Gastric Secretion And Emptying Flashcards
How many muscle layers does the stomach have?
3
Outer longitudinal
Middle circular
Inner oblique** unique to stomach :)
How does the orad stomach know to relax when food is on its way down your esophagus?
Via receptive relaxation, a vagovagal reflex**
What does the size of the stomach depend on?
Volume of the contents
What is a vagovagal reflex?
A reflex in which the afferent AND efferent signals are both carried by the vagus nerve
What happens to your vagovagal reflexes if you cut you vagus nerve>
No more
What kind of cells are in the gastric pits?
Parietal cells
Chief cells
What part of the stomach has gastric pits (with parietal and chief cells)?
Body
What part of the stomach are G cells and Mucous cells?
Antrum
What do Parietal cells secrete**
HCl
Intrinsic Factor
What do chief cells secrete?
Pepsinogen
“Have a Pepsi, Chief” 🥤➡️👮🏼♂️
What are the 4 major components of gastric juice?
HCl
Pepsinogen/Pepsin
Mucus
Intrinsic Factor
Is pepsinogen active?
No, it needs to get turned into Pepsin to be active
What is the only thing that the stomach secretes that we can not live without?
Intrinsic Factor (if you lose that part of your stomach , you need B12 injections)
What are the functions of HCl?
Reduces pH
Activates pepsin
Protein digestion
Kills bacteria
What does pepsin do?
Digests proteins
What does mucus do for the stomach?
Protects the gastric mucosa from the corrosive actions of HCl
What does Intrinsic Factor do?
It is necessary for the absorption of vitamin B12
How are H+ and HCO3- formed inside parietal cells?
Hydration of CO2 by Carbonic Anhydrase
H2O+CO2= HCO3- + H+
After Carbonic Anhydrase makes H+ and HCO3-, where do they each go/
HCO3- goes into the blood in exchange for a Cl-
H+ goes into the stomach in exchange for a K+
What is the alkaline tide?
The flow of HCO3- out of the parietal cells when they make H+
How does H+ get out of the parietal cell and into the stomach?
In exchange for K+ via ATPase
How does Cl- get out of the parietal cell and into the stomach?
Passively through chloride channels
What are the functions of Gastrin?
Stimulate Acid and pepsinogen secretion (mostly acid)
Growth of gastric and intestinal mucosa (trophic effects**)
Antral and intestinal motility
If you have too much gastrin what happens to the thickness of the stomach?
Stomach and intestine mucosa grow too thick, plus there will be a lot of acid
What stimulates G cells to release Gastrin?
Small peptides/amino acids in stomach
Distention of stomach
Vagal stimulation
What inhibits the release of Gastrin?
Low pH (don’t need any more acid!)
What are the 2 ways that gastrin can communicate with parietal cells
- Bind to ECL -> releases histamine -> histamine binds to H2 receptor on parietal cell
- Gastrin can just bind directly to a CCKb receptor on the parietal cell
What do ECL cells do?
When gastrin binds to ECL, ECL releases histamine* which then will bind to an H2 receptor** on the parietal cell and stimulate acid production.
How does ACh released from the vagus nerve affect parietal cells?
ACh will bind to an M3 receptor and stimulate acid production
(Parasympathetic stimulation, anyone?)
What two things can inhibit the release of HCl from the parietal cell?
PGE2
Somatostatin
What is the cephalic phase of HCl secretion?
Influence that comes from your head (tasting, smelling, chewing, swallowing food)
How does the signal get to your stomach to tell it to secrete HCl when you smell a juicy burger cooking?
Vagus nerve directly stimulates parietal cells
OR
PNS stimulates G cells to release gastrin, which will enter the circulation, and then influence Parietal cells
What % of total HCl release is due to the Cephalic phase?
30%
What neurotransmitter is released by the PNS onto G cells to tell them to release gastrin?
GRP (Gastrin releasing peptide)
What are the primary stimulatnts of HCl release in the Gastric Phase of HCl release?
Amino acids
Small peptides (via G cells)
Distention of stomach
How does distention stimulate HCl secretion?
LOCAL reflex arc- reflex is in the wall of the stomach
AND
Vagovagal reflex arc- vagus detects distention and then loops back around to tell it to release HCl
**** he talked about this A LOT
How does Histamine stimulate HCl release?
Binds to H2 receptors on parietal cells
What does cimetidine do?
Blocks H2 receptors on parietal cells = histamine cant bind and cause HCl release
What % of total HCl release is due to the Gastric phase?
60% (main influence of HCl secretion)
What do alcohol and caffeine do to HCl release?
Stimulate it
What causes pepsinogens to become active?
Acid as well as autocatalysing each other once active (pepsin directly activates pepsinogen)
What is the optimum pH for Pepsin?
1.5-2.0
At what pH is pepsin denatured?
7.0
What is the function of pepsin?
Cleaves proteins to peptides at aromatic links
digests 10-20% protein in a typical meal (most will be done in duodenum)
What is most important for the release of pepsinogen:
Cephalic phase
Gastric phase
Cephalic phase*****🧠
What stimulates the release of pepsinogen from chief cells?
Vagus nerve stimulation (cephalic phase)
Luminal HCl locally will stimulate release
Gastrin and secretin stimulate release
What is the primary barrier for gastric mucosa from acid, enzymes, and physical damage?
Mucus
What cells secrete mucus?
Mucous neck cells
Surface epithelium
What is gastric mucus made up of?
Mucins (glycoproteins)
High bicarbonate levels***
What stimulates mucus and Bicarb secretion?
PNS (vagus)
Gastric distention
Prostaglandins*****
Why do NSAIDs lead to ulcers?
NSAIDs= no prostaglandins= less stimulation to secrete mucus and bicarbonate
How does pH change across the mucus layer from the lumen to the gastric epithelial cells?
pH is ~2.0 in the lumen
~7.0 at the surface of gastric epithelial cells
What are 4 things that protect the gastric mucosal barrier?
HCO3- and mucus
Prostaglandins
Mucosal blood flow
Growth factor
What are 6 things that are damaging to the gastric mucosal barrier
H+ and pepsin
H pylori
NSAIDs**
Stress
Smoking
Alcohol
What are the 3 components of gastric motility?
- Relaxation of orad stomach to accept food from esophagus (receptive relaxation. Vagal reflex involving VIP)
- Mixing motions to reduce size of bolus
- Propulsion of chyme through pyloric valve into duodenum
What factors will increase gastric motility and emptying?
PNS stimulation
Gastric distention
Gastrin
Motilin(released in interdigestion periods as a housekeeping hormone)
Are gastrin and motilin ever present at the same time?
No
Gastrin is released during actual digestion
Motilin is released in interdigestion periods
What factors decrease gastric mixing and emptying?
SNS stimulation
Secretin, CCK and GIP (from duodenum)
H+, digestion products of fat/protein in the duodenum, duodenal distention
(Basically things that mean food is in the duodenum now and the stomach needs to calm tf down while the duodenum works on the food before the stomach squirts more in)
What kind of reflex tells the stomach to hit the brakes for a minute before it squeezes more food into the duodenum?v
Enterogastric reflex- (a nervous, not hormonal signal)
Is the pyloric valve a wide opening or very narrow?
Very narrow. Only VERY small particles can pass into the duodenum
What drives the bolus toward the pyloric valve?
Antral peristaltic waves
What happens if the stomach tries to push food particles that are too big through the pylorus?
They get reflected back into the antrum via retropulsion so that the stomach can churn them more into smaller pieces
What 3 things will the duodenum release into the blood when its full of food to tell the stomach to hit the brakes?
Secretin
CCK
GIP
What are some of the things that can cause you to vomit?
Stomach stretch and inflammation
Rotation (seasickness etc)
Inreacranial pressure
Pain
Smells/touches
Visual stimuli
Pregnancy
Medications
Toxins
What muscles will be RELAXED during vomiting?
Stomach !!*
Esophagus
Lower esophageal sphincter
What is the order of events when your vomiting reflex is triggered?
Diaphragm lowers to just above stomach
Glottis closes
Abdominal muscles contract to increase intra-abdominal pressure
Stomach, esophagus, and LES relax
Stomach gets squeezed between your diaphragm and viscera like a tube of toothpaste
UES relaxes, vomit projected into mouth
🤮
What prevents aspiration of vomit when you’re vomiting
Closed glottis
What causes Peptic Ulcer Disease?
Excess acid secretion
Damage to mucosa barrier
What can cause damage to the mucosal barrier/
Acid-destroys mucosal cells and liberates histamine
Hitramine- stimulates more acid secretion, vasodilation, increases capillary permeability and edema
How do you treat H pylori?
Clarithromycin, amoxicillin
Dont know if this is important
Name 2 H2 blockers
Cimetidine (Tagamet)
Ranitidine (Zantac)
Name 2 proton pump inhibitors?
Omeprazole (Prilosec)
Lansoprazole (Prevacid)
What does colloidal bismuth (Pepto Bismol) do to your stomach?
Coats and protects ulcers
What proton pump is inhibited by PPIs like omeprazole?
The ATPase that pumps H+ into the stomach in exchange for one K+ (on a parietal cell)
