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233 Cards in this Set
- Front
- Back
GI system includes? |
Esophagus all the way from mouth to anus. Stomach. Intestines/Colon. Liver. |
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Roles of GI system? |
Digestion Absortion Metabolism (breaking down complex carbs) Excretion |
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Secretion helps_______. |
Start digestion process. Lubricate food particles. Secrete enzymes and acids in stomach. |
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Which of the following substances isreleased from neurons in the GI tract andproduces smooth muscle relaxation? (A) Secretin (B) Gastrin (C) Cholecystokinin (CCK) (D) Vasoactive intestinal peptide (VIP) (E) Gastric inhibitory peptide (GIP) |
(D)-VIP, mediates therelaxation response of the lower esophageal sphincter when a bolus of food approaches it,allowing passage of the bolus into the stomach. |
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4 main activities of the GI tract? |
1.Digestion●2.Absorption●3.Secretion●4.Motility |
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Cells in esophagus? |
Sampled squamous epithelium |
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Stomach has ____ glands. |
gastric |
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Which parts of vili? |
Duodenum, Jejunum, & Ileum |
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What makes up the mucosa? |
Epithelium lining, Lamina propria (connective tissue), and muscular mucosa. |
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Villi is lined with__________. |
Columnar epithelium |
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Intestinal gland is __________. |
Sometimes called crypts. Where villi dips down. Has cells for secretory activity. |
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Stem cells? |
Able to make cells to repopulate epithelium. |
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Types of CBC (Crypt stem cells)? |
Enterocytes, Paneth cells, enter endocrine, mucus cells, and tuft cells. |
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Which crypt cell(s) is/are involved in absorption? |
enterocytes |
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Are enterocytes short or long lived? |
short |
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Which crypt stem cells are involved in secretion? |
Paneth cells (fight bacteria in the Lumen), Entero endocrine (hormone secretion), mucus cells (lube up GI tract), and tuft cells (sensory cage) |
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Enter endocrine cells are __________? |
endocrine-paracrinecells of the gut |
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Voluntary system engagement? |
When you swallow and deficate |
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Features of endocrine-paracrine cells? |
•Sensitive to luminal contents•Release hormones••Can act locally (ex. Gastrin secreted by G cells acting onparietal cells)•Can act on more distance organs (ex.Secretin secreted in duodenum acting on pancreatic duct cells) |
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Parasympathetic and sympathetic nervous system make up the _______ system. |
Extrinsic |
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_________ makes up the intrinsic system. |
Enteric nervous system. |
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Parasympathetic system is used through the ____ nerve and ____ area. |
Vagus, sacral |
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Both the parasympathetic and sympathetic nervous system act upon the ___________. |
Enteric nervous system |
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Sympathetic system and GI? |
CNS and sympathetic ganglia |
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Sympathetic ganglia acts upon the _____ and the ______. |
Enteric system and blood vessels |
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Enteric nervous system has approximately ____ neurons. |
100 million |
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Enteric nervous system neurotransmitters? |
•Acetylcholine•Norepinephrine•ATP•Serotonin•Dopamine•Cholecystokinin•SubstanceP•Vasoactiveintestine polypeptide•Somatostatin•Leu-enkephalin•Met-enkephalin•bombesin
|
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____ and Innervation tend to go together. |
Musculature |
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Muscle types of Gi tract? |
Striated or smooth |
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Striated muscle is found in the _______. |
anus and esophagus |
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Major functions of muscles in GI tract? |
Churning (MIXING FOOD), Propulsion(peristalsis), and Reservoir (contain stuff) |
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Variations in GI tract muscles? |
•location:mucularis mucosa(thin), muscularis externa(robust) • thickness (sparse vs robust)• •innervation • •function |
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There are as many neurons in the enteric system as the spinal cord, true or false? |
TRUE |
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The striated muscle type in the GI tract? |
Visceral |
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Smooth muscle is made up of_________. |
Myofibers •Spindle-shaped fibers •Nucleus – ‘Corkscrew’ shape when cell contracts DenseBodies Slide against each other to cause contractions |
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Magnitude of resting membrane potential? |
•mean -60mV |
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_____ fluctuations in the circular layer of the smooth muscle. |
Rhythmic |
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Rhythmic fluctuations in smooth muscle are called ______________. |
Myogenic slow waves |
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•Basal electrical rhythm (BER) ? |
= frequency of slow waves. 5-15 mV |
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Do myogenic waves ALWAYS lead to contractions? |
No |
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Interstitial cells of Cajal (ICC)? |
"Pacemakers" - make slow wave on to the smooth muscle |
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BER? |
Basal electrical rhythm. determines the frequency of the contractions in the gastrointestinal (GI) tract 3-12 contracts per minute. |
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Most contractions per minute (BER) is in the? |
Duodenum |
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Muscle contractions only occur at _________. |
peaks |
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The threshold for GI muscle contracts is at _________. |
-40mV |
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Peaks last about? |
10-20ms, 10-40x as long than nerve |
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What type of channels does the gI tract use? |
Calcium-sodium. These channels are slow, offer more action potential. |
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Slow waves don't lead to__________. |
Contractions and calcium entry. |
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Spikes lead to ______________. |
Contractions and calcium entry. |
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Slow waves determine? |
timing, rate and STRENGTH |
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Sphincters: |
• Areas of high intraluminal pressure • Divide the tube into functional segments • Prevent reflux of contents |
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Where are sphincters located? |
esophagus – upper and lower pyloric ileocecal anal – internal and external |
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Tongue is a ___________. |
•Fibromuscularorgan with roles in movement and lubrication of food, vocalization, immunedefense, innate defense, etc. |
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Ectoderm forms ____ of tooth. |
top |
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Mesenchyme forms the ________of a tooth. |
Inside, dentin/root |
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•Ameloblasts become? |
Enamel |
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Odontoblasts become? |
Dentin |
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Types of salivary glands? |
Major and Minor. |
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Minor Salivary glands? |
Lips, Lingual, and Buccalmucosa |
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Major Salivary glands? |
Parotid, Sublingual, and Submandibular |
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Which salivary gland produces most of secretions when you smell something? |
Submandibular |
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What is saliva made of? |
*Water - about 1-1.5 liters/day *Ions - esp. K, Na, Bicarbonate, Chloride *Enzymes and other glycoproteins *Antibacterial agents (“licking your wounds”) §Immunoglobulins *Cells - including lymphocytes, ‘shed’ epithelia *Other - including R protein (facilitates binding of Vitamin B12 by Gastric Intrinsic Factor) (R protein is now known as Haptocorrin. Sometimes called transcobalamin I) |
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Ions in saliva are mainly? |
Potassium, sodium, chloride, and bicarbonate |
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Functions of saliva? |
*Moisten/lubricatefood; wash out salts/sugars that stimulate taste buds - thus triggeringcephalic phase of gastric and intestinal activities; provide buffering solutionto keep pH near neutral (6-8) *Initiatedigestion of carbohydrates (amylase) and fats (lingual lipase) *Bacteriostatic/bacteriocidalactions; also contains IgA (produced by plasma cells, modified by acini) *Facilitatespeech by lubricating surfaces of tongue, cheeks, teeth, lips *Cleanseteeth, kill bacteria, and provide ionic milieu that “stabilizes” enamel;reduces incidence of caries |
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ionicmilieu? |
Stabilizes enamel |
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Acini dump their material into ______. |
Ducts |
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Two main secretory cells? |
Serous– alpha- amylase Mucous– mucinglycoprotein and proline–rich glycoprotein |
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Ion transportdrives _____ transfer to lumen. |
Water |
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Fluid is _______ at low flow rates |
hypotonic |
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At_____ flow rates, the ductalcells have less time to modify the saliva and final saliva most closely resembles plasma |
high |
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Compositionof saliva varies based on _____. |
flow rate |
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HCO and saliva |
Lowest at low flow rates andhighest in saliva at high flow rates due to the fact that secretion isselectively stimulated when saliva production is stimulated by parasymstimulation. |
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1)Salivary secretion is exclusively underneural control by the ____________,whereas the other GI secretions are under both neural and hormonal control |
autonomic nervous system |
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Salivary secretion is increased by both __________, although parasym is dominant |
parasympathetic and sympathetic stimulation |
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Parasympathetic |
Leadsto copious flow &vasodilation; lowin organic contents Up to a 20-fold increase in blood flowand 10 fold increase in secretion anti-cholinergic medications can lead to”dry mouth” Menopause and lower estrogen tend todecrease salivary rates. |
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Sympathetic system? |
increasesflow butalso causes vasoconstriction) rich in organic content Stimulates myoepithelial cells |
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Esophagus is made up of what two muscle layers? |
Longitudinal and circular |
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Upper part of esophagus is _____ muscle? |
striated |
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Middle 1/3 of esophagus is ________. |
Smooth and striated |
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Lower 1/3 of esophagus is _________. |
Smooth muscle. |
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No _______ in the esophagus. |
Serosa (maybe some near stomach) |
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Nerves involved in swallowing? |
nucleus retrofacialis and nucleusambigus Projectsto the Upper third of the esophagus Somaticnerves – acetylcholine via nicotinic receptors |
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Parasympathetic? |
Dorsalmotor nucleus |
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Sympathetic nervous system? |
•T5-T6to lower 2/3 esophagus and T6-T10 to theLES |
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Sensory affects? |
•Vagusto the nucleus tractus solitarius- connection back to the n. ambiguus to complete the circuitry |
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Swallowing is ___________. |
Conscious and voluntary. |
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Everything after swallowing is ________. |
Autonomic |
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Tongue moving back prevents _________ and pushes down on the _________. |
food going up the nose, pushes down on epiglottis and pulls up hyoid to prevent food from going into trachea |
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Constriction from upper espousal sphincter causes pressure which drives ______. |
food down the throat |
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Primary peristaltic wave? |
First wave from pressure of UES closing. |
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Secondary peristaltic wave? |
Food continuing down tube. If food is stuck in throat, muscles keep contracting. |
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UES has most or least pressure? |
Most, +100 mm Hg |
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Esophagus has about _____ pressure. |
-5 mm Hg |
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LES has _____ pressure. |
+20 mm Hg |
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Stomach has _____ pressure. |
+5 mmHg |
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If LES doesn't work properly, leads to? |
acid reflux |
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Peristalsis is controlled by what two mechanisms? |
Smooth Muscle and striated muscle involved. |
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Instriatedportion, because CNS neurons areactivated sequentially; suppressed by ________. |
vagotomy |
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In smoothmuscle portion, because of a latency gradient for __________. |
"Off response“. |
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Intrinsic characteristicof _____________ causes delay ofcontraction keyto peristalsis |
smooth muscle |
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Which hormones increases pressure in LES? |
1.Gastrin2.Motilin3.Substance P4.Pancreatic polypeptide5. Pitressin(vasopressin)6.Angiotensin II |
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Which hormones decrease pressure in LES? |
1.Secretin2.Cholecystokinin3.Glucagon4.Gastric Inhibitory Polypeptide (GIP)5.Vasoactive Intestinal Polypeptide (VIP)6.Progesterone. |
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Atomic areas of the stomach? |
Cardia, Fundus, Corpus, Antrum, and Pylorus. |
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Functional/physiologic areas of stomach? |
Oxyntic and Pyloric |
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Parietal cells secrete? |
Protons and chloride ions |
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Chief cells? |
Make enzymes that begin to breakdown protein, zymogens. |
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Entero endocrine cells? |
Hormones for controlling GI activity. |
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Exocrine secretions? |
H+, Ions (Na+, K+,Cl-, HCO3-), Pepsinogens, Water, Intrinsicfactor, and Mucus |
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What does hydrogen ions do in the stomach? |
generated by parietal cells - kills bacteria and denatures proteins converts pepsinogen to pepsin |
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What do Ions (Na+, K+, Cl-, HCO3-) do in the stomach? |
protect mucosa |
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Pepsinogens do what? |
Secreted by chief cells - secretion stimulated by vagal impulses - converted to pepsin, which digests proteins • |
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Water? |
Dissolves and dilutes ingested materials |
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Intrinsic factor? |
secreted by various GI epithelial cells |
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Mucus in the stomach does what? |
(merocrine secretion, i.e. exocytosis) protects surface of stomach from high concentration of protons |
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Parietal cell makes HCL, which is? |
stomach acid |
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What activates the chemical pathway for gastric secretion? |
Histamine, gastrin, and acetylcholine. |
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Inhibitory hormones for gastric secretion pump? |
prostaglandin and somatostatin |
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Entero Chromaffin like cell? |
Like an endocrine cell. Secrete histamine. |
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In an entero chromatin like cell, what are the excitatory hormones on the pathway? |
catecholamines, acetycholine, gastrin, and prostaglandins. |
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In an entero chromatin like cell, what are the inhibitory hormones on the pathway? |
TGFa, Somatostatin, and histamine. |
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Cephalic phase? |
Haven't eaten in awhile, walk by cafeteria and smell food. Haven't tasted food yet. |
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What happens during cephalic phase? |
1) Parietal cells stimulated by vagus nerve to create HCL. 2) vagus nerve can also stimulate ECL to make histamine. 3) Stimulates g-cell (entero-endocrine), secretes gastrin. Gastrin acts on parietal cell, activates it even more. |
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Gastric phase? |
Food in stomach. |
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What happens during gastric phase? |
1) food stimulates G cells 2) Acid stimulates D cells (Somastatin) 3) Acid inhibits G cells |
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Intestinal phase? |
Food moves out of stomach into intestinal. Digestion and absortion. |
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What happens during the intestinal phase? |
Act to inhibit I cell (CCK) - acts upon pancreas, stimulates enzyme secretion S cell (Secretin) -acts upon pancreas, alkaline secretion Pancreas secretes information to beginning of intestines. |
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Mucus cells prevent? |
Stomach acid from boring through stomach. |
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pH of lumen is around ____. |
1.5 |
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pH of mucus cells are approximately ________. |
7 |
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Histamine receptors antagonists do what? |
Block histamine receptor, parietal cell won't feel effects. |
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Other types of inhibitory drugs on parietal cells? |
Anticholinergic or proton pump inhibitor (most effective) |
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Food enters and then.... |
vagovagal reflex and possibly lower muscle tone. Ex. if you wait a little after eating then you won't feel as full. |
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Gastric transit? |
1) start in fundus 2)moves to antrum |
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Larger food tends to be in the _______, while smaller food is in the __________. |
Fundus, antrum. Contents get layered, like pebbles at a river. |
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THE GASTRIC TRANSIT tends to be slow or fast? |
Pretty fast (100 ml/min, w/o increased pressure |
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Weak peristalsis starts in the middle of the stomach and moves toward the _______. |
antrum and becomes stronger. |
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How often is a new wave in the stomach? |
low rhythmic contractions every 20 seconds |
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Retropulsioncreatesmore mixing by the ________. |
Duodenum |
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Sphincter by duodenum narrows as wave approaches.... leads to... |
Enhanced retropulsion. |
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Keeping contents around longer puts the stomach at more danger for acid problems, true or false. |
False. Breaking food down helps the duodenum be protected from the acid. |
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Emptying contractions in the stomach are _____ times stronger. |
6X, 20% of the time that food is still in stomach. |
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Gastric motor patterns? |
Fed and Fasting. |
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Fed state? |
–Receptive Relaxation •Initiated by swallowing, enhanced by vasovagal reflex –Slow sustained contractions •Mixing contractions. –Gastric emptying and peristaltic contractions |
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Fasting state? |
Migrating Motility Complex |
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During fasting state, you get a strong contraction every _____ that travels all the way down GI tract. |
an hour and a half. Migrating mortality complex. |
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If you snack all the time_____. |
Never enter an MMC. |
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If you have fatty substances in the illeum? |
Fat takes awhile to digest, so they tell the stomach to slowwww everything down. Ileum brake. |
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Gastric ileum reflex? |
Potty training. When you eat food, the body sends a signal to use the bathroom. Feed dog in morning...natural reflex to use the bathroom. When you eat...body stimulated to dedicate. |
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MCC? |
time 0 -nothing time 2- infrequent contractions time 3 - intense contractions, small intestines sweeps food through. |
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Small intestines comprised of? |
Duodenum(~25 cm), Jejunum(~2.5 m), &Ileum(3.5 m) Actual living person may be smaller. |
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Function of small intestines? |
Digestion,absorption (transportation), and motility. |
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Structure of small intestines? |
Mucosa (large surface area made up of place, villa, and microvilli). Muscular externa, enteric nervous system. |
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Place circulares? |
Small folds that increase surface area of small intestines. |
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EM of enterocytes |
tall columnar absorptive cell |
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Brush border is made up of? |
microvilli, sub cellular projections. Increase surface area. |
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Lymphocytes fight off ______ that have snuck into small intestines. |
bacteria |
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Digestion occurs in what 3 places? |
1) Inthe lumen of the intestine: Intraluminal 2) Atthe apicalmembrane of enterocytes 3) Withinthe cytoplasm of enterocytes |
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Paneth cells secrete products in the lumen of intestines to... |
fight off bacteria |
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Three things we break down? |
Protein, Carbs, and fat |
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Major source of carbs? |
Starches |
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Breakdown of starch? |
1) Starts in salivary gland area 2) Continues in stomach w/ pancreatic amylase 3) Breakdown to glucose and oligomers 4) hydrolyzed by sucrase, lactase, and lathes into glucose, fructose, and galactose. 5) transported out of the cell into interstitial and blood. |
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Protein digestion in small intestine? |
1) Protein becomes pepsin in stomach 2) peptidases come from pancreas into the lumen 3) broken down into amino acids and oligomers 4) Hydrolyzed at the brush border of the cell 5) turned into di and try amino acids 6) hydrolyzed by cytoplasmic proteases 7) turns into amino acids |
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Fat is water soluble, true or false? |
False |
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Digestion of lipids and absorption? |
1) Emulsification/solubilization: bile salts, lecithin. 2) digestion by lipase (fat triggers CCK release that triggers pancreatic enzyme secretion) 3) Uptake 4) intracellular metabolism |
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Lacteals are? |
Specialized capillaries of the sympathetic system. |
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Intestinal motility? |
Aid absorption, substances moved through small intestines. |
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How long does it take food to go down the esophagus? |
2-5 seconds |
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How long does it take food to go through the stomach? |
1.5-2 hours |
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How long does it take food to go through the small intestines? |
2-5 hours |
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BER faster or small intestine motility? |
BER is faster. Peristaltic waves occur but don't travel the entire length. |
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Speed of food in small intestines? |
12 in duodenum area and slows down to 8-9 by ileum area. |
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Fed patterns? |
Irregular contractions and periodically brief squeezing contractions which stimulate peristalsis |
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Peristalsis controlled by _____ nervous system? |
Enteric. |
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Peristalsis can't occur unless there are two layers of muscle, true or false? |
TRUE Push and release |
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MCC occurs in the small intestines in the same pattern as the stomach, true or false? |
TRUE |
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Water transport in the colon is active, true or false? |
FALSE, it is passive. |
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Water follows the ______ gradient? |
osmotic |
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Stomach intakes about ____ L of water. |
2 |
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Endogenous secretions put in about ____ L of water. |
7 |
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The duodenum and jejunum absorb about ____ L of water. |
5.5 |
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Ileum and Colon absorb less water at ___ and ____, respectively. |
2, 1.3 |
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Actual feces contains about ____ ml of water. |
<200mL |
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If we absorb too much water.... |
constipation |
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If we secrete too much water then it may lead to... |
diarrhea |
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Water movement in the colon can be_________. |
Bidirectional. Through water actual channels through the cell (aqua pores). Or through para sailor fashion (junctions hold epithelial cells together). Tight epithelial cell junctions don't let stuff pass through the cells. |
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Pancreas,liver and gall bladder are considered the _______. |
Accessory organs. |
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Pancreas is similar to a ___________. |
Salivary gland. |
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Isletsof Langerhans are the? |
Endocrine portion of the pancreas. Cells are located that secrete insulin. |
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In the acinus of the pancreas... |
1) CCKand acetylcholine stimulated and have spontaneous secretion. 2) Sodium, Potassium, HCO3, and Cl act upon the protein. 3) Secretin is then stimulated and higher bicarbonate levels result. |
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Secretions from the pancreas combine with _____ secretions and empty into the duodenum, through the major duodenum papilla. |
bile |
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Liver is a _____. |
•Large and important organ withmultiple functions, involving both EXOCRINEand ENDOCRINE secretions - by same cells(HEPATOCYTES) |
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Liver helps break things down and synthesize ______. |
proteins, except hemoglobins |
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Functions of the liver? |
•Regulatesmetabolism (carbohydrates, lipids, protein) * Breaksdown proteins and dissipates ammonia•Synthesizesproteins and other molecules (almostall of plasma proteins) •ProducesBile •Storesvitamins and iron •Degradeshormones and inactivates and excretes drugs and toxins |
|
Bile is needed to digest _____ substances. |
fatty |
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Liver vein still needs _____ from the veins to sustain cells. |
oxygen |
|
Portal triad? |
Blood coming in (venous blood w/ nutrients) coming in through portal vein, arterial blood with oxygen and they meet in sinusoids (mix together). Bile goes in opposite direction, through small spaces into bile duct. |
|
in sinusoids Oxygenated blood mix, where and blood vessels come together. |
"hepatocytes" |
|
pH of liver bile? |
7.5 |
|
pH of gallbladder bile? |
6.0 |
|
The liver is primarily made up of? |
Sodium (141-165), Potassium (2.7-6.7), Calcium (1.2-3.2), Chloride (77-117), HCO3(12-55), total phosphorus (.15), bile acids (3-45), total fatty acids (2-7), bilirubin (1-2), phospholipids (1.4-8.2), cholesterol (1-3.2), and proteins (2-20). |
|
The gallbladder is primarily made of? |
Same composition as the liver but mostly Sodium (220), Chloride (31), Bile acids (32), total fatty acids (24), Chloride (15), and HCO3 (19) |
|
Live is comprised of both? |
Inorganic (electrolytes) and organic (bile acids, bile pigments, cholesterol, phospholipids, and protein. |
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The primary section of both pancreas andliver are stimulatedby ____. |
CCK |
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In both the liver and the pancreas, the primary is isotonic to _____, and the levels of Na, K and Cl areclose to plasma levels. |
plasma |
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When stimulated by secretin, the ductular epithelial cells in the pancreas andliver contribute an _________with a high bicarbonate concentration. |
aqueous secretion |
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Bile collects in the ________. |
gallbladder |
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Relaxation of the schihphter allows bile to flow down to the _________. |
intestines |
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Bile helps _____ break down. |
fat |
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Enterohepatic circulation? |
bile recycling back from the intestines to the liver. |
|
Phases of gallbladder activity? |
•Interdigestive phase •Cephalic phase •Gastric phase •Intestinal phase |
|
Interdigestive phase? |
Gallbladder–Stores & concentrates bile (5 to 15 fold) –Capacity of 15 to 60 ml –Absorbs Na +, Cl-, HCO3- and water |
|
Cephalic phase? |
Gall bladder contraction and sphincter of Oddi relaxation (vagal) |
|
Gastric phase? |
Gallbladder –Vago-vagal |
|
Intestinal phase? |
CCK major stimulant –Highest rate of emptying |
|
The bile in the gallbladder contains_____concentrations of bile acids, phospholipids and cholesterol as a resultof the reabsorption of water and electrolytes. |
higher |
|
Epithelial cells in the GI tract are? |
Specialized in different parts for secretion and absorption. |
|
Muscular mucosa contractions causes? |
A change in surface area. |
|
Circular muscle contraction causes? |
decrease in diameter of the lumen and GI tract. |
|
Longitudinal muscle contraction causes? |
shortening of GI tract segment. |
|
Submucosal plexus and mesenteric plexus comprise? |
The enteric nervous system and integrate/coordinate the morality, secretory, and endocrine functions of the GI tract. |
|
efferent fibers carry information from the ___ and ____ to the GI tract. |
brain stem and spinal cord |
|
Preganglionic parasympathetic fivers synapse in the ____ and _____. |
myenteric and submucosal. |
|
Vasovagal reflexes are? |
Reflexes in both afferent and efferent pathways in the vagus nerve. |
|
Myenteric plexus primarily controls what? |
Motility of the GI smooth muscle. |
|
Submucosal plexus primarily controls what? |
secretion and blood flow. Receives sensory information from chemoreceptors and mechanoreceptors in the GI tract. |
|
4 official GI hormones? |
gastrin, CCK, secretin, GIP. |
|
Gastrin is? |
In the G cells of the stomach. Stimulated by small peptides and amino acids, distention of stomach, vagus, inhibited by hydrogen ions in the stomach, and inhibited by somatostatin. Causes increased gastric hydrogen ion secretion and stimulates growth of gastric mucosa. |
|
CCK is? |
In the I cells of the duodenum and jejunum. Stimulated by small peptides and amino acids, and fatty acids. Causes contraction of gallbladder and relaxation of the Oddi sphincter. Increased pancreatic enzyme, growth of exocrine oancrease, and inhibits gastric emptying. |
|
Secretin? |
S cells in duodenum, stimulated by hydrogen ions in duodenum, fatty acids and duodenum. Causes increased pancreatic HCO3 secretion, increases billiard secretion, and decreased gastric secretion. |
|
GIP? |
In the duodenum and jejunum Stimulated by fatty acids, amino acids, and oral glucose. Causes insulin secretion and decreases hydrogen ion secretion |
|
Paracrines? |
released from endocrine cells in the GI mucosa. Diffuse over short distance to act on target cells. somastatin and histamine |
|
Somatostatin? |
secreted by cells throughout GI tract in response to H+ in the lumen. Inhibits release of GI hormones. |
|
Histamine |
secreted by mast cells of the gastric mucosa. |