GI Hepatosplanchnic circulation and bile formation Flashcards
Hepatosplanchnic circulation
supplies blood flow to viscera (liver, stomach, small intestine, colon, pancreas, and spleen)
oxygenated blood
hepatic artery (25%)
Deoxygenated blood
portal vein (70%)
Is splanchnic circulation arranged in series or in parallel to the hepatic portal circulation?
Series - facilitates the delivery of absorbed nutrients to the liver
SNS - hepatosplanchnic circulation (arerioles, venuoles, veins)
a1 receptors - constriction of vascular smooth muscle in arterioles venules and veins
PNS- hepatosplanchnic circulation (arterioles, venules, veins)
Parasympathetic increases contraction and secretion of the GI tract creating vasoactive metabolites
Increased vagal stimulation creates and increase in vasoactive metabolites which causes vasodilation and increased blood flow (SECONDARY to contractile and secretory effects)
PNS on salivary glands
Vasodilation
Myogenic vasoconstriction
response to sudden increase in profusion pressure
increases local vascular resistance in order to protect the capillaries from high systemic pressures and excess fluid filtration
intrinsic response to low profusion pressure
low profusion results in decreased blood flow and decreased substrate delivery = accumulation of locally produced metabolic factors
metabolic factors can cause vasodilation and increase blood flow
increased secretory activity leads to increased _____ blood flow
mucosal
increased motor activity to the gut leads to increased ______ blood flow
muscularis
Escape phenomenon
sympathetic stimulation causes constriction of both arterioles and veins resulting in decrease in splanchnic flow (fight or flight - shunted away from the gut)
Despite continued stimulation the splanchnic arterioles (NOT veins) will spontaneously vasodialate (i.e escape)within a matter of minutes
Attempt to avoid counter current exchange and save the gut from necrosis
Counter current exchange
oxygenated blood dissolved in the plasma shunts from the arteriole to the venule without reaching the capillaries.
This gets exaggerated in states of low blood flow (ischemia) due to slowed blood flow velocity- risk necrosis to the villous tip
Primary Bile acids
from salts or newly synthesized by hepatocytes
Cholic Acid and Chenodeoxycholic Acid
Secondary Bile Salts
formed from the action of bacteria in the digestive tract
deoxycholic acid and lithocholic acid
Bile Pigments
senescent red blood cells (degraded by reticuloendothelial cells- hgb is broken down to form bilirunin)
the bilirubin is removed form the plasma by the liver and is conjucated and secreted into bile
BILE PIGMENTS ARE NOT PART OF THE MICELLE
What determine whether bile flows into the gallbladder or into the duodenum
resistance at the sphincter of Oddi
Vagal stimulation and CCK cause ____ of the gallbladder and ____ of the sphincter of Oddi
contraction
relaxation
presence of fats and partially digested proteins in the duodenum will cause the release of what gastrointestinal regulatory stubstance
CCK
What is the mechanism of concentration of bile in the gallbladder
absorption of water from the gallbladder (NaCl pumped out into intracellular lumen and water follows)
water and electorlyes are then moved into capillaries by hydrostatic pressure
where are bile salts absorbed
Ileum
