GB 16. Liver Biosynthetic Functions Flashcards
What are the 3 main functions of the liver? (just list them)
[1] Metabolism
[2] Synthesis
[3] Excretion + Detoxification
What is involved with the Metabolism function of the liver?
- glycogen synthesis (glycogenesis)
- glycogen breakdown (glycogenolysis)
- gluconeogenesis
- fatty acid metabolism
metabolizes:
[1] Carbohydrates
[2] Fats
[3] Protein
What is involved with the Synthesis function of the liver?
- plasma proteins (including albumin)
- coagulation factors
- haem
- lipoproteins
- bile acids (primary)
What is involved with the Excretion + Detoxification function of the liver?
- bilirubin
- amino acids + NH3 (urea cycle)
- cholesterol and steroid hormones
- drugs
- toxins
What are the 3 “zones” in the liver?
Zone 1: Periportal Zone
- O2 rich
- has the portal tract, hepatic artery, bile duct + portal vein
Zone 2:
- space between Periportal and Perivenous zones
Zone 3: Perivenous Zone
- has the central hepatic vein
In which direction does the blood flow in the zones of the liver?
- it flows from the Periportal Zone to the Perivenous Zone
- from Zone 1 to Zone 3
What is ammonia detoxification? Why is it important?
- ammonia (NH3) is toxic to the CNS
- it is converted to urea in the liver (through the urea cycle)
- NH3 is also used to convert glutamate to glutamine in the liver
What is the overall mechanism of carbohydrate metabolism in the liver? What are the important pathways?
GOAL: maintain blood glucose
[1] Glycogenesis
- excess glucose after meal is taken up by liver and stored as glycogen
[2] Glycogenolysis
- glycogen broken down + glucose then exported into blood to go to tissues
- when low blood glucose levels arise
[3] Gluconeogenesis
- glucose synthesized from amino acids + non-hexose carbohydrates when glycogen reserves depleted
Explain the process of fat metabolism in the liver.
- hydrolysis of triglycerides releases 2 products:
(A) Glycerol - metabolized by glycolytic pathway
(B) Fatty Acids
- beta oxidized to acetoacetate (AcAc)
- AcAc then used as an energy source in remote tissues
Explain how proteins are metabolized in the liver (hint: there are 2 processes involved)
[1] deamination + transamination of amino acids
- conversion of non-nitrogenous part to glucose/lipid
(glucogenic or ketogenic amino acids)
[2] removal of ammonia from body by synthesis of urea
- ammonia is produced from leftover amino acids
- it is toxic to the CNS
What are some of the proteins (and protein components) that are synthesized in the liver?
[1] non-essential amino acids (e.g. glutamine)
[2] plasma proteins (e.g. albumin - contributes to oncotic pressure)
[3] clotting factors
[4] acute phase proteins
What are some of the fats that are synthesized in the liver?
[1] Triglycerides
- liver converts excess carbs + proteins into fatty acids and triglycerides (exported + stored in adipose tissue)
[2] Cholesterol + Phospholipids
- some packaged with lipoproteins and made available to rest of body
- remainder excreted in bile as cholesterol or as bile acids
[3] Lipoproteins
What are some other molecules/things that are synthesized in the liver?
[1] Ketones - beta-hydroxybutarate and acetoacetate - ^^ 2 types of ketones [2] Haem [3] Bile Acids [4] Urea [5] Nucleotide Precursors - e.g. purines + pyrimidines
List all the molecules/things that can be synthesized in the liver.
[1] Proteins/Protein Components [2] Carbohydrates [3] Fats [4] Ketones [5] Haem [6] Bile Acids [7] Urea [8] Nucleotide Precursors
What are the 2 categories of proteins that are synthesized by the liver?
[1] Liver-Tissue Proteins
- structural proteins
- enzymes
[2] Exported Proteins
- plasma proteins
- albumin
- alpha and beta globulins
- fibrinogen
Where is the plasma protein, Albumin, synthesized?
ONLY in hepatic cells
- approx. 15 g/d in healthy adult
- althought rate varies with physiologic stress
What is the function of albumin?
- transports many substances (e.g. bilirubin, fatty acids, metals, ions, hormoes, exogenous drugs…)
- provides 75-80% of the ONCOTIC PRESSURE
What is Oncotic Pressure?
the pressure driving fluid into the vessel due to the presence of plasma proteins INSIDE the vessel
- it forces the vessels closed
What is the opposite of oncotic pressure?
Hydrostatic Pressure/Blood Pressure
- it keeps the vessel open
- blood pressure pushing the walls outwards
In oedema, where is there a higher concentration of albumin? Inside or outside the blood vessels?
Outside the blood vessels
- drawing water into the tissues
What are alpha- and beta- globulins?
they are plasma proteins!
What is the structure of alpha- and beta- globulins?
glycoproteins
How are alpha- and beta- globulins cleared from the cell?
cleared by ASIALOGLYCOPROTEIN receptors on the surface of hepatocytes
What are some of the functions of alpha- and beta- globulins?
- transport proteins
- protease inhibitors
- clotting factors
