Gastrointestinal Module #1 Flashcards
What are the layers of the GI tract (from inner to outer layers)?
Mucosa
Submucosa
Muscularis
Adventitious (serosa)
What is the muscosa layer made of?
Mucosa Epithelium
Lamina Propria
Muscularis Mucosae
What can you find in the submucosa layer?
Glands
Associated Ducts
What are the layers of the muscularis layer?
Circular Layer
Longitudinal Layer
What is the adventitious (serosa) layer made of?
Connective Tissue
What is the enteric nervous system?
Intrinsic Nervous System of the GI tract
**considered part of the autonomic nervous system
What influences the enteric nervous system?
Parasympathetic = excitatory
Sympathetic = inhibitory
What is unique about the enteric nervous system?
Functions autonomously (w/o having to go up to the brain)
What are the 3 Enteric Plexuses?
Submucosal Plexus (Meissner Plexus)
Myenteric Plexus (Auerbach Plexus)
Subserosal Plexus
Where is the submucosal plexus located?
Located in submucosa
What is the function of the submucosal plexus?
Secretion and absorption
Where is the myenteric plexus located?
Between circular/longitudinal layers of the muscularis
What is the function of the myenteric plexus?
Motility
Where is the subserosal plexus located?
Mesentery
What does the subserosal plexus innervate?
ANS innervation of blood vessels and connective tissue
What are the 3 general functional components of the enteric plexuses?
Sensory
Motor
Interneurons
What do the sensory neurons of the enteric plexuses monitor?
Distention and chemical status of GI tract
**Sensory afferents via sympathetic nerves
What do the motor neurons of the enteric plexuses control?
Motility of the gut wall
Smooth muscle of GI vasculature
Secretions of the mucosa/submucosa
What does the interneurons of the enteric plexuses do?
Communication between sensory and motor neurons
What is the definition (for this class) of appetite?
Hunger
What is the definition (for this class) of satiety?
Sensation of fullness/satisfied
Where are the 2 centers that control appetite and satiety located?
Hypothalamus
What are the names of the centers that control appetite and what are they specifically controlling?
Lateral Center = Appetite
Medial Center = Satiety
What are the stimuli of the lateral center (appetite center)?
Smell (CN1), Vsiual, Taste (CN7, 9), Hearing (CN8)
Physiological Depletion of nutrient/energy stores
Memory/Fantasy
Gastric Hormone = Ghrelin
Where is ghrelin released from?
Stomach
What is ghrelin known as?
Hunger Hormone
What is the function of the medial center (satiety center)?
Suppress appetite
What are the stimuli of the medial center (satiety center)?
GI Hormones released during food ingestion (CCK, GLP-1, etc)
Leptin
PYY
Insulin
Where is leptin released from?
Fat Cells
Chief Cells
Where is PYY released from?
Small Intestine after meal
What extrinsilically influences the enteric system?
Autonomic Nervous Center:
Sympathetic System = nerves of sympathetic tract in thoracic and upper lumbar regions Parasympathetic System = Vagus Nerve and pelvic nerves of sacral plexus
How does the sympathetic system influence the enteric system?
Inhibitory effects on the GI tract:
decrease peristalsis and secretions inhibit blood flow to GI tract
How does the parasympathetic system influence the enteric system?
Excitatory to GI Tract:
increase peristalsis and secretions relax involuntary sphincters of GI tract facilitate blood flow to GI tract
What is the intrinsic regulation of the enteric system?
Can feedback on itself and function autonomously = “brain in the gut”
What are the specific functions of the enteric nervous system?
Control Motility
Regulation of fluid exchange and local GI blood flow
Regulation of gastric and pancreatic secretion
Regulation of gastrointestinal endocrine cells
Defense reactions
Entero-enteric reflexes
ENS/CNS interaction
How does the enteric nervous system control motility?
Peristalsis
Sphincter Control
Etc.
How does the enteric nervous system regulate fluid exchange and local GI blood flow?
Regulate permeability to ions thus influence fluid
Influence vasodilation of BV
Influence fluid secretion
How does the enteric nervous system regulate gastrointestinal endocrine cells?
Signal release of GI hormones (ie excessive seratonin released from GI walls = nausea/vomiting)
What are the entero-enteric reflexes?
Signaling system between regions of the GI tract
What are examples of the entero-enteric reflexes?
Gastric activity stimulating Si motility and releaxation of iliocecal valve
Small intestine activity signals release of pancreatic enzymes
What is secreted in the mouth that is important for the GI tract?
Saliva
What controls the release of salivia?
BOTH parasympathetic and sympathetic systems stimulate salivary glands
NOT CONTROLLED BY HORMONES!
What does saliva contain (8 things)?
Water
Mucus
Na+
Bicarbonate
Chloride
K+
Salivary Amylase
Immunoglobulin A (IgA)
What is the function of bicarbonate in saliva?
Maintain pH in mouth to neutrolize bacteria (tooth decay)
What does salivary amylase do?
Begins first steps to break down (digest) carbohydrates
What is the purpose of IgA in saliva?
Prevent Infection
Where is the upper esophageal sphincter located?
Junction of lower pharynx and esophagus
Approximately @ level of cricoid cartilage
What is the function of the upper esophageal sphincter?
Prevent air from entering esophagus during ventilation
Is the upper esophageal sphincter considered a “true” sphincter?
Yes
Where is the lower esophageal sphincter located?
Narrowing of esophagus proximal to junction of esophagus and stomach
What is the function of the lower esophageal sphincter?
Barrier to reflux (regurgiation) of acidic content of stomach
Is the lower esophageal sphincter a true sphincter?
No
So if the lower esophageal sphincter is not a true sphincter, how is it maintained?
Increased smooth muscle tone –> 20 mmHg
What happens to the lower esophageal sphincter smooth muscle tone during swallowing?
Relaxed by peristaltic waves
What are the 2 phases of swallowing?
Voluntary Phase (oropharyngeal phase)
Involuntary phase (esophageal phase)
What happens during the voluntary phase (oropharyngeal phase) of swallowing?
Food broken down and tongue pushes bolus posteriorly
Soft palate (superior constrictor muscles) contract to close nasopharynx
Epiglottis closes of larynex/trachea
How long does it take for food to be pushed into the esophagus during the voluntary phase (oropharyngeal phase) of swallowing?
1 - 2 seconds
When does the involuntary phase (esophageal phase) of swallowing begin?
As bolus enters esophagus
When does the involuntary phase (esophageal phase) of swallowing end?
As bolus enters stomach
How long does the voluntary phase (esophageal phase) of swallowing last?
5 - 10 seconds
How is the bolus moved toward the stomach in the esophagus?
Peristalsis
What is peristalsis?
Coordinated contraction/relaxation of the longitudinal/circular muscles
How does the esophageal muscular pressure range?
Ranges from 35 - 85 mmHg
What is the esophageal pressure in the upper and lower esophagus?
60 - 80 mmHg
What is the esophageal pressure in the middle esophagus?
30 - 45 mmHg
What happens to food in the esophagus if contractions are < 30 mmHg?
Food residue may get stuck
What is the nervous system that controls peristalsis?
Vagus Nerve for both excitatory and inhibitory pathways (works to coordinate contraction/relaxation)
What are the bodily chemicals that control peristalsis?
ACh = excitatory
NO = inhibitory
What is secondary peristalsis?
Involuntary wave
What would cause secondary peristalsis?
Food residue from ineffective primary peristalsis
OR
Bolus that is “stuck”
Describe what happens when bolus/food residue gets stuck in the esophagus and causes a distention
Feedback to:
Constrict esophagus above distention Relax esophagus below distention Which pushes residue/bolus along
What happens when you are swallowing food?
Single swallow initiates esophageal peristaltic contraction that lasts 5 - 10 seconds follwed by short refractory period
After swallowing a bite of food, what does the short refractory period following peristaltic contraction do?
Inhibits ability to swallow second bite of food more frequently than 10 - 15 seconda
How often do you swallow when drinking a liquid?
Every 1 - 2 seconda
What is the name of the inhibitory reflex in your esophagus and what does that reflex do when you’re drinking a liquid?
Deglutitive Inhibition (made w/ quick subsequent swallows)
Prevents esophagus from ongoing contraction –> esophagus stays relaxed to allow more liquid to descend = gulping
What are the 3 factors that create the basal tone of the lower esophageal sphincter?
Myogenic Tone (independent of neural input)
Excitatory Vagal Tone (Cholinergic - ACh)
Inhibitory Vagal Tone (Nitrergic - NO)
What are some factors that increase lower esophageal sphincter pressure?
Vagus Nerve –> excitatory pathways of vagus nerve
Gastrin
Meds for GERD
Why does gastrin increase lower esophageal sphincter pressure?
Gastrin promotes acid secretion/motility so you need to keep LES closed to prevent acid reflex in esophagus
What are some factors that decrease lower esophageal sphincter pressure?
Vagus Nerve –> inhibitory pathways
Hormones: progesterone, secretin, glucagon
Fried fatty foods
Tomatoes
Citrus
High Protein Diet
Chocolate
Peppermint
Tobacco
Alcohol
Caffeine
What happens to cause GERD?
Decreased LES pressure and ineffective clerance mechanism of secondary peristaltic waves
Chronic acid reflux reslts in in flammation/pain and eventual destruction of esophageal wall (esophagitis)
What are some causes of decreased lower esophageal pressure/risk factors for GERD?
Hiatal Hernia
Pregnancy
Excessive ETOH
Tobacco
Obesity
What is achalasia?
Rare disease in which lower esophageal sphincter fails to relax
Causes pain with eating and drinking
What happens to cause achalasia?
Unknown exactly but it is a mechanical result of peristalsis of the esophageal musculature and the failure of the lower esophageal sphincter to relax
What is esophageal varices?
Severely dilated sub-mucosal veins in the esophagus
**usually d/t portal hypertension
What can esophageal varices lead to?
Bleeding –> Chronic GI bleeding –> severe systemic consequences
What is Barrett’s Esophagus?
Condition in which normal mature cells (esophageal squamous epithelium) lining the esophagus are replaced w/ abnormal cells (metaplastic columnar mucosa) d/t exposure to stomach acids
What is metaplasia?
1 mature adult cell type is replaced by another
What are the symptoms of Barrett’s Esophagus?
“Heart Burn”
**metaplasia = histologic reflexion of esophagus being exposed to stomach acid
Will all patients with GERD develop Barrett’s esophagus?
No!
What can Barrett’s esophagus develop into?
Adenocarcinoma of the esophagus
Will all patients with Barrett’s esophagus develop esophageal cancer?
No!
Risk = 1:3000
**amount of dysplasia present increases risk of cancer
What id dysplasia?
Abnormal development/maturation of cells
Delay/abnormal differentiation of cells results in # of immature cells
Indication of early neoplastic process
What are the regions of the stomach?
Cardiac = region where esophagus enters stomach
Fundus = area above cardiac region
Pyloric = area near duodenum
Lesser and Greater curvature
What is the gastric function?
Digestion = secretion and some absorption
Motility = propel food into duodenum
What is partially digested food called?
Chyme
How is food digested in the stomach?
Gastric juices
Which foods are absorbed in the stomach?
Aspirin
NSAIDs
Alcohol
What relaxes the stomach musculature?
Swallowing (prepares stomach for bolus)
What stimulates the motility of the stomach?
Vagus (cholinergic)
Hormones: Gastrin and Motilin
Describe the sequence of gastric motility
Series of alternating small waves travel toward the pylorus
4 or 5 sequential peristaltic waves push chyme back and forth (churn)
Last wave forces pyloric sphincter to open and chyme is pushed into duodenum (pylorus is open about 1 - 2 cm which is not enough to regurgitate back into stomach)
What is the average total time to empy the stomach?
50% after 2 - 3 hours
Total emptying after 4 - 5 hours
What are the factors that increase rate of gastric emptying?
Larger food volume
What are the factors that decrease gastric emptying?
Hyper/hypotonic fluid
Fatty Foods
Increased rate of acids entering the duodenum
Why do you need decreased rate of gastric emptying when ingesting a hyper/hypotonic fluid?
Allow time to create/facilitate isoosmotic environment for the duodenum
When ingesting fatty foods what is the hormone that inhibits gastric motility and where is it released?
CCK (cholecystokinin)
Synthesized/released by duodenum/SI
**also decreases acid production)
Where are fats digested?
Duodenum
What happens if too much fat enters the small intestine?
Feedback loop slows down rate to allow time to properly digest fats
Where is acid neutralized?
Duodenum
What happens if too much acid enter the small intestine?
Feedback loop inhibits gastric emptying to decrease acid entering duodenum
What is pyloric stenosis also know as?
Infantile Hypertrophic Pyloric
Stenosis (IHPS)
What is going on with pyloric stenosis?
Muscles of pyloric sphincter are
hypertrophied which impairs
gastric emptying
How is pyloric stenosis treated?
Surgery = Pyloromyotomy
What is gastric juice?
Acid
Mucous
Pepsinogen
What are the major secretions of the stomach?
Mucus
Acid
Proteases
Hormones
Intrinsic Factor
What is the function of mucus?
Protect mucosal layer from acid and pepsin (protease)
**stomach acid pH = 1.5
How does mucus protect the mucosal layer from stomach acid?
Provides transitional layer to protect the epithelium
Contains high levels of bicarbonate (HCO3-) to neutralize the H+ –> pH of stomach = 1.5 and pH @ epithelial layer = 7
What are some stimuli of mucus secretion?
Prostaglandins (pathway = disrupted by NSAIDs)
Nitric Oxide
What are some things that disrupt the mucus barrier?
Aspirin
NSAIDs
Alcohol
Bile Salts (regurgitated from SI)
Helicobacter pylori (bacteria)
What is the function of stomach acid?
Dissolve Food
Inactivate bacteria/microorganisms that have been ingested
Convert pepsinogen to pepsin
What cells secrete stomach acid?
Parietal cells in the body/fundus of the stomach
What molecule is “exchanged” for acid formation in the stomach?
Bicarbonate into the plasma
**can lead to Alkaline Tide or Wave”
What stimulates acid secretion in the stomach?
ACh via vagus nerve (parasympathetic)
Gastrin
Histamine
What inhibits acid secretion in the stomach?
Gastrin inhibitory peptide (GIP)
Somatostatin
Secretin
Prostaglandin
Where is somatostatin secreted from in the gastrointestinal tract?
Stomach
Intestine
Pancreas
What does secretin do?
Works synergistically w/ CCK to inhibit gastric motility
What cells produce and secrete pepsinogen?
Chief Cells
What does pepsinogen need to be converted to pepsin?
Acidic Environment (pH < 2)
What is the function of pepsin?
Proteolytic enzyme that breaks down proteins in the stomach
Where is pepsin inactivated?
Small Intestine (more alkaline environment)
What are the gastric hormones?
Gastrin
Motilin
Gastrin Inhibitory Emptying Peptide (GIP)
Grehlin
What does gastrin do?
Promote gastric juice (acid) secretion and gastric motility
What cells secrete gastrin?
G Cells in stomach (located in antrum)
What does motilin do?
Promote stomach/SI motility
Where is motilin secreted?
From endocrine cells located in the small intestine
What does gastric inhibitory emptying peptide do?
Inhibit gastric juice (acid) secretion and gastric motility
Where is gastric inhibitory emptying peptide secreted?
Endocrine cells in the small intestine
What is Grehlin?
The “hunger hormone”
Plays role in appetite sensation/feeding behavior
**levels rise just before meals
Where is grehlin secreted?
Endocrine cells mostly located in the stomach
Also from: kidneys, hypothalamus, pituitary, placenta
What is Intrinsic Factor?
Necessary for Vitamin B12 absorption in the small intestine
Where is intrinsic factor secreted?
Parietal Cells of the stomach
What are the epithelial folds of the stomach called?
Rugae
What are the cell types that are found at the surface of the folds of rugae?
Mucous Cells
What do the mucous cells in the rugae do?
Produce thick mucous = protection from abrasion of food and from pH levels in stomach
What cells are found at the base of the folds of rugae?
Gastric Glands (vary by stomach region)
Which cell type is found in the gastric glands in the body/fundus region of the stomach?
Mucous cells –> located @ neck of gastric glands
Parietal Cells
Chief Cells
Enterochromaffin-like Cells
What do mucous cells do in the gastric glands @ the body/fundus of the stomach?
Secrete thin, watery mucus to liquefy stomach contents
What do parietal cells do in the gastric glands @ the body/fundus of the stomach?
Secrete acid (HCl)
Secrete intrinsic factor
What do chief cells do in the gastric glands @ the body/fundus of the stomach?
Secrete pepsinogen (promote protein digestion)
What do enterochromaffin-like cells do in the gastric glands @ the body/fundus of the stomach?
Secrete histamine (promote acid secretion)
Which cells are found in the gastric glands in the cardiac region of the stomach and what do they do?
Mucous Cells –> secrete thin, watery mucus to liquefy stomach contents
Which cells are found in the gastric glands in the pyloric (antrum) region of the stomach?
Mucous Cells
G cells
What do mucous cells do in the do in the gastric glands @ the pyloric region of the stomach?
Secrete thin, watery mucous to liquefy stomach contents
What do G cells do do in the gastric glands @ the pyloric region of the stomach?
Secrete gastrin (promote acid secretion/motility)
What are the 3 types of weight loss procedures?
Adjustable gastric band (LAP Band)
Ventrical Banded Gastroplasty (VBG) –> stomach stapling w/ lap band”
Gastric Bypass
Describe the adjustable gastric band procedure
Placement of band creates small pouch @ top of stomach
Small pouch “fills” w/ food quickly and passage of food from top to bottom of stomach is slowed
Upper part of stomach experiences sensation of fullness
Describe the Vertical Banded Gastroplasty (VBG)
Both band and staples are used to create a small stomach pouch
Small opening in bottom of pouch through which food can pass through to rest of the stomach
**smaller pouch helps person eat smaller portions and lose weight over time
What are the initial outcomes seen with VBG?
Vary from:
“complete” weight loss
some weight loss
poor weight loss
What are the longterm outcomes seen with VBG?
Many patients will regain weight by gradually stretching small pouch
Describe gastric bypass procedures
Physically redirects anatomy of GI tract –> bypass created so chyme bypasses proximal small intestine
Point is to limit absorption of calories (and nutrients) in small intestine
What are the outcomes of gastric bypass?
Long/short term outcomes suggested to be better than banding/stapling procedures
What is the most common restrictive operation for weight control?
Vertical Banded Gastroplasty (VBG)
What are the complications of gastric bypass?
Nutritional deficiencies –> need long term supplementation plan
Dumping syndrome –> rapid gastric emptying
Direct complications to GI tract –> bleeding, infections, etc
What exactly is dumping syndrome?
Jejunum rapidly fills w/ undigested food from stomach?
What are the signs/symptoms of dumping syndrome?
Cramping
Bloating
Nausea
Vomitting
Diarrhea
Shortness of Breath
What is gastritis?
Inflammation (diffuse through lining) of gastric mucosa)
When would you see acute gastritis?
W/ injury to the gastric mucosa
What are some causes of acute gastritis?
Drugs/Chemicals –> NSAIDs
H. pylori infection
Alcohol
Smoking
How long will acute gastritis last?
A few days but want to remove offending facotr ASAP
What is chronic gastritis?
Degenerative gastritis –> Chronic inflammation, mucosal atrophy and epithelial metaplasia
When do you see chronic gastritis?
More common in elderly
What are the 2 types of chronic gastritis?
Type A = chronic fundal gastritis –> in fundus/body
Type B = chronic antral gastritis
Which type of chronic gastritis is more common?
Type B = 4x more common than A
Which type of chronic gastritis is considered autoimmune dysfunction?
Type A –> antibodies attack parietal, chief cells and intrinsic factor
If Type A chronic gastritis is autoimmune, what is the problem with Type B?
Seems to be more of motiltiy problem; no loss of acid secretion, parietal cels, intrinsic factor
Where in the stomach do you see most gastric ulcers?
Antrum
What kind of feedback is involved w/ gastric uclers?
(+) feed back:
Chronic exposure to various substances –> breakdown of protective mucosal lining of stomach
Damaged mucosa releases histamine –> increased release of acids/pepsinogen, increased capillary permeability
Do gastric ulcers possess higher risk of cancer?
Yes (vs. risk for duodenal ulcer)
What are the 2 major risk factors for benign gastric ulcers?
Chronic use of aspirin, NSAIDs
H pylori infection
What are the clinical signs and symptoms of a gastric ulcer?
Food provoking pain pattern –> pain immediately after eating