A day at the sauna. How does the body react to change?. Saving energy?. Sayid has decided to save energy by staying in bed all day. How much of his energy do you think this will save?. Surprisingly, the answer is only about 30%.
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How does the body react to change?
Sayid has decided to save energy by staying in bed all day.
How much of his energy do you think this will save?
Surprisingly, the answer is only about 30%.
The other 70% keeps his body temperature at 37°C, and the solutions around his cells at just the right concentration.
The body uses so much energy, even during sleep, because it must maintain a constant internal environment.
This process of keeping things the same is called homeostasis.
A series of automatic control systems ensures that the body maintains a constant temperature, and steady levels of water, ions and blood sugar.
Homeostasis allows the body’s cells to work at their optimum.
Environmental temperature is constantly changing. One minute it can be very hot, the next very cold.
Despite this, the body must be kept at a constant temperature of 37°C. Why?
This is the optimum temperature for the body’s enzymes.
Even slight changes in body temperature can have a life-threatening effect on health. If body temperature falls too low, reactions become too slow for cells to survive: too high, and the body’s enzymes are at risk of denaturing.
The vital organs located deep within the body, such as the heart, liver and kidneys, are maintained at 37°C. This is the core body temperature.
Skin temperature at the body's extremities, such as the fingers and toes, is usually lower than the core body temperature.
On a warm day, skin temperature may be just 1°C lower than the core body temperature, but on a very cold day it could be up to 9°C lower.
Core temperature is maintained by balancing heat gain and heat loss.
How can heat be gained?
How can heat be lost?
Body temperature is monitored and controlled by temperature receptors in the skin and brain.
These receptors detect changes in the temperature of blood flowing through those areas.
The thermoregulatory centre in the brain is called the hypothalamus.
If body temperature deviates from 37°C, the hypothalamus and skin receptors send out electrical signals that trigger actions or behaviours that increase or decrease heat loss.
When core body temperature drops, muscles begin to twitch. This rapid and contraction and relaxation of the muscles is called shivering.
Shivering generates heat, which raises body temperature.
Goose bumps involuntarily appear when a person becomes cold. Goosebumps are caused by the tiny muscles at the base of body hairs pulling the hairs erect.
The upright hairs trap an insulating layer of air, which helps reduce heat loss.
Why do people go pale when they are cold?
When core body temperature falls, blood vessels in the skin get narrower. This is called vasoconstriction.
Vasoconstriction is caused by contraction of the muscular wall of the blood vessels.
This reduces the volume of blood flowing near the skin surface, and reduces the amount of heat lost from the body.
Why do people turn red when they are hot?
When core body temperature rises, blood vessels in the skin get wider. This is called vasodilation.
Vasodilation allows a larger volume of blood to flow near the skin surface, transferring heat to the environment. This cools the body down.
Additional cooling occurs with the production of sweat from sweat glands.
As the sweat evaporates it transfers heat away from the body.
Sayid has a baby sister. Samira was born premature and is too young to control her temperature. An incubator helps to control her temperature, using negative feedback.
The air around Samira is kept at 32°C. Why is it not keep at 37°C?
The human body is about 60-70% water.
Water molecules and ions constantly move in and out of cells, and are essential for all life processes.
Dehydration (loss of too much water from the body) damages cells.
How is water gained and lost?
Just a 1% decrease in body weight due to water loss is enough to cause mild dehydration.
Mild dehydration can cause dizziness, a dry mouth and concentrated urine. Severe dehydration can cause death.
What causes dehydration?
Glucose is a type of sugar used by the body to provide energy.
Sometimes there is too much glucose in the blood, and sometimes there is not enough.
What affects the level of blood glucose?
How does the body regulate blood glucose levels?
Between meals, blood glucose levels are topped up from stored deposits in the liver and muscles.
After a meal, blood glucose rises but quickly returns to normal. Where does the excess go? Why not leave it in the blood?
Excess glucose makes the blood plasma and tissue fluid around cells too concentrated. This can severely damage cells, for example, causing crenation in red blood cells.
However, low blood sugar levels can be equally as dangerous, as it can make cells swell up and burst. This is called lysis.
Blood glucose levels are monitored and controlled by the pancreas.
The pancreas produces and releases different hormones depending on the blood glucose level.