Lecture 9 - Overview of the Liver Flashcards
7 functions of liver? What 3 groups can they be made into?
METABOLIC:
1. Regulation of carbohydrate and protein metabolism
2. Beta-oxidation of fatty acids
SECRETORY/EXCRETORY:
3. Regulation of cholesterol excretion through bile
4. Bile production and secretion
VASCULAR:
5. Degradation of hormones and detoxification and excretion of drugs and toxins into bile
6. Vitamin storage
7. Synthesis of blood plasma proteins: albumin, globulins, clotting factors
Where does the hepatic vein drain? What is the pressure in it?
IVC
Around < 1 mmHg
What % of lymph does the liver produce? What % of lymph in thoracic duct is produced by liver?
50%
25-50%
What are the Kupffer cells of the liver? Role?
Big fixed phagocytotic cells (aka macrophages) that line the liver sinusoids
Roles:
- Cleanse the blood rapidly
- Take care of ~ 99 % of the bacteria entering the portal blood from the intestines
- Metabolize old red blood cells (NOT BILIRUBIN) once they have been eliminated in the spleen and some antigens
Describe the 4 roles of the liver with regards to carb metabolism. Overall?
1) conversion of galactose and fructose to glucose
2) gluconeogenesis
3) glycogen storage (used during fasting (~18 hr supply)
4) formation of chemical compounds from intermediates of carbohydrate metabolism
OVERALL: maintain blood glucose levels
Describe the 4 roles of the liver with regards to lipid metabolism. Overall?
1) has a high rate of beta-oxidation of FAs
2) forms most lipoproteins
3) synthesizes lots of cholesterol and phospholipids
4) converts unused carbohydrates and proteins to FAT!!!!
Overall: provides another energy source, provides the building blocks for membranes, intracellular structures, as well as steroid hormones, and can bulk up your fat stores
Describe the 4 roles of the liver with regards to protein metabolism.
1) deamination of amino acids
2) forms urea to remove ammonia from body fluid (excreted in urine)
3) forms 90% of the plasma proteins
4) interconversion among different AAs via transamination
What vitamins does the liver store?
A, D, B12
Liver role with coagulation?
Formation of blood coagulation products: fibrinogen, prothrombin, factor VII
Liver role with regards to iron?
Stores it in ferritin pools (Fe2+) as free iron is toxic
What are the bile acids formed from in the liver?
Cholesterol backbone
What are the 2 primary bile acids formed by the liver? Are these hydrophilic or hydrophobic?
- Cholic acid
- Chenodeoxycholic acid
Both hydrophobic
What are primary conjugated bile acids? Purpose?
Primary bile acids conjugated with taurine or glycine => makes them amphipathic (polar), which increases their water solubility to be able act on lipids by getting through the water layer
What are bile salts?
Bile acids with NaCl and HCO3- (which is almost always the case)
What are secondary bile salts? Where are these produced? Are these hydrophilic or hydrophobic or amphipathic? What does this mean?
Bile salts produced in the intestines when bacteria can dehydroxylate the primary bile salts and DECONJUGATE THEM:
- Deoxycholic bile salt
- Lithocholic bile salt
Mainly in the colon
Hydrophobic => harder to reabsorb them into enterocytes
What is bilirubin? What does build up cause? Describe the excretion pathway and whether the bilirubin is hydrophilic or hydrophobic.
Major end-product of hemoglobin degradation => carried to liver by albumin (HYDROPHOBIC) => uptook at sinusoidal membrane by organic anion transporters => transported/stored in liver => conjugated with 1 or 2 glucuronide (80%) or sulfate (10%) (HYDROPHILIC) => excreted into bile canaliculi by MRP2/ABCC2 and into the intestines as a “bile pigment” => bacterial deconjugation and degradation forms: urobilinogen reabsorbed into portal circulation (90%) (HYDROPHOBIC) WITH CONJUGATED BILE ACIDS (HYDROPHILIC) => portion of urobilinogen is converted to stercobilin (HYDROPHOBIC) and excreted in feces (10%) => a portion of urobilinogen (2%) is filtered at the kidneys and excreted into the urine, making the urine yellow, the rest (CONJUGATED AND NOT) is reabsorbed by the kidney
Build-up in the blood (eg, from obstructive liver disease) associated with jaundice
What can bilirubin levels be used for?
As diagnostic criterion for hemolytic blood diseases and liver disease
Normal pressures of liver capillaries and veins?
VERY low
What do we call the capillary net of the liver?
Sinusoids of the liver
What are liver cells called?
Hepatocytes
What is hepatic cirrhosis? What is it due to?
Chronic degenerative disease in which normal liver parenchyma is damaged and then replaced by scar tissue due to repeated toxic insults to liver (e.g. alcoholism, viral hepatitis) => obstruction of blood flow + decrease in functional hepatocytes
Where are lymphatics found in the liver?
EVERYWHERE
Role of production of lymph in liver?
Removes fluid and proteins from the Space of Disse to drain it into the venous blood
What is the Space of Disse in the liver?
Interstitial space between liver sinusoids and hepatocytes
Other name for Kupffer cells?
Littoral cells
Describe the formation of ascites.
Portal hypertension => pooling of blood and lymph in liver sinusoids => increased hydrostatic pressure => increased transudation of fluid (since liver capillaries already have a high permeability) AND proteins from the plasma and space of Disse into peritoneal cavity = ascites
What would happen if there was increase hydrostatic pressure in other peripheral organs of the body? Difference between this and process of ascites?
Edema in interstitial space
Ascites do not accumulate in interstitial space, they go in the peritoneal cavity and also they include proteins which edemas do not
Does the liver normally leak?
Yes, a little which is absorbed by the greater omentum
What is hepatomegaly?
Increase in liver size usually due to fluid retention (400 mL to 1 L)
Can you have ascites without hepatomegaly?
YUP
Can you have hepatomegaly without ascites?
NOPE
What is jaundice?
Yellowing of skin, nail beds, whites of eyes etc due to an increased bilirubin in the blood
4 types of jaundices? Provide multiple names when appropriate.
- Obstructive jaundice = posthepatic jaundice
- Hepatic jaundice
- Hemolytic jaundice = prehepatic jaundice
- Neonatal jaundice
What is obstructive jaundice? Examples?
Results from obstruction of the bile ducts (e.g. cirrhosis, gallstones, biliary atresia, cancer). In each case, the bilirubin that is usually incorporated into bile enters the blood, instead.
What is hepatic jaundice? Examples?
Results from acute or chronic hepatitis, drug hepatotoxicity or cirrhosis causing a reduced ability of the hepatocytes to metabolize bilirubin
What is hemolytic jaundice? Examples?
Results from anything that increases hemolysis of RBCs (eg, malaria, sickle cell anemia, spherocytosis), and increases bilirubin production faster than bile can excrete it (normally RBCs last 3 months)
What is neonatal jaundice? Examples?
Usually is not pathologic, but results from metabolic changes, as the liver starts to function appropriately after birth:
- Immature hepatic 2 UDP-glucuronosyl transferase enzyme causing them to not appropriately conjugate bilirubin
- Impaired ligandins to uptake the bilirubin in the hepatocytes
- High rate of RBC turnover aka hemolysis right after birth
Congenital pathologic conditions such as G6PD deficiency and spherocytosis can also cause neonatal jaundice.
Is acute jaundice damaging?
NOPE
Is chronic jaundice damaging?
YUP => causes irreversible neurological issues because the bilirubin settles in the gray matter of the brain = kernicterus
What differentiates acute from chronic hepatitis?
6 months + duration
Treatment of neonatal bilirubin?
Put babies under UV light (phototherapy) which conjugates the bilirubin in the blood vessels so that the kidneys can excrete it
What is an example of an obstructive liver disease?
Cirrhosis
What enzyme in the liver converts excess blood glucose to glycogen?
Glucokinase
What hormones stimulate the release of glucose from liver glycogen stores? How?
Epinephrine and glucagon stimulate phosphorylase to release glucose
Describe gluconeogenesis by the liver.
AAs and glycerol from tryacylglycerol are converted to glucose
Through what mechanism does the liver uptake glucose? What other organs use this?
GLUT2 transporters which are insulin-independent and allow for high capacity transport
GLUT2 also found in brain, kidneys, pancreas, and basolateral side of enterocytes
Can the liver use galactose and fructose to enter the glycolytic and glycogenesis pathways?
YES, by using ATP
What other chemical compounds can the liver make through carbohydrate metabolism? Purpose?
- Pyruvic acid
- Lactic acid
- Succinic acid
- Acetyl CoA
Purpose: feed into energy producing metabolic pathways
What are the 3 monosaccharides absorbed by the GIT?
- Glucose
- Galactose
- Fructose
What would happen to blood glucose without the liver after a meal?
Would be 3 x as high
Describe the beta oxidation of FAs by the liver.
Tryacylglycerols are hydrolyzed to FAs and glycerol and beta oxidation is conducted in the mitochondria to produce acetyl CoA, which then enters the TCA
Describe the 3 types of lipoproteins formed by the liver and their contents.
- VLDLs: high tryacylglycerol content, some cholesterol and phospholipids, very little proteins
- LDLs: high cholesterol and phospholipid content with low tryacylglycerol, some proteins
- HDLs: 50% protein, less cholesterol and phospholipids (formed in the liver, and circulates around the vasculature collecting cholesterol)
Which lipoproteins contribute to atherosclerosis and plaque formation?
LDLs
How are fats (triacylglycerides) transported from the small intestine to target cells and then the liver? 8 steps
- Bile salts emulsify TAGs so that they can access the more aqueous environment
- Pancreas secretes lipases to degrade TAGs into FAs and glycerol
- Mucosa takes up FAs + glycerol, re-esterifies them into TAGs, and packages them into chylomicrons
- Chylomicrons travel through the lymph and bind to target tissues
- Liver collects excess chylomycrons and chylomycron remnants and repackages them with TAGs and cholesterol into VLDLs (very low density lipoproteins)
- TAGs in VLDLs are broken down and taken up by tissues => half of VLDLs remnants are taken up by tissues and half are sent to liver to be converted to LDLs
- Extrahepatic tissues send cholesterol back to the liver via HDLs
- Liver collects HDLs
What is the main form of circulating cholesterol targeted for extrahepatic tissues?
LDL
Why is HDL is considered good cholesterol in comparison to LDL?
Because HDL means there is more cholesterol transported back to the liver rather than to the periphery: you are getting rid of the cholesterol within your cells (presupposing you had too much in them though)