102 Intermediary Metabolism

Catabolic pathways

Glycolysis

Glycogenolysis

TCA Cycle (Kreb’s Cycle)

Respiratory Chain

Oxidative Phosphorylation

β-oxidation

Lipolysis

Anabolic pathways

Gluconeogenesis

Glycogenesis

Fatty acid biosynthesis

Lipogenesis

Intermediary Metabolic roles of the liver

synthesize and store glycogen

synthesize and redistribute lipids

synthesize glucose from glycogen

synthesize glucose from non-carbohydrate precursors

High Blood Glucose Liver

anabolic state

build glycogen

build lipids

presence of insulin activates most pathways except pentose phosphate pathway and TCA cycle

what is active in High Blood Glucose Liver

Glycogenesis

Glycolysis

PDH

Fatty acid biosynthesis

Lipogenesis

Low Blood Glucose Liver

catabolic state

Degrade Glycogen (synthesize glucose)

Degrade fatty acids (fuel)

what is active in Low Blood Glucose Liver

Glucagon activates

Glycogenolysis

Gluconeogenesis

Liver Reciprocal Regulation

When catabolic pathways are on, correspsonding anabolic pathways need to be off

Insulin inactivates these pathways

Glycogenolysis

Gluconeogenesis

B-oxidation

Glucagon inactivates these pathways

Glycogenesis

Glycolysis

Fatty acid biosynthesis

Glucagon activates these pathways

Glycogenolysis

Gluconeogenesis

Intermediary Metabolic roles of the Skeletal Muscles

Synthesize and store glycogen (for itself)

Use a lot of post-prandial glucose (up to 80%)

Skeletal Muscle: High Blood Glucose

Resting skeletal muscles are in an anabolic state (builds glycogen)

Active skeletal muscles are in catabolic state (burn glucose for fuel)

What is not very active in skeletal muscle under high blood glucose

Fatty acid biosynthesis

lipogenesis

But too much intramuscular fat production contributes to type 2 diabetes

How is glycolysis activated in high blood glucose in skeletal muscle

Glycogenesis and pyruvate dehydrogenase is activated in presence of insulin

Glycolysis is NOT activated by insulin in skeletal muscle

Instead, glycolysis is activated by low energy

Insulin activates the following pathways under high blood glucose skeletal muscle

Glycogenesis (Glycogen Synthase)

PDH Complex (Pyruvate Dehydrogenase)

Skeletal Muscle: Low Energy State

Energy generating pathways are active (glycogen is primary source of fuel)

β-oxidation is more active when glucose levels drop

As glycogen levels are depleted, skeletal muscles will take up glucose from blood stream

Skeletal Muscle: High Energy State

Energy generating pathways that utilize glucose are inactive

β-oxidation is active for base line energy production

Intermediary Metabolic roles of the Adipose Tissue

Synthesize and Store triacylglycerol

Most pathways geared towards synthesizing to degrading triacylglycerol

Adipose Tissue: High Blood Glucose

anabolic state

Build triacylglycerol

Store triacylglycerol

Insulin activates the following pathways under high blood glucose adipose tissue

Glycolysis

PDH

Fatty acid biosynthesis

Lipogenesis

Adipose Tissue: Low Blood Glucose

catabolic state

Degrade triacylglycerol

Export fatty acids

Degrade fatty acids (fuel)

Intermediary Metabolic roles of the Cardiac Muscles

Burn fuel as needed

Cardiac Muscle: High Blood Glucose

Under high blood glucose, cardiac muscles burn glucose for fuel

Under homeostatic or low blood glucose, cardiac muscles burn fatty acids for fuel

Glycolysis

PDH

TCA

Insulin activates the following pathways under high blood glucose cardiac muscle

Glycolysis

PDH complex

Brain

Under high, homeostatic, or low blood glucose, the brain wants glucose

Will also utilize ketone bodies under low blood glucose