The human body is beautifully put together – a seemingly ideal combination of form and function. But while some parts do their job brilliantly others aren’t quite as effective. We look at the body’s five best and worst designs.
It may not be all that pretty but it’s pretty amazing. The brain controls movement, interprets the senses and is the seat of intelligence. It’s a complex network of neural fibres – more complex than any computer – that acts as the operating system for the whole body. It never rests: even when you’re asleep your brain is working.
You can thank this organ for clear eyes and healthy skin – the liver detoxifies the body by removing harmful substances such as alcohol. It also releases energy from sugar and fat and produces bile, necessary for getting rid of cholesterol and digesting fat. It’s an amazingly resilient organ and one of the few capable of natural regeneration – as little as a quarter of a remaining liver can grow back into a whole one.
These small organs play a big role, filtering just under 200 litres of blood every day. The kidneys also reclaim any useful salts and nutrients from urine while clearing out harmful waste and toxins. They’re perfectly attuned to keeping the body’s fluid volume constant. In fact they’re so important there’s plenty of reserve – just a third of one kidney is enough to ensure normal functioning.
There are about 50 trillion cells in the human body and nearly all contain DNA, a molecule that’s the blueprint for every part of the body. Each time a cell divides its DNA must be copied perfectly to make sure no errors are introduced into that blueprint. Ultraviolet light, radiation and toxins from cigarette smoke are just some of the things that can damage DNA and result in mutations – but special genes check DNA and slow down the growth of any abnormal cells.
Smooth, silky, durable . . . the skin is more than just pretty packaging. This self-renewing , waterproof, flexible and stretchable covering protects us from a harmful environment. The skin also cleverly controls our body temperature: a layer of insulating fat helps to trap heat while sweat glands cool the body through evaporation.
Flaws of the human body
Apart from producing mucus and strengthening the facial bones somewhat they don’t really have a function in humans. In animals sinuses are important for smell and drain downwards into the nasal passages through small holes called ostia. Unfortunately the positions of our ostia haven’t adapted to our upright posture which means our sinuses no longer drain by gravity. The result? Allergies and viruses cause inflammation that blocks our ostia and since they can’t drain effectively the sinuses become infected.
Our ancestors had a coarse diet that included foods such as nuts and hard vegetables – good reason for a large jaw and extra molars. Our diet and lifestyle have changed over the millennia but the arrangement of our teeth hasn’t kept pace. These extra teeth in our now smaller jaws are nothing but a source of discomfort for us – and provide a welcome income for orthodontists!
This small blind-ended tube lies near the junction of the small and the large intestines. In other primates the appendix is better developed and some scientists think in humans it’s a remnant of a larger tube once used to digest leaves. Others think it provides a safe place for useful bacteria to hide when illnesses such as diarrhoea flush them from the rest of the intestines. Whatever its original function it’s now a liability – blockage can lead to appendicitis, an illness that can be fatal if the appendix isn’t removed.
Weight bearing joints
Our ability to walk on two legs, which frees our hands for other activities, has come at a cost. Instead of our weight being distributed among four limbs our upright posture puts extra pressure on the lower back, hips and knees. Walking, running and jumping cause wear and tear to these load-bearing joints. We live so well nowadays that we’re also heavier than in the past – which places even more strain on these vulnerable areas.
This is both a wonder and a fl aw. The system that protects us against invading microbes can sometimes be too vigilant, mistaking proteins that belong to the body for those of a bacterium or virus. This can lead to one of many auto-immune diseases where the response usually directed at invading organisms is mistakenly aimed at the body’s own tissue.