GI lecture Flashcards
What are the 4 protective mechanisms to protect the GI tract?
-mucus
-bicarbonate
-prostaglandins
-mucosal blood flow
what are the 4 mechanisms of the GI tract that are aggressive and break things down?
-acid
-pepsin
-NSAIDS
-Helicobacter pylori
Review the food stimulus diagram. What is the pathway? (SR = short reflex, LR = long reflex)
- Food sensed -> signal to medulla oblongata –(LR)–> preganglionic parasympathetic neuron in vagus nerve –(LR)–> enteric plexus –(SR+LR)–>postganglionic parasympathetic and intrinsic enteric neurons –(SR+LR)–> effector cells –(SR+LR)–> secretion and motility
- food ingested -> hits gastric mucosa –(SR)–> sensory input –(SR)–> enteric plexus
What is the differences between long and short reflexes?
Long:
-integrated in CNS
-originate in or outside of GI tract
Short:
-integrated in enteric NS
-originate from internal change (pH, osmolarity, products etc.
What are cephalic reflexes?
-feedforward and emotional reflexes
-initiated and integrated outside GI
What is the pathway for the cephalic phase?
food stimulus -> cerebral cortex, hypothalamus, amygdala signal -> activate neurons in medulla -> sends ANS signal to
1. Salivary Glands via facial nerve, glossopharyngeal nerve, and symp innervation = inc. saliva, amylase, lysozymes, and lingual lipase (babies)
2. Enteric NS via vagal nerve = inc. gastric secretions and motility, accounts for 20% of gastric secretions while eating
What are the different cell types involved in the cephalic phase?
-Mucous neck cells
-parietal cells
-enterchromaffin-like cells
-chief cells
-D cells
-G cells
What is secreted by the mucous neck cells?
Mucus and bicarbonate
What stimuli release Mucus and bicarbonate from mucous neck cells?
-mucous = tonic secretion, irritated mucosa
-bicarbonate = secreted with mucus
what are the functions of mucous and bicarbonate?
-mucous keeps physical barrier between lumen and epithelium
-bicarbonate buffers gastric acid
What is secreted by parietal cells?
-gastric acid (HCl)
-Intrinsic factor
What is the stimulus needed to release HCl and intrinsic factor from parietal cells?
-Acetylcholine
-gastrin
-histamine
What is the function of Gastric acid and intrinsic factor?
-gastric acid = activates pepsin, kills bacteria
-intrinsic factor = complexes with vitamin B12 to permit abs.
What is secreted by enterochromaffin-like cells?
Histamine
What stimulus is required to release histamine from enterochromaffin-like cells?
-acetylcholine
-gastrin
what is the function of histamine?
-stimulates gastric acid secretion
what substances are secreted by Chief cells?
Pepsinogen and Gastric lipase
What is the stimulus required to release pepsinogen and gastric lipase from Chief cells?
-Acetylcholine
-acid
-secretin
What is the function of pepsinogen and gastric lipase?
-pepsinogen = digests proteins
-gastric lipase = digests fats
What is secreted by D cells?
Somatostatin
What is the stimulus required to release somatostatin from D cells?
acid in the stomach
What is the function of somatostatin?
inhibit gastric acid secretion
What is secreted by G cells?
gastrin
What stimulus is required to release gastrin from G cells?
-Acetylcholine
-peptides
-A.A.
what is the function of gastrin?
-stimulates gastric acid secretion
What does gastrin target?
-ECL cell
-parietal cells
What inhibits gastrin release?
somatostatin
Where does Cholecystokinin come from and what stimulates its release?
-the intestine
-stimulated by fatty acids and AA
What does cholecystokinin (CKK) target?
-gallbladder
-pancreas
-stomach
What is the function of CCK?
-stimulate gallbladder contractions
-pancreatic enzyme secretion
-inhibit gastric emptying
What feeling does CCK create?
satiety
What two secretions are part of the gastrin family?
-gastrin
-cholecystokinin (CKK)
What does motilin do?
-stimulates migrating motor complex
-helps keep things moving even when you’re not consuming food
What stimulates the release of motilin?
-fasting
-released every 1.5-2h of fasting
what is the target of motilin?
-gastric smooth muscle
-intestinal smooth muscle
What secretion is in the peptide family?
motilin
what secretions are part of the secretin family?
-secretin
-gastric inhibitory peptide (GIP)
-glucagon-like peptide 1 (GLP-1)
What does secretin do?
-stimulates bicarbonate secretion
-inhibits gastric emptying and acid secretion
What are the targets of secretin?
-pancreas
-stomach
What stimulates the release of secretin?
acid in small intestine
What does gastric inhibitory peptide do?
-stimulates insulin release
-inhibits gastric emptying and acid secretion
What is the target for gastric inhibitory peptide?
-beta cells in pancreas
what stimulates the release of gastric inhibitory peptide?
-glucose
-FA
-AA
What does Glucagon-like peptide 1 do?
-stimulates insulin release
-inhibits glucagon release and gastric function
What is the target for GLP-1?
endocrine pancreas
What stimulates the release of GLP-1?
-mixed meal with fats and carbs entering the lumen
What are the three main sections to the stomach lining?
-preepithelial
-epithelial
-subepithelial
what is part of the epithelial layer of the stomach?
-cellular resistance
-growth factors
-prostaglandins
-cell proliferation
Pathway for gastric HCl secretion
stimuli -> brain -> increased enteric neural discharge -> histamine secretion -> parietal cell secretes acid -> inceased HCl
-too much HCl inhibits gastrin secretion and no gastrin means no histamine and discharge simulation so HCl stops being produced
Receptor Level of Gastric HCl secretion
-Acetylcholine input = neurocrine
-gastrin hormonal input = endocrine
-histamine input = paracrine
-Acetylcholine and gastrin receptors on ECL cell which secretes histamine
-histamine receptor on parietal cell -> transduction events -> H/K+ pumps secrete HCl
Why do NSAIDS cause stomach issues?
-decreases prostaglandins = increase gastric acid, decrease sodium bicarbonate, decrease blood flow
-****
What are some characteristics of the mucous layer?
-0.5mm thick
-has mucus gel that sodium bicarbonate is secreted into
-mucosa synth PGs, E2 and I2 = cytoprotective action
What is triple therapy and quadruple therapy for eradicating H. Pylori?
-Triple therapy = 7day, PP inhibitor + amoxicillin/tetracycline + metronidazole/clarithromycin
-Quadruple therapy = 3 day, plus bismuth
-both are 80-85% effective
What are the 2 ways H. Pylori causes ulcers?
- has urease activity -> increases pH -> causes G cell to produce more gastrin -> increases acid secretion
- has inflammatory mediators -> inhibit D cell -> no somatostatin -> no inhibition of gastrin release -> acid secretion not inhibited
How does the urea breath test work?
-pt ingests urea with C13 -> if theres HP, it will produce urease and hydrolize the ingested urea into 13CO2 -> pt breath will be analyzed and if HP, then 13CO2 will be much higher than 12CO2
What causes the dysregulated immune response for IBD?
-genetics
-environment
List main Crohn’s symptoms
-chronic/nocturnal diarrea
-rectal bleeding
-abdominal pain
-weightloss
-fever
-fatigue
-extraintestinal = skin, eye, joint
How is IBD treated and what are the treatment goals?
-symptomatically
-prevent complications
-improve QOF
-limit surgery
-suppress inflammation and reaction
What are the two main types of IBD?
-Crohn’s Disease
-Ulcerative Colitis
What are the risks with using anti-TNF drugs?
-5% get infusion reaction
-infection can lead to sepsis
-lymphoma
-drug induced lupus
-hepatotoxicity
-demyelinating disorder
How does laxative abuse occur?
- using a laxative empties the colon so it will take longer to refill and eliminate waste than normal. This can be perceived as constipation
- constantly using a laxative = water is not absorbed from stool = body senses decrease in salt and water absorption = release of aldosterone = kidneys retain water and release potassium = potassium released from both stool and kidneys = hypokalemia = potassium required for peristalsis = low/no peristalsis = constipation
