Category Human Body

Over millions of years, evolution is changing the way humans look. Over a shorter period, improved nutrition and medical discoveries have meant that people in some parts of the world today are generally bigger and stronger than their ancestors. But we are also losing some abilities that no longer seem useful. The smallest toe, for example, can no longer be moved independently by most people. As recently as Roman times, some people may have been able to “prick up their ears”, moving them slightly towards sounds as some animals can.

Humans are getting taller; they’re also fatter than ever and live longer than at any time in history. And all of these changes have occurred in the past 100 years, scientists say. So is evolution via natural selection at play here? Not in the sense of actual genetic changes, as one century is not enough time for such changes to occur, according to researchers.

Most of the transformations that occur within such a short time period “are simply the developmental responses of organisms to changed conditions,” such as differences in nutrition, food distribution, health care and hygiene practices, said Stephen Stearns, a professor of ecology and evolutionary biology at Yale University.

But the origin of these changes may be much deeper and more complex than that, said Stearns, pointing to a study finding that British soldiers have shot up in height in the past century. ”Evolution has shaped the developmental program that can respond flexibly to changes in the environment,” Stearns said. “So when you look at that change the British army recruits went through over about a 100-year period, that was shaped by the evolutionary past.”

And though it may seem that natural selection does not affect humans the way it did thousands of years ago, such evolutionary mechanisms still play a role in shaping humans as a species, Stearns said.

“A big take-home point of all current studies of human is that culture, particularly in the form of medicine, but also in the form of urbanization and technological support, clean air and clean water, is changing selection pressures on humans,” Stearns told Live Science.

Picture Credit : Google

Veins are blood vessels that carry blood to the heart, while arteries carry it from the heart. The heart acts as a pump, pushing blood to every part of the body. Adults have between five and six litres (between nine and ten pints) of blood. As well as containing red cells to carry oxygen to the body’s organs, blood also plays an important part in fighting infection. White blood cells attack and digest harmful bacteria, while platelets in the blood form clots so that wounds can heal and no further infection can enter the body.

Arteries and veins both carry blood around the body, and they each have three main layers of tissue (a ring of endothelial tissue at the centre of the blood vessel surrounded by a layer of muscle and elastic fibres, which is surrounded by a layer of connective tissue). However, there are several differences between them:

1. Arteries carry blood from the heart to the rest of the body, whereas veins carry blood from the rest of the body back to the heart.
2. Almost all arteries carry oxygenated blood and almost all veins carry deoxygenated blood. The only exceptions are the pulmonary artery, which carries deoxygenated blood from the heart to the lungs, and the pulmonary vein, which carries oxygenated blood from the lungs to the heart.
3. Arteries have a thick elastic muscle layer, whereas the muscle layer for veins is much thinner. This is because the heart pumps blood into the arteries at high pressures, so the walls of the arteries must be able to cope with the changes in pressure during a heartbeat. Veins carry blood at much lower pressures so do not need such a thick wall.
4. Arteries have a much narrower lumen (the hole at the centre that the blood flows through) than veins. This helps keep higher blood pressures in the arteries, which is needed to keep blood flowing quickly to body tissues.
5. Veins have valves and arteries do not. In arteries, blood flows in the right direction because of the heart pumping it forwards at high pressures. The lower blood pressure in veins means that valves are needed to stop blood flowing backwards (for example, in veins in the legs, blood needs to flow upwards against the pull of gravity).

Food is the fuel that our bodies need for movement. But we also need some fuel simply to maintain all the parts of our bodies. Individual cells are being renewed all the time. And even if we do not move the outside of our bodies at all, there are many parts inside that are constantly in motion. How much food we need depends on our size, age, gender and level of activity.

Nutrition is how food affects the health of the body. Food is essential—it provides vital nutrients for survival, and helps the body function and stay healthy. Food is comprised of macronutrients including protein, carbohydrate and fat that not only offer calories to fuel the body and give it energy but play specific roles in maintaining health. Food also supplies micronutrients (vitamins and minerals) and phytochemicals that don’t provide calories but serve a variety of critical functions to ensure the body operates optimally.

Protein: Found in beef, pork, chicken, game and wild meats, fish and seafood, eggs, soybeans and other legumes included in traditional Central America cuisine, protein provides the body with amino acids. Amino acids are the building blocks of proteins which are needed for growth, development, and repair and maintenance of body tissues. Protein provides structure to muscle and bone, repairs tissues when damaged and helps immune cells fight inflammation and infection.

Carbohydrates: The main role of a carbohydrate is to provide energy and fuel the body the same way gasoline fuels a car. Foods such as corn, chayote, beans, plantains, rice, tortilla, potatoes and other root vegetables such as yucca, bread and fruit deliver sugars or starches that provide carbohydrates for energy.

Energy allows the body to do daily activities as simple as walking and talking and as complex as running and moving heavy objects. Fuel is needed for growth, which makes sufficient fuel especially important for growing children and pregnant women. Even at rest, the body needs calories to perform vital functions such as maintaining body temperature, keeping the heart beating and digesting food.

Fat: Dietary fat, which is found in oils, coconut, nuts, milk, cheese, meat, poultry and fish, provides structure to cells and cushions membranes to help prevent damage. Oils and fats are also essential for absorbing fat-soluble vitamins including vitamin A, a nutrient important for healthy eyes and lungs.

 Picture Credit : Google

There are more than 600 muscles in the human body. Over 100 of these are in our faces, which is why we can have so many different expressions. Although we can perform a great variety of movements, each muscle can only do one thing: contract. That is why muscles often work in pairs, so that one muscle can move a part of the body in one direction, while its partner can move it back again. Perhaps the most important muscle in the human body is the heart, which is contracting and relaxing all the time to pump blood around the body.

There are about 700 named skeletal muscles in the human body, including roughly 400 that no one cares about except specialists. There is just one important cardiac muscle. And there are literally countless smooth muscles (which do the work of the autonomic nervous system, mostly squeezing and squishing stuff in tubes).

It’s surprisingly hard to tell. You wouldn’t think the total number would be ambiguous, but it’s difficult to know what to include and exclude, and anatomists don’t always agree. Some muscle tissue really can’t be separated into countable muscles. And, believe it or not, the science of anatomy is still advancing. No, entirely new muscles aren’t being discovered — but novel variations in individual muscle anatomy are found more or less constantly, and supernumerary muscles — extra muscles — are not unusual. Many muscles, like the four-part quadriceps, are normally split into different parts that may or may not traditionally count as separate muscles — but then some people’s muscles are more divided than others. It makes a firm count just about impossible.

There are only about 200 to 300 muscles that anyone, even a massage therapist, might actually be interested in knowing about. When most people ask how many muscles are in the human body, they mean the serious bone-movers — Pecs, delts, lats, traps, glutes, biceps & triceps, hams & quads & let’s not forget the cloits & dloits!muscles that do real work, muscles like pecs, delts, lats, traps, glutes, biceps and triceps, hams and quads, and let’s not forget the cloits and dloits! There are maybe another hundred muscles if you include the fiddly little muscles of the hands and feet, and the major face muscles.

But that’s including about 600 muscles that, mostly, no one cares about except specialists. I am aware of a few that have clinical importance to a massage therapist, but I’m mostly just barely aware of their existence — like the smaller facial muscles, like the mess of little muscles around and under the tongue and around the voice box, like the muscles around the eyeball, or the crazy trampoline of muscles on the pelvic floor.