GI Module 2 Flashcards
Gastric functions
Digestion (secretion and minimal absorption)
Motility (moving food into duodenum)
Partially digested food in the stomach
Chyme
Describe absorption in the stomach
No absorption EXCEPT NSAIDs, alcohol
When does the stomach musculature relax?
- Swallowing stimulates relaxation of stomach
- Prepares the stomach to be a reservoir for incoming food
Describe vago-vagal reflex with regards to the stomach
- Food enters stomach
- Stomach distends in response
- Vagal mechanoreceptors are stimulated which reflexively stimulates vagal VIP (vasointestinal peptide)
- VIP relaxes smooth muscle of stomach wall
What stimulates gastric emptying?
Parasympathetic activity
Describe the sequence of gastric emptying
- Retropulsion (4-5 peristaltic waves churn chyme)
2. Last wave forces pyloric sphincter open to move small amount of chyme into duodenum
Define retropulsion
Contractions of the stomach that push food back towards the body of the stomach
The pylorus is normally open ____ cm
1-2 cm
Why is the pylorus normally only open a small amount?
Prevents duodenum from regurgitating chyme back into antrum (pylorus)
Solids pass into the duodenum ____ than liquids
Slower
Fats empty out of the stomach ____ than carbs/proteins
Slower
How long does it take to empty 50% of the stomach? 100%?
2-3 hours to empty 50%
4-5 hours to empty 100%
Rate of gastric emptying is dependent on:
Volume
Osmotic pressure
Type of food ingested
Larger food volume ____ rate of gastric emptying
Increases
How does decreased blood glucose affect gastric motility and emptying?
Increases motility, but does NOT incraese emptying
Factors that decrease rate of gastric emptying:
- Hyper/hypotonic fluid
- Fatty foods
- Increased rate of acids entering duodenum
How does CCK affect gastric motility?
Inhibits motility (and decreases acid production)
Define enterogastric reflex
Inhibition of gastric motility and acid secretion
Pyloric stenosis is also known as:
Infantile hypertrophic pyloric stenosis
What is pyloric stenosis and how is it treated?
- Hypertrophy of the pyloric sphincter (which impairs gastric emptying)
- Treated with surgery (pyloromyotomy)
What does “gastric juice” consist of?
Acid, mucus, pepsinogen
What are hormones secreted from the stomach?
Gastrin Histamine Somatostatin Serotonin Ghrelin
Function of mucus in the stomach
Protects mucosal layer from acid and pepsin (protease)
Acid in the stomach has a pH of approximately:
1.5
Define “transitional layer” of the stomach
- Layer of mucus that protects epithelium of stomach
- Neutral pH (approx 7) and high levels of bicarb to neutralize H+
What stimulates mucus secretion in the stomach?
Prostaglandins and NO
Functions of acid in the stomach:
- Dissolve food
- Inactivate digested bacteria/microorganisms
- Convert pepsinogen to pepsin
Parietal cells secrete:
HCl and intrinsic factor
Proton pump of parietal cells secrete H+ into ___ while HCO3- is secreted into ____
H+ into stomach
HCO3- into GI interstitial/plasma fluid
What stimulates acid secretion in the stomach?
ACh
Gastrin
Histamine
*Synergistic - if just 1 present then a smaller amount of acid production
What inhibits acid secretion in the stomach?
Somatostatin PGE2 Secretin GIP Glucagon
Phases of gastric acid secretion
Cephalic
Gastric
Intestinal
Cephalic phase of gastric acid secretion
Sight, smell, taste of food stimulates acid secretion via the vagus nerve
Gastric phase of gastric acid secretion
- Mechanical stretch of stomach stimulates vagus nerve to stimulate acid secretion
- Peptides/AAs in food stimulate G cells to release gastrin which stimulates acid secretion
- Food also increases pH which inhibits somatostatin release (allowing increase of acid secretion)
Intestinal phase of gastric acid secretion
Negative feedback from food entering duodenum inhibits acid secretion in stomach
What med classes are used to reduce acid production in the stomach?
- H2 receptor antagonists
- Proton pump inhibitors (PPIs)
How do H2 receptor antagonists work?
Inhibit histamine signaling on parietal cells
How do PPIs work?
Inhibit proton pump of parietal cells
Function of pepsin and secreted by?
- Proteolytic enzyme in stomach
- Secreted by chief cells of stomach
How is pepsin activated?
- Pepsinogen (inactive) is converted to pepsin
- In an acidic environment (pH
How is pepsin inactivated?
As chyme passes into alkaline conditions (pH > 5) of duodenum
Functions of gastrin?
- Indirectly stimulates acid production from parietal cells:
- Stimulates release of histamine from ECL cells
- Gastrin receptors are also located directly on parietal cells - Stimulates gastric mucosa growth (promotes parietal cell proliferation)
What is gastrin secreted by?
G cells in the antrum of stomach
What stimulates the secretion of gastrin?
Parasympathetic (ACh) and presence of digested proteins
Zollinger-Ellison Syndrome
Excessive acid production caused by gastrin producing tumors
Functions of histamine
- Stimulates acid secretion from parietal cells
- Attaches to H2 receptors on parietal cells
What stimulates secretion of histamine?
Gastrin
What inhibits secretion of histamine?
Somatostatin
What is histamine secreted by?
ECL cells in stomach
Functions of somatostatin
“Universal inhibitory function” throughout GI tract (parietal, chief, ECL cells)
What is somatostatin secreted by?
Delta cells in antrum/stomach, pancreas, intestines
What stimulates the release of somatostatin?
Acid
What is the function of serotonin in the GI tract?
Regulate/promote gut motility
*Also inflammatory role
Where is serotonin produced?
Enterochromaffin (EC) cells in GI tract
What is serotonin’s role clinically?
- Thought to contribute to GI disorders (IBD, diverticulitis)
- Serotonin syndrome (diarrhea, vomiting)
What is the function of ghrelin?
“Hunger hormone”, fast acting
- Appetite sensation/feeding
- Stimulates GH
Levels of ghrelin ____ just before meals
Rise
Where is ghrelin secreted from?
Endocrine cells mostly located in stomach
*Also kidneys, hypothalamus, pituitary, placenta
What hormones stimulate the release of ghrelin?
Glucagon
What hormones inhibit release of ghrelin?
Leptin
Glucose
Insulin
*Other indicators of feeding
What is intrinsic factor secreted by?
Parietal cells of stomach
What is the function of intrinsic factor?
-Necessary for Vit B12 absorption in small intestine
B12 helps mature RBCs
What does a deficiency of B12 absorption result in?
Pernicious anemia
What are rugae?
Epithelial folds in the stomach
Cells of the stomach
- Mucus
- Parietal
- Chief
- EC
- ECL
- G cells
- D cells
What are the cells of stomach rugae?
Mucus cells (surface epithelial)
What is the function of mucus cells in the rugae of the stomach?
-Produce thick mucus
Protection from abrasion of food and acidic pH levels
What is located at the base of the rugae in the stomach?
Gastric glands
Types of cells in the body/fundus of stomach
Mucus Parietal Chief EC ECL
Where are mucus cells located in the body/fundus regions of stomach?
“Neck” of gastric glands
What is the function of mucus cells in the body/fundus of stomach?
Secrete thin, watery mucus to liquefy stomach contents
What is the function of parietal cells in the stomach?
Secrete acid (HCl) and intrinsic factor
What is the function of chief cells in the stomach?
Secrete pepsinogen to promote protein digestion
What is the function of EC cells in the stomach?
Secrete serotonin to increase motility/GI regulation
What is the function of ECL cells in the stomach?
Secrete histamine to promote acid secretion
What cells are located in the cardiac region of the stomach?
Only mucus cells
secrete thin, watery mucus to liquefy stomach contents
What types of cells are located in the pyloric (antrum) region of the stomach?
- Mucus
- G
- D
What is the function of G cells in the pyloric region of the stomach?
Secrete gastrin which promotes acid secretion/motility and gastric mucosa growth
What is the function of D cells in the pyloric region of the stomach?
Secrete somatostatin which is inhibitory to parietal, chief cells (HCl, intrinsic factor, pepsinogen)
Describe adjustable gastric band
“Lap band”
- Creation of a small pouch at the top of the stomach
- Small pouch “fills” with food quickly
- Passage of food from top to bottom of stomach is slowed
- Upper part of stomach experiences a sensation of fullness
What is the MC restrictive operation for weight control?
Vertical banded gastroplasty
What is a vertical banded gastroplasty (VBG)?
A band and staples used to create small stomach pouch
What are the initial and long term outcomes of VBG?
- Initial: will vary from “complete” to some or poor wt loss
- Long term: many pts may regain wt by gradually stretching small pouch
What are gastric bypass procedures?
Wt loss procedures that:
- Reduce stomach size by creating small pouch
- Physically redirects anatomy of GI tract
How does a gastric bypass work if the GI tract is redirected?
- Bypass created so chyme bypasses proximal small intestine
- Purpose is to limit absorption of calories and nutrients in small intestin
Which has better outcomes? Lap/banding or bypass?
Bypass
What are the complications of gastric bypass?
Nutritional deficiencies
Dumping syndrome
GI bleeding, infections
What is dumping syndrome?
- Complication of gastric bypass
- Rapid gastric emptying
- Results in cramping, bloating, N/V, diarrhea, SOB
What is gastritis?
Inflammation of gastric mucosa
Causes of acute gastritis
- Drugs or chemicals (NSAIDs)
- H pylori infection
- Alcohol
- Smoking
How does acute gastritis heal?
Can be within a few days if the offending factor is removed ASAP
Describe chronic gastritis
- Degenerative, MC in elderly
- Results in chronic inflammation, mucosal atrophy and epithelial metaplasia
- 2 types (A and B)
Type A chronic gastritis
- Fundal
- Less common than Type B
- Suggested to be autoimmune
- Loss of parietal, chief cells, acid, intrinsic factor
Type B chronic gastritis
- Antral
- MC than Type A
- NOT autoimmune
- NO loss of acid, parietal, IF, etc.
- Extrinsic causes (H pylori, alcohol, tobacco, NSAIDs)
Which type of chronic gastritis is MC?
Type B
Where is a gastric ulcer most likely to occur?
Antrum
Pathophys of gastric ulcers
- Chronic exposure to various substances that break down mucosal lining
- Lining becomes more permeable to H ions
- Submucosa exposed to acids and secretions
- Damaged mucosa releases histamine (which increases release of acids/pepsinogen and capillary permeability)
Which type of ulcer results in higher risk of cancer - duodenal or gastric?
Gastric
Two major risk factors for benign gastric ulcers
- Chronic use of NSAIDs, aspirin
- H pylori infection
How does H pylori infection cause an ulcer?
- Metabolic byproducts damage D cells
- This promotes increased acid production
- H pylori is present in 60-80% gastric ulcers and 95-100% duodenal