Hormones and the teenage body
The body has two messaging systems. The nervous system is like a phone call: very fast, and aimed at one spot. Hormones are more like an announcement over a loudspeaker: slower, but they reach every cell that has a receiver. This lesson looks at which gland sends which message, why the body changes so fast between ages 10 and 16, and why teenagers get sleepy later at night than younger children.
Endocrine glands are spread all through the body
Endocrine glands have no outlet tube. They release their hormones straight into the bloodstream, so a hormone travels through the whole body. But it only acts on cells that carry its receptor, like a key that opens only the lock it matches. Tap each gland to see.
| Topic | Nervous system | Hormone system |
|---|---|---|
| Sends messages with | Electrical signals and neurotransmitters | Hormones carried in the blood |
| Speed | A split second | Seconds to hours |
| Who it reaches | The target cells it is wired to | Every cell that has a receptor for that hormone |
| How long it lasts | Very short | Hours to years |
| Example | Pulling your hand back from something hot | Growth and puberty |
How the body keeps blood sugar under control
Blood sugar has to stay inside a narrow range all the time. Too high and it damages blood vessels; too low and the brain cannot work. So the pancreas has two kinds of cells that push it up and down, like an accelerator and a brake. Drag the time slider to see what happens after a meal.
What is happening right now
What really helps, starting at this age: fewer sweet drinks, more fiber, and moving your body every day. Working muscles pull sugar into their cells using less insulin.
The fastest the body ever changes, after the first year of life
Puberty starts when the hypothalamus in the brain begins sending pulses of signal to the pituitary gland, which then tells the ovaries or testes to make sex hormones. After that the body changes in a fairly fixed order, but the age it begins varies a lot. Drag the age slider to see what happens.
Why do pimples show up?
Teenage hormones make the oil glands at the base of each hair work harder. When the oil mixes with skin cells that have flaked off and blocks a pore, the bacteria living there multiply and cause inflammation. So acne is not caused by being dirty, and scrubbing hard actually makes the inflammation worse. Washing your face twice a day with a gentle soap is enough. If you have a lot of acne, or it leaves scars, see a skin doctor.
Why does sweat start to smell?
The second kind of sweat gland, the one in the armpits and groin, switches on at this age. Its sweat contains protein and fat, which have no smell on their own, but bacteria on the skin break them down and that is what smells. Showering, changing clothes, and using a deodorant really do help.
What makes a voice crack?
Hormones make the voice box grow and the vocal cords get longer and thicker, so the voice gets deeper. While it is changing, the muscles are not used to the new length yet, so the voice cracks or slips now and then. That is temporary and goes away on its own.
Why am I hungry all the time?
During the fastest part of the growth spurt, the body needs much more energy and protein than usual, so feeling hungrier is normal. What matters is choosing food that really carries nutrients, and getting enough calcium and vitamin D, because most of the bone mass of your whole life is laid down in this period.
The teenage brain is doing a big rewiring job
At this age the brain is not growing much bigger any more, but it is trimming away connections it does not use and wrapping the ones it uses often in insulation to make them faster. The last part to finish developing is the front of the brain, which handles self-control and thinking about long-term results, while the reward circuits are already running at full speed.
Melatonin is the hormone that tells the body it is time to sleep. In teenagers it naturally starts being released about one to two hours later, so teenagers really do get sleepy later; they are not just being difficult. But school still starts at the same time, so lost sleep piles up, and that is a problem all over the world.
What really helps, according to research
Morning light Getting outside in the morning sunlight for about 15 minutes helps shift your body clock so you feel sleepy earlier the next night.
Screens off before bed Bright light from screens at night holds back the release of melatonin. The later it is, the bigger the effect.
A steady wake-up time Waking up at the same time every day, weekends included, keeps the whole system steadier than sleeping in for hours on Saturday and Sunday.
Caffeine Tea, coffee, soda, and energy drinks stay in the body for hours. Even a late-afternoon drink can still disturb your sleep that night.
Things worth telling a parent or a doctor
Most of the changes at this age are completely normal. But a few are worth having an adult look at, not because they are frightening, but because the sooner you know, the easier they are to handle.
About your body
Changes starting before age 8, or nothing started by age 13 to 14 · period cramps bad enough to keep you home from school · unusually heavy periods · severe acne or acne that leaves scars · weight going up or down fast without meaning to
About your feelings
Moods going up and down at this age are normal. But if you feel sad or lose interest in things you used to enjoy for more than two weeks in a row, cannot sleep for a long stretch, or have thoughts of hurting yourself, tell an adult right away. This can be treated, and it is nobody's fault.
About the internet
If a stranger messages you asking for photos or personal information, or asks to meet you, tell a trusted adult right away, and do not worry about being told off. Speaking up early is always the right thing to do.
Things you can do every day
Sleep 8 to 10 hours · move your body 60 minutes a day · eat enough protein, calcium, fruit, and vegetables · shower and change clothes every day · and talk with a trusted adult whenever you are unsure about anything. No question is too embarrassing for a doctor.
Test yourself
Fancy a game on this lesson?
Every question from this lesson is in the Body 101 arena. Race the clock, duel someone at home, play as a team, beat the bosses, or practise with no timer at all.