Intro to GI Flashcards
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
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
two sphincters
-upper sphincter
-lower esophageal sphincter
-esophageal sphincters preserves the vacuum of esophagus
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
lower esophageal sphincter
-excludes gastric contents from refluxing back into esophagus
four main parts of stomach
-cardia
-fundus
-body
-antrum
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
fundus
-Above and to the left of the cardia
-Continues to form the main portion of the stomach
body
body tapers to form the antrum
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
two openings
-cardiac/LES
-pyloric sphincter- surrounded by circular band of muscle
-mucosa is lined with columnar, goblet, paneths and endocrine cells
layers
-mucosa
-mucularis mucosa
-submucosa
-muscularis externa (3 layers of smooth muscle)
-serosa
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
parietal cells
-secrete HCL and intrinsic factor (B12 absorption)
G cells
-secrete gastrin (stim parietal cells)
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
