Liver Physiology Flashcards
Is the rate of absorption of nutrients from the GIT constant?
no
Digestion rate depends on what?
composition of food
What is the pathway through which all fuels are converted from acetyl-CoA into carbon dioxide, water, and ATP?
Krebs cycle
What are the metabolic fuels?
- glucose
- amino acids
- fatty acids
- ketone bodies
What is the basic metabolic fuel that is essential for CNS?
glucose
Glucose is stored as glycogen where?
- liver
- skeletal muscle
What initiates oxidation of glucose?
glycolysis
Each glucose yields what?
two pyruvates
The two pyruvates yielded by glycolysis can enter what pathways?
Acetyl-CoA OR oxaloacetate
Gluconeogensis occurs where?
in the liver and very small amount in kidneys
What are the building blocks for proteins and substrates for gluconeogenesis?
amino acids
Fatty acids are stored where as triglycerides?
adipose tissue
Fatty acids can’t be converted to glucose, but can be converted to what?
ketone bodies
What is derived from fat but is water soluble, can cross the BBB, and can provide energy to CNS during dietary energy deprivation?
ketone bodies
What starts as a meal is ingested to ensure tissues are primed for arrival of glucose?
insulin secretion
All glucose travels to the liver first via what?
portal vein
Is glucose to fatty acid conversion reversible?
no
Acetyl-CoA and oxaloacetate make up what?
citrate
After fatty acids are formed from glucose, transfer to storage sites (adipose or muscle) is needed. Describe transport of fatty acids from liver.
- liver forms triglyceride-rich serum lipoproteins (specifically VLDLs)
- triglycerides transferred from chylomicrons and VLDLs to adipose tissue via lipoprotein lipase
What are VLDLs?
very low density lipoproteins
What are glucogenic amino acids?
amino acids that can be converted into glucose via gluconeogenesis
What are ketogenic amino acids?
amino acids that can be converted into ketone bodies
What amino acids are analogues in the portal vein?
- glutamate and alpha ketoglutarate
- alanine and pyruvate
Glutamate and aspartate are removed by what from the portal vein?
enterocytes
What proteins are synthesized in the liver?
most serum proteins such as albumin and blood clotting factors
Most amino acids arriving in portal blood are deaminated in the liver and enter?
carbohydrate metabolism
True carnivores have very little carbohydrate, so they must synthesize glucose from?
amino acids
Ruminants use what to synthesize glucose?
propionate
Fermentation in ruminants produces what?
volatile fatty acids (VFAs)
True or false: most essential amino acids are not removed by the liver and go directly to periphery.
true
Non essential amino acids can be synthesized where?
protein producing tissues
Supply of amino acids to periphery and removal of amino acids by the liver can constantly be adjusted based on what?
dietary supply and needs
Insulin promotes the uptake of glucose and amino acids by?
skeletal muscle
When protein synthesis is greater than protein breakdown it leads to what?
increase in muscle size
Overall, hepatic metabolism results in removal of what?
glucose and amino acids
What are synthesized in the absorptive phase of amino acids?
protein and fat
During the post-absorptive phase, nutrients will be mobilized from storage pools to maintain what?
energy availability
Once blood glucose falls below normal, glucagon is released which stimulates what two enzymes in the liver?
- glycogen phosphatase
- fructose 1,6 biphosphatase
As blood glucose and insulin decrease, skeletal muscle starts to what?
mobilize amino acids
What are the primary source of energy in muscle cells?
Branched chain amino acids (BCAAs)
The liver has limited capacity for uptake of BCAAs, so conversion to what is necessary?
alanine
In the liver, alanine is broken down into what?
urea and glucose
A lack of insulin stimulates what in adipose tissue?
hormone sensitive lipase
What can be used for energy by many tissues or taken up by the liver for ketone body production or VLDL synthesis?
non-esterified fatty acids (NEFAs)
What enzyme releases fatty acids from adipose into blood where they then bind to albumin for transport and form non-esterified fatty acids (NEFAs)?
hormone sensitive lipase
During fasting and starvation, utilization of adipose tissue stores spares what?
proteins
During periods of prolonged undernutrition, fat is mobilized in the form of NEFAs for what?
- oxidized for energy
- esterification to form triglycerides
- production of ketone bodies
In ruminants, _____ is precursor for glucose, enters Krebs cycle as ____, and forms _____.
- propionate
- succinate
- oxaloacetate
Acetate and butyrate enter the Krebs cycle at which point?
Acetyl-CoA
In ruminants, most fatty acids are made from what?
acetate
In uncontrolled diabetes mellitus, a lack of insulin production leads to what?
glucagon production even though blood glucose is high
In diabetes mellitus, what inhibits fatty acid synthesis, causing malonyl CoA to be low and CPT1 activity to be high which leads to ketone body production?
glucagon
In diabetes mellitus, lack of insulin suppresses HSL, so blood NEFA is high or low?
high
