Antarctic icefish have colourless blood with no red blood cells and no
haemoglobin, the oxygen-carrying pigment. This probably
comes down to a genetic mutation, and means their
blood carries 90 per cent less oxygen than red blood.
They survive partly because frigid Antarctic
waters are oxygen-rich. Icefish also have
enormous hearts that pump huge volumes
of blood around their bodies, making
sure they get enough oxygen.
Antifreeze in their blood stops
them from freezing (the salty
Southern Ocean gets down
to -2°C) but as they are so
well-adapted to the cold,
their future in a warming world
remains uncertain. HSWhy do some fish have
colourless blood?
WHAT HAPPENS IN MY BODY...- Pituitary gland
During non-REM sleep, the pituitary gland produces
growth hormone and secretes prolactin. This
counteracts dopamine, to lower general arousal levels. - Heart
Your pulse drops by 10-30bpm while you sleep, lowering
your blood pressure. Less blood flows to the brain, and
more is diver ted to your muscles.
5. Limbs
The extra blood swells your arms and legs slightly.
Muscles are paralysed while dreaming, but between
dreams you change sleeping position 35 times a night.
6. Bladder
Vasopressin hormone levels rise. This reduces the
amount of urine collected in the bladder to between a
half and a third of normal daytime levels.
2. Mouth
You produce less saliva, which reduces the need to
swallow. Five per cent of adults also grind their teeth at
night, mostly during the early stages of sleep.
3. Lungs
The throat muscles relax so your airway narrows when
inhaling. This can cause snoring, or temporarily halt your
breathing for a few seconds (sleep apnoea).
...WHEN I SLEEP?
Sleep consists of two radically different physiological states. There is rapid eye movement sleep (REM) and non-rapid eye movement sleep
(NREM). The sleep stages seem to have different functions, but why we sleep is still not completely understood. Babies spend half of their
sleep in REM, but this drops to a quarter by the age of two. It is therefore thought that REM sleep is particularly vital for the developing brain.
In NREM sleep, brain activity slows and a person woken at this stage may feel groggy.