Topic 68 - Thermogenesis at the cellular level Flashcards

1
Q

Words to include

A
  • Increase heat production at a cellular level:
    • Mitochondrial heat production in brown adipose
    • Fish experiment
      • Heating cells differentiated from muscle cells

Cellular level: brown adipose

  • Thyroxine
  • Thermogensis
  • Uncoupling of ATP synthesis in brown adipose tissue
  • UPC thermogenin
    • Uncoupling protein
    • Produced in response to thyroid hormones
  • Epinephrine
    • β-receptor
    • cAMP
    • PK-pathway
    • Generates free fatty acids in cells → opens thermogenin channel
      • Transparent to protons
  • O2 & H2 → H2​O
    • Avoiding respiratory chain

Cellular level: heater cells, futile cycle

  • Thermogenin pathway
    • Only significant in species (or young animals) with large amounts of brown adipose tissue
  • Ca2+ pump of sarcoplasmic reticulum
    • Ø muscle contraction
  • Heater cells
    • Modified muscle cells
  • Modified ryanodine receptor
    • Lekage of Ca2+ from SR
    • Ca2+ pump activated → high heat production
  • Futile cycle
    • Skeletal muscle increases Ca2+ pump activity with other cation pumps
      • Na+ permability ↑
        • Na+/K+ pump ↑

Maligant hyperthermia

  • Swine disease
    • Inherited on a single locus:
      • H antigen
      • Phospho-hexo-isomerase (PHI)
      • Defective ryanodine receptor
    • Result:
      • Stress sensitivity
      • Pathological hyperthermia
  • Muscle is an organ of thermogenesis
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2
Q

Topics to include in the essay

A
  1. Accepted basic mechanisms
    • Brown adipose tissue (mitochondrial heat production)
    • Fish experiment (heating cells differentiated from muscle cells)
  2. Brown adipose
  3. Heater cells, futile cycle
  4. Malignant hyperthermia
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3
Q

What are the mechanisms which increases the heat production at a cellular level?

A
  1. Mitochondrial heat production in brown adipose tissue
  2. Fish experiment
    • ​Heating cells differentiated from muscle cells may have important thermogenic functions all around the body
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4
Q

Brown adipose

A
  • Theorie: effects of thyroxine upon the thermogenesis led to the conception of uncoupling of ATP synthesis in brown adipose tissue
  • UCP thermogenin (uncoupling protein) is produced as a response to thyroid hormones
    • ​Settes in the inner membrane of mitochondria
  • Epinephrine (β-receptor cAMP, PK-pathway) generates free fatty acids in the cells → opens thermogenin channel and becomes transparent to protons
  • O2 and H2H2O
    • Avoiding respiratory chain, and there is no synthesis of ATP, just heat production
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5
Q

Heater cells & futile cycle

A
  • Fish experiment
  • Thermogenin pathway can only significantly assist heat production in species (or young animals) with a large amount of brown adipose tissue
  • The most effective way of cellular thermogenesis:
    • Operating the Ca2+ pump of the sarcoplasmic reticulum without muscle contraction
    • The heater cells are modified muscle cells with very few contractile elements, but their SR is developed and they have a lot of mitochondria
    • A modified ryanodine receptor allows lekage of Ca2+ from SR → activates Ca2+ pumps → high heat production
  • Futile cycle:
    • In mammals, the skeletal muscles increases the Ca2+ pump activity (heat production) due to thyroxine and epinephrine stimulation
    • This is also possible with other cation pumps:
      • ​Na+ permability ↑ → function of Na+/K+ pump ↑
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6
Q

Maligant hyperthermia

A
  • Disese of swine
    • Hleps to clarify the thermogenic role of Ca2+ pumping proteins of the SR membrane
  • Inherited on a single locus:
    • ​H antigen
    • Phospho-hexo-isomerase (PHI)
    • Defective ryanodine receptor
  • Result:
    • Stress sensitivtity
    • Pathological hyperthermia
  • This phenomenon proves the fact that the muscle is an organ of thermogenesis
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