Page 83 - BBC Focus - August 2017

WHAT HAPPENS IN MY BODY…

...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.

1. Pituitary gland 2. Mouth 3. Lungs
During non-REM sleep, the pituitary gland produces You produce less saliva, which reduces the need to The throat muscles relax so your airway narrows
growth hormone and secretes prolactin. This swallow. Five per cent of adults also grind their teeth when inhaling. This can cause snoring, or temporarily
counteracts dopamine, to lower general arousal levels. at night, mostly during the early stages of sleep. halt your breathing for a few seconds (sleep apnoea).

4. Heart 5. Limbs 6. Bladder
Your pulse drops by 10-30bpm while you sleep, The extra blood swells your arms and legs slightly. Vasopressin hormone levels rise. This reduces the
lowering your blood pressure. Less blood flows to Muscles are paralysed while dreaming, but between amount of urine collected in the bladder to between
the brain, and more is diverted to your muscles. dreams you change sleeping position 35 times a night. a half and a third of normal daytime levels.

Why do some fish have colourless blood?

LORELY MASKELL, BUCKINGHAMSHIRE

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. HS

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