Hibernation Flashcards
What is metabolism?
- sum of all the chemical reactions occurring in an organism.
- the rate of a chemical reaction increases with temperature, therefore the metabolic activity of an animal is closely linked to its body temperature
How to physiologically classify animals using thermal biology?
Poikilothermy: body temperature fluctuates with environment
Ectothermy: Body heat derived from environment
Heterothermy: in some animals temperature may vary widely upon time (temporal heterothermy)or in different regions of their body (regional heterothermy)
Endothermy: Body heat derived from metabolism
Homeothermy: Body temperature remains constant
What is basal metabolic rate (BMR)?
- stable rate of energy metabolism measured in mammals and birds under conditions of minimum environmental and physiological stress and after fasting has temporarily halted digestive and absorptive processes.
- in humans, an estimate of maintenance metabolism
- measured as steady state whole body oxygen uptake or heat production
What is standard metabolic rate (SMR)?
Animal’s resting and fasting metabolism at given body temperature.
Maintenance metabolism in ectotherms during periods of minimal activity under defined conditions.
What is hypometabolism?
a reduction of metabolic rate (below SMR) to a level that maintains balance between energy demand and energy supply.
Extends the time that cellular energy reserves can sustain life… until more favourable environmental conditions arise.
There are two types: Hibernation (winter) and Aestivation (summer).
• periods of inactivity or dormancy in ectotherms & endotherms
• low nutrient intake - fasting (extension of survival time during food shortage in extreme weather conditions (cold or drought))
• depressed metabolic rate (hypometabolic state, energy conservation)
• either short- or long-term (daily ‘torpor’ to months of overwintering)
Pros of hibernating?
Consistently emerge from winter with little atrophy, frequently accompanied by slight shift to more oxidative fibre types.
Down-regulation of glycolytic pathways and increase reliance on lipid metabolism instead.
Protein synthesis and degradation are reduced.
Minimal loss of skeletal muscle protein and oxidative capacity.
This enables hibernating animals to resume active behaviour such as predatory avoidance, foraging and mating immediately following terminal arousal in the spring.
Oxygen stores in diving frogs?
• Mainly lung stores of oxygen (blood O2 capacity of 5 – 10 % and low blood volume, but high relative lung volume)
• Buoyancy control
In the frog O2 assumption through the skin is practically constant for the whole year, and the higher O2 demand during summer is supported by higher intake from the lungs
• low lung dead space (lack of re-breathing of lung gas means alveolar PO2 is higher in amphibians)
• large pre-dive inhalation to load lung stores
• maximum dive depth of a few metres (minimal ‘lung collapse’)
• The lung O2 store is relatively large
- lung ventilation increases lung PO2
- PO2 changes are mirrored by PCO2 changes - PO2 drops during dive while PCO2 is stable
Breathing movements concurrent with increased pulmocutaneous blood flow and slightly lower systemic blood flow.
During ‘breath hold’ lung flow ceases but flow to body tissues remains intact.
Structure of typical anuran amphibian heart?
heart consists of two atria and one ventricle along with the distinct arches that lead to the systemic and pulmocutaneous circulation
Single Ventricle: blood exiting is ‘mixed’, oxygenated/deoxygenated
Breathing…a so-called left-to-right (L-R) shunt predominates
Diving…a right-to-left (R-L) shunt predominates
Effect of ice cover in environment of diving frogs?
Ambient temperature gradient
Zero photosynthesis
Ambient po2 gradient
Are hibernating frogs responsive to the pond temperature and oxygen level?
In the lab, frogs in low oxygen actively seek out lower temperature
How does the frog remain submerged for months?
(i) Low temperature & avoid hypoxia
(ii) Hypometabolism, especially if hypoxia is unavoidable, to prolong on-board
fuel supply
(iii) ‘Fuel up’ before hibernation. Build substrates stores (glycogen).
(iv) Avoid ‘self-polluting’ end-products (lactate, H+)
(v) Blood flow btw skin & core organs (heart, brain, liver, kidney)
Frogs seem to prefer to remain aerobic while submerged
Frogs store of lung-oxygen depletes quickly
To remain aerobic, there is greater dependence on cutaneous gas exchange
How is metabolic rate effected in an endothermic homeotherm?
Within the thermal neutral zone, body temperature is regulated entirely by changing the heat conductance of the body surface, which requires essentially no change in metabolic effort.
Above and below this zone, the metabolic rate must rise, either to increase thermogenesis or to increase active dissipation of heat, if body temperature is to remain constant.
Temperature sensitive neurons input into thermostatic centres in brain. If body temp lowers a lot, conductance is minimised (vasoconstriction and piloerection). If temp increases a lot, conductance maxed (vasodilation and pilorelaxation).
02 consumption in bats?
02 consumption in bats increased as temp decreases. But when they enter torpor, 02 consumption drops to very low.
Metabolic rate in golden squirrel
Both experimentally induced hypothermia and natural hibernation reduce metabolic rate.
Metabolism increases briefly during an episode of arousal from hibernation.
Metabolism in hibernating marmot?
They arouse in synchrony and when they do they lose less body mass.
