10 Extraordinary Facts About the Human Body

Millions of years of evolution have given the human body various abilities, mental and biological, voluntary and involuntary, not just to survive but also to thrive. Though there are various other life forms on this planet with amazing capabilities, humans have gained an edge over them especially because of their ability to conceive new ideas and create new things. Here are some extraordinary facts about the human body we’re sure you’ll enjoy reading about.

1. Humans are the best endurance runners among all running animals. Given long enough distances, they can outrun any animal on Earth.

Endurance Running
Image Source: Steve Gregory

According to Harvard’s anthropology professor Daniel Lieberman, “Humans are terrible athletes in terms of power and speed, but we’re phenomenal at slow and steady.” Unlike other species of mammals, humans evolved to be bipeds two to three million years ago. Humans used persistence hunting. That means they would run, walk, and track game animals over long distances gaining an advantage over other carnivores. Also, unlike all other animals, humans participate in marathons voluntarily. Even the best of distance runners in animals, like horses or dogs, only do so if forced, though humans are far better at it.

Humans are better endurance runners because of their center of mass and ability to sweat. Quadruped animals have their center of mass in front of their hind legs, whereas, for humans, it is above their legs. So, the bones and muscles are different in structure and have different energy demands. While other animals dissipate their metabolic heat by panting through mouth or nose, humans sweat all over their body. So, as the sweat evaporates, the body cools down to a much greater extent that it would for other animals.(1, 2)

2. In the womb, a fetus grows 250,000 new neurons per minute. That is a million neurons every four minutes for nine straight months. 

Human Brain During Gestation
Image Source: ncbi

The human brain starts developing from the tip of a neural tube that’s just three millimeters long. Within three to four weeks after conception, the brain’s three regions — hindbrain, midbrain, and forebrain — start forming. In three months time, the brain would have grown several times in size, especially the forebrain which grows quite fast dominating the other regions. In 15 to 20 weeks time, around the midpoint of the pregnancy, the number of brain cells starts to increase rapidly, and by six months the cerebral cortex begins to separate into two lobes. By the end of nine months, the brain is recognizably human and continues to grow until the baby reaches 18 months of age. Throughout this time, the brain grows at an average rate of 250,000 nerve cells per minute. By the time a baby is born, the brain has more than 100 billion neurons which soon form 100 trillion interconnections.(source)

3. In many instances, if a blood vessel is blocked, like in a stroke, the human body tries to compensate for it by branching new vessels around the part that is circulating poorly. 

Collateral Circulation in Arteries
Image Source: drmorepennow

Human body’s blood circulation system has many redundant branches that become useful when the vessel nearby is blocked. These redundant branches could be preexisting or newly formed. An example of preexisting vascular redundancy is the circle of Willis present in the brain. It has a circular structure and if one part of the circle is blocked or narrowed, or if one of the arteries supplying blood to it is blocked or narrowed, the blood will still flow to the brain preventing stroke.

Forming of new branches around a troubled blood vessel is called “neovascularization.” Functional micro, blood vessel networks large enough for red blood cells to pass through form in response to poor circulation or ischemia and serve as collateral circulation. It has been observed in both animals and humans that after a heart attack new vessels form to bypass the main artery blockage and supply enough oxygen for cardiac tissue repair. It also happens in the eyes, though the bulk of these new branches often causes glaucoma by blocking aqueous humor drainage.(1, 2)

4. When people are electrocuted and thrown far distances, it is a result of sudden and violent muscle contraction and not the result of the shock. 

Electrocution and Muscle Contraction
Image Source: giphy

When there is danger, the brain triggers the hypothalamus which is responsible for maintaining the balance between stress and relaxation. It then signals the adrenal glands which in turn releases adrenaline and noradrenaline hormones, starting the fight-or-flight response in our body. This raises the heart rate, increases respiration, dilates the pupils, slows digestion, and most importantly helps the muscles contract. Together, all these factors make our body agile. When confronted with extreme stress, the muscles contract far more than they would in a neutral state or that is voluntarily possible. It can be observed when a person is electrocuted and gets thrown a considerable distance from the source of shock. This is not because of the electric shock itself but because of the involuntary contraction of muscles when the electric charge flows through the body. Scientists believe this demonstrates the potential capabilities of muscle contraction that aren’t used in normal situations. (1, 2)

5. Despite being only 4% of an adult human’s total body mass, the bone marrow produces 500 billion blood cells per day.

Cells in Bone Marrow
Image Source: Mysid

The bone marrow is a spongy tissue inside the bones responsible for producing red blood cells, platelets, and white blood cells. It is also an important part of the lymphatic system and supports our body’s immune system. In an adult, bone marrow is present in the spine, hip bones, shoulder bones, ribs, breastbone, and skull. An average adult weighing 65 kilograms has 2.6 kilograms of bone marrow which produces 500 billion blood cells per day.

When the blood cells are mature, they pass through the bone marrow’s circulatory system to enter the blood vessels and start functioning. The bone marrow also contains mesenchymal stem cells which are multipotent stem cells that are capable of becoming a wide variety of cells including cells that form bones, muscle cells, marrow adipose tissue cells, and pancreatic cells. Scientists have recently transformed these stem cells into functional neural cells successfully.(source)

6. The human eye is sensitive enough that if the Earth was flat and there was total darkness, it could spot a candle flame flickering up to 30 miles (48 kilometers) away.

Human Eyesight
Image Source: Julizs, Bangin

The ability of a human eye to perceive an object something depends on how many photons are either emitted or reflected by that object. We can see the stars that are millions and billions of light-years away from Earth, the nearest being the Andromeda galaxy 2.6 million light-years away. In 1941, scientist Selig Hecht and his colleagues at Columbia University tried to find out the minimum number of photos that must fall on the retina for the eye to register the light. Initially, they found that it was between 54 and 148 photons. But when they measured how much the retina actually absorbed, they found that it was just five to 14 photons or rather the activation of five to 15 rod cells.

It takes the eye around four seconds to adapt to uninterrupted darkness and half an hour for 80% of the rod cells to fully adapt. A complete adaption, however, depends on the health of and blood flow to the eyes. When the eyes are adapted, they can easily spot a candle about 30 miles away in absolute dark.(source)

7. If a pregnant woman suffers organ damage, like a heart attack, the fetus can send stem cells to help repair the damage.

Pregnant Women and Embryonic Stem Cells
Image Source: Swangerschaft, Nissim Benvenisty

While treating pregnant women or women who had recently given birth for heart conditions, doctors observed better recovery rates than any other group of patients. When researchers experimented on mice to understand what is happening, they found that the mice that had a heart attack had eight times as many cells from the fetus in their hearts as the mice that didn’t have a heart attack. They also found that the embryo’s stem cells became various types of heart tissue, including cardiomyocytes, the muscle cells that are responsible for the heartbeat.

There have also been other curious clinical observations in which the hearts of two human mothers who were suffering from heart weakness were found to have cells derived from male fetus cells years after giving birth to their sons. What’s more, it isn’t just the damaged heart that the fetal cells try to repair. They also show up in the brain, lung, and liver when a pregnant woman suffers damage in any of these organs.(source)

8. The human brain consumes over 20% of body’s energy despite accounting for only 2% of total body’s weight, or on average 1.4 kilograms.

PET of a Human Brain
Image Source: Jens Maus

The brain is the central organ of our nervous system and controls most of the bodily functions, both voluntary and involuntary. Its primary source of energy is glucose, though when glucose levels are low it can also use ketone bodies as fuel. Though the amount of energy the brain consumes does not vary over time, the active regions consume more energy than the inactive regions, a fact that is the basis of MRI and PET scans. Most of the brain’s energy consumption is due to neuronal activity, that is neuronal computation and information processing. The brain receives 15% of the cardiac input, 20% of the total oxygen consumption, and 20%t of total glucose consumption, that is approximately 5.6 milligrams of glucose per 100 grams of human brain tissue per minute.(1, 2)

9. Our immune system is so advanced that it actually kills cancerous cells every single day before they lead to cancer.

White Blood Cells
Image Source: National Cancer Institute

Two of the three types of lymphocytes, a type of white blood cell, present in our body are B-cells and T-cells. B-cells develop in the bone marrow and T-cells develop in the thymus gland, hence their names. The function of T-cells is to detect and kill virus-infected cells, as well as to help B-cells create antibodies to fight any infection. To generate these antibodies, the B-cells undergo an immense number of mutations and, unfortunately, can sometimes turn cancerous. In a healthy individual, these cancerous B-cells are detected and eliminated by the T-cells every single day protecting us from non-Hodgkin’s lymphomas. It is also the reason why non-Hodgkin’s lymphomas are rare when compared to other types of cancers unless the individual has a suppressed immune system as in the case of HIV/AIDS.(source)

10. The liver is the only internal organ in the human body that can regenerate itself. As little as 25% is enough to regenerate back into a whole liver.

Liver Regeneration
Image Source: Karin Komposch & Maria Sibilia

One of the key functions of the liver is to remove toxins which can damage cells in the body. The liver also produces bile to digest fats and stores carbohydrates in complex forms known as glycogen to preserve homeostasis making it essential to survival. However, unlike other internal organs, the liver is capable of rebuilding itself in case of chemical injury or following partial surgical removal because of fibrosis or tumor.

The cells known as hepatocytes are replicated first after which the bile duct cells and other cells are formed. The regeneration of the liver is a very rapid process, and in doing so, it prevents its own failure. Another interesting and astonishing fact is that, even while the regeneration process is going on, the liver’s primary functions such as albumin and bile production are barely affected, although there is a decrease in drug metabolism.(source)

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