The Stomach Flashcards
Functions of the stomach
- temporary storage
- start digestion of protein
- small amount of carb digestions
- disinfect (acidic environment)
What controls the release of chyme into the duodenum from the stomach?
Pyloric sphincter
What type of epithelium lines the stomach?
Simple columnar epithelium
Outline the lower oesophageal sphincter
- at the junction of the oesophagus + stomach
- decreases reflux into oesophagus
- intrinsic smooth muscle of stomach
- right crus of diaphragm loops around +acts to close when intra abdominal pressure increases
Adaptations to prevent reflux
- lower oesophageal spinchter
- acute angle of food entering stomach from oesophagus
What is receptive relaxation?
- peristalsis alert stomach that food is on its way
- reflex relaxation of proximal stomach due to rugae
- receptive relaxation
- fundus distended
- stomach can fill without significant rise in pressure
Describe the muscles of the stomach
Oblique
Circular
Longitudinal
Thinner proximal
Thicker distally
Describe the epithelial surface of the stomach including the cells and their functions
- epithelial surface lined with surface mucous cells: produce mucus which acts as a protective layer
- parietal cells: produce HCl + intrinsic factor
- chief cells: secrete pepsinogen > pepsin (facilitated by acidic condition of stomach)
- G cells: produce gastrin
- gastric pits > gastric glands | contain parietal, chief + enerteroendocrine cells
What cells are in gastric pits??
Parietal cells
Chief cells
Enteroendocrine cells
Parietal cells
Location
Function
Stimulated by
- body + fundus of stomach
- Produce HCl > makes the stomach acidic
- produce intrinsic factor > aids B12 absorption in terminal Ileus
- stimulated by gastrin from G cells
Chief cells
Location
Function
- in body + fundus of stomach
- Secrete pepsinogen
- Converted to pepsin (protease)
- Facilitated by the acidic condition of the stomach
G cells
Location
Function
Stimulated by
- pyloric antrum of stomach
- secrete gastrin > increases gastric acid secretion
- stimulated by GRP, ACh + amino acids
Mucous cells
Location
Function
- cardia, body + fundus of stomach
- secrete mucus + HCO3- ions > forms thick alkaline mucus layer adhered to epithelium > protects from acidic damage
Protective mechanisms of the stomach
- surface mucous cells: secretes mucous + alkaline HCO3 > alkaline mucous layer
- cells of stomach replaced regularly
- release prostaglandins
Outline the role of prostaglandins as a protective mechanism of the stomach
- increase mucosal blood flow
- support mucus layer
- generally protective
What stimulates stomach acid production?
- sensory triggers: sight, smell, taste
- gastric triggers: stretch, present of amino acids + peptides, food acts as buffer (pH increases)
- intestinal triggers: chyme in duodenum > presence of partially digested proteins
What decreases stomach acid production?
- reduction in stomach distension
- low pH detected
How do parietal cells produce acid?
Proton pump
H+ and K+ exchange
Outline the resting and active state of parietal cells
Resting phase
- proton pumps are in tubulovesciles
- tubulovesciles lack K+ permeability + not in contact with apical membrane
Active phase
- tubulovesicles attach to apical membrane (contains K+ channels)
- apical membrane has microvilli + canaliculi to increase SA
What are the phases of digestion?
What is their % of HCl production in stomach?
Cephalic 30% HCl
Gastric 60% HCl
Intestinal 10% HCl
What stimulates parietal cells?
Gastrin receptors
Histamine receptors
Muscarinic receptors
Outline gastrin stimulation
- G cells stimulated by peptides + amino acids
- gastrin released into blood stream
- binds to choleocystokinine receptor
. - GRP due to stretch
- ACh (muscarinic receptor) due to sensory triggers
Outline histamine stimulation of parietal cells
- entero-chromaffin cells stimulated by ACh (muscarinic receptor) + gastrin (CCK receptor)
- entero-chromaffin like cells produce histamine
- bind to H2 receptor on parietal cell > HCl produced
How is acid secretion inhibited?
- drop in pH detected by D cells
- produce somatostatin
- bind to G cell via somatostatin receptor + prevent gastrin release
How is HCl produced in the parietal cell?
- within the parietal cells: H2O + CO2 > H+ + HCO3-
- Cl- ions actively transported into cell from blood by Cl-/HCO3- exchanger (HCO3- out into blood > alkaline tide)
- Cl- passively diffuse into stomach lumen through Cl- channels
- H+ enter stomach lumen by H+/K+ ATPase
- secretion of HCl into stomach
How many parts does the stomach have?
Name them
5 parts
Cardia
Fundus
Body
Antrum
Pylorus
What vertebral level does the pyloric sphincter lie at?
L1
On the transpyloric plane
What anatomical structures lie on the trans pyloric plane?
Pyloric sphincter
Neck of pancreas
SMA origin
Portal vein forms
Spinal cord ends
Hilum of kidneys (ish)
How do the pyloric sphincter and lower oesophageal sphincter differ?
- pyloric sphincter is a strong + bulky muscular sphincter
- lower oesophageal sphincter has smaller muscle + relies of acute angle with stomach + right crus of diaphragm
What causes the alkaline tide following a meal?
- movement of HCO3- across the basolateral membrane of pariteal cells into blood in exchange for Cl- via Cl-/HCO3- exchanger
- pH of blood transiently rises after a meal
What is the alkaline tide?
The transient increased of blood pH after a meal due to movement of HCO3- from parietal cells into blood in exchange for Cl-
Fuction of stomach acid
- sterilising luminal contents
- denaturing enzymes
- activation of protease enzymes (pepsinogen > pepsin via acidic environment)
- does NOT break fats down
