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 → H2O
- 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 ↑
- Na+ permability ↑
- Skeletal muscle increases Ca2+ pump activity with other cation pumps
Maligant hyperthermia
- Swine disease
- Inherited on a single locus:
- H antigen
- Phospho-hexo-isomerase (PHI)
- Defective ryanodine receptor
-
Result:
- Stress sensitivity
- Pathological hyperthermia
- Inherited on a single locus:
- Muscle is an organ of thermogenesis
2
Q
Topics to include in the essay
A
- Accepted basic mechanisms
- Brown adipose tissue (mitochondrial heat production)
- Fish experiment (heating cells differentiated from muscle cells)
- Brown adipose
- Heater cells, futile cycle
- Malignant hyperthermia
3
Q
What are the mechanisms which increases the heat production at a cellular level?
A
- Mitochondrial heat production in brown adipose tissue
-
Fish experiment
- Heating cells differentiated from muscle cells may have important thermogenic functions all around the body
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 H2 → H2O
- Avoiding respiratory chain, and there is no synthesis of ATP, just heat production
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 ↑
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