GI Flashcards
What are the segments of the GI tract?
Mouth, pharynx,esophagus, stomach, SI, LI, anus
What are the layers of the GI tract?
- serosa 2. longitudinal muscle 3. myenteric (auerbach’s) nerve plexus 4. circular muscle 5. submucosa 6. submucisal (Meissner’s) nerve plexus 7. muscularis mucosae 8. mucosa 9. epithelial lining
What is the primary control over the intrinsic control of the GI tract?
ENS
What is the primary control over the extrinsic control of the GI tract?
ANS
Describe the intrinsic control of the GI tract.
via the myenteric plexus: in the longitudinal and circular SM layers: functions to control motility by controling the tonic contraction and frequency/intensity and sphincter tone
Submucosal plexus: local control of secretion,absorption, and contraction of muscularis (helps control SA of the epithelium)
Which component of the ANS stimulates extrinsic control? inhibits?
PNS thru vagal nerves and pelvic nerves, SNS via ganglia
All of the blood that flows through the gut, spleen, and pancreas flows to the liver via what?
portal vein
Blood passes through minute liver sinusoids and leave via what?
hepatic veins
What does the blood flow through the liver allow?
reticuloendothelial cells to remove bacteria and other particulate matter
What are the main controllers of blood flow?
Local activity, induced by activity, and Nervous control
Briefly describe the local control of blood flow.
based on demand - if eat = increased blood flow for 3-6 hours
Briefly describe the nervoue control of blood flow.
The PNS increases gut activity which increases blood flow (by vasoconstriction) and the SNS directly decreases blood flow (for things like exercise, shock, and autoregulatory escape)
What are the causes of activity-induced blood flow?
vasodilator hormones (gastrin, secretin, CCK), vasodilator kinins, low O2 (high adenosine)
True/False: Due to the opposite flow of veins and arteries, O2 diffuses out of the arterioles directly into the adjacent venules without being carried to the tips of the villi.
true
In diseases conditions (such as shock), what happens to the blood flow and O2?
blood flow to the gut becomes curtailed and O2 deficiency in the tips of the villi develops -> ischemic death and disintegration = diminished absorptive capacity
What are the types of GI regulatory substances?
endocrines (hormones), neurocrines (neurotransmitters), and paracrines
Describe the MOA of endocrines.
released into blood to act on distant target cells
Describe the MOA of neurocrines.
released via nerves to diffuse to target cells
Describe the MOA for paracrines.
endocrine cells release for diffusion to local target cells (not released in circulation)
What are the main GI hormones?
Gastrin, secretin, CCK, GIP
What is the function of gastrin?
Promotes H+ secretion by gastric parietal cells, stimulates growth of mucosi
What releases gastrin?
G cells in antrum and duodenum
Surgical removal of the antrum of the stomach causes what?
atrophy
What stimulates gastrin release?
protein digestion products, nervous, physical distention, Ca2+, decaf coffee, wine
What inhibits gastrin release?
acidification of antrum (negative feedback: G cells stimulated by high pH release gastrin which will then release H+ to lower pH which will stop releasing gastrin)
Gastrinoma/Zollinger-Ellison Sydrome cause what to happen with gastrin secretion?
continuous secretion of gastin into blood
What does hypergastrinemia cause?
hypersecretion of acid
What are the effects of hyper secretion of acid?
increased parietal cell mass, constant stimulation of hyperplastic muscosa, hypertrophy of gastric mucosa
What are symptoms of Gastrinoma/ZES?
peptic ulcers, diarrhea, steatorrhea (fat in feces), hypokalemia
What is the function of CCK?
promote fat digestion and absorption
What release CCK and in response to what?
I-cells in duodenum and jejunum in response to MG or FA, peptides and single AA, acid
What are the major actions of CCK?
empty gallbladder (contracts it and relaxes the sphincter or Oddi), secrete pancreatic enzymes and HCo3- 3. inhibits gastric emptying 4. growth of exocrine pancreas and GB mucosa
What is the function of secretin?
counteract acidity - inhibit gastric acid secretion, stimulates pancreatic and bile bicarbonate secretion for fat digestion, and growth of exocrine pancreas
What releases secretin and what stimulates its release?
S-cells of duodenal muscosa,
acid in dudoenum (pH <4.5), FAs in duodenum
What are the effects of GIP?
Glucose-dependent Insulinotropic peptide = stimulates insulin release also called “Gastric inhibitory peptide” = inhibits gastric acid secretion
Describe the release and stimuli of GIP.
released from K cells of duodenum and proximal jejunum, released in response to all major nutrients (CHO, AA, fat), oral glucose (incretin)
What are the candidate hormones?
motilin, pancreatic polypeptide, enteroglucagon, Glucagon-like peptide (GLP-1)
What is motilin and when/where is it secreted from?
secreted from upper duodenum during fasting states, increases GI motility by inititating myoelectric complexes at 90 minute intervals
What is Pancreatic Polypeptide and when/where is it secreted from?
secreted by the pancreas in response to ingestion of CHO, proteins, or lipids. inhibits pancreatic secretion of HCO3 and enzymes
What is enteroglucagon and when/where is it secreted from?
released fro intestinal cells in response to a decrease in blood glucose concentration, stimulates the liver to increase glycogenolysis and gluconeogenesis
What is GLP1 and when/where is it secreted from?
Produced from proglucagon, secreted by L cells of the S1, is classified as an incretin becise it stimulates insulin secretion
What are treatments of ZES?
administration of H2 receptor-blocking drugs (cimetidine), admin of H+ pump inhibitors (omeprazole), removal of tumor, gastric resection
What are the two paracrines discussed for the GI tract?
somatostatin and histamine
What is the function of somatostatin?
inhibit secretion of other GI hormines, inhibits gastric H+ secretion
What is the function of histamine?
along with gastrin and Ach, stimulate H+ secretion by gastric parietal cells
What are the neurocrines of the GI tract?
ACh, NE, Vasoactive Intestinal Peptide, Gastrin-Releasing Peptide/Bombesin, Enkephalins (opiates), Neuropeptide Y, and substance P
What effect does ACh have on GI?
contraction of SM in wall, relaxation of sphincters, increase salivation, increase gastric and pancreatic secretion
What effect does NE have on GI?
Relaxation of SM in wall, contraction of sphincters, increase salivation
What effect does VIP have on GI?
Relaxation of SM, increase intestinal secretion, pancreatic secretion
What effect does enkephalins have on GI?
contract SM, decrease intestinal secretion
What effect does neuropeptide Y have on GI?
Relax SM, decrease intestinal secretion
What effect does Substance P have on GI?
contraction of smooth muscle, increase salivary secretion
What does circular muscle contractions do?
shorten lumen
What does longitudinal muscle contractions do?
decrease the length of the segment
What are the types of contractions?
phasic, tonic