What is the cleanest part of the body?

What is the cleanest part of the body?

Paolo Molander, 11

The body the cleanest part must be looked for elsewhere than on the skin. No part of our skin is really clean, because it is completely covered with microbes, i.e. tiny organisms.

There are especially many bacteria and yeasts on the skin. Skin microbes are mostly beneficial because they prevent disease-causing microbes from settling and multiplying on the skin.

All our mucous membranes are also rich in microbes. It is important because our mucous membranes are also in direct contact with the microbes in our environment. There are a huge number of microbes, for example, on the mucous membranes of the mouth, respiratory tract, intestinal tract, the surface parts of the eyes and the genital area.

The cleanest parts of the body are closed cavities that are bounded by membrane structures. They contain a liquid or gel-like substance that normally does not contain any microbes.

Such cavities include the cerebrospinal fluid cavity, synovial cavities, abdominal cavity, chest cavity surrounding the lungs, pericardium and deeper structures of the eye, such as the lens and vitreous cavity.

Maria Lönnrot

docent of dermatology and allergology, senior physician

Tampere University Hospital

Why is there so much salt in all the foods that children like, such as store-bought meatballs and naks?

Nooa Tiihonen, 5

Salt brings a salty taste to food, emphasizes other flavors and covers the bitterness of, for example, many vegetables and legumes. The taste buds in the mouth detect saltiness very easily. Both children and adults will like the salt.

Children often like even saltier food than adults. Early childhood food experiences have a significant impact on taste preferences. However, adults and children are very individual when it comes to their preference for salt.

Salt is also needed as a preparation, so that, for example, nakiki and meatballs stay pleasantly moist. Namely, salt binds, meaning it absorbs water. Sodium, which is contained in some additives used in some foods, also brings a little more salt to the snacks.

You shouldn’t eat too much salt, but getting used to low-salt food is good for your health, because too much salt raises blood pressure. An excessive amount of salt can be avoided by choosing snacks and meatballs with less salt and also by eating them less often. There is less salt in those naks and meatballs with the distinctive red Heart symbol on the package.

It is also recommended that play-aged children do not eat more than two snack meals per week, so that they do not get too much of an additive called nitrite, which is harmful to them. Meatballs are also quite easy to prepare at home, so you can reduce the amount of salt by using other spices.

Fortunately, not all foods that children like have a lot of salt. You also get used to less salt – and the food still tastes really good.

Marina Heinonen

professor of food safety

University of Helsinki

Mari Sandell

professor of food sensory quality research

University of Helsinki

How do birds flying in a flock not collide with each other?

Justus Kontra, 10

This the matter has been investigated both by following flocks of birds and by mathematically modeling their flight. It has been observed that the flock does not have a leader, but each bird keeps the distance to its neighbor the same and constantly follows the movements of those flying closest, reacting to them.

Birds that fly in dense flocks include starlings, many waders, such as terns, and the million-weaver, considered the most abundant bird in the world. When flying straight ahead, the risk of collision is small even in dense flocks. But if an individual in the flock makes a sudden turn, a chain reaction follows, which travels through the entire flock at lightning speed.

The basis of everything is the birds’ very fast reaction ability with the help of hearing and sight. To the human eye, it seems that, for example, a flock of waders on a migratory flight would turn completely simultaneously, as if on command, but this is not really the case.

In very large flocks, such as winter flocks of hundreds of thousands of starlings, the birds can sense the “avoidance wave” advancing in the flock and anticipate its arrival. In large swarms, there can be several turning waves at the same time, when they collide, the swarm seems to bulge. All species moving in such flocks are relatively small in size.

Large birds usually do not fly in dense and bulging flocks because their ability to change flight direction is slower. If they form flocks, they are furrows and lines, like geese and pelicans. Flying quickly and in a very straight line, loons form migratory flocks, but the distance between their individuals can be tens of meters.

That Hohtola

Emeritus Professor of Animal Physiology

University of Oulu

Why aren’t the clouds frozen, even though the clouds are a mass of water and the sky is cold?

Bruno Nenonen, 6

In the sky it’s really cold. When you go up a kilometer, the temperature usually drops by about 5–10 degrees. When the air is cold enough, even the clouds are frozen.

Summer cumulus clouds and low-hanging fog clouds usually consist of unfrozen water droplets. Instead, the thin down and gauze clouds shimmering high in the sky consist of small ice crystals. Clouds can also contain water droplets and ice crystals mixed in.

However, sometimes the water droplets in the clouds are not frozen, even though their temperature is below zero degrees, i.e. below the freezing point. This is called supercooled water.

Subfreezing can occur when the water molecular parts wander around in the droplet, and cannot decide where to start freezing.

If, for example, a dust particle hits the drop, the water molecules immediately begin to form ice crystals around it and the drop freezes. The dust particle then acts as a freezing nucleus. If subcooled water rains from the sky during winter frost, it freezes as soon as it hits the ground or, for example, the windshield of a car.

Tiera Laitinen

investigator

Department of Meteorology

Send the question, the questioner’s full name and age to lasten.tiedeskö[email protected]. The column is provided by Touko Kauppinen.