Human ecology
Human ecology is about the distribution of the human species, and how they have
adapted to survive in extreme conditions.
For an introduction, read the first part of chapter 4 on pages 64 and 65 of your
textbook.
Revision – homeostasis is
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Temperature regulation
The ability to control body temperature is extremely important if animals are to
survive.
Poikilotherms (e.g. reptiles) are animals which rely on heat from the external
environment to maintain their body temperatures. They rely on specific behaviours to
regulate their heat gain and heat loss.
Homeotherms or endotherms (e.g. mammals) are animals which are able to generate
enough internal metabolic heat to maintain their body temperatures.
Normal body temperature for humans is ……………………………………
Humans hold their inner body temperature (core temperature) just below 37C.
When the external temperature is low, however, only the temperature of the trunk is
held constant. The body temperature falls progressively from the trunk towards the
end of the limbs.
The core temperature fluctuates in a diurnal (daily) rhythm. See the paragraph at
the bottom of page 65 to answer the following.
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Temperatures reach a peak from ……………………………………………………………………………………
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Temperatures are lowest …………………………………………………………………………………………………
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In women the temperature is lowest ……………………………………………………………………………..
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In women the temperature is highest …………………………………………………………………………..
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The core temperature can be raised by …………………………………………………………………………
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The core temperature can be raised in response to ……………………………………………………
It is still necessary to fine tune the endotherm's body temperature in response to
fluctuations caused by either external influences (very hot or very cold) or internal
events (raised or lowered metabolic rate, and its accompanying heat generation).
See figure 4.4 page 66 for a diagram of heat loss and gain by the body.
Thermoregulation is achieved by a combination of functional and behavioural
responses. See separate sheet of notes on this.
The control of temperature is regulated by the hypothalamus, a region of the
forebrain. It contains a heat loss centre and a heat gain centre. Temperature
sensitive neurones (thermoreceptors) are situated in the hypothalamus. They detect
changes in the temperature of the blood flowing through the brain. The
thermoregulation centre of the hypothalamus also receives information via sensory
nerves from thermoreceptors located in the skin and internal organs.
The hypothalamus connects with the rest of the body by the nervous system. When
the body temperature is lower then normal, the heat gain centre inhibits activity of
the heat loss centre, and impulses are sent to the skin, hair erector muscles, sweat
glands and elsewhere that decrease heat loss and increase heat production. When
the body temperature is higher than normal the heat loss centre inhibits the heat
gain centre activity. Impulses are sent to the skin, hair erector muscles, sweat
glands and elsewhere that increases heat loss and decrease heat production.
Draw a flow diagram to illustrate this process.
The role of the skin in thermoregulation
See sheet on skin structure.
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At capillary networks, the arteriole supplying them is widened (vasodilation) when
the body needs to lose heat, but constricted (vasoconstriction) when it needs to
retain heat.
include diagram of vasoconstriction/vasodilation
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The hair erector muscles contract when heat must be retained but relax when
more heat needs to be lost.
The sweat glands produce sweat only when the body needs to lose more heat.
Evaporation of sweat has a cooling effect.
See fig 15.9 Jones and Jones page 334. Also read pages 65-68 in your textbook.
Effects of high temperature and effects of low temperature
You need to do some research!
Find out about the following and make brief notes on each.
Effects of high temperature (heat stress) on the body including:
1. salt loss
2. heat cramp
3. moderate and severe dehydration
Effects of low temperature (cold stress) on the body including:
1. cold injury
2. trench foot
3. frostbite
4. wind chill and exposure
5. hypothermia
Your textbook will have information on these, also look in the library or go to
www.spolem.co.uk then A level biology then Human ecology.
Effects of high altitude
The conditions in high mountains are difficult. They include low levels of oxygen
(hypoxia), low atmospheric pressure, low temperature, low humidity, high winds and
increased solar radiation.
As before, use your book and other sources to make brief notes on:
Physiological effects of high altitude:
1. hypoxia
2. hyperventilation
3. changes in lung volume
4. changes in pulmonary diffusing capacity
5. changes in number of red blood cells
6. changes in haemoglobin concentration
7. changes in cardiac output
High altitude stress:
1. mountain sickness
2. increased secretion of ADH
3. redistribution of body fluids
4. impairment of mental reactions
Adaptation vs acclimatisation
There is a difference between the “adaptations” of a native to extremes of
temperature and altitude, and the “acclimatisation” of a visitor.
Hot climates – adaptations
 tall thin physique – large surface area to volume ratio
 high rate of sweat loss
 traditional clothing
Hot climates – acclimatisation
 sweat loss will increase and sweat will have lower salt concentration
 adopting suitable clothing
Cold climates – adaptations
 Inuits have higher blood flow through extremities
 short fat physique with low surface area to volume ration
 traditional clothing
Cold climates – acclimatisation
 increased appetite – increase food intake
 adopt suitable clothing
 take part in physical activity
High altitude – adaptations (note – see page 84 second paragraph)
 increased lung volume
 higher pulmonary diffusing capacity
 “barrel-shaped” chest in Quechua Indians in the Andes
 Sherpas have an oxygen dissociation curve which is shifted to the left
High altitude – acclimatisation
 hyperventilation
 increased red blood cell count