GI lecture Flashcards by Aki Smith

What are the 4 protective mechanisms to protect the GI tract?

-mucus
-bicarbonate
-prostaglandins
-mucosal blood flow

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what are the 4 mechanisms of the GI tract that are aggressive and break things down?

-acid
-pepsin
-NSAIDS
-Helicobacter pylori

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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

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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.

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What are cephalic reflexes?

-feedforward and emotional reflexes
-initiated and integrated outside GI

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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

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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

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What is secreted by the mucous neck cells?

Mucus and bicarbonate

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What stimuli release Mucus and bicarbonate from mucous neck cells?

-mucous = tonic secretion, irritated mucosa
-bicarbonate = secreted with mucus

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what are the functions of mucous and bicarbonate?

-mucous keeps physical barrier between lumen and epithelium
-bicarbonate buffers gastric acid

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What is secreted by parietal cells?

-gastric acid (HCl)
-Intrinsic factor

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What is the stimulus needed to release HCl and intrinsic factor from parietal cells?

-Acetylcholine
-gastrin
-histamine

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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.

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What is secreted by enterochromaffin-like cells?

Histamine

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What stimulus is required to release histamine from enterochromaffin-like cells?

-acetylcholine
-gastrin

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what is the function of histamine?

-stimulates gastric acid secretion

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what substances are secreted by Chief cells?

Pepsinogen and Gastric lipase

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What is the stimulus required to release pepsinogen and gastric lipase from Chief cells?

-Acetylcholine
-acid
-secretin

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What is the function of pepsinogen and gastric lipase?

-pepsinogen = digests proteins
-gastric lipase = digests fats

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What is secreted by D cells?

Somatostatin

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What is the stimulus required to release somatostatin from D cells?

acid in the stomach

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What is the function of somatostatin?

inhibit gastric acid secretion

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What is secreted by G cells?

gastrin

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What stimulus is required to release gastrin from G cells?

-Acetylcholine
-peptides
-A.A.

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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?

1. has urease activity -> increases pH -> causes G cell to produce more gastrin -> increases acid secretion 2. 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?

1. using a laxative empties the colon so it will take longer to refill and eliminate waste than normal. This can be perceived as constipation 2. 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

GI lecture Flashcards

(61 cards)