W11 Upper GI Flashcards
What are the 4 basic GI processes ?
Motility
Secretion
Digestion
Absorption
What actions are mixing movements involved with ?
Redistributing luminal contents locally
Enhancing the exposure to digestive secretions
Exposing luminal contents to GI tract absorbing surfaces
What is the purpose of propulsive movements in the GI tract ?
Move luminal contents forward
Rate of propulsion varies with specific function of region
What actions do the inner circular layer and outer longitudinal layer of the muscularis externa have ?
Inner: contraction—> constriction of lumen
Outer: contraction —> shortening of the GI tract
Where does the myenteric plexus lie and what is its purpose?
Between 2 layers of muscularis externa
Coordinates muscularis externa contractions
What initiates contraction of smooth muscle ?
Increased cytoplasmic calcium
Where does the sarcoplasmic reticulum associate with the plasma membrane ?
At indentations known as cavaeoli
How are contractile acto-myosin filaments arranged ?
Obliquely
Where are cytoskeleton filaments anchored ?
Dense body junctions
Where are smooth muscle cells physically and electrically coupled?
Gap junctions
What activates myosin light chain kinase (MLCK)
Calcium binding to calmodulin when there is increased intracellular calcium concentration
What occurs when MLCK phosphorylates myosin light Chain
Myosin can bind to actin and begin the shortening process
What terminates the contraction of smooth muscle
Myosin light chain phosphatase
How does a voltage change in smooth muscle lead to a release of Ca2+ ?
Depolarization of SM membrane —> activate voltage gated calcium channel
—> Ca2+ influx —> SR calcium channel release —> calcium induced calcium release in SM cell
Outline pharmacy-mechanical coupling for the release of Ca2+
Compound triggers production of IP3 at sarcolemma —> diffuse through cytosol —> activate IP3 receptor to open —> Ca2+ diffuses out of SR into cytosol —> initiate contraction
no change in membrane potential
What 4 factors regulate GI motility ?
Intrinsic electrical properties of smooth muscle cells
Enteric nervous system
Autonomic nervous system
Other systems (eg. Brain, immune, hormones)
What are the pacemaker cells in smooth muscle ?
Interstitial cells of Cajal (ICC)
What are slow waves ?
Depolarising potentials
Where do slow waves propagate ?
From pacemaker cells into adjacent SM cells through gap junctions —> electrical signals flow between cells
What helps modulate the duration and amplitude of slow waves ?
Neurotransmitters/agonists that are released by enteric motor neurons
If slow wave depolarizations reach AP threshold what is the result ?
A burst of action potentials
What is the number of APs stimulated by a slow wave proportional to ?
The duration the slow wave remains above the AP threshold
How does the speed at which [Ca2+] increases in myoplasm of SM when it is depolarizer compared to skeletal and cardiac muscle ?
How do the kinetics of the contraction compare?
Very slow
Equally slow
What comprises the enteric nervous system ?
The submucosal and myenteric plexuses
Why is the enteric nervous system considered reflexive ?
It can operate entirely within the GI wall w/o external input
What are the 3 main components of the enteric nervous system?
Sensory neurons (mechanoreceptors, osmoreceptors, chemoreceptors)
Interneurons (excitatory and inhibitory)
Secretomotor cells
What do secretomotor cells influence ?
Smooth muscle
Epithelial cells that secrete or absorb fluid/electrolytes
Enteric endocrine cells
What can the intrinsic reflex arc for motility respond to and what actions does it have ?
Mucosa can sense mechanical, chemical or thermal change —> activate reflex arc which can inhibit or contract SM cells
How does the ANS influence GI motility ?
Influences ongoing ENS activity
Directly affects SM and glands
Alters GI hormone levels
How does parasympathetic input affect GI tract in general ?
Increases motility and GI secretions
How does sympathetic drive affect the GI system ?
Decreased motility and decreased volume of secretions
How is swallowing coordinated ?
Initiation is voluntary —> reflexive and is coordinated by swallowing center of medulla oblongata
Describe the oral phase of swallowing
Push food bolus toward back of oral cavity and up against palate by using the tongue —> activate sensory receptors in the back of the throat
Describe the pharyngeal phase of swallowing ?
Touch and pressure receptors in the pharyngeal palate are activated by food bolus —> info sent to medulla via trigeminal nerve (CN V) —>
Initiate reflexive component of swallowing —> contraction of pharyngeal wall behind bolus pushes food toward esophagus
- tongue prevents food from travelling back to mouth
- uvula elevates to seal nasal passages
- epiglottis closes over trachea
Describe the esophageal phase of swallowing
Swallowing centre relaxes pharyngoesophageal sphincter
Swallowing center initiates primary peristaltic waves by enteracting with the ENS
Gastroesophageal sphincter opens when food bolus is against this region
(Reflexive relaxation mediated by vagus nerve)
Describe primary peristalsis
Inner circular muscle contacts —> pinching ring
Outer longitudinal muscle contracts in front of pinched ring —> decrease length of tube
Sequence propagates along length of esophagus
Takes 5-9 seconds
Describe secondary peristalsis
Reflexive
Activated when luminal contents become lodged
- distension of GI walls —> stretch receptors —> stimulate ENS —> coordinate strong peristaltic wave to dislodge contents
What are the 2 dominant motility paradigms in the small intestine
Segmentation
- ensures thorough mixing
Migrating mobility complex
- moves luminal contents along
Describe small intestine segmentation
During meal
Alternating contractions and relaxations of adjacent sections of small intestine
What initiates segmentation in small intestine ?
Distension of lumen
Presence of enterogastrone gastrin
Parasympathetic input
Describe the action of migrating mobility complex in small intestine
- following absorption of meal
- begins at duodenal-gastric junction
- weak parastaltic contractions
- second wave begins slightly more distally —> travel slightly further
~2 hours from stomach to large intestine
Acid neutralizing/lower drugs
Antacids
Histamine H2 receptor antagonists
Proton pump inhibitors
Antacids and their mechanism of action
Hydroxide and/or carbonate salts
Direct neutralization of stomach acid
—> increase gastric pH
How might antacids affect the absorption of other drugs ?
Counter ions are poorly absorbed and may chelate other drugs and effect their absorption
Increased pH may also affect absorption of other drugs
Indications for antacids
Heartburn/ mild GERD
Dyspepsia
Side effects of antacids
Carbonate based salts —> belching
Ca2+ containing: hypercalcemia
Al3+ containing: constipation, hypophosphatemia —> impaired absorption
Mg 2+ containing : diarrhea
Suffix of H2 receptor agonists
Tidine
Mechanism of action of H2 receptor antagonists
Competitive, selective block of histamine H2 receptors —> reduced (60-70%) acid secretion
Most effective in nocturnal acid secretion
Pharmacokinetics of H2 receptor antagonists
Oral, IM and IV formulations
Oral: bioavailability ~50%, peak absorption in 1-3 hours, twice daily administration
Indications for H2 receptor antagonists
GERD
Peptic ulcer disease
Dyspepsia
Prevention of bleeding from stress related gastritis
Common Side effects of H2 receptor antagonists
Diarrhea or constipation
Headache
Drowsiness/fatigue
Muscle pain
Rare side effects of H2 receptor antagonists
Confusion/agitation Delirium/hallucinations Slurred speech Gynecomastia Blood dyscrasias
Suffix of PPIs
Prazole
Mechanism of action of PPIs
Irreversible inactivation of Proton pump common to all triggers of gastric acid secretion
Indications for proton pump inhibitors
Gastric and duodenal ulcers
GERD
Prevention of bleeding from stress related gastritis
Gastric hypersecretory conditions
Common side effects of PPIs
Nausea
Diarrhea (or constipation)
Abdominal pain
Flatulence
What are up to 80% of peptic ulcers correlated with ?
Presence of H.pylori in GI tract
What is the standard triple therapy for peptic ulcer disease with H. Pylori infection ?
- PPI + two antibiotics for 2 weeks
- clarithromycin and amoxicillin or metronidazole - PPI alone for 6 weeks
What is misoprostol
Prostaglandin E1 analogue
Mechanism of action of misoprostol
Direct parietal cell inhibition and mucus cell stimulation
Pharmacokinetics of misoprostol
Short half life —> frequent dosing
No impact on cytochrome P450 enzymes
Indications for misoprostol
NSAID- induced ulcers
Contraindications for misoprostol
Pregnancy
Side effects of misoprostol
Diarrhea
Abdominal cramping
Uterine contraction
Composition of sucralfate
Al(OH)3-sucrose surface complex
Mechanism of action of sucralfate
Acid interaction —> anionic surfaced sucrose —> bind to charged ulcer proteins —> viscous, sticky, protective barrier
- indirect stimulation of PGE2 production
Pharmacokinetics of sucralfate
Localized action
Short affect ~6 hours
Take on empty stomach
Indications for sucralfate
Gastric and duodenal ulcers
Side effects of sucralfate
Al3+ induced constipation
May reduce absorption of some other drugs
Bismuth subsalicylate (pesto-bismo) mechanism of action
Coat ulcers —> protective barrier
Increased PGE2, HCO3- and mucus production
Antimicrobial against H. Pylori
Reduces stool frequency
Pharmacokinetics of Bismuth subsalicylate
Dissociates in stomach —> acts locallly
Only salicylate substantially absorbed
Indications for bismuth subsalicylate
Adjuvant to triple therapy for H.pylori- induced ulcers
Acute diarrhea
Contraindications for bismuth subsalicylate
Children with viral infections —> Reye’s syndrome
Allergies to ASA
Side effects of bismuth subsalicylate
Black stool
Blackening of tongue
Constipation
Examples of pro kinetic drugs
Metoclopramide and domperidone
Mechanism of action of pro kinetic drugs
Dopamine D2 receptor antagonists
Metoclopromide has activity as agonist of serotonin (5-HT) receptors
Relieve basal dopamine inhibition of upper GI tract, stimulating peristalsis and facilitating gastric emptying
Pharmacokinetics of pro kinetic drugs
Metoclopromide: PO and parenteral formulations
Domperidone: greater fast pass metabolism
Short (1-2 hour) duration of action
Hepatic metabolism
Indications for prokinetic drugs
GERD
Impaired gastric emptying (gastroparesis)
Nausea and vomiting
Postpartum lactation stimulation
Contraindications for prokinetic drugs
Situations where GI motility is harmful
Side effects of prokinetic drugs
GI cramping
Diarrhea
Hyperprolactinemia
Metoclopromide crosses blood brain barrier
- dystonias, Parkinson’s-like syndromes, tardive dyskinesia
- drowsiness, restlessness, insomnia, anxiety
What does anti-emetic pharmacology target ?
Gastric stimuli
Motion sickness
Basis for gastric stimuli
Based on vagal afferents activating brain stem “vomiting centre” and/or chemoreceptor trigger zone
Anti emetic drug that targets gastric stimuli
Ondansetron
Drugs used to target motion sickness
Dimenhydrinate
Scopolamine
Ondansetron mechanism of action
Agonist of serotonin 5-HT3 receptors
—> vagal afferents, chemoreceptor trigger zone, and vomiting centre
Indications for ondansetron
Chemo induced nausea and vomiting
Post-op and post radiation nausea and vomiting
Side effects of ondansetron
Headache
Dizziness
Constipation
Dimenhydrinate mechanism of action
Antagonist of histamine H1 receptors
- some anticholinergic activity
Relatively weak anti-emetic activity
Indications for dimenhydrinate
Motion sickness
Side effects of dimenhydrinate
Dizziness
Sedation/drowsiness
Dry mouth
Urinary retention
Scopolamine mechanism of action
Antagonist of muscarinic receptors
Indications of scopolamine
Motion sickness
Side effects of scopolamine
Anti muscarinic when given orally or parenterally
3 primary functions of the stomach
Mixing and mechanical breakdown of stomach contents
Storage of ingested food and regulated delivery of processed stomach contents to the duodenum
Secretion of HCl and enzymes involved in protein digestion
What lines the fundus and body of the stomach ?
Oxyntic mucosa
What lines the antrum of the stomach ?
Pyloric gland area (PGA)
Exocrine glands of the stomach
Mucous cells
Chief cells
Parietal cells
What do mucous cells secrete ? What stimulates this ? What is the function ?
Alkaline mucous
Mechanical stimulation by contents
Protects mucosa against mechanical, pepsin and acid injury
What do Chief cells secrete ? What stimulates this ? What is the function of the secreted product ?
Pepsinogen
Ach, gastrin
When activated begins protein digestion
What do parietal cells secrete ? What stimulates this ? What is the function of the secreted product ?
HCl
ACh, gastrin, histamine
Activates pepsinogen, breaks down CT, denatures proteins, kills microorganisms
Intrinsic factor —> facilitates absorption of vitamin B12
What are the endocrine/pans rinse cells
Enterochromaffin- like (ECL) cells
G cells
D cells
What do ECL cells secrete ? What stimulates this? What is the function of the secreted product ?
Histamine
Ach, Gastrin
Stimulates parietal cells
What do G cells secrete ? What stimulates this ? What is the function of the secreted product ?
Gastrin
Protein products, ACh
Stimulates parietal, chief and ECL cells
What do D cells secrete ? What stimulates this ? What is the function of the secreted product ?
Somatostatin
Acid
Inhibits parietal, G and ECL cells
Where are mucous cells, parietal cells and chief cells located ?
All gastric pits
Oxyntic mucosa
Oxyntic mucosa
Where are ECL cells, G cells and D cells located ?
Gastric glands of:
- oxyntic mucosa
- PGA
- PGA
How do parietal cells secrete HCl ?
Actively
- ionic pumps move H+ and Cl- ions against their concentration gradients into the lumen
What 4 functions does HCl perform that assist in GI activity ?
- Converts pepsinogen into active pepsin
- Breaks down CT and muscle fibres of ingested food
- Breaks the tertiary structure of proteins
- Protection: kills some ingested microorganisms
What activates pepsin
HCl
What is the function of Pepsin?
Cleaves peptide bonds between certain amino acids
Where is pepsinogen stored
In inactive form in zymogen granules within chief cells
What 3 main components of the gastric mucosal barrier protect the epithelial layer from acid injury ?
- Acid cannot penetrate hydrophobic epithelial membrane
- Tight junctions: prevent acid from diffusing out of lumen
- Mucous from mucous cells lining gastric pits is protective.
- lubrication of luminal contents —> decreased friction
- inhibits pepsin to protect against auto-digestion of stomach wall
- neutralizes gastric acid at the epithelial surface
Mechanism of H.pylori induced peptic ulcers
H.pylori and its toxins —> weaken mucosal barrier —>
Acid and pepsin penetrate mucosal barrier —> histamine is released from damaged epithelium —> enhance gastric acid and pepsin production
Chronic alcohol use, NSAIDs and stress can also contribute
What is B12 needed for ?
DNA replication (mitosis) in RBC formation
What 4 chemical messengers regulate the secretion of gastric juices ?
Acetylcholine
Gastrin
Histamine
Somatostatin
What does acetylcholine stimulate ?
Parietal, chief, ECL, and G cell secretions
What does gastrin stimulate ?
Parietal, chief and ECL cell secretions
What is the primary factor responsible for increasing gastric secretions during the ingestion of a meal ?
Gastrin
What does gastrin promote the growth of ?
The gastric and duodenal mucosa
What type of substance is histamine ?
Paracrine
What does histamine stimulate ?
Parietal cell H+ production
What is the function of somatostatin ?
Acts in a negative feedback manner to turn off gastric H+, pepsinogen and histamine production
What are the 3 phases of secretion of gastric juice during the ingestion of a meal
Cephalic
Gastric
Intestinal
What happens during the cephalic phase of gastric secretions ?
Secretion of pepsinogen and H+ in response to sight, smell or thought of food and the process of swallowing
Initiated in the hypothalamus and mediated by vagal efferents
Vagal input —> G cell production of gastrin
Describe the gastric phase of gastric secretions
Begins when food enters the stomach
Proteins and peptides within lumen are most potent stimuli
Receptors in ENS —> short reflexes —> gastrin release from G cells
Long reflexive loop —> activate H+ and gastrin secretion via vagal and ENS activity
Histamine release is also stimulated —> H+ secretion
Distension/caffeine/alcohol can also stimulate gastric juice production
Describe the intestinal phase of gastric secretion
Inhibitory
Begins when chyme empties into duodenum
As protein is removed from stomach —> stop secretions in gastric pits and glands
Somatostatin is released from D cells in PGA gastric glands in response to drop in pH —> inhibit parietal, chief and HCl cell activity
What happens during the intestinal phase of gastric secretions when there is fat, acid, hypertonic chyme and distension in the duodenum ?
Negative feedback:
Influence on gastric secretions via enterogastric reflexes and the enterogastrones CCK and secretin
These factors decrease gastric emptying
Typical history of presenting illness for patient with heartburn
Character: vague discomfort vs burning vs pain
Onset: often post-prandial
Location: retrosternal
Intensity: variable
Duration: minutes to hours
Aggrevating: supine position, foods which relax lower esophageal sphincter or delay gastric emptying
Relieving: antacids
Associated symptoms with heartburn
Sour taste
Water brash
Odynophagia
Dysphagia
Historical clues for heartburn
Meds - opioids Social history - smoking - alcohol
Red flags with heartburn
Vomiting Weight loss Bleeding Anorexia Dysphagia
What is reflux esophagitis and what are the possible causes ?
Acid damage to esophagus
- increased abdominal pressure
- increased volume of regurgitant
- decreased esophageal clearance
Describe the stepwise treatment of reflux esophagitis
Correct the underlying cause
- reduce or stop meds that drop LES pressure
Lifestyle changes
- smoking cessation
- alcohol cessation
- weight reduction
Medications
Surgery
Medications for treating reflux esophagitis
Antacids
Sucralfate
H2RAs
PPIs
Complications of esophagitis
Pain Bleeding Stricture Barrett’s esophagus Adenocarcinoma
GI causes of retrosternal burning
GERD
Esophagitis
Esophageal spasm
Esophageal cancer
Cardiac causes of retrosternal burning
MI
Pericarditis
Aortic dissection
Different types of esophagitis
Infectious: herpes, cytomegalovirus, candida
Inflammatory: eosinophilic
Trauma: pill
Presentation in patients with herpes and CMV esophagitis
Odynophagia - typically very painful
Often immunosuppressed
Candida esophagitis presentation
Dysphagia May or may not have thrush Usually Immunosupressed - diabetic - HIV -chemo
Presentation of eosinophilic esophagitis
Dysphagia
History of atopy
Furrows, rings, exudates
Often in younger population
Treatment for eosinophilic esophagitis
Viscous budesonide and PPI
Six food elimination diet (wheat, milk, eggs, soy, nuts, shellfish)
Common causes of pill esophagitis
NSAIDs
K+
Alendronate
Antibiotics such as tetracycline and doxycycline
Rome iii definition of dyspepsia
One or more of:
- post prandial fullness
- epigastric pain or burning
- early satiety
Associated symptoms of dyspepsia
Nausea
Bloating
Anorexia
Causes of dyspepsia
Functional (60%): no obvious cause - non-ulcer dyspepsia - ulcer-like symptoms - dysmotility-like symptoms Organic (40%) - detectable etiology
Etiology of functional dyspepsia
Impaired gastric motor function
Visceral sensitivity
Psychosocial factors
Gastritis vs gastropathy
Gastritis- inflammation of gastric mucosa associated with injury
Gastropathy- epithelial cell damage and regeneration without inflammation
Two main patterns of gastritis
Antral based
Corpus predominant
Describe antral based gastritis
Infection increases gastrin secretion —> increased parietal acid production —> duodenal damage —> gastric metaplasia in duodenum —> +/- H. Pylori moves into duodenum —> duodenal ulcers
Low pH —> H.pylori don’t move into body as readily
Describe corpus-predominant atrophic gastritis or pangastritis
Genetically lower acid production —> easier for H.pylori to move into body —> pangastritis —> risk factor for gastric ulcers as well as intestinal metaplasia —> dysplasia —> gastric carcinoma
What is peptic ulcer disease
Damage to the mucosal lining of the intestinal surface where acid is implicated in pathogenesis
Ulcer: damage extends into the muscularis mucosa
Causes of peptic ulcer disease
Ischemia H.pylori Smoking, alcohol Zollinger-Ellison syndrome, carcinoid Chron disease, radiation, chemo Adenocarcinoma NSAIDs ICU
Complications of peptic ulcer disease
Pain
Penetration / perforation
Bleeding
Obstruction
Management of peptic ulcer disease
Correct underlying cause Lifestyle changes Pharmacological: PPI Endoscopic - injection - coagulation - clipping Radio graphic Surgical
Possible investigations for patients presenting with dysphagia
Labs: serology, urea breath test, stool studies
Radiology: X-rays, upper GI series, fluoroscopy, CT, MRI
Endoscopy: gastroscopy (esophagogastroduodenoscopy), enteroscopy, ERCP, cholangioscopy, colonoscopy
Endoscopic ultrasound
Manometry
What conditions would give an abnormal AXR ?
Ileus, SBO, LBO
Volvulus
Constipation
Severe colitis
Pros and cons of UGI series (barium swallow)
Pros: Easy Cheap Good test in dysphagia Cons: Low sensitivity Low specificity
What is the best test for severe abdominal pain ?
CT abdomen
What is CT enterography
Same as CT abdomen, but with negative PO contrast and with IV contrast
What can be used for distinguishing between motility disorders of esophagus ?
Esophageal manometry
What are the major structures of the exocrine pancreas ?
Ductal cells
Acinar cells
What is the function of acinar cells ?
Produce digestive enzymes
~15-100 grams of protein secreted per day
What is the function of ductal cells ?
Produce basic bicarbonate fluid
—> about 1.5 L of fluid per day