Stomach Flashcards
What are the main function of the stomach ?
- Receive food
- Disrupt food
- Continue digestion
- Disinfect
Describe the basic structure of the stomach
LOS, Cardia , Fundus , Body , Antrum , Pylorus
What are the different type of cells in the stomach ?
Parietal Enteroendocrine cells (G, D) Chief cells Enterochromaffin like cell Mucous cells
How is the stomach different in terms of wall composition ?
Extra Oblique layer of muscle
Where is the main site of strong peristalsis and why ?
Lower stomach : contractions every 20 seconds ,proximal to distal
Can’t be upper stomach because needs to be able to relax when receiving food to prevent increase of pressure , and reflux
What mechanism allow the stomach to receive food and how is it mediated ?
Receptive relaxation : allows food to enter stomach without raising pressure > prevents reflux of stomach content during swallowing
Possible thanks to Rugae and mediated by Vagus nerve
How does acidic conditions aid digestion ?
- unravel proteins
- activates protease (pepsinogen > pepsin )
- disinfect stomach
What does the stomach secrete in the lumen ?
HCL
IF
Mucus / HCO3
Pepsinogen
Which cells are predominant in the cardia ?
Mucous cells
What type of cells are found in the fundus and body ?
Mucous cells
Parietal cells
Chief cells
What cells are found in the Pylorus ?
Enteroendocrine cells : D cells and G cells
Which cells secrete Gastrin and when(stimuli )?
G cells (Antrum)
Stimulated by :
- Peptides/amino acids (made by pepsinogen from proteins )
- Vagal stimulation : Gastrin releasing peptide GRP and Ach
How is Gastrin production inhibited ?
Food leaves : pH drops
Stimulates D cells
Secrete Somatostatin which inhibits G cells
Which cells produce HCL and when (stimuli )?
Parietal cells
Stimulated by Gastrin ,Histamine , Ach from vagus nerve
How is HCL production inhibited ?
- Drop of pH when food leaves > D cells secrete Somatostatin > inhibition of G cells > no Gastrin
- Somatostatin also inhibits Enterochromaffin like cells > no histamine
- Stomach distension reduced when food leaves > reduced Vagal activity
Explain the “alkaline tide “phenomenon
HCL production needs H+ to be excreted in lumen by HKATPase
H+ produced in cell from H2O
By product is HO- which react with CO2 to form HCO3 which is released at basolateral membrane in blood
> > blood leaving stomach slightly alkaline
What are the phases of digestion ? (In relation to secretion )
Cephalic
Gastric
Intestinal
Briefly describe the cephalic phase of digestion
Smelling,tasting,chewing,swallowing induce parasympathetic stimulus by vagus nerve of Parietal cells and G cells (Ach + GRP)
Anticipating food also increases gastric motility
Briefly describe the gastric phase of digestion
- distension of stomach: vagus stimulation>parietal cells and g cells stimulation
- Presence of aa and small peptides >stimulation of G cells
- Food act as buffer to remove Gastrin inhibition (from D cells)
- Enteric NS and Gastrin cause SM contraction
What are the two phases of Intestinal digestion ?
- Chyme initially stimulate Gastrin secretion( protein detected )
- But presence of lipids activates enterogastric reflex (reduced vagal stimulation ,secretion of CCK and Secretin > inhibition of G cells)
What are the 3 defence mechanisms of the stomach to acid damage ?
- Mucus/HCO3 : released by surface mucous cells , for alkaline protection
- High turnover of epithelial cells
- Prostaglandins : maintain mucosal blood flow for nutrients
Why do NSAIDs cause gastric side effects ?
NSAIDs inhibit prostaglandins release > less vasodilation >less blood flow to epithelium > damage
Which substances can breach stomach defences ?
Alcohol : dissolve mucus
Helicobacter pylori : chronic gastritis
NSAIDS: prostaglandin inhibition
Give some eg of common gastric disorders
- GORD
- Gastritis
- Peptic ulcer disease
- Zollinger-Ellison disease
- Cancer
- Stress ulcers
