Lecture 31: Thermoregulation Flashcards
(43 cards)
What is an endotherm?
Warm blooded e.g. human
What is the core temperature of the body and how is this maintained?
36.5 - 37.5°C
1. Behaviour modification in cortex; awareness, choice, action
2. Homeostatic mechanisms in hypothalamus; autonomic control of thermoregulation
What is the thermoneutral zone?
21 - 30°C
The range of environmental temperatures where:
1. Body’s basal rate of heat production = rate of heat loss to environment
2. Core body temp is maintained with minimal metabolic regulation at rest (via small changes in skin blood flow)
What type of rhythm does core temperature follow?
Circadian rhythm with:
▪ ~1˚C range
▪ High at 4pm and low at 4am
Why does core temperature follow this rhythm?
- Mostly due to melatonin, secreted by pineal gland
- Time-zone shift upsets rhythm - gradual reset over time
What happens when core body temperature increases too much?
Heat exhaustion, stroke, death
What happens when core body temperature decreases too much?
Hypothermia, confusion, cardiac arrhythmias, death
How is heat balance maintained?
Balancing heat loss and heat gain:
▪ 3 heat transfer: loss or gain
▪ 1 heat loss only: evaporation
▪ 1 heat gain only: metabolism
What are the 3 methods of heat transfer?
1.Conduction: Transmission of heat through physical contact (requires a gradient)
2. Convection: Transmission of heat through movement of fluid or air
3. Radiation:
Transmission of heat through electromagnetic waves
What is the mechanism of heat loss only?
Evaporation: Loss of heat through conversion of water (sweat) to gas
▪ Energy (heat) imparted into moisture, which then evaporates from the skin
What secretes sweat onto skin and how much?
Sweat glands: ~600mL/day at rest in neutral environment
What does heat loss require and what does this determine?
- Temperature and moisture gradient for water to evaporate
- The size of the gradient (humidity) determines the speed of evaporation
What is the mechanism of heat gain only?
Metabolism: Gain of heat through oxidation of nutrients to make ATP, and hydrolysis of ATP
* Heat is produced as a byproduct during both processes.
How much does heat resting (basal) metabolism generate?
At rest, 70% from internal organs e.g. liver, kidney, GI tract, brain
How does exercise contribute to the heat gain mechanism?
Increases ATP production and use -> increasing heat production
How does shivering thermogenesis contribute to the heat gain mechanism?
- Cold-induced involuntary muscle contractions
- Increases ATP production and breakdown
- Increased production of heat as a byproduct
How does non-shivering thermogenesis contribute to the heat gain mechanism?
- Hypothalamus activates sympathetic NS when core body temp drops causing release of noradrenaline and thyroid hormones
- Activation of uncoupling proteins in the mitochondria of
brown adipose tissue - Increased heat production from oxidation of fatty acids and some glucose due to making heat rather than ATP
What is the main mechanism for heat gain in infants under 1 year?
Non-shivering thermogenesis
Does brown fat cell metabolism or shivering generate more heat?
Metabolism in brown fat - has more mitochondria so more ATP and more heat production
What is hypothermia?
- Core body temperature < 35˚C
▪ Heat loss > Heat gain
What are the physiological effects of hypothermia?
Slows physiological functions
▪ Decreased metabolic rate
▪ Reduced ventilation and heart rate
▪ Electrolyte disturbances (low potassium, acidosis)
▪ Slower neural conduction
What homeostatic mechanisms correct heat loss?
- Feedforward (anticipation)
- Negative feedback (correction)
-> stop sweating, vasoconstriction, shivering, increased metabolic rate and heat production
What homeostatic mechanisms correct heat gain?
- Feedforward (anticipation)
- Negative feedback (correction)
-> sweating, vasodilation, decreased metabolic rate and heat production
How does exercise effect the perception of a decrease in core body temperature?
Don’t feel ”as cold” as with the same drop in core body temp when not exercising
