Our Gut Reactions To Food Flashcards
What happens in phase 1/oral phase of deglutition?
Food bolus is formed by mastication
Tongue moves up and backwards
VOLUNTARY
What happens in phase 2/pharyngeal phase of deglutition?
Soft palate rises Epiglottis closes Pharynx contracts UOS relaxes INVOLUNTARY
What happens in phase 3/oesophageal phase of deglutition?
UOS contracts
Bolus moved by peristalsis
LOS relaxes
What does the pharynx stimulate?
Tactile/distension receptors on pharynx send signals to brain stem which sends signals causing the UOS to relax
What happens when food enters the stomach?
Signals travel up vagal afferent fibre to brain stem
Brain acts to change gut environment by signals down vagal efferent fibres
Eg Ach down phrenic nerve
Reflex contractions of lower oesophageal sphincter
What are the regions of the stomach?
Lower oesophageal sphincter Fundus Corpus - acid secreting Antrum - muscular pump where endocrine cells lie Duodenum Pyloric sphincter
How is food mixed in the stomach?
Retropulsion
What keep food in the stomach?
Pyloric sphincter
What happens in the pacemaker zone of the stomach?
Peristaltic contractions
How do we accommodate a large meal?
Receptive relaxation of the body of the stomach (corpus)
Brainstem acts on intrinsic nerves in stomach wall, switches off nerves giving stomach tone and switches on nerves that relax
What is released when we have had enough food?
At the end of a meal CCK acts on vagal afferent fibres
Lowers appetite and lowers food intake
How do fatty meals delay gastric emptying?
By releasing CCK from the duodenum
What delays and controls gastric emptying?
Fat rich, hypertonic and acidic meals, and meals with high viscosity all delay gastric emptying
Rate of emptying is controlled by the duodenum
What is the major cell type in the fundus of the stomach?
Surface epithelial
What is the role of mucus in the fundus?
Contains Mucins which detects against proteases
Barrier against forces and mechanical damage
What is the role of HCO3 in stomach?
Creates a pH diffusion barrier
Protects against acid
What is the role of gastric lipase in fundus of stomach?
Facilitates the breakdown of fat
What are the 4 types of cell in the corpus of the stomach?
Surface epithelial
Chief cells (zymogen)
Parietal cells
Enterochromaffin like (ecl)
What is function of surface epithelial cells in corpus of stomach?
Mucus and hco3- secretion
What do chief cells / zymogen n the corpus secrete?
Pepsinogen which is an auto catalyst - activates its own precursor (zymogen)
What s the function of parietal cells in the corpus of the stomach?
Acid secreting cells
HCl - sterilising food content and provides pH for Pepsins breaking down food
Intrinsic factor for uptake of B12
What is the function of enterochromaffin-like cells in the corpus of the stomach?
Histamine - an acid stimulating factor for production of HCl
Endocrine cell
What is the muscular part of the stomach?
Antrum
What are the major cells types n the antrum?
Surface epithelial
Some chief cells
G cells
D cells
What do G cells in the antrum produce?
Gastrin
What is the role of gastrin?
Activates acid secretion and histamine release
What do D cells in the antrum secrete?
Somatostatin
What is the role of somatostatin?
Endogenous inhibitor in the gut
What are the cells of the gastric corpus gland?
Top= Surface epithelial cells (protective role)
Proliferating cells
Parietal cells - acid secretion
Enterochromaffin-like cells - secrete histamine
Chief cells - secrete pepsinogen to lumen
What are acid secreting parietal cells full of?
Mitochondria
What is H+ exchanged for at the apical surface?
K+
What channels are there on the apical surface?
H+/K+ATPase pump (H+ OUT K+ IN)
K+ channel(K+ OUT)
Cl- channel(Cl- OUT)
What is HCO3- exchanged for at basolateral surface?
Cl-
What channels are there on the basolateral surface?
Cl-/HCO3- exchanger ( HCO3- OUT Cl- in)
Na+/K+ exchanger (Na+ OUT K+ IN)
K+ channel (K+ OUT)
What is released into the lumen at the apical surface?
HCl
What is released into the blood at the basolateral surface?
NaHCO3
What occurs at the cephalic stage of gastric acid secretion?
Thought/sight/smell/taste of food initiates Ach and GRP (neural)
Ach —> histamine (paracrine)
GRP —> Gastrin (endocrine)
What occurs at gastric phase of gastric acid secretion?
Distension of food in stomach —> Ach (neural) and gastrin (endocrine)
Ach —> histamine (paracrine)
Gastrin —> Histamine (paracrine)
What happens in the intestinal phase of gastric acid secretion?
Distension/food in duodenum —> Ach (neural) and Gastrin from duodenal G cells (endocrine)
Ach—>histamine (paracrine)
Gastrin—>histamine (paracrine)
What as acid secretion controlled by?
Gastrin and Ach activate histamine secretion of ECL cells which activates secretion of H+ into the gland lumen from parietal cells
Gastrin and Ach also directly activates H+ secretion from parietal cells
Somatostatin is endogenous inhibitor
Noradrenaline, CCK, VIP & CGRP activates D cells which produce somatostatin
What controls antral G cell function?
Protein/Peptides/amino acids activate G cells
GRP activates G cells to secrete Gastrin into circulation which acts of ECL/Parietal cells in corpus
H+ activates D cells to produce somatostatin which inhibits G cells release of gastrin
What is helicobacter pylori associated with in the antrum?
Decreases somatostatin secretion
Increases Gastrin secretion
Increases acid secretion
—> duodenal and peptic ulcer disease
What s helicobacter pylori associated with in the antrum and corpus?
Increases gastrin
Decreases acid secretion
—> atrophic gastritis and gastric cancer
