GI Mod 4 Flashcards
what divides R/L lobes of liver
Cantlie’s line
top and bottom borders of liver
IVC
gallbladder
connective tissue of liver
- falciform ligament
2. Glisson’s capsule-surrounds liver, invaginates at hilum of the liver
what is the functional unit of the liver
- hexagonal arrangement of hepatocytes and microvasculature
- at center of the hexagon is the central vein
- at each outer corner of hexagon is a portal triad
- microvasculature consists of sinusoids and bile canaliculi
what does the portal triad of liver consist of
- terminal branch of hepatic artery
- terminal branch of portal vein
- terminal bile duct
bile canaliculi drain into
terminal bile ducts
terminal bile ducts eventually drain into
R/L hepatic ducts
R/L hepatic ducts merge to form
common hepatic duct
common hepatic duct eventually divides into
- cystic duct which connects to gallbladder
2. common bile duct which descends to merge with pancreatic duct and drain into duodenum
t/f hepatocytes have ability to regenerate
true
what are 3 signaling mechanisms for liver regeneration
TGF - transforming growth factor
HGF - hepatocyte growth factor
EGF - epidermal growth factor
there is a critical ratio bw _______ _________ mass and ________ mass
funcational hepatocyte mass and body mass
fluctuations in the ratio of functional hepatocyte mass vs body mass signal what
regeneration or apoptosis
what is the duration of liver regeneration if 50-60% of liver is damaged from 4 days of tylenol overdose
completely regenerates in 30 days
hepatic circulation
- afferent pathways to liver
- sinusoids
- efferent pathway from liver
- lymphatic circulation of lymph - large production of lymph
what are the afferent pathways to the liver
- portal pathway - 75% from hepatic portal vein
2. arterial pathway - 25% from hepatic artery
what are sinusoids in liver
microvasculature within liver
what are the efferent pathway from liver
- central veins drain into hepatic veins
2. hepatic veins eventually drain into IVC
avg weight of the liver
2-3 lbs
portal pathway - hepatic portal vein
- receives blood from GI tract, spleen and pancreas
- contains large amount of nutrients from GI tract
- relatively small amount of oxygen
- divides into R/L branches and then further divides until it finally delivers blood to portal vein
portal pathway - hepatic portal anastomosis
-4 veins
collateral venous circulation with numerous veins of abdominopelvic region
- gastroesophageal vein
- rectal vein
- paraumbilical vein
- portorenal vein
portal pathway - portal HTN
portal circulation congested and reverse portal blood flow towards portal anastomoses
-occurs when cirrhosis develops
liver arterial pathway - hepatic artery
delivers oxygenated blood to liver
accounts for approx 25% of blood flow to liver
originates from celiac trunk
arterial pathway of liver - hepatic artery and portal HTN
blood flow to liver from hepatic artery is not impaired
the relative high amount of O2 delivered to hepatocytes is synergistic with regeneration
sinusoids act as what for hepatocytes
capillary bed
sinusoids receive blood from
2 or 3 portal triad vessels
- terminal branches of hepatic portal veins and hepatic artery
- merges nutrient rich blood and O2 rich blood
sinusoids are lined with what
hepatocytes - expose hepatocytes to hepatic blood flow
sinsuoids drain into
central vein
structure of sinusoid/hepatocyte interface
- Kupffer cells
- fenestrated endothelium
- space of Disse - stellate cells
- pit cells
- microvilli of hepatocytes
what are Kupffer cells
monocyte/macrophage origin
located along surface of endothelium
function: phagocytic removal immune complexes, cell debris, etc; and removal of damaged RBC
serves as early or front line defense against liver injury
what is fenestrated endothelium
- large holes in endothelial lining of sinusoid vessel
- allows nutrients/lipids to travel thru sinusoidal wall and flow to microvilli of hepatocyte
- endothelium also has pinocytosis function to active transport molecules to microvilli of hepatocyte
what are stellate cells
location: Disse Space
function: store vit A, produce/secrete hepatic growth factors for liver regeneration
what happens if stellate cells are stimulated via pathology/disruption of environment homeostasis
transform into fibroblastic function (produce collagen) and myblastic function (contractile)
-role in fibrosis
what are pit cells
aka granular lymphocytes or NK cells (natural killer)
location: surface of endothelium
function: front line immune defense against tumor formation, viruses, etc (attacks tumor/virus)
also plays role in liver regeneration
lymph system of liver - hepatic lymphatics
- what % of total lymph fluid
- drain fluid from where
- function
- liver produces largest amount of lymph fluid in body
- approx 20% of total lymph fluid
- drain fluid from Disse space, glisson’s capsule and other interstitial spaces of liver
- play critical defensive role in protecting against intestinal bacteria/antigens
what are the two regional zones of hepatocytes in the lobule zone circulation
periportal hepatocytes
centrilobular hepatocytes
what is the third regional zone sometimes described in the lobule zone circulation
mid way bw periportal and centrilobule zones
what are periportal hepatocytes
- first to receive blood
- O2 and nutrient rich
- functional: last to experience necrosis; first to regenerate
what are centrilobular hepatocytes
last to receive blood
less O2 and nutrient availability
functional: susceptible to ischemia/necrosis; region of drug metabolism (biotransformation)
liver metabolizes what macromolecules
carbs, fats, proteins
liver stores what
fat soluble and some water soluble vitamins
- vitA
- vitK (critical for clotting cascades)
- vitD (precuresor involved in conversion of inactive D to active D)
- vit B12 (water soluble)
liver as endocrine function
vit D conversion & T4 to T3 conversion
remove some circulating hormones: insulin, glucagon, GI hormones
liver role in drug metabolism/biotransformation
liver serves as intermediate step
drugs ingested in hydrophobic form
liver converts to hydrophilic form to allow excretion
function of liver in carb metabolism
regulate blood glucose
inital mechanism to reduce blood glucose - insulin mediated
synthesis of glycogen (glycogenesis)
liver stores glucose for future energy needs
glycogen is approx 10% of total liver weight
glycogen synthesized from glucose, amino acids, and pyruvate
gluconeogenesis
- production of glucose from non carb sources
- glucose can be produced from fatty acids, amino acids, and lactate (rate limiting step is the amount of available substrate NOT liver enzymes)
- important role to maintain blood glucose during fasting
- stimulated by glucagon and sympathetics (inhibited by insulin)
what removes FFA and lipoproteins from plasma
liver
what is the fasting state of fat metabolism with liver
released into plasma from adipose tissue FFA are removed from plasma by liver FFA in liver have two fates: 1. used in energy production - B oxidation, ketone body formation 2. used to synthesize VLDL
feeding state of fat metabolism with liver
chylomicron remnants are removed from plasma by liver
- TGs from chylomicron remnants can be used from energy production (FFA formation) or to synthesize VLDL
- cholesterol from chylomicron remnants used to synthesize VLDL
lipoprotein synthesis in liver
the liver plays impt role in synthesizing lipoproteins needed for lipid transport in plasma
classes of lipoproteins
- chylomicrons
- VLDL
- LDL
- HDL
what are chylomicrons
largest diameter, most lipid, least concentration of proteins
lipids - 99% lipids, TG rich
-synthesized in intestines, transport TGs (digested fats)
what is VLDL
very low density lipoprotein
smaller diameter than chylomicron
lipids-90%, TG rich not as much as chylomicron
-synthesized in liver (small amnt in intestines)
-transport TGs to periphery