GI Physio | Secretions I (Salivary, Gastric, Intestinal) Flashcards
A majority of GI secretions are _____. The 2 major contributors to secretions are what?
Passive;
Water (predominantly) and mucus
The production of sugars, amino acids and peptides in the lumen ______ osmolarity. This causes water to _____.
Increases lumenal osmolarity;
Water gets PULLED into the lumen of the small intestine.
Absorption of small molecules in the intestinal lumen, ______ the osmolarity. This causes water to _____.
Decreases lumenal osmolarity; Water DIFFUSES back into the body by the time food gets into the large intestine.
Describe the 3 general rules of fluid secretion, pertaining to electrolytes and water.
- Movement of ions requires energy at first.
- Counter ions follow = electroneutrality
- Water follows = isotonicity
Define 3 key characteristics about salivary fluid
- HYPOTONIC Concentrations of electrolytes change with rate of secretion.
- Salivary Na and Cl are in lower concentration than in plasma.
- Saliva is richer in HCO3- and K+ than in plasma.
An extensive loss of saliva will most likely result in a decrease in which ion concentration?
Potassium (K+), because saliva is so rich in this ion as compared to the lower amount in plasma.
Within the cells of the salivary glands, what channel is the primary energy source for driving ion secretions?
Na/K ATPase on the serosal side of the acinar and ductal cells.
The sympathetics major contribution to salivary secretion is ___. Whereas the parasympathetics contributions to saliva are ____ and ____.
SNS (T1-T3) contributes mucus.
PSNS (CN IX, X and VII) contributes fluid and enzymes to saliva.
PSNS nerves offer a major trophic factor
List 3 factors that stimulate salivary secretion. What are some factors that inhibit this?
Smell, taste, pressure or nausea can stimulate salivary secretion; whereas, fatigue, lack of sleep, fear or dehydration can inhibit this (leading to a dryer mouth).
When stimulated, oxyntic cells secrete _____ ____ into the lumen and _____ into the interstitium.
Stimulated oxyntic cells secrete ISOTONIC HCl into the lumen + HCO3- into the interstitial area.
What ion is highest in concentration within gastric juices at low and high rates of secretion?
Cl- ions are highest in concentration, even more than H+ at low and high secretory rates.
What are the 2 major secretions of gastric juices? Briefly describe the consistency of each.
- Oxyntic component consisting of HCl from parietal cells (aka oxyntic cells)
- Non-oxyntic component composed of mucus, Na+, HCO3-, pepsinogen and diffuse interstitial fluid
What microbes are able to resist the inactivation of HCl in the stomach?
Helicobacter pylori, E. coli and other bacteria that can withstand a pH = or < 2.0.
What morphological change occurs in parietal cells from resting to secreting phases?
Tubulovesicles rich in H+ pumps from resting phase fuse with the intracellular canaliculi in order to secrete H+ into gastric juices.
What is alkaline tide and how does it work? What are the 2 main causes of this?
This refers to an increase of pH in the gastric (portal) vein after gastric acid secretion. Because more H+ is secreted into the lumen, more HCO3- is secreted into the blood of the portal vein. This is a physiologic process after a big meal (post-prandial alkaline tide) or pathological as from metabolic alkalosis (sustained alkaline tide) after vomiting.
Administration of a proton pump inhibitor (PPI) such as omeprazole after a major meal will have what effect? Why?
This will decrease the potential difference across the stomach from -70-80 mV to -30-50 mV. This is because less H+ is being secreted into the gastric lumen simultaneous to the reduced HCO3- secretion into the blood.
Rank the top 3 phases of control for acid secretion from the stomach in order. Briefly describe what stimulates and mediates each.
- Gastric phase (50% HCl) - stimulated by food in the stomach
- Cephalic phase (30%) - stimulated by sight, smell, chewing, tasting and swallowing of food.
- Interdigestive phase (15%) - basal; no stimulation
* These are all mediated by PSNS, gastrin and histamine to produce acid*
Why does acid secretion drop significantly (10-fold) after the gastric phase? What are the mediators of the intestinal phase?
After chyme has been digested in the stomach, we don’t want intestinal enzymes to be destroyed by excess acid in lumen. Secretin, CCK and GIP inhibit gastrin’s effect to increase acid production.
Define the major inhibitors or gastric acid secretion and their MOA.
- Secretin, CCK and GIP indirectly reduces acid secretion by nullifying gastrin’s effects.
- Prostaglandins and somatostatin work DIRECTLY to inhibit acid secretion by reducing cAMP activity in the parietal cells.
Define the major trophic stimulator of parietal cells.
The more gastrin we have, the LARGER the parietal cells and more cAMP activity for acid production.
How strong is the H+ gradient of acid contained within my stomach?
3-million fold from outside stomach to inside. The acid is so strong that it can reduce rust.
Describe the 2 modes of containment for HCl in the stomach. What is the significance of this for anti-inflammatory drugs?
- Mucosal barrier (mucus glycoproteins and HCO3-)
- Prostaglandins - directly inhibit acid secretion. This is significant since people who take anti-inflammatory drugs, such as NSAIDs, have trouble with gastric secretion and therefore properly digesting foods.
Pancreatic enzymes are usually secreted in ______ into the duodenum. What is the limiting factor for digestion and what anatomic structure controls it?
Pancreatic enzymes in Excess into the duodenum;
Rate of Gastric emptying, controlled by the Pyloric Sphincter, is the limiting factor for digestion
Describe what occurs if the pyloric sphincter is damaged or removed from surgery?
Dumping Syndrome - a SEVERE condition where the body loses A LOT of fluid resulting in watery, painless diarrhea
Explain the pathophysiology of Dumping Syndrome and list its systemic effects on the body.
- Rapid gastric emptying causes a sudden INCREASE in osmotic pressure (water diarrhea).
- This also causes distention of the lumen increasing motility (reduces absorption).
- Fermentation of unabsorbed nutrients in large intestine leads to gas.
- Loss of blood volume results in weakness and tachycardia.
- Sudden increase in blood sugar causes over-secretion of insulin. This leads to hypoglycemia, diaphoresis and tachycardia.
Define pancreatitis. What are some common causes?
Pancreatitis is inflammation of the pancreas from untimely activation of pancreatic enzymes that results in self-digestion.
3 Common causes include:
1. Congenital trypsin inhibitor deficiency
2. Abdominal trauma (proteases from injured pancreatic cells activate trypsin)
3. Cystic fibrosis (enzyme is stuck in pancreas)
Why do we not have amylase as part of the pancreatic secretions?
By this time starch has been broken down in the mouth and stomach. Remaining peptides, amino acids and fats in the lumen explains why we have more lipases, proteases and DNAases instead.
Explain the significance of pancreatic fluid secretion in relation to its enzymes.
Fluid helps to deliver the enzymes from the pancreas into the small intestine. This HCO3- rich fluid also protects enzymes by neutralizing remaining H+ in lumen.
Why don’t we feed newborns foods high in starch?
The exopancreas is only partially developed at birth. Don’t give starchy foods, even if liquified.
