What is an adaptation of the body?
An adaptation is a change that helps the body cope with a new situation. Some changes are quick and last only a short time (breathing faster). Others take days or weeks and last longer (more red blood cells). The aim is always homeostasis: keeping the inside steady, even when the outside changes.
Thermoregulation: heat and cold
Your core temperature stays near 37 °C. The control centre is the hypothalamus in the brain.
- Too hot: skin blood vessels widen, so more heat leaves the skin. Sweat glands release sweat. When sweat dries, it takes heat away.
- Too cold: skin vessels narrow, so less heat is lost. Muscles shiver quickly and make heat. Hair stands up (goosebumps).
Drink water in heat, because sweat uses water. In cold, wear layers to hold a warm layer of air.
Hypoxia: thin air at high altitude
Hypoxia means too little oxygen for the body's needs. At 5000 m the air has about half the oxygen pressure of sea level, so each breath brings less oxygen.
- At once: breathing and heart rate go up.
- After days to weeks: the kidneys send a signal and the bone marrow makes more red blood cells, which carry oxygen.
- After a long time: people born at height have larger lungs and more blood vessels.
If you climb too fast you may get mountain sickness: headache, sickness, tiredness. Climb slowly and rest, so the body has time to adapt (acclimatisation).
Nutrient deficit: living with too little food
When food is short, the body uses its stores in order:
- Sugar store (glycogen) in liver and muscle lasts about a day.
- Fat becomes the main fuel for weeks. The body also slows its work to save energy.
- Muscle protein is burnt when fat is almost gone. This damages the body.
Lack of a particular vitamin or mineral also causes problems (for example iron lack causes anaemia). A balanced diet prevents this.
Circadian rhythms: the 24-hour body clock
The body has an inner clock, set by the brain, that repeats about every 24 hours. It is a circadian rhythm. Light is the main signal that sets it.
- Daytime: alertness and body heat rise; melatonin (sleep hormone) is low.
- Night: melatonin rises, body heat falls, we feel sleepy.
Long flights across time zones (jet lag) and night shifts clash with the clock and cause tiredness. Regular sleep times, morning light and dark rooms at night help. Bright screens at night can delay sleep.
Training: the body gets stronger
Regular exercise is a safe stress. The body answers by growing stronger.
- Muscles grow bigger and stronger.
- Bones get denser.
- The heart pumps more blood per beat, so the resting pulse becomes lower.
- Lungs and blood supply improve, so you tire less.
Rest is part of training, because the body builds itself during recovery.
Weightlessness: the body in space
In orbit, nothing pulls the body down, so muscles and bones do not have to hold it up. If this lasts, muscles shrink and bones lose minerals (about 1 % a month). Body fluids move up towards the head, so faces look puffy. Balance and heart fitness also change.
Astronauts exercise about two hours a day with special machines and eat enough calcium to slow the loss. Back on Earth, they need weeks to recover.
Try it: a practical
In the 3D, move each slider and say what the three bars will do before you look. At home: count your pulse for 30 seconds, multiply by 2, then walk fast for 3 minutes and count again. A fit person's pulse returns to normal sooner.
Key formulas and definitions
- Core body temperature ≈ 37 °C (kept steady by thermoregulation)
- Heat: vessels widen + sweating. Cold: vessels narrow + shivering
- Altitude: more breaths at once, more red blood cells after days
- No food: sugar store → fat → muscle protein
- Use it or lose it: load builds muscle and bone; no load weakens them
Worked examples
1. On a hot day your skin looks red and you sweat. Explain.
Skin blood vessels widen so more blood and heat reach the skin, which turns red. Sweat dries on the skin and takes heat away. Both keep the core at 37 °C.
2. A trekker climbs from sea level to 4000 m and feels breathless. After ten days she feels better. Why?
At first the thin air gives less oxygen, so she breathes faster. Over ten days her body makes more red blood cells, which carry more oxygen, so she copes better.
3. Why does a person with no food lose fat before muscle?
The sugar store is small and ends in about a day. Fat is the big store and the main fuel for weeks. Muscle protein is used only when fat is almost finished.
4. Why does an athlete have a resting pulse of 50 while another person has 72?
Training makes the heart stronger. A stronger heart pumps more blood in every beat, so fewer beats are needed per minute.
5. Why do astronauts exercise every day?
In weightlessness muscles and bones do not carry any load, so they get smaller and weaker. Daily exercise gives them a load and slows the loss.
Common mistakes
- Thinking that the core temperature falls in the cold or rises in the heat. The body works hard to keep it near 37 °C.
- Thinking red blood cells increase at once at altitude. It takes days; breathing faster comes first.
- Thinking fasting only burns fat. After the fat is nearly gone, muscle is used too.
- Thinking that body clock depends only on tiredness. Light is the main signal.