Stomach Flashcards
How many layers of smooth muscle in the stomach?
Three:
Oblique
Circular
Longitudinal
3 Stomach functions?
Mechanical processing
Digestion
Secretion
What are the folds in the stomach called?
Rugae
Gastric motility roles of the stomach?
Accepting and holding food
Relaxation
Accommodation
What reflex does accommodation require in the stomach?
Vaso-vagal
What are the 3 phases of peristaltic waves traveling over the antrum?
Propulsion
Emptying
Retropulsion
Which cells secrete HCl and intrinsic factor in the fundus and body of the stomach?
Parietal (oxyntic) cells
Where is peptide hormone (gastrin) released from?
G cells of stomach and duodenum
What are the 2 forms of gastrin?
G17 (17 amino acids) – main form secreted from antrum
G34 (34 a.a.: the C-terminal 17 are the same as G17) - main form secreted from the duodenum
What is the release of gastrin stimulated by?
Lumenal proteins / amino acids
Parasympathetic input (cephalic, and in response to gastric stretch), mediated by gastrin releasing peptide from interneurons
What inhibits release of gastrin?
Release inhibited by lumenal [H+] – negative feedback
What are the 2 main functions of gastrin?
Main actions on the stomach are to stimulate acid secretion, and promote mucosal growth
an endocrine regulator of acid production
In parietal cells, what inhibits acid secretion?
Somatostatin
What two things protect the surface epithelium in the stomach?
bicarbonate and mucus
What is intrinsic factor and where is it released from?
55 kDa glycoprotein
Released from parietal cells into the stomach
What does intrinsic factor do and why is it important?
Binds to cobalamin (Vit B12), but not until the small intestine.
Essential for cobalamin uptake in the ileum.
What is the effect of gastrin mediated by?
The effect of gastrin is mediated by CCK-a receptors
Where are pepsins secreted from?
from the chief and mucus cells
When are pepsins secreted?
Secreted in response to ACh, [H+]. Minor effects of secretin, CCK and gastrin (latter two via CCK-A receptor)
How are pepsins initially secreted?
Secreted as prohormones (pepsinogens)
Cleave spontaneously at low pH (<pH3)
Cleaved by pepsin (autolysis)
What is the optimum pH of pepsins?
pH 2-3
At what pH are pepsins denatured?
pH5-7 (once they reach the small bowel)
What does gastric lipase do?
Cleave the outer fatty acids off triglycerides, leaving diacyl glycerol
What is the optimum pH of gastric lipase?
pH Optimum is about 4: Stable in the stomach, but denatured by pancreatic proteases. Works together with lingual lipase
Which enzyme initially digests polysaccharides?
Ptyalin α-Amylase
What is the optimum pH of Ptyalin α-Amylase?
pH 7, denatured at 4.
Still hangs around in the fundus and body, where there is lots of food, but it isn’t well mixed with acid yet.
What are 5 causes of vomiting?
- Vagal afferents, in response to irritants in or around the bowel
- Psychogenic: pain, revulsion
- Motion sickness / labyrinthine -disorders
- Drugs or toxins with a direct effect
- Pregnancy
How is vomiting controlled?
Centrally controlled: area postrema = chemoreceptor trigger zone
What are the consequences of vomiting?
Salivation (waterbrash), Sweating, Hyperventilation
Loss of normal gut motility – retrograde peristalsis
Retching: involuntary contractions of the diaphragm and abdominal wall muscles
Displacement of the cardia into the thorax
Emptying of gastric (+/- small bowel) content
