Thermoregulation, Pyrexia and Hypothermia
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- Poikilotherm - an animal who's temperature fluctuates with the environment.
- Homeotherm - an animal who can maintain a steady body temperature by increasing or decreasing their body temperature.
Match the following correctly to a poikilotherm/homeotherm: a) activity levels are related to body/environmental temperature b) remain active at all environmental temperatures?
- a) poikilotherm
- b) homeotherm
Which has a very narrow/wide range of temperature: a) core body temperature b) shell/oral/skin temperature?
What organs are affected by core body temperature?
Organs in the cranium, thoracic cavity and abdominal cavity
Describe the difference in circadian rhythms of temperature in diurnal vs nocturnal animals
Diurnal animals have a higher temperature during the middle of the day whereas nocturnal animals have a higher temperature in the middle of the night
Give examples of changes in temperature for the following: a) seasonal changes b) environment c) exercise d) digestion?
- a) increased temperature in summer/decreased temperature in winter
- b) a hot environment will cause a slight increase in body temperature
- c) as a result of muscular contraction
- d) 'specific dynamic action' associated with the packaging of nutrient derived energy into stores
How might gender affect temperature?
Body temperature in females is influences by steroids and thus varies with ovarian/menstrual cycles
How can heat be transferred by the following: radiation, conduction, evaporation?
- Radiation - energy given off or absorbed by an object
- Conduction - energy transferred between an object and the material next to the object by direct passage. Conduction is increased by convection.
- Evaporation - loss of water from an organism in the form of water vapour
Define the zone of thermoneutrality
The zone of thermoneutrality is the range of ambient temperature over which little work has to be done to maintain body temperature
What is the upper and lower ends of the zone of thermoneutrality called?
The lower critical temperature and upper critical temperature
Describe the control of thermogenesis
Peripheral and central temperature sensors send information to the pre optic area of the hypothalamus --> POA acts as an integrating centre for the 'set point' --> POA sends information about the 'error' to either the a) heat promoting centre to promote shivering, peripheral vasoconstriction, etc b) heat losing centre - to promote sweating, panting, behavioural changes, etc
A decrease in ambient temperature necessitates a/an ...?
Increase in heat production/promotion
List two behavioural changes to decrease heat loss
- Curled up posture
- Huddled together
List five physiological changes to decrease heat loss
- Cutaneous vasoconstriction
- Countercurrent exchange systems
- Shivering thermogenesis
- Non-shivering thermogenesis
An increase in ambient temperature necessitates ...?
List four behavioural changes to increase heat loss
- Open posture
- Expose areas with low insulation
- Minimal touching
- Cool location
List two physiological changes to increase heat loss
- Altering conductance
- Evaporative heat loss - sweating, panting or spreading saliva on fur
How do animals adjust to chronic cold temperatures?
- Increase thermal gradient
- Increase metabolic rate
- Decrease core temperature
How do animals adjust to chronic hot temperatures?
- Decrease thermal gradient
- Decrease metabolic rate
- Increase core temperature
What is pyrexia?
An alteration from the set point i.e. an increase in core body temperature
Why is pyrexia a normal protective mechanism?
As it promotes interferon activity, increases metabolic rate and accelerates tissue repair and decreases bacterial and viral replication
List the steps involved in pyrexia
- Neutrophils and macrophages secrete pyrogen IL1. IL1 stimulates the anterior hypothalamus to secrete PGE.
- PGE raises the set point for body temperature.
- Shivering and peripheral vasoconstriction increases body temperature. Liver and spleen hoards zinc and iron depriving bacteria of the minerals needed to reproduce.
- When infection is gone pyrogen secretion decreases and the set point is reset.
- Heat loss mechanisms are activated.
What are the three thermoregulatory disorders associated with heat stress?
- Heat cramps
- Heat exhaustion
- Heat stroke
What is the thermoregulatory disorder associated with cold stress?
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