Question

Hyperthyroidism is a condition that occurs when the thyroid secretes an excess of hormones, leading to an increase in the metabolic rate of all the cells in the body. Hyperthyroidism increases the demand for glucose and for substrates for oxidative phosphorylation. Which metabolic pathways are active in the fasted state in the liver, muscle, and adipose tissue in order to meet this demand? Explain.

Answer 1

LIVER

Liver is the principal and primary organ where gluconeogenesis takes place. In the fasted state, the brain requires glucose and the liver converts the degraded proteins from muscles to glucose by the process of gluconeogenesis. Degradation of proteins will release ammonia, leading to the functioning of urea cycle as well. Also, to provide the substrates for oxidative phosphorylation, beta oxidation of fatty acids would take place in the liver. The fats will be degraded to acetyl CoA molecules in order to enter the krebs cycle. Also, pyruvate will be carboxylated to form oxaloacetic acid. oxaloacetic acid and acetyl CoA could together run the krebs cycle and give rise to all the substrates. The energy generated/ ATP from krebs cycle will be used for gluconeogenesis. NADH and FADH₂ generated will be converted to ATP through electron transport chain.

MUSCLE

In the fasted state, the muscles will degrade the proteins, converting them to alanine to be sent to the muscles for gluconeogenesis by cahill's cycle. Also beta oxidation will take place in the muscles to generate acetyl CoA molecules. the krebs cycle will function using these acetyl CoA molecules and the extend of glycolysis will be reduced. NADH and FADH₂ generated will be converted to ATP through electron transport chain.

ADIPOSE TISSUE

Beta oxidation of fatty acids will take place to generate acetyl CoA and krebs cycle will be functional. The stored fats will be degraded and glycolysis will be restricted. NADH and FADH₂ generated from beta oxidation and krebs cycle will be converted to ATP through electron transport chain in mitochondria.