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What are the different sections of the stomach
- Fundus - Top of the stomach above the opening of the esophagus
- Cardia - Emptying of the esophagus
- Body - Central portion (largest)
- Pyloris - Portion leading to the opening of the duodenum
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Gastric pits
Invaginations of the mucosa of the stomach which terminates as gastric glands
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Mucosa pits with glands do not go past
Muscularis mucosae
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Mucosa of the stomach is made up of
Simple columnar surface mucous cells which produce a thick mucus layer to protect it
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What is the lamina propria of the stomach made up of
Loose connective tissue which is richly vascularized
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What is the makeup of the Cardia portion of the stomach
- Epithelium which provides mucous for protection from reflux
- Pits and Glands present
- No goblet cells
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What is the makeup of the glands in the Cardiac portion of the stomach
- They are deep, long, and branched (stem length = pit)
- They secrete mucus
- Stem cells and enteroendocrine cells (EEC) are present
- Few parietal cells secreting HCl are present
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What is the surface make up at the Pylorus
- Deep pits (2 x the depth of the glands)
- Short glands
- Enteroendocrine cells
- - G cells
- - D cells
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What do G cells secrete
Gastrin (inducing HCl production)
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What do D cells in secrete
Somatostatin (inhibits gastrin)
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What is the surface makeup of the Fundus/Body of the stomach
- Shallow pits (1/4 the depth of the glands)
- Deep, straight gastric glands
- Neck and base of the glands are histologically distinct
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What is found in the neck and base of the glands in the Fundus/Body
- Neck - Mucus cells, Parietal cells, Stem cells
- Base - Chief cells, Mucus cells, Enteroendocrine cells
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What do the parietal cells secrete, and how do they stain
- HCl
- Intrinsic factor
- Stain Acidophilic
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What do the Chief cells secrete, and how do they stain
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What is the alternate name of Parietal cells, and where are they found
- Oxynitic cells
- Only found in gastric glands (more numerous in the upper half of the gland)
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Intrinsic factor is important for, and is secreted by
- Absorption of Vit B12 in the Ileum
- Secreted by Parietal cells
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Pernicious anemia can be caused by atrophy to what cells, having what effect
- Parietal cells
- Decrease in Intrinsic factor production leading to a decrease in B12 uptake
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Chief cells are found where
Only found in the Gastric glands where they predominate the lower 1/3 of the gland
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What do Chief cells look like
- Triangular shaped
- Basally located nuclei
- Strongly basophilic
- Granules visable
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Why do parietal cells stain acidophilic
They contain a lot of mitochondria
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What are the alternate names for Enteroendocrine (EEC) cells
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Where are enteroendocrine cells found
They are found throughout the entire GI tract at the base of the glands
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What are mucus neck cells
- Mucus secreting cells found in all 3 regions of the stomach
- Irregular shaped
- Secrete less viscous mucus (foamy)
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What is in the submucosa of the stomach
- No glands
- Large blood vessels and nerves
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What is found in the Muscularis externa layer of the stomach
- Inner oblique layer
- Middle circular layer
- Outer longitudinal layer
- (unique in that it has 3 layers instead of 2)
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What is the Serosa layer of the stomach made of
Connective tissue covered with mesothelium
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What does the Fundus and body of the stomach secrete
- H+
- Intrinsic factor
- Mucus
- HCO3
- Pepsinogens
- Lipase
- "Hydrogen PHILM"
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What is the role of the Fundus and body of the stomach
- Reservoir
- Tonic force during emptying of the stomach
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What does the Pylorus of the stomach secrete
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What is the role of the Pylorus of the stomach
- Mixing
- Grinding
- Sieving
- Regulation of emptying
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How does the pH level of the acid in the stomach compare in the fasting state and fed state
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What happens in a Parietal cell to make it secrete acid
It contains Tubulovesicles which break open and cause the cell to undergo a morphological change causing secretion of their contents through new crevices created
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What channels and pumps are found on the lumen (apical end) of the Parietal cells
- K+ channel leaking into the lumen
- Cl- channel leaking into the lumen
- H+/K+ pump powered by ATP pumping K+ in and H+ out
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What channels and pumps are found on the Basal end of the Parietal cells
- Cl-/HCO3 exchange pumping Cl- in, HCO3 out
- K+ channel pushing K+ out
- Na/K pump pushing 3Na out, 2K in (uses ATP)
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What reaction takes place in the Parietal cells creating the HCO3 and H+ that is secreted
- Carbonic Anhydrase
- H2O and CO2 react making H+ and HCO3
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What is the alkaline tide
- The pH of the blood leaving the stomach in the veins is more alkaline then that entering the stomach through the arterial system
- This happens following a meal due to the active HCO3/Cl pump
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When does an alkaline tide return to normal
- About an hour following a meal
- Returns to normal when the acid absorbed in the small intestines meets with the bicarbonate created in the stomach
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What are the intraluminal levels of Cl, K, Na, H+ before and after secretion from the Parietal cells
- Na is relatively high before, extremely low following
- Cl goes up slightly
- H+ goes up dramatically
- K+ only slightly rises
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What are the three phases of gastric secretion in the stomach
- Cephalic phase (seeing/smelling food)
- Gastric phase (food in stomach)
- Intestinal stage (food in intestines)
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Cephalic stage of gastric secretion is controlled by
Parasympathetics that excite pepsin and acid secretion in the stomach (vagus nerve)
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The Gastric phase of gastric secretion is controlled by
- - Local nervous secretory reflexes
- - Vagal reflexes (Vagal center of medulla)
- - Gastrin-Histamine stimulation
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The intestinal stage of gastric secretion is controlled by what two mechanisms
- Nervous mechanisms
- Hormonal mechanisms
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What happens in the Oxyntic area
- Digestion of proteins (pepsinogen & HCl)
- Protection of the stomach (HCO3 & mucus)
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Regulation of acid secretion in the Parietal cells works by what three systems
- Neural
- Paracrine
- Endocrine
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Neural control of the release of acid from the parietal cells happens via what steps
- Acetylcholine release
- Muscarinic receptor stimulated
- PLC
- IP3
- Ca+ release
- H+/K+ ATPase pump is activated
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Paracrine regulation of acid release from the parietal cells happens via what steps
- Gastrin release
- CCK2 on Enterochromaffin cell activated
- Enterochromaffin like cells (ECL) release Histamine
- H2 receptor on parietal cell activated
- G-Protein
- Adenylyl cyclase
- cAMP
- K+/H+ ATPase pump activated
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Endocrine regulation of acid secretion from the parietal cells happens via what steps
- Gastrin release
- CCK2 receptors on parietal cells activated
- Ca+ dependent pathway activated
- K+/H+ ATPase pump activated
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C20 fatty acids have what effect on parietal cell acid secretion
- They trigger Prostaglandin release
- Prostaglandins bind to a receptor on the parietal cell
- Inactivation of acid release
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While the neural signals trigger the parietal cell to secrete acid what is it causing in the superficial epithelial cells
- Acetylcholine is causing Mucus and Bicarbonate release providing protection
- Prostaglandins also contribute to this signal
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H+ secretion and motility from the stomach is lowered by the release of
- Cholecystokinin (CCK)
- Somatostatin
- Secretin
- GLP (Glucogon-like Peptide)
- VIP (Vasoactive Intestinal Polypeptide)
- GIP (Gastric Inhibitory Peptide)
- Serotonin
- "Triple S double G.... CV"
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What are the primary secretagogues for the stomach
- Gastrin
- Histamine
- Acetylcholine
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Enterogastrone
- Any molecule that inhibits motility and secretion from the stomach to the anus
- Secretin and CCK are the most important
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With the stomach at such an acidic environment, how do the surface epithelial cells stay at 7.4 pH
- They secrete mucus and HCO3 which buffers the cells from the damaging acidic environment
- Secretions of the mucus increase with food intake and acid secretion
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How is the enzyme Pepsinogen activated to Pepsin
- By a low pH, inactivated by a high pH
- pH< 5 Pepsinogen is activated to Pepsin
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How is the mucus that lines the stomach for protection from the acidic environment renewed
Pepsin breaks it down preparing for more secretion of mucus upon ingesting more food
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Pepsin and mucus secretion in the stomach is regulated by
Acetylcholine
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When damage is done to the surface epithelial cells of the stomach how do they regenerate
Stem cells found in the neck of the gland generate new surface cells in approximately 3-7 days
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NSAIDs have what effect on the stomach
They decrease mucus secretion making the stomach more prone to ulcers
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What is the most common cause for gastric ulcers
- H. pylori bacteria infection in the stomach
- (NSAIDs ingestion is the second)
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Motilin
Hormone synthesized in the Duodenal mucosa believed to play an important role in Migrating Motor Complex (MMC) patterning in the gut
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When is Motilin released
Just before phase 3 of MMC
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Migrating Motor Complex (MMC)
This is the movement of food down the intestines beginning in the proximal stomach
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What are the phases of MMC
- Phase 1 - Quiescent
- Phase 2 - Increasing amplitude
- Phase 3 - Peak electrical and mechanical activity
- Phase 4 - Declining activity (prep for phase 1)
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MMC predominates under what conditions
Fasting
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Interstitial cells of Cajal (ICC) are
Slow wave pacemakers in the Gut
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Interstitial cells of Cajal (ICC) are found where
- Between the circular and longitudinal layers of the gut
- Highly interconnected
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How does the emptying of different foods compare in the stomach
- Glucose is emptied much faster then Proteins
- Carbohydrates are emptied faster then Fats
- Hypertonic and acidic foods are slowly released
- Liquids are emptied the fastest
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What symptoms precede and or accompany vomiting
- Tachypnea
- Copious salvation
- Dilation of pupils
- Sweating
- Pallor
- Nausea
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What nerves and nuclei are involved in vomiting
- Glossopharyngeal
- Vagus
- Nucleus tractus Solitarius
- Brain stem vomiting center
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