Physiology of GI Tract: Secretions, Digestion and Absorption I Flashcards
In what two functional regions is gastric mucosa found?
Oxyntic Gland Area- 85%
- Cardia
- Fundus
- Corpus
Pyloric Gland Area- 15%
- Antrum
- Pylorus
What are two significant cell types found the pyloric gland?
- Mucosal cells
- G-cells
Ulcers tend to occur near ___________.
Mucosal junctions
As you distend the stomach, food will go into the body of the stomach and then go up into the _______ region for storage.
Fundic
NOTE: Eventually, when you increase the contractility of the stomach, the food will move into the greater curvature and then into the distal stomach
How are stomach emptying waves elicited?
As you fill the stomach and increase distenstion of the stomach and icnrease vagal afferents going to the brain, vagal efferents retun to superimpose their higher electrical activity on the pacemaker cells found in the cardia of the stomach. These cells begin to reach the threshold of the mid-stomach cells which are going to depolarize. They’ll give rise to stronger AP that will move across the distal stomach.
Which substances are secreted by mucous neck cells? What is the stimulus for release and function of each secreted substance?
-
Mucus
-
Stimulus
- Tonic secretion
- Irritation of mucosa
-
Function
- Physical barrier between lumen and epithelium
-
Stimulus
-
Bicarbonate
-
Stimulus
- Secreted with mucus
-
Function
- Buffers gastric acid to prevent damage to epithelium
-
Stimulus
Which substances are secreted by parietal cells? What is the stimulus for release and function of each secreted substance?
-
Gastric acid
-
Stimulus
- Acetylcholine
- Gastrin
- Histamine
-
Function
- Activates pepsin; kills bacteria
-
Stimulus
-
Intrinsic factor
-
Stimulus
- Acetylcholine, gastrin, histamine
-
Function
- Complexes with vitamin B12 to permit absorption
-
Stimulus
Which substances are secreted by enterochromaffin-like cell? What is the stimulus for release and function of each secreted substance?
Histamine
-
Stimulus
- Acetylcholine, gastrin
-
Function
- Stimulates gastric acid secretion
Which substances are secreted by chief cells? What is the stimulus for release and function of each secreted substance?
Pepsinogen
-
Stimulus
- Acetylcholine, secretin
-
Function
- Digests proteins
Gastric Lipase
-
Stimulus
- Acetylcholine, secretin
-
Function
- Digests fats
Which substances are secreted by D cells? What is the stimulus for release and function of each secreted substance?
Somatostatin
-
Stimulus
- Acid in stomach
-
Function
- Inhibits gastric acid secretion
Which substances are secreted by G cells? What is the stimulus for release and function of each secreted substance?
Gastrin
-
Stimulus
- Acetycholine, peptides, and amino acids
-
Function
- Stimulates gastric acid secretion
Ionic concentrations in gastric juic vary with secretory rate
Gastric acid secretion
KNOW THIS SLIDE
- Lumen= Apical membrane
- Plasma= Basolateral membrane
KNOW THIS SLIDE
Components of mucus
85% H2O
15% glycoproteins
NOTE: The upper gastrointestinal mucosa is covered by a layer of mucus that is relatively impermeable to pepsins
What substances are released by mast cells?
PGs, leukotrienes, histamines, and chemotactic factors
NOTE: During damage histamine, acid and other vasoactive agents increase capillary filtration
How can a patient get blood in the abdomen?
- This comes from breakdown of the mucosal barrier.
- If you get a break in the mucosal barrier and the acid is allowed to get into the underlying mucosa, you can get hemorrhaging becuase of the small arterioles and venules that are found in that area.
Where is H. Pylori located?
Mucus layer overyling the gastric epithelium
Which products are released by H.pylori?
- Urease
- Cytotoximes
- Mucinase
- Degrages mucus glycoproteins
- Phospholipase
- Damage epithelial cells
- Platelet-activating factor
- Mucosal injury, thrombosis in microciculation
How does H.pylori survive in acid?
Prouces own urease, which converts urea to ammonia and CO2
What substances does H.Pylori decrease the release of?
- Antral D- cells
- Somatostatin
*This leads to an increase in gastrin and possibly acid secretion
There are 3 substances that stimulate parietal cell secretion. What receptor does each substance bind to respectively?
-
Acetycholine
- M-2 receptor
-
Histamine
- H-2 receptor
-
Gastrin
- CCkb receptor
How does acetylcholine stimulate parietal cell secretions?
- Binding Ach to its receptor causes an increase in intracellular calcium, which stimulates the proton pump in the production of acid
How does histamine stimulate parietal cell secretions?
cAMP
How do prostaglandins function to regulate acid secretion?
Blocks increase in cAMP
Omeprazole is trapped and activated in the __________
Secretory canaliculus
NOTE: This drug is very effective against acid secretion because it forms a covalent bond and forms an active sulfur group
What are the 4 phases of the stimulation of acid secretion?
Acetylcholine acts on the _________ cell, while bombesin acts of the ________ cell.
Oxyntic cell; G-cell
The cephalic phase is mediated by the ____________ nerve.
Vagus
NOTE: Bombesin, acetylcholine and somatostatin are released from the vagal nucleus, with the latter inhibiting bombesin.
What factors stimulate the gastric phase?
Distension and protein digestion products
NOTE: Distension will lead to the activation of local reflexes and the vago-vagal reflex. These stimuli stimulates the release of gastrin and acetylcholine.
What factors stimulate the intestinal phase?
Hormones and absorbed amino acids
Which factors influence acid secretion?
pH, food buffering, and gastric emptying
When do you have the highest concentration acid in your stomach?
4-5 hrs after a meal
*This is why we have to advise our patients to eat multiple small meals a day to decrease long amounts of acid in your stomach
