Why do men have nipples, and how does the eye adapt to light?

Men have nipples, but are they used for anything?

Men’s nipples certainly don’t serve any important physiological function, unlike the nipples of women; rather, they are a hangover from the early days in the womb.

The fundamental differences between boys and girls do not begin to become evident until between the tenth and fifteenth week after conception. Prior to this, males and females in the womb are anatomically identical.

If the foetus carries a Y chromosome from its father, hormones are produced which alter the internal “piping and ducts” to produce a boy. If the second chromosome is an X, then the foetus develops into a girl as a result of a different set of hormones.

However, by this point the nipples have already been formed, and they cannot be unmade. So they remain – as a legacy of the days when all life was “female”.

Is a cold caused by a bacteria or a virus?

In a way, it is caused by both. Initially, the common cold is caused by a virus. That itchy feeling you get in your nose and throat when you first feel as though you have a cold is caused by the virus.

However, because it damages the inside of your nose and throat, bacteria can then cause further damage – when this happens, bacteria start to grow and cause further problems.

This is what causes the uncomfortable “bunged up” feeling a couple of days after you first get the sore throat. Only when your body manages to fight off the virus and the bacteria, do the signs of the cold disappear.

Is there any difference between fingernails and toenails?

Not really: they are very similar. Nails are also like hair in a lot of ways. They, too, consist of modified epithelial cells and are mainly composed of keratin.

Nails help protect the ends of the fingers and toes. The fingernails are especially important in humans and primates because we use our hands so much. Nails allow us to grip and pick at things which soft skin would not permit: they also allow us to have a good scratch!

The only difference that we know of is that fingernails grow faster than toenails, increasing in length by 0.5mm per week.

Why does blood turn a rust-like colour when it dries?

Blood contains small amounts of iron. When exposed to the air, this iron oxidises – in other words, its chemical make-up changes as the iron joins with the oxygen in the air.

This is exactly what the iron that we use for constructing things does if it is not protected from the air.

In effect, therefore, it is true to say that our blood, just like iron railings or a car, rusts when it is exposed to air.

What happens to brain cells after they die?

A dead cell in the brain, or anywhere else in the body, starts to break down when it dies. Cell fragments are “eaten up” by the large white cells in the body, called macrophages. These surround the dead cell fragments and take them into their cytoplasm.

Lysosomes, enzyme-containing bags, are then emptied into the internal sac that contains the nerve cell fragment and it is digested. The macrophages use anything useful and get rid of the waste into the bloodstream. This waste ultimately goes to the kidneys for excretion.

What is the smallest bone in the ear?

The stirrup bone, one of the three auditory ossicles in the middle ear, measures between 2.6mm and 3.4mm in length and weighs from 2mg to 4.3mg – roughly the same dimensions as a grain of rice.

How do our eyes adapt to light and dark?

If you are in the dark, or in very dim light, for over half an hour, the rate at which photopigments in the eye are formed is much faster than the rate at which they are broken down. Your eyes are dark-adapted.

If your eyes are exposed to bright light for a long period of time, much of the light-sensitive pigment in the rods and cones is broken down and the sensitivity of your eyes to light is much reduced. In this situation, your eyes are said to be light-adapted.