Flashcards in GI Deck 2 Deck (40):
2 forms of primary regulation of colon
- local reflexes- activated by bolus, secrete Cl & fluid
- long reflexes- gastrocolic & orthocolic
what do enteroendorine cells secrete? what is the nickname for this molecule? what does it respond to?
PYY; ileal break; fat in terminal ileum
what two structures provide colonic motility? what type of muscle are they and what is the duration of their contractions?
haustra- circular muscle- short
taeniae coli- 3 layers of longitudinal muscle- long
what kind of stimulation enhances motility?
- vagal in haustra, cecum, ascending & transverse colon
- pelvic nerves is descending, sigmoid colon, rectum and anus
what is an important product of colonic bacteria? what is it cotransported with?
SCFAs (short chain fatty acids)
cotransported with sodium using SMCTs
how is sodium absorbed in the distal colon? what is this known to be?
using ENaCs (epithelial sodium channels); is final defense mechanism for the absorption of water
what kind of muscle is in the rectum?
only longitudinal for storage (no circular for motility)
what kind of muscle is present in the anus?
smooth and skeletal (VOLUNTARY!!) muscle
filling of the rectum _____ the internal anal sphincter
where does the majority of blood to the liver come from?
- 70-80% is venous from portal vein
what is the major cell type in the liver and what are some of it's important functions?
hepatocytes- metabolize major nutrients, are the origin for the biliary system (make bile acid)
what are HsCs in the context of the liver?
hepatic stellate cells- normally inactivated, serve as a storage site for vitamins; over-activation causes them to produce collagen (BAD)
what are sinusoids?
low resistance liver capillaries which can be collapsed during fasting, and expanded with flow
what is the portal triad
portal vein, hepatic artery, bile duct
what are zone 1 hepatocytes?
- closest to triad
- receive max nutrients and O2
- affected by ischemia last
- see virus/toxins first
what are zone 3 hepatocytes?
- closest to central vein
- die first with ischemia
what are the cells that line the bile duct and modify bile called
what are canaliculi?
adjacent hepatocytes form canals for biles
why is carbohydrate metabolism important in liver?
- has role in gluconeogenesis (sugar-glucose)
- if backed up, can cause hyperglycemia (stores glucose it produces)
4 important functions of protein metabolism in liver
- non-essential AAs
- plasma proteins (albumins & clotting)
- ammonia- urea
- maintains oncotic pressure with albumin
what are kupffer cells?
macrophages in sinusoids
bile is a byproduct of ________ metabolism; what are the two types of primary bile acids?
- cholic acid, chenodeoxycholic acid
What are secondary bile acids?
primary bile acids enter colon and are dehydroxylated by colonic bacterial enzymes
T/F Primary and secondary bile acids are conjugated, making them more water soluble
TRUE- known as bile salts when ionized due to high pH of intestine
what are primary and secondary bile acids conjugated with?
glycine or taurine
T/F Conjugated bile acids are reabsorbed passively in colonic epithleium
False- UNconjugated forms are reabsorbed
Is bile acidic?
no- alkaline, due to CFTR Cl- channels and HCO3- exchange
what is bile outflow blocked by in between meals?
sphincter of oddi
what is enterohepatic circulation?
the recycling of bile from intestine to liver using ASBTs
where does bilirubin come from? is it soluble?
breakdown of heme
when unconjugated is very un-soluble
binds to albumin for transport
where is bilirubin taken up and by what; is it unconjugated or conjugated
liver by OATP
What is UGT?
- UPD glucuronyl transferase; enzyme that conjugates bilirubin; lacking in newborns
where does bilirubin go after the liver?
1) excreted in urine
2) added to bile, deconjugated and converted to urobilogen by bacteria
- can be absorbed via enterohepatic circulation
- excreted in feces
two causes of high unconjugated bilirubin in blood
1) oversupply of heme, eventually overwhelms liver
2) problem with UGT
two causes of high conjugated bilirubin in urine
1) defect in the transporter that secretes conjugated bilirubin into the bile
2) blockage of bile flow
what is the major source of urea for the urea cycle?
colonic bacteria (also have protein catabolism)
where does the urea cycle take place?
what is the major stimulus for bile secretion? what are the two actions it causes?
- contraction of gall bladder & relaxation of oddi
what are gallstones?
precipitated bile constituents- cholesterol & Ca2+ bilirubinate stones