GI tract Flashcards
What is the pylorus?
regulates passage of chyme
What is chyme?
partially digested food and gastric juices formed in stomach
What is gastric emptying?
stomach moves chyme into small intestine via pyloric sphincter
How do fats affect gastric emptying?
they slow down gastric emptying due to releasing the hormone CKK
How do carbohydrates affect gastric emptying?
speed up emptying
What role does the vagus nerve play in gastric emptying?
regulates the contractions of the stomach and pyloric sphincter, influencing the rate of gastric emptying through parasympathetic control
How does the hormone gastrin influence gastric emptying?
increases gastric motility and promotes the emptying of the stomach by stimulating muscle contractions in the stomach.
How do hypertonic and acidic chyme affect gastric emptying?
slows down gastric emptying
What does hydrochloric acid (HCl) do in the stomach?
HCl, secreted by parietal cells, lowers stomach pH to activate pepsinogen into pepsin and helps kill bacteria.
What is the role of pepsinogen in digestion?
is secreted by chief cells
HCL converts pepsinogen to pepsin to break down proteins
What function does mucus serve in the stomach?
protects stomach lining for gastric juices and digestive enzymes
What is the function of gastric lipase?
is secreted by cheif cells
breaks down lipids
How does histamine influence stomach activity?
is secreted by enterochromaffin like cells
stimulates parental cells to secrete HCL
What does the hormone gastrin do?
secreted by G cells
stimulates parietal cells to release HCL
enhancing gastric motility
What is the role of bicarbonate in the stomach
neutralises acid in mucous layer
Which cells produce HCl in the stomach?
parietal cells
What enzyme is involved in HCl production inside parietal cells?
carbonic anahydrase converts C02 and water into carbonic acid which then dissociates into bicarbonate and hydrogen
How are hydrogen ions (H+) secreted into the stomach lumen?
primary active transport via H/K ATPase pump (proton pump)
What happens to bicarbonate (HCO3-) during HCl production?
exchanged for chloride at basolateral membrane
Which hormone stimulates HCl production and what pathway does it follow to do so?
gastrin
binds to CCK2
receptors on parietal cells
with subsequent activation
of PLC
PLC increases Calcium activating proton pump
explain the pathway histamine follows to increase HCL production
upon stimulation by acetylcholine histamine binds to H2 receptors on basolateral membrane increasing adenyl cyclase activity therefore increasing cAMP and proton pump activity
explain the pathway of Achieving effect on HCL production?
ACh is released by
parasympathetic cholinergic
neurons binding to
muscarinic (M3) ACh
receptors on parietal cells
with subsequent activation
of PLC therefore increasing proton pump activity
What inhibits HCl secretion in the stomach?
somatostatin secured by D cells inhibits HCL secretion by suppressing gastrin release and directly inhibiting parietal cells
What is the role of proton pump inhibitors (PPIs) in controlling HCl production?
blocks H/K ATPase pump (proton pump)
which other lipid inhibits HCL secretion?
and the pathway it follows
Prostaglandins
bind to basolaterial membrane via EP3 receptors inhibiting adenyl cyclase activity
What are the three phases of gastric secretion?
cephalic
gastric
intestinal
What triggers the cephalic phase of gastric secretion?
thought , sight or smell of food
stimulates gastric secretion via vagus nerve
How is the cephalic phase of gastric secretion regulated?
CNS sends signals from brain activating vagus nerve to stimulate parietal, chief, and G-cells in the stomach
What initiates the gastric phase of secretion?
when food enters the stomach stretching stomach walls activating stretch receptors
How is the gastric phase of secretion regulated?
gastrin release from G cells stimulating HCL secretion
What triggers the intestinal phase of gastric secretion?
when chyme enters duodenum
How is the intestinal phase regulated?
secretin and CCK
inhibit gastrin secretion and motility
What is the main purpose of the intestinal phase?
controls rate of emptying
How does acetylcholine enhance the activity of the H+/K+ ATPase?
is released from vagus nerve and binds M3 receptors on parietal cells increasing intracell Ca increasing proton pump activity
Which second messenger system is activated by acetylcholine and gastrin to enhance H+/K+ ATPase activity?
increase intracellular Ca that activated H/K ATPase activity
Which second messenger system is activated by histamine to enhance H+/K+ ATPase activity
activates cAMP
What hormone is primarily responsible for stimulating the secretion of pancreatic enzymes and bile?
CCK
Which hormone promotes the secretion of gastric acid in the stomach and is released when food enters the small intestine?
gastrin
What hormone is released in response to low pH in the small intestine and stimulates the secretion of bicarbonate from the pancreas?
secretin
How do hormones like CCK and secretin affect the motility of the small intestine?
slow down motility
What effect does CCK have on gallbladder function?
stimulates contraction of gallbladder to eject bile into duodenum
what type of cells of duo and jej secrete GIP ?
what does it stimulate and inhibit
K cells
stimulates released of insulin from pancreatic B cells
inhibits gastric emptying
what type of cells secretes GLP-1(small intestine)
GLP-1 stimulates =
GLP-1 inhibits=
GLP-1 decreases=
L cells
insulin secretion
glucagon secretion from pancreatic a cells
gastric emptying and appetite
what type of cells of duo and jej secrete motilin
and when are they secreted
M cells
during fasting
Ghrelin is secreted from ___ cells and stimulates ____
Gr appetite
How does the pancreas contribute to digestion via its exocrine function?
secretes digestive enzymes into small intestine
Which hormones does the pancreas secrete to regulate blood sugar levels?
insulin and glucagon
role of goblet cells
create mucus layer
What are the two main functions of the pancreas in relation to the GI tract?
endocrine = hormonal
exocrine= digestive enzymes
