CM- Approach to Stomach Disease Flashcards
What is the primary purpose of the stomach?
- store ingested nutrients and dispense them into the small intestine in an orderly fashion
- HCl prevents pathogens from causing enteric infections [it is NOT necessary for digestion]
What kind of cells are found in the glands of the cardia?
mucous cells that secrete mucus and pepsin
What type of gland is found in the body and fundus of the stomach?
What cells make up this gland?
Oxyntic glands made of:
- parietal cells
- chief cells
- enterochromaffin cells (ECL)
- endocrine
- mucus
What types of glands are found in the antrum of the stomach? What cells make up this gland?
Pyloric glands made of:
- mucous cells
- G cells (gastrin)
- D cells (somatostatin)
What glands are found in the duodenum? What is their role?
Brunner’s glands are located in the submucousa. They are a source of bicarbonate
As food enters the proximal stomach, what process occurs?
Receptive relaxation-
vagus efferents inhibit fundus and body muscular tone to allow volume expansion without pressure
How are liquids emptied from the stomach?
Once in the stomach, liquids rapidly redistribute and are emptied by a tonic pressure gradient from the proximal stomach and duodenum
How are solids emptied from the stomach?
- After storage for 30 minutes, they move to the antrum
- vagally mediated segmental contractions in the greater curve of the body mix the food
- when the food is 1mm or less, it is emptied into the pylorus
What 2 problems arise with the stomach if there is vagal nerve dysfunction/destruction?
- there is no receptive relaxation -> early satiety
2. there is no mixing–>delayed emptying
What happens to non-digestible (over 1mm) retained gastric solids?
Interdigestive Migrating Motor Complex contracts and pushes out undigested particles every 1.5-2 hours in the non-fed state.
How does the small intestine keep from being overwhelmed during digestion?
What 4 things are sensed?
What are suggested hormones that play a role in these reflexes?
There are receptors that respond to :
- low pH
- osmolarity
- fatty acids
- high caloric density
that signal back to slow gastric emptying
Suggested: CCK, secretin, GIP
At what concentration do parietal cells secrete HCl? What is the tonicity?
What happens when the patient vomits?
Parietal cells secrete HCl at a concentration of 160mmo/L and a volume determined by the number of partietal cells secreting.
It will be isotonic with NO sodium ions.
If the patient vomits, they lose [H+] but must keep the same concentration so there will be more Na in the gastric juices. This leads to Na depletion
What determines the volume and acidity of gastric juice?
The relative proportion of parietal and non-parietal secretions
What is the most important stimulant of gastric acid secretion?
What 2 cells is it released from?
What 2 receptors does it interact with?
Histamine is released from:
- ECL
- mast cells in the lamina propria
It acts on :
1. H2 receptor on parietal cells to release acid
2, H3 receptors on D cells to block somatostatin release
[somatostatin inhibits parietal AND ECL cells]
What are the 3 things Ach controls in gastric acid secretion?
- M3 receptor on parietal cells
- ECL to release histamine
- D cells to inhibit somatostatin release
What are the 3 things that stimulate acid release from parietal cells?
- Histamine
- Ach
- Gastrin
What 2 things stimulate the release of gastrin?
What 2 cells does gastrin act on?
Gastrin release from G cells in the atrum is stimulated by:
- presence of food
- neural release of gastrin releasing peptide (GRP)
It acts on:
- parietal cells to release acid
- ECL to release histamine (** more accepted scenario)
How does somatostatin regulate gastrin release?
What turns D cells on and off?
Somatostatin released from D cells can act in a paracrine manner on adjacent G cells to inhibit the release of gastrin.
Hydrogen in the gastric lumen turns on D cells which inhibit gastrin release.
Ach turns off D cells inhibiting somatostatin release
How do parietal cells release acid after Ach or Histamine has bound to it?
Ach–> Ca
Histamine->Gs->adenylate cyclase->cAMP
cAMP and Ca open the tubulo-vesicles that had been storing acid. They open into canaliculi with microvilli to increase the surface area from which acid is excreted into the lumen
H goes in the lumen in exchange of K by a proton pump. The protein pump relies on K in the lumen however.
Transcellular pathways for K and Cl must be open
What are the 2 proposed mechanisms of H3 receptors?
- on D cells to inhibit somatostatin release (pro acid)
2. on ECL to inhibit more histamine release (antacid)
What are the 2 MAIN inhibitors of acid secretion from parietal cells?
What are some others?
- Prostaglandins & somatostatin inhibit adenylate cylase which stops cAMP production in parietal cells
- Somatostatin also inhibits ECL directly stopping histamine release
Others: secretin, GIP, peptide YY
What are the mucosal defense factors against acid?
It is hypothesized to be prostaglandins because: 1. NSAIDS (which block COX) leads to ulcers.
2. In experiments, when prostaglandins were inhibited, ulcers developed as well.
What are the 3 means by which PGs protect gastroduodenal mucosa?
- secretion of mucus
- stimulation of bicarb secretion
- maintaining mucosal blood flow during periods of potential injury
Describe the process of vitamin B12 (cobalamin) absorption.
- B12 is separated from food by pepsin and acid
- B12 attaches to R proteins present in saliva
- In the alkaline duodenum, pancreatic enzymes hydrolyze the R protein-B12 complex
- Free cobalamin binds IF
- IF-cobalamin complex passes through the intestines to the ileum where it is actively absorbed.
What are the 4 things that can lead to failure to absorb cobalamin?
- IF deficiency
- pancreatic exocrine insufficiency (rare)
- small intestine bacterial overgrowth (achlorhydria)
- ileal disease (Crohn’s)
Why does deficiency of B12 not occur in a timely manner to pathology (failure to absorb)?
Liver stores of B12 can last up to 5 years with NO absorption
Who is the Schilling test performed on? What are the steps?
If is performed on people with low serum cobalamin after parenteral repletion of the vitamin.
- Radiolabeled B12 alone. If urine B12 is low,
- Radiolabeled B12 AND IF
- if it normalizes–> pernicious anemia
- if it is still low, - Radiolabeled B12 + antibiotics
- if normalizes–> bacterial overgrowth
- if not … - Radiolabeled B12 + pancreatic enzymes
- if normalizes = pancreatic exocrine insufficiency
Little digestion takes place under the influence of pepsin in the stomach. How does pepsin indirectly aid in digestion?
The release of AA and peptides by pepsin trigger the release of important digestive hormones like gastrin and CCK.
What are major symptoms of delayed gastric emptying?
- early satiety
- epigastric fullness/bloating
- nausea
- vomiting
A patient present with early satiety, epigastric fullness, nausea and vomiting. You are not sure if they have delayed emptying [motility disorder] or a mechanical obstruction. What test should you do?
Endoscopy
You CANNOT do a barium swallow in a patient suspected of mechanical obstruction
What is the only diagnostic study that can confirm delayed gastric emptying?
Radionucleotide scan using labeled mixed meal.
What are major causes of gastoparesis?
- post-surgical state
- diabetes, hypothyroidism
- muscular disorder (systemic sclerosis, ALS)
What are 2 situations that lead to rapid gastric emptying or “dumping syndromes”?
- gastric surgery
2. abnormal myoelectric function
Describe the difference between early dumping syndrome and late dumping syndrome,
Early- 30 to 60 minutes after eating. Rapid movement of food into the duodenum causes fluid shifts leading to faintness.
Late = 2-3 hours after eating. It is associated with excessive insulin secretion and rebound hypoglycemia