GI 3 Flashcards
duodenum
common bile duct and pancreatic duct; lots of secretions occur; place where very acidic chyme enters (needs to be neutralized)
Jejunum
largest section of small intestine; where most of absorption is taking place
Ileum
Peyer’s patches or lymph nodules (defensive mechanisms), ileoceal valve
structures to support the unique functions of the small intestine
circular folds/plicae, villi, microvilli
What increases gastric empyting?
increase in peristaltic waves in the gastric pump, increased tone in the gastric reservoir, increased action of VIP on the pyloric sphincter
What neurotransmitters are involved in openning the pyloric sphincter?
NO and VIP
What promotes gastric emptying?
increased gastric volume, neural (ACh), hormone (gastrin)
What inhibits gastric empyting?
distension plus acid in duodenum, hormonal: GIP, CCK, secretin
Dumping Syndrome
when gastric emptying is not controlled because of a gastrectomy which could be affecting the feedback control of emptying; partly digested good draws excess fluid into the intestines
The symptoms of dumping syndrome (heart palpitations, nausea, ect) are due to…
hypo-and-hyper-glycemia
Dumping syndrome may lead to…
malabsorption; since you are affecting the feedback signals (like GIP)- you are affecting glucose homeostasis; and you are eliminating intrinsic factor emitting cells which leads to less B12 absorption
What is more predominant in the small intestine? Sementation or peristalsis?
sementation
In segmentation, the slow propulsion is possible due to…
a frequency gradient (higher frequency in duodenum and then decrease as you go distal)
What stimulates the migrating motor complex?
motilin
What inhibits the migrating motor complex?
feeding
What does the migrating motor complex do?
It is a bunch of peristalsis waves that clean out the system so that a new meal can come in and be digested
Secretin is secreted by what cells and where?
secreted by S cells, and secreted from the mucosa of the upper small intestine
What is the function of secretin?
to stimulate pancreatic bicarbonate secretion (to augment CCK functions), inhibits gastric emptying and gastric secretion
What triggers secretin?
acid (most prominent signal), products of protein digestion
What inhibits secretin?
when products of digestion move on to the lower portion
CCK is secreted by what cells and where
secreted by I cells, and in the mucosa of the upper small intestine
what are the functions of CCK
stimulates pancreatic enzyme secretion, contraction of gallbladder, relaxation of sphincter of Oddi, inhibits gastric empyting and gastric secretion
What triggers the secretion of CCK?
amino acids, peptides, and fatty acids
bile digests
fat
CCK secretion is inhibited by
the production of digestion moving to the lower portion
What are similiarities between CCK and secretin?
they are both secreted by the 1st portion of the small intestine, both in small intestine lining, helping with pancreas secretion, both inhibit gastric emptying/ secretion, both inhibited when food moves away
What are the functions of the liver?
metabolic regulation, synthesis, storage, and detoxification
What does the liver do in term of metabolic regulation?
maintains normal glucose levels; carb, lipid, amino acid metabolism
What does the liver synthesize?
bile, plasma protein, clotting factors, and cholesterol
What does the liver store?
iron, glycogen, blood, fat-soluble vitamins
Bile is synthesized by
hepatocytes
What is one of the only ways that cholesterol is regulated?
by being secreted into the bile
Bile is composed of
bile salts, bilirubin, cholesterol, and bicarb
Bile is stored…
in the gallbladder
Secretin increases the secretion of what by what
secretin increases secretion of bicarb by biliary tract
CCK causes the…
contraction of the gallbladder and the release of stored bile ( allows sphincter to open-NO, VIP)
Where is bile passively reabsorbed?
in the duodenum
Where is bile actively absorbed?
The terminal ileum
What is the only way to get rid of cholesterol?
through bile; cholesterol is added into bile and then eliminated from the body through the feces
What is the pancreas exocrine function?
acini cells; secreting enzymes: precursors of proteases, lipase, and amylase (also secretes bicarb)
What is the endocrine function of the pancreas?
islets: to secrete hormones ( beta cells and alpha cells)
When there is low pH, the pancreas secretes…
secretin ( secretion high in bicarb)
when fatty acids are present, the pancreas secretes…
CCK (secretion high in enzymes)
What kind of nervous stimulation stimulates pancreas secretion?
vagus nerve (10th cranial nerve)
What is digestion?
macromolecules into absorbable units
Describe absorption
mostly takes place in the small intestine; water and ions in the large intestine (primarily influenced by motility and secretion in the GI)
Can carbohydrates be absorbed as disaccharides?
no, carbohydrates can only be absorbed as monosaccharides
What is the function of amylase
amylase breaks carbohydrates into disaccharides (smaller glucose chains)
What is the function of brush border enzymes?
break disaccharides into monosaccharides (to then be digested); located in the microvilli
What is the function of SGLT1 in carb absorption?
it is a secondary active transporter(apical side); using the Na gradient established by Na/K ATPase to push glucose against its gradient into the cell and then into the blood using the GLUT2 transporter
What kind of transport does GLUT5 use?
facilitated diffusion
describe GLUT2
moves all monosaccharides and it is on the basolateral side
If glucose is equal inside and outside the cell and lumen, what will happen
since we still have the Na gradient, we can still have some absorption of glucose into the blood (smaller amount tho due to the gradient)
What will happen to transport of glucose in a low Na condition (lumen)
there will be little to no transport of glucose because glucose need the sodium gradient to be transported into the cell
What is the purpose of endopeptidases?
they are proteases that attack peptide bonds; secreted by stomach, intestine, and pancreas as inactive proenzymes (pepsin, trypsin)
What is the purpose of exopetidases
release single amino acids, secreted by pancreas (carboxypeptidase)
Can proteins be absorbed as dipeptides?
yes, they can be absorbed as amino acids, dipeptides, tripeptides, and as larger peptides
How are amino acids absorbed?
mostly by Na+ dependent active transport (cotransport with Na)
How are dipeptides and tripeptides absorbed?
H+ dependent; PepT1 (cotransport with H+)
how are larger peptides absorbed?
by transcytosis
What is the first step in the digestion of fats?
emulsification (with bile salts)
What is emulification?
a process that breaks down large lipid droplets to smaller bits; increases surface area available for lipase action
What is step 2 of digesting fat?
enzymatic fat digestion
What occurs during enzymatic fat digestion?
lipase and colipase digest triglycerides into monoglycerides and fatty acids; phospholipase digests phopholipids
What is step 3 in fat digestion?
formation of bile micelles
What occurs during the formation of bile micelles?
final end product; break down to be absorbed
How are monoglycerides and fatty acids absorbed?
by diffusion (small and lipid soluble), then they recombine inside the cell to form the chylomicron, then the chylomicrons leave through the basolateral by exocytosis
How is cholesterol absorbed
same as monoglycerides and fatty acids, but because cholesterol is a large molecule it uses a transporter to enter the cell
What is the 1st step in the absorption of fat
monoglycerides and fatty acids enter the smooth ER and get converted into triglycerides
What is the 2nd step of fat absorption?
in the rough ER, a protein coat is put onto the triglycerides and cholesterol and you get a chylomicron
What is the 3rd step in fat absorption?
the chylomicron is too large to be transported in the blood, so it is transported by the lacteal ( in the lymphatic system)
What products are absorbed into the hepatic portal system
carbohydrates and proteins (because they are water soluble)
What products enter the lacteal?
chylomicrons
describe the hepatic portal system
blood leaving gut, enters hepatic portal vein, second exchange site at liver sinusoids
describe the blood in the hepatic portal vein
deoxygenated by nutrient rich
most absorbed nutrients goes where first (and except for what)
the liver and (except for products of fat digestion- lacteal)
Unique structures in the large intestine that support its functions
the tenia coli and the smooth muscle transition to skeletal muscle
What occurs in the large intestine
segmentation and mass movement (when you have to poop); mucus secretion and water absorption, digestion of complex carbs and proteins through fermentation
