Gastrointestinal System Flashcards
what separates the oesophagus from the pharynx?
upper oesophageal sphincter
what separates the stomach from the oesophagus and the small intestine?
- between stomach / oesophagus: lower oesophageal or cardiac sphincter
- between stomach / small intestine: pyloric sphincter
where does the small intestine terminate?
ileoceaecal junction (sphincter muscle)
describe the structures of the large intestine (4)
- caecum
- appendix
- colon: ascending, transverse, descending
- rectum
what are the 3 main arterial supplies to the GI tract? what structures does each supply?
- coeliac: liver, gall bladder, pancreas, stomach, spleen
- superior mesenteric: pancreas, small intestine, most of the large intestine
- inferior mesenteric: terminal portions of large intestine, rectum
describe the organisation of the microanatomy of the gut
4 layers: mucosa, submucosa, muscle and serous / adventitia
in the GI tract, what is the difference between serous and adventitial layers? what particular structures is adventitia associated with?
- serous: continuous with parietal peritoneum, slippery to reduce friction
- adventitia: fibrous connective tissue, present in oral cavity, upper oesophagus, asd. + desd. colon, rectum
describe mucosa of the GI tract (3)
- epithelial layer: type changes according to function of particular part of tract (eg. secretory, protective or absorptive)
- lamina propia: loose connective tissue containing BVs and lymph vessels (called lacteals in small intestine)
- muscularis mucosa / interna: smooth muscle, contracts to break down food
describe submucosa of the GI tract (3)
- loose connective tissue
- sometimes contains glandular structures
- submucosal nerve plexus found here - parasympathetic neurones
describe the layers and actions of muscularis external in the GI tract (2)
- inner circular layer: prevents food travelling back (closes behind contents)
- outer longitudinal layer: shortens and lengthens to pull contents along
what are the 2 plexi of the GI tract lining?
- submucous plexus - Meissner’s
* myenteric plexus - Auerbach’s
what type of epithelium lines the mouth and oesophagus?
non-keratinised stratified squamous epithelium (no secretion or absorption through epithelium)
describe the functions of mastication (4)
- saliva dissolves chemicals to stimulate taste buds
- lubricate food to ease swallowing
- mix starch-containing foods with salivary alpha amylase
- increase SA of food to facilitate digestion in stomach and duodenum
describe the salivary ducts (3, with 3 descriptions)
- parotid - lie in cheek, 25% of saliva, serous gland producing water saliva with increased amylase
- submandibular - under mandible, 70%, serous and mucous gland producing more viscous saliva
- sublingual - floor of mouth (many small ducts), 5%, mostly mucous cells producing thick, viscous mucus
describe the 4 anatomical regions of the stomach
- cardia - adj. to lower oesophageal sphincter
- fundus - upper portion, acts a reservoir for food and swallowed air
- corpus - main site of secretion
- pyloric antrum - adj. to duodenum, involved in mixing of food with secretions
describe the musculature of the stomach (3)
- outer longitudinal layer and inner circular layer (as in rest of GI tract)
- these layers are thicker in pyloric region
- fundus and corpus contain additional oblique layer of smooth muscle below circular layer
describe gastric mucosa (3)
- thick mucous membrane, smooth when distended
- develops rugae (folds) when empty
- luminal surface contains gastric pits, branching from tubular-shaped glands, which reach in towards level of muscularis mucosae
describe the 3 gastric glands, where they are found, and what they secrete (incl. cell types)
- cardiac - adj. to lower oesophageal sphincter: mucous cells secrete mucus for lubrication
- parietal - fundus and corpus: parietal cells secrete HCl, chief cells secrete pepsinogen, endocrine cells secrete somatostatin and ghrelin
- pyloric - pylorus: chief cells secrete pepsinogen, mucous cells secrete mucus, endocrine cells secrete somatostatin and gastrin
what are the functions of HCl in the stomach? (4)
- converts pepsinogen (a zymogen) to pepsin to facilitate protein digestion
- stimulates release of bile and pancreatic enzymes into duodenum
- promotes absorption of some vitamins and minerals
- kills microorganisms
describe the production and release of bile (3)
- produced in liver
- stored in gallbladder
- released into duodenum after meal via common bile duct
describe bile salts (3)
- derived from cholesterol - form cholic acid and chenodeoxycholic acid (bile acids)
- conjugated with amino acids glycine and taurine to form bile salts
- amphipathic - hydrophobic (cholesterol) component and hydrophilic (amino acid conjugate) component
describe the function of bile salts (2)
- emulsify lipid aggregates to increase surface area
* solubilisation and transport of lipids in aqueous environment
describe the action of different pancreatic enzymes (3)
- some pancreatic enzymes are secreted as active forms into duodenum (pancreatic lipase, pancreatic amylase)
- trypsinogen is activated by brush border enzymes (enteropeptidase), and then goes on to activate more trypsinogen (autoactivation) and other zymogens
- other proteases are also released as zymogens to prevent them from digesting the pancreas itself
describe digestion in the mouth (mechanical digestion, carbs, proteins and lipids)
- mechanical digestion via mastication
- carbohydrates: starch broken down by alpha-amylase to maltriose, maltose and alpha-limit dextrin
- no protein digestion
- lipids: minor contribution though lingual lipase
describe digestion in the stomach (mechanical digestion, carbs, proteins and lipids)
- churning action
- no carb digestion
- proteins: HCl denatures proteins and activates pepsin which cleaves proteins into small oligopeptides
- lipids: minor contribution through gastric lipase
describe digestion in the duodenum (mechanical digestion, carbs, proteins and lipids)
- chyme is mixed with pancreatic juice and bile (slightly alkaline to neutralise stomach acid)
- carbohydrates: alpha-amylase, brush border disaccharidases (maltase, sucrase, lactase) producing monosaccharides
- proteins: cleaved by trypsin, chymotrypsin and elastase to produce small peptides / dipeptides, brush border peptidases produce dipeptides / amino acids
- lipids: pancreatic lipase digests lipids to monoglycerides and fatty acids
describe the absorption of lipids (4)
- if fatty acids are less than 12 carbons long, they enter straight into portal blood
- if larger, triglyceride reformed into protein / lipid structure -> chylomicron
- chylomicrons are secreted into lymphatics via lacteals
- enter blood stream via thoracic duct
how are monosaccharides transported on the apical and basolateral sides of small intestine epithelium?
- apical: SGLT1 co-transporter (glucose, galactose), GLUT5 facilitated diffusion (fructose)
- basolateral: GLUT2 facilitated diffusion (all 3)
