small blood and lymph vessels into which absorbed nutrients pass. This layer also contains wandering immune cells such as macrophages and lymphocytes
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peyers patch
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small nodules formed in the intestine from lymphnoid tissue adjoining the epithelium
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muscularis mucosae
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seperates the mucosa from the submucosa. contraction of this layer alters the effective surface area for absorption by moving the villi back and forth
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what are the two nerve networks in the enteric system?
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submucosal plexus and the myenteric plexus
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the muscularis externa consists of what types of muscles?
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two layers of smooth muscle
an inner circular layer and an outer longitudinal layer |
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what nerve plexus controls and coordinates the motor activity of the muscularis externa?
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myenteric plexus
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what is the outer covering of the entire digestive tract?
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serosa
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what is the serosa an extension of?
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the peritoneal membrane
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what are the sheets called that hold the intestines in place so that they don't become tangled?
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mesentary
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what are the two purposes of motility in the GI tract?
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1. moving food from the mouth to the anus.
2. mechanically mixing food to break it into uniformly small particles. |
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tonic contractions
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are sustained for a few minutes or hours occur in some smooth muscle spinchters and in the anterior portion of the stomach
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phastic contractions
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contraction-relaxation cycles lasting only a few seconds, occur in the posterior region of the stomach and in the small intestine
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slow wave potentials
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cycles of smooth muscle contraction and relaxation are associated with depolarization and repolarization
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interstitial cells of cajal
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slow waves originate in modified smooth muscle cells called cells of cajal and pass into smooth muscle cells through gap junctions
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migrating motor complex
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between meals when the tract is largely empty, a series of contractions begins in the stomach and passes slowly from section to section, each taking about 90 minutes. AKA housekeeper function that sweeps food remnants and bacterial out of the upper GI into the large intestine
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Peristalsis
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progressive waves of contraction that move from one section of the GI tact to the next. Circular muscles contract just behind a mass or bolus of food. This pushes the bolus foward into a receiving segment.
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segmental contractions
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segments of the intestine alternately contract and relax. Circular muscles contract while longitudinal muscles relax. this causes mixing and contact with the absorptive epithelium
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in a typical day, how many liters of fluid pass through the lumen of a GI tract. How much of that is excreted
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9 liters
.1 liters excreted |
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what happens during acid secretion?
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1. H+ from inside the parital cell is pumped into the stomach lumen by a H+-K+-ATPase in exchange for K+.
2. Cl- follows H+ through an open chloride channel 3. HCl stays in the lumen 4. HCO3- goes to the blood, made from CO2 and OH- |
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what is the alkaline tide?
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from acid secretion, bicarbonate is formed in the parietal cells and then goes to the blood
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what is the purpose of bicarbonate secretion?
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to secrete bicarbonate into the exocrine pancreas and the duodenum.
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what is the enzyme needed for production of bicarbonate?
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carbonic- anhydrase
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what is exchanged for what for bicarbonate secretion on the apical membrane (lumen of pancreas)
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HCO3- for Cl
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what is exchanged for what for bicarbonate secretion on the basolateral membrane (interstitial fluid)
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H+ is exchanged for Na+
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acini
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lobules in the exocrine portion of the pancreas that secrete digestive enzymes, and duct cells secrete NaHCO3.
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what secretes NaCl in the digestive tract?
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crypt cells in the small intestine and colon secrete an isotonic NaCl solution
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what is the active step in NaCl secretion?
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Cl- secretion, followed by Na+ and water moving through the paracellular pathway.
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how does chloride enter the cell in NaCl secretion?
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through NKCC transporter
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how does chloride exit the cell in NaCl secretion?
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via an apical CFTR channel.
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what is the purpose of NaCl secretion?
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the saline mixes w/ mucus secreted by goblet cells to help lubricate the contents of the gut.
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mucins
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the glycoproteins that make up mucus
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mucus is made in what 3 places?
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1. mucus cells in the stomach
2. goblet cells in the intestine 3. salivary glands |
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what are the 3 key components of bile?
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1. bile salts that facilitate enzymatic fat digestion
2. bile pigments such as bilirubin are waste products of hemoglobin degradation 3. cholesterol which is excreted in the feces |
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what are bile salts made of?
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steroid bile acids and amino acids which act as detergents to solubulize fats during digestion.
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what is saliva composed of?
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water, ions, mucus and proteins such as enzymes and immunoglobuluins
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which part of the autonomic system controls saliva secretion?
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parasympathetic innervation is the primary stimulus for secretion of saliva
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how are carbohydrates digested in the saliva?
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amylase breaks starch down to sugar (Maltose)
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how are carbohydrates digested in the stomach?
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acid denatures amylase
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how are carbohydrates digested in the duodenum?
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pancreatic amylase continues to break down dissacharides. the process of chyme entering the small intestine activates CCK which tells the pancreas to secrete pancreatic enzymes
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what are the brush border enzymes in the small intestine used to break down carbohydrates?
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lactase
maltase sucrase which completes the breakdown of dissacharides to monosacharides |
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what absorbs the monosaccharides after they are broken down by the carbohydrate enzymes?
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the liver
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what are the three major pancreatic proteases?
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Trypsin, Chymotrysin, and Carboxypeptidase
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how do trypsin and chymotrypsin break down proteins?
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cleave proteins into smaller peptides and single amino acids
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how does carboxypeptidase break down peptides?
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cleaves on amino acid at a time for the carboxyl end of a protein
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Aminopeptidase and dipeptidase
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futher break down di and tri peptides
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are di and tri peptides absorbed?
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yes
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where does fatty acid digestion take place?
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in the small intestine
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what is the enzyme that breaks down triglycerides?
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pancreatic lipase
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what helps to break down large fat drops into smaller dorps in the small intestine?
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segmentation
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what enzyme digests glyercides?
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lipase
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how do bile salts break down lipid droplets?
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they hydrophobic regions of bile salts associate with the surface of lipid droplets. While the polar side chains interact with water, creating a stable emulsion of small water-soluble fat droplets.
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colipase
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a protein cofactor secreted by the pancreas it diplaces bile salt, thus allowing lipase to access the fats inside the bile salt coating
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chylomicrons
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once the micelle is absorbed, they are resynthsized into triglycerides and combine with cholesterol and proteins to form chylomicrons.
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lacteals
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lymph vessels that chylomicrons move through b/c they are too large to go anywhere else.
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