Gut Reaction To Food Flashcards
Swallowing (degluttion)
▪️phase I-oral -voluntary, striated muscle -chewing-forms a food bolus -tongue moves back and forwards -hypoglossal nerve (12) ▪️phase II-pharyngeal -involuntary, reflex action due to stretch receptors -soft palate rises, epiglottis closes -pharynx contracts -upper oesophageal sphincter relaxes -Cn9,10,12 ▪️phase III-oesophageal - involuntary, smooth muscle -UOS contracts -bolus moves due to peristaltic wave which increase in amplitude as it goes down -Increased pressure of the food relaxes LOS -LOS contracts after to prevent acid reflux
Entry of food into stomach
▪️tactile receptors (stretch) detect pressure from bolus
▪️signals sent to brain stem
▪️signals sent back down to
-phrenic nerve to contract diaphragm
-vagus nerve to LOS to release relaxant factors (vasoactive intestinal polypeptide and nitrogen oxide)
-vagus nerve also inhibits ACh to prevent contraction
Regions of the stomach
▪️cardiac
▪️fundus
-pacemaker zone for peristaltic contractions regulated by distension cause by food
-peristaltic contractions help mix and churn the food towards pylorus
▪️regal folds
-channel food that’s in a form suitable for absorption eg liquids
▪️corpus (body)
-acid secretions cells
▪️antrum
-muscular pump which grinds and mixes food causing reteropulsion
-endocrine cells-release gastric
How to accommodate a large meal
▪️stomach has tone-contraction happening to give shape
▪️tactile receptors responding to stretch initiate receptive relaxation of the body of the stomach
▪️signal sent by vagus nerve to brain stem, brain then sends signals to intrinsic nerves of stomach wall to inhibit ACh release and promote VIP/NO release
▪️when full:
-over-distension turns off motility of stomach
-I-cell in duodenum responds to fatty acids in food when it exits stomach, normally last to exit stomach
-CCK is released by I-cell which acts on vagus nerve fibres which signals to stop motility and signals to brain satiety
Gastric emptying
▪️liquids empty more rapidly than solids
▪️solids need to be broken down mechanicly and by enzymes
▪️inert object takes a long time to be emptied
▪️fat rich and acidic meals delays gastric emptying
▪️controlled by pyloric canal otherwise sites of absorption would be overloaded leading to water-retainment therefore diarrhoea
Fundus cells
▪️surface epithelial cells
- produce mucus HCO3 barrier
- gastric lipase which breaks down fats
- protect against mechanical damage and acid damage
Corpus cells
▪️surface epithelial -mucus and HCO3 barrier ▪️chief (zymogen) -precursors for enzymes (pepsinogen-inactive) -breakdown protein ▪️parietal -acid secreting cells (HCl) -sterilises food and right ph for pepsin -relaxes intrinsic factor which helps uptake of VB12 ▪️enterochromaffin-like -endocrine -histamine release- produces HCl
Antrum cells
▪️surface epithelial -mucus, HCO3 barrier ▪️chief -pepsinogen ▪️G-cells -gastrin secretion -activates acid secretion and histamine release ▪️D-cells -somatostatin secretion -switches everything off
Cells of gastric gland
▪️surface epithelial cells-exposed to lumen
▪️proliferating cells-neck of gland
▪️parietal cells- middle of gland
▪️ECL cells
▪️chief cells- bottom of gland
-as the pepsinogen moves up from CC it is activated by acid into pepsin-prevents auto digestion of gland
Parietal cell of stomach
▪️acid secreting cell
-packed with mitochondria- need energy to drive acid against in conc gradient into lumen
▪️resting:
-tubulovesicular membrane and intracellular canaliculus are separated
-TVM contain proton pump producing acid
▪️stimulated:
-TVM and ICC merge together and are open to gland lumen
-creates a LSA of acid pumps ready to secrete the acid
Parietal cell transport for acid secretion
▪️H+/K+ ATPase pump (apically) -pumps H+ out and K+ in ▪️K+ channel (apically and basolaterally) -K+ pumped out ▪️Cl- channel (apically) -Cl- pumped out ▪️Na+ pump (basolaterally) -Na+ pumped out, K+ in ▪️Cl-/HCO3- exchanger (basolaterally) -Cl- in, HCO3- out
▪️CO2 and water from respiration converts into HCO3 and H+
Last 8 slides of L6
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