From your Lips to your hips in just 3 hours

From digesting a cupcake to healing after surgery or even having an orgasm, how long it takes your body to work

take about 20 to 30 seconds to empty their bladder,’ says Mr Rees.

Passing little and often could also be a sign of an overactive bladder, he says. here there are faulty signals between the bladder and the brain, meaning the brain thinks it’s time to empty before the bladder is full. Drugs, Botox and nervetingling devices can all help an overactive bladder.

BRAIN GROWTH: 25 years

‘the first three or four years of life are what we call the critical period for the brain,’ says David Price, professor of developmental neurobiology at the university of edinburgh. ‘It’s like a telephone system where the main wiring is there, but all the fine wiring still needs connecting.’

After four years of life, the brain loses the ability to form these fine connections. By the time of puberty, the brain is pretty much fully developed, apart from one crucial part — the prefrontal cortex, just behind the forehead. this only reaches completion around the age of 25.

In 2004, a seminal study of brain scans of teenagers showed they had less brain tissue in their frontal lobes — where the prefrontal cortex is — than adults, but this increased as they got older.

the prefrontal cortex is associated with organising thoughts, planning and controlling impulse — and teenagers’ lack of it is thought to explain their tendency for unpredictable and risky behaviour.

PUBERTY: Three to eight years

PuBeRtY usually starts between the ages of nine and 12 in girls, says Dr Mark Vanderpump, endocrinologist at Royal Free London Nhs Foundation trust. It then lasts between three to five years.

‘the mean age of onset of breast development for girls is nine years, and the average age of periods starting is 12 — although they can start any time from eight to 20.’ Completion of puberty is defined by reaching your maximum height, and girls tend to do this within two years of their periods starting, he says.

‘When a girl’s periods have started, it means she has enough oestrogen in her body to fuse bones, and once our bones fuse, we can’t grow any longer.’

In boys, puberty starts between ten and 13, and lasts longer than in girls, for between five to eight years. It’s signified by an increase in testicular volume, getting taller, growing hair, and the voice deepening. But boys won’t reach their final height until their late teens, says Dr Vanderpump, with the process taking five to eight years.

A number of studies have shown children — particularly girls — are reaching puberty earlier, ‘probably because of genetics, nutrition improving and other environmental factors’, says Dr Vanderpump.

this may have implications for their health, with girls who start at a very young age at much higher risk of breast cancer than those who start their periods at 16, suggests Dr Marion Kavanaugh- Lynch, an oncologist and director of the California Breast Cancer Research Program in Oakland. this is because most breast cancers are fuelled by oestrogen.

Late puberty could put girls at greater risk of osteoporosis, say researchers from the saban Research Institute at Children’s hospital Los Angeles — oestrogen is needed for healthy bones, and puberty is a key time for bone mass development.

there seem to be fewer problems for boys hitting puberty early, but u.s. studies suggest they might be more likely to be sexually active early and to engage in risky behaviour.

LUNG DEVELOPMENT: 18 to 22 years

hAVe you ever noticed your singing voice isn’t as good as it was in your youth?

Your lungs reach their peak capacity during your teens or early 20s, and decline thereafter.

‘A person’s airways form in the womb, and the complete set are there by 16 weeks of gestation,’ says John henderson, professor of paediatric medicine at the university of Bristol.

‘After birth, the passages get bigger, and the air sacs continue to develop, as the size of the lungs grow with the rest of the body.

‘this process continues throughout childhood, and because women reach puberty earlier than men they reach peak lung function earlier, too — around their late teens. In men, it’s the early 20s.’

Certain things can stop you hitting your potential peak lung function, says Professor henderson.

‘Cigarette smoking by parents or by the mother during pregnancy, probably being born early, or being underweight at birth, recurrent lung infections or diseases such as asthma during childhood, can all make a small difference to your peak lung function.

‘that means that when it declines, you’re starting from a lower level, so you’re more likely to suffer breathing problems sooner.

‘It can also mean you’ll be more prone to chronic obstructive pulmonary disease.’

MENOPAUSE: Two to ten years

the median age for the onset of the menopause is 51, although the ‘normal’ range is from 40 to 55, says Dr Vanderpump.

‘I have seen the odd 55-year-old woman who is still having regular periods and it’s nothing to be worried about,’ he says.

however, menopause later than this may raise the risk of breast cancer because it means the woman has had more exposure to oestrogen throughout her life. A woman having the menopause at 55 has a 30 per cent higher risk than a woman at 45, according to Cancer Research uK.

A 2011 study by Imperial College London showed increasing numbers of women are hitting the menopause early — before the age of 40 — with some even starting it in their teens.

In most cases, the menopause had been triggered by surgery or chemotherapy, but for 6 per cent of the women it was unexplained.

early menopause carries a raised risk of osteoporosis, heart disease and stroke, because of oestrogen’s protective effect.

Once the menopause has begun, most women will experience a number of typical symptoms — such as hot flushes — for around two years, says Dr Vanderpump, although a significant proportion won’t even notice that the change has happened until they realise that their periods have stopped coming altogether.

some women are less fortunate — a 2011 study of 400 women by the university of Pennsylvania school of Medicine found hot flushes can last ten years.

‘the younger you are when you start the menopause, the more likely you are to suffer.

‘this is because the oestrogen levels tend to drop more steeply in younger women.’

the menopause typically lasts for two years. One in five men over 65 will suffer the ‘male menopause’, or andropause, according to the european Association of urology.

here, diminishing levels of testosterone trigger symptoms such as fatigue, low sex drive and hot flushes. While some men say the symptoms are over within a couple of months, others report them going on for up to ten years. the condition has been linked to obesity and diabetes, and even to premature death.

however, it’s still a relatively new and controversial concept, and not easy to diagnose definitively, says Dr Vanderpump.