Intro to GI Flashcards by Steph Nicolette

esophagus

-23-37 cm long/diameter of 1-2 cm and is divided into three parts:
-Cervical: continuous with the hypopharynx, begins at the lower border of cricoid cartilage (at level of C5/6) or cricopharyngeus muscle
-thoracic: from superior thoracic aperture (T1) to the esophageal hiatus (T10) in the diaphragm
-abdominal: from esophageal hiatus and is continuous with the cardia of the stomach at the gastro-esophageal junction

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layers of esophagus

-inner to outer
-mucosa
-submucosa- meissner’s plexus -> mucous
-muscularis externa- inner circular (auerbach’s plexus (motility) is between) and outer longitudinal
-no serosa- cancer can spread faster

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two sphincters

-upper sphincter
-lower esophageal sphincter
-esophageal sphincters preserves the vacuum of esophagus

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upper esophageal sphincter

-closure muscles- cricopharyngeus and inferior pharyngeal muscle -> important for air not going into stomach and bloating -> also for food
-opening muscles:
-anteriorly- superior and inferior hyoid muscles
-posteriorly- superior pharyngeal muscles
-exclude air during respiration
-prevents reflux of esophageal contents into pharnyx during peristalsis

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lower esophageal sphincter

-excludes gastric contents from refluxing back into esophagus

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four main parts of stomach

-cardia
-fundus
-body
-antrum

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cardia

-Where the esophagus opens into the stomach at the gastroesophageal junction behind the 7th costal cartilage at the level of the T11 vertebra
-Left of the midline

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fundus

-Above and to the left of the cardia
-Continues to form the main portion of the stomach

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body

body tapers to form the antrum

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antrum

-To the right is the wider pyloric antrum, which narrows to form the 2.5-cm long pyloric canal
-Opens into the duodenum at the pyloric orifice located at the level of the L1 vertebra

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two openings

-cardiac/LES
-pyloric sphincter- surrounded by circular band of muscle
-mucosa is lined with columnar, goblet, paneths and endocrine cells

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layers

-mucosa
-mucularis mucosa
-submucosa
-muscularis externa (3 layers of smooth muscle)
-serosa

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mucosa

-cardiac glands- secrete mucous
-gastric glands: parietal and chief
-pyloric glands- secretes mucous -> G cells and D cells
-rugae or gastric folds
-muscularis mucosa
-submucosa
-muscularis externa (3 layers of smooth muscle)
-serosa

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parietal cells

-secrete HCL and intrinsic factor (B12 absorption)

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G cells

-secrete gastrin (stim parietal cells)

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D cells

-secrete somatostatin (inhibits gastrin)

chief cells

-secrete pepsinogen

functions of stomach

-food reservoir
-blender
-important substances secreted into lumen -> hydrochloric acid pepsin, mucous, bicarbonate, intrinsic factor and water
-releases 2 hormones into blood- gastrin and somatostatin

small intestine

-duodenum
-jejunum
-ileum
-primary site for absorption of ingested materials
-extends from pylorus to ileocecal valve

function of small intestine

-digestion- breakdown of large molecules into small molecules
-done in lumen
-absorption- transport across the intestinal mucosa

layers of small intestine

-mucosa-3 layers
-submucosa
-muscularis externa
-subserous layer
-serosa

mucosa layer of the small intestine

-mucosa is the innermost layer which consists 3 layers
-epithelium- absorption and secretion occur here
-lamina propria- connective tissue and heterogenous cells
-muscularis mucosae- thin sheet of smooth muscle cells

contents of mucosa

-villi- finger like projections of epithelium
-villi contains blood and lymphatic (lacteals) vessels that extend into intestinal lumen
-villi increases SA for absorption
-crypts- crypts of lieberkuhn
-estimated to increase the absorptive surface area of the small intestine by up to 40 fold

duodenum

-shortest part 25 cm long
-bile and main pancreatic ducts enter descending part of duodenum
-ducts unite to form hepatopancreatic ampula

jejunum and ileum

-approx 6-7 long (20 feet) -the more distal ileal small bowel is capable of assuming the functions of proximal jejunal small bowel -reverse does not occur because the jejunum does not contain specific transport mechanisms for bile acids and vitamin B12

nutrient absorption: duodenum

-first 25 cm beyond stomach -initial fat digestion by pancreatic enzymes -micellar solubilization of fat -absorption of iron

duodenum and jejunun nutrient absorption

-digestion and absorption of carbohydrates, proteins, fats -absorption of most vitamins and minerals

ileum nutrient absorption

-major site of absorption of water and electrolytes -last 100 cm is obligate site of absorption of vitamin B12 and bile acids -unique to ileum -> jejunum cant take over this responsibility -if this is damaged -> malabsorption

epithelial layer of small intestine

-distinctive crypts, mucous coat, lamina propria (inflammatory cells) -muscularis mucosa -submucosa- rich in fibrous and neural tissue -circumferential circular layer of muscle -longitudinal muscle layer (thinner) -restricted to taenia coli in ascending, transverse, and descending colons as 3 narrow strips -taenia coli is very involved and surrounding the rectum -is continuous in rectum

subserosal and serosal layers of small intestine

-intraperitoneal regions of colon

adventitial layer of SI

-retroperitoneal regions -rectum, ascending, descending colon

colon haustra

-circular muscle folds -result from muscle contractions that remain constant for several hours at a time

function of colon

-principal site of absorption of electrolytes (naCl, H2O) -Approximately 1.5 L of fluid enters colon but 100-200 mL is excreted in the stool -a lot of bacteria in the colon and should stay there -Colonic bacteria are the main source of short-chain fatty acids (nutritious to the colon) -Butyrate and acetate -Localized nutritional value to the colonic absorbing cells

great number of bacteria than elsewhere in the GI tract

-Bacteria digest undigested food products such as complex sugars contained in dietary fiber -Forming the short-chain fatty acids (SCFAs) butyrate, propionate and acetate -Important energy source for the cell -Fermentation of sugars is a source of colonic gases such as hydrogen, methane and carbon dioxide

probiotics

-change bacteria to reduce fermentation -less gassy