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40 Cards in this Set
- Front
- Back
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Regional variations in gut layers
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Esophagus: stratified epithelium, non-keratinized
Submucosa glands for lubrication Stomach: mucosa has multiple types of secretory cells in large quantities Smooth muscle layer is larger Small intestine: mucosa includes secretory and absorptive cells Large intestine: absorptive cells and goblet cells for lubrication |
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esophagus histology
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Proximal – striated muscle
Distal – smooth muscle Both are stratified squamous Lamina propria contains lymphatic tissue and lymphoid nodules Esophageal cardiac glands in lower esophagus produce neutral mucus to neutralize stomach acid Subepithelial glands for secretion – produce acidic mucosa for lubrication Muscularis – longitudinally and circumferentially arranged muscle Innervated by vagus nerve Esophagus coated in adventitia – blood vessels and nerves At lower end, elastic fibers attach esophagus to diaphragm |
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sphincters in esophagus
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Closed normally, except during swallowing
(a)upper – associated with larynx – pulls larynx up and way, routing food to esophagus (b)lower – joins esophagus to stomach |
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esophagogastric junction
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Esophagogastric Junction – transition squamous epithelium to columnar epithelium
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stomach function
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Function:
Short-term storage reservoir Enzymatic digestion – proteins in particular Liquefaction of ingesta Ingesta slowly released into small intestine Absorption – lipid soluble compounds – aspirin, NSAIDs, ethanol Can cause gastritis |
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stomach muscle structure
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Structure: outer layer – longitudinal muscle
Middle layer - Circumferential muscle Inner layer - Oblique muscle layer |
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histology of stomach
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Histology: gastric pits
Parietal cells in neck to fundus Chief cells only at fundus of gastric pit |
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secretory products of gastric epithelium
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Secretory products of epithelium:
Mucus – mucous cells cover luminal surface and extend into the glands Secrete bicarb mucus Acid – HCL by parietal cells Proteases – pepsinogen (inactive when secreted) by chief cells Acid activates to pepsin Hormones – gastrin influences acid secretion and gastric motility Miscellaneous - Lipase, gelatinase, Intrinsic factor |
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gastric pit cell types
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nonsecretory - stemm cells
primarily in the isthmus of glands secretory - surface mucous cells mucous neck cells parietal cells chief cells enteroendrocrine cells |
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surface mucous cells of gastric pits
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– surface mucous cells
Contain mucinogen granules, released forms viscous coat adhering to epithelial surface Mechanical and acid protection |
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mucous neck cells of gastric pits
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Mucous neck cells
Shorter than surface cells, less mucinogen Produce more soluble mucus under vagal control |
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parietal cells of gastric pits
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Parietal cells – acid and intrinsic factor
Fried egg appearance Acid secretion: water dissociates, forms bicarb Bicarb transported out of basolateral membrane in exchange for CL, CL and K transported to lumen of cannaliculi by passive conductance, H/K ATPase used to bring H in losing K, H creates gradient driving water across membrane, Receptor regulation for: ACh Gastrin Histamine |
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chief cells of gastric pits
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Chief cells – pepsinogen
Abundant rER – basophilic basally Zymogen granules apically – eosinophilic |
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enteroendrocine cells of gastric pits
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Enteroendocrine cells
Most prominent at base of pit Apex doesn’t reach lumen, secrete basally Poorly stained granules, specialized for particular type of secretion Histamine, CCK, gastrin, secretin, VIP, GIP, motilin, somatostatin |
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cardiac region variations
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Cardiac glands – vary by region
More mucus producing in cardiac and pyloric regions Cardiac region – moderately deep pits, tortuous, loosely packed tubular glands |
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fundic region variations
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Fundic – shallow pits, long straight tubular glands
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pyloric region variations
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Pyloric – deep pits, coiled and branched glands
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gastroduodenal junction variation
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Gatroduodenal junction:
Mucosa – change from gastric pits and glands to intestinal villi Submucosa – begin seeing Brunner’s Glands (all in duodenum) Secrete bicarb and glycoproteins to neutralize chyme Muscularis externa – thicker in pyloric stomach, thinner in duodenum |
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small intestine function and structure
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Site of absorption with final stages of digestion occurring at small intestine surface
Absorption of most water and electrolytes and all dietary organic molecules Regulates water and acid-base balance Structure: plicae circularis – involves submucosa and mucosa Villi – invaginations of mucosa Crypts – invaginations of epithelium Microvilli on absorptive cells Glycocalyx – formed by glycoproteins projecting from apical plasma membrane |
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small intestine cell types
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nonsecretory -
stem cells intermediate cells - differentiating cells enterocytes - absorptive cells secretory enterocytes - produce digestive enzymes goblet cells - mucus paneth cells - lysozyme enteroendocrine cells - peptides |
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absorption in the small intestine
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Absorption:
Routes: paracellular – across tight junction Transcellular – across plasma membrane Organic molecules Cells – microvillus border – contain actin microfilaments (brush border) Extensive apical SER – packaging of nutrients for transport through cytoplasm Cells tightly opposed apically Enterocytes: Electrochemical sodium gradient across epithelial cell boundary Maintained with Na/K ATPase in basolateral membrane Create sodium gradient to bring in water, amino acids, and carbohydrates Fatty Acids: Diffusion across plasma membrane, transported to ER, used for triglycerides Then packaged with cholesterol, lipoproteins to make chylomicrons Chylomicrons transported to basolateral aspect, and exocytosed into lymphatics |
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goblet cells of small intestine
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Goblet cells:
Produce mucus barrier Carbohydrates on mucin molecules bind bacteria Reduce diffusion of hydrophilic molecules that are dangerous |
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paneth cells of small intestine
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Paneth Cells
Defense against microbes – similar to neutrophils Alpha-defensins that interact with phospholipids in membranes, creating pores Lysozyme and phospholipase A2 |
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regional variations in small intestine
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Regional histology of small intestine
Jejunum and ileum lack Brunner’s glands Jejunum is main absorptive site – plicae and complex villi Ileum has greatest amount of lymphoid GALT and Peyer’s Patches |
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large intestine function and structure
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Function:
Recovery water and electrolytes Formation/storage of feces Microbial fermentation Sections – cecum with appendix Colon Rectum – continuous with anal canal Structure – no villi Muscularis externa – three equally spaced bands of teniae coli Crypts – straight and unbranched, absorptive cells apically, goblet cells deeper No submucosal glands Inner circular layer of muscle thicker except at teniae coli |
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regional variations in large intestine
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Regional difference – absorptive cells predominate until distal colon, then goblet
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absorption in the large intestine
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Absorption – water, Na, CL
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secretion in large intestine
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Secretion – bicarb, mucus
Secrete mucus in response to tactile stimuli and parasympathetic stimuli |
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appendix structure and function
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Structurally similar to colon, but no taeniae
Mucus similar – straight glands Lamina propria and submucosa contain abundant lymphoid tissue, accumulates during childhood, then progressively disappears and replaced with fibrous tissue |
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rectoanal junction structure
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Rectoanal Junciton
Colorectal zone – columnar epithelium Anal transitional zone – simple columnar to stratified squamous Squamous zone – stratified squamous that is continous with perineal skin |
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Liver Functions
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Digestive – bile production and excretion
Metabolic –metabolism of fats, proteins, carbohydrates Storage of glycogen, vitamins, minerals Excretion of bilirubin, cholesterol Enzyme activation Synthesis – plasma proteins Clotting factors Endocrine factors Detoxification/purification/anti-pathogen |
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blood supply to liver
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25% from hepatic arteries – oxygenated
75% from portal system – deoxygenated First to see nutrients and toxins Blood supply is mixed in sinusoidal capillaries Drain into terminal hepatic venules (central veins) which empty into sublobular veins Blood reservoir: Store and release blood Stores 10-15% of total blood volume Can eject blood to adjust for blood loss or can absorb to buffer from increased volume |
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organization of liver
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Organization:
Human liver lobules merge, but functional separate by blood supply Scheme 1: classic hepatic lobule Emphasizes vascular organization Polyhedral with portal triads at each corner with terminal branches of hepatic artery, portal vein, and bile duct Connective tissue around each part Sinusoids between hepatocytes Scheme 2: emphasizes exocrine function Axis is an interlobular bile duct within portal area Outer margins are three imaginary lines connecting three closest veins Defines a block of tissue that contains the liver parenchyma that secretes bile into an axial bile duct Bile is central component Scheme 3: the liver acinus Combines the two Short axis defined by two adjacent portal triads Long axis defined by two central veins Allows description of exocrine that is comparable to portal lobule |
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cytology of hepatocytes
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Cytology of Hepatocytes:
Eosinophillic with significant intracellular glycogen – cytoplasm appears granular Central nucli with prominent nucleoli Portions of the surface of each hepatocyte face the sinusoids Other surfaces face adjacent hepatocytes Bile canaliculi form at intercellular surfaces |
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structure of sinusoids and kupffer cells
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Structure of sinusoids and Kupffer Cells
Sinusoids – fenestrated walls Large openings for passage material out of circulation into spaces around hepatocytes Kupffer cells – phagocytic cells in sinusoid walls Form part of lining (not on epithelial cells) and can extend into lumen Function: Part of the moncyte/macrophage system Engulf pathogens, debris, damaged blood cells, heavy metals Remove particular materials and microbes from circulation Particularly microbes from GI tract |
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space of Disse
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Space of Disse – between hepatocytes and discontinuous epithelium lining sinusoids
Microvilli from hepatocytes extend into space Reticulin fibers for support Canaliculi form at intercellular surfaces by apposition shallow gutters on surfaces adjacent Opposite side of hepatocyte Bile is transported from hepatocytes into canalicular system |
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lymphatics of liver
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Lymphatic system of liver:
Approximately half of lymph arises in liver Fenestrations and space of Disse provide space for lots of proteins and fluid to form Lymph flows thorugh space of Disse to collect in small lymphatic capillaries associated with portal triads Periportal space of Mall Liver ascites – lymph accumulates with high pressure in sinusoids |
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gall bladder histology
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Mucosa highly folded
Columnar epithelium with microvilli No muscularis mucosa or submucosa Interlacing bundles of smooth muscle in muscularis externa Adventitia toward liver side, serosa on other Columnar cells – look like typical absorptive cells with microvilli Apical junctional complexes separating lumen from lateral intercellular space During active transport – salt is pumped form cytoplasm to intercellular space and water follows, more salt and water diffuse into cell from lumen and intercellular space becomes extended Fluid moves intercellular space to connective tissue and then into blood vessels |
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pancreas histology
exocrine |
Endocrine and exocrine function by separate population of cells
Exocrine – serous gland that secretes into duodenum Secretory units = acinar or tubuloacinar shape comprising simple epithelium There is little connective tissue around acini but lobes are surrounded by collagenous connective tissue Endocrine pancreas is dispersed as discrete cell masses (islet of langerhans) within exocrine pancreas Zymogen granules in apical cytoplasm Granules contain proenzymes critical for digestion Trypsinogen, pepsinogen, procarboxypeptidase, amylase, lipase Basophilic staining basally because of lots of rER |
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pancreas endocrine
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Endocrine pancreas:
Islets of langerhans – lack acinar organization Supplied by capillaries Initial duct leads = intercalated duct begins within acinus Duct cells = centroacinar cells Intercalated ducts are difficult to identify – appear linear arrays of squamous to cuboidal Intralobular ducts: drain into larger ducts within lobules Intralobular ducts Cuboidal epithelial cells and cylindrical arrangement of duct cells Interlobular ducts – intralobular drain into interlobular ducts Run in connective tissue between lobules often along with blood vessels |
