The human body is a marvel, to say the least. It took 3.8 billion years for it to evolve from a single cell into what it is today. Since we first achieved self-awareness, our curiosity about our body and our origins has helped us understand much and aided the field of medicine immeasurably. It is no wonder that no matter how much we learn about our body, there are always things about it that will amaze and astonish us. So, here are some amazing facts about the human body that we are sure you would enjoy reading about.

1 The brain itself cannot feel pain. It has no pain receptors.

Receiving and processing sensory input such as vision, smell, touch, or taste are part of all the innumerable complex functions that brain performs. Among these sensory inputs is pain which can come from any part of the body. These inputs and signals are interpreted by the brain as “pain” which indicates that something bad is happening.  The brain then initiates actions which it determines are required to deal with it. However, the brain itself cannot feel pain if anything happens to it because it has no pain receptors. So, if you are experiencing headache, the pain is probably coming from the membranes surrounding the brain, the connective tissue over your skull or the scalp. (source)

2 If you donate or damage a part of your liver, it will grow back to its full size. 

The liver is the only internal organ that has regenerative abilities. If the liver is either surgically removed or suffers chemical damage, it can regenerate. It is said that as little as 25% of the liver is enough for it to regenerate itself back to full size, though for donation there are several criteria that has to be met. The donors must have a matching or compatible blood type, should be between 18 and 60 years old and healthy. However, the regeneration process in mammals is not true regeneration. The liver can only restore its function and mass, but not its original form. The liver lobes do not grow back. True regeneration, that is restoration of function, mass, and form, only happens in lower species such as fish. (1, 2)

3 The acid in our stomach is strong enough to dissolve razor blades. 

The stomach is the organ that digests the food we eat and along with that has to take care of the bacteria and other harmful things that enter it. The gastric acid it releases is composed of hydrochloric acid, potassium chloride, and sodium chloride. It kills the bacteria and activates the digestive enzymes. It has a pH between 1.5 and 3.5 which makes it a very strong acid. Scientists experimented on razor blades, disc batteries, and pennies by putting them in simulated gastric juice to find out how the best way to deal with them when they are accidentally swallowed. They found that after twenty-four hours the blades weighed 63% of their original weight and became fragile. The disc batteries, however, showed no leakage, and the pennies were not affected by the acid. (1, 2)

4 We shed differently structured tears depending on the reason we’re crying. When put under the microscope, tears due to grief, hope, or onions all show unique structure. 

We produce three different types of tears. Basal tears are those produced naturally by any healthy mammal to keep the eyes wet and lubricated. Reflex tears are those produced as a result of irritation due to foreign particles, chemicals, onions, when eating hot or spicy foods, or sudden exposure to light. Crying or weeping tears are those that we shed due to emotional stress, pain or even pleasure, like during uncontrollable laughing.

All these types of tears have a different composition because they are meant for different purposes. Basal tears contain oils, salts, liquids and antibacterial elements, whereas crying and weeping tears contain protein-based hormones relevant to the emotion you are experiencing. Photographer Rose-Lynn Fisher took microscopic photographs of her tears during various situations as part of the project “The Topography of Tears”. These photographs show how uniquely these tears are structured. (source)

5 Nobody knows the exact number of muscles in a human body. Depending on how you count, it varies between 656 to 850 to over 50 billion!

There are essentially three types of muscles in our body: skeletal, cardiac, and smooth muscles. The reason we don’t know the exact number of muscles is because there are varied opinions about what could be called a muscle. The skeletal muscles are those that could be voluntarily controlled by us and are what we use to move our body. Skeletal muscles are always in pairs, and there are 320 pairs of them. However, considering there are different ideas about how they are grouped, there is a total of anywhere from 640 to 850 skeletal muscles in the human body.

The second type of muscle, the cardiac muscle, is just a single piece of muscle. Smooth muscles are those that are found in our intestines, the urinary tract, trachea and in the linings of arteries and blood vessels, the iris of the eye, and skin. These muscles function involuntarily and exist in huge numbers. In total, it could be said that there are over 50,100,000,701 (over 50 billion) muscles in our body. (1, 2)