HUMAN BODY

How many chemicals in the human body?
24 elements are used by the body in its functions and processes. Oxygen (65%); Carbon (18.5%); Hydrogen (9.5%); Nitrogen (3.3%); Calcium (1.5%); and Phosphorous (1.0%).

How many chromosomes in the human body?
A human being normally has 46 chromosomes (23 pairs) in all but the sex cells.

How many cells in the human body?
It varies from 50 trillion to 75 trillion cells.

Endorphins defined:
These are chemical substances produced in the brain. They act as opiates, in that they interfere with the sensation of pain by binding to opiate receptor sites involved in pain perception. This action increases the threshold for pain.

Do people sleep less as they get older?
As a person ages, the time spent in sleeping changes. The following table shows how long a night’s sleep generally lasts.

Why people snore?
Snoring is produced by vibrations of the soft palate, usually caused by any condition that hinders breathing through the nose. It is more common when a person is sleeping on the back.
When a person swallows solid or liquid food, what prevents it from going down the windpipe?
Once food is chewed, voluntary muscles move it to the throat. In the pharynx (throat), automatic involuntary reflexes take over. The epiglottis closes over the larynx (voice box), which leads to the windpipe. A sphincter at the top of the esophagus relaxes, allowing the food to enter the digestive tract.

How much heat is lost through the head when a person is not wearing a hat?
Between 7% and 55% of total body heat can be lost through the head. The amount of blood going to the head is controlled by cardiac output and the harder the body works, the more blood is circulated to the head, where heat from the blood is quickly radiated away.
How many bones are in the human body?
Babies are born with about 300 to 350 bones, but many of these fuse together between birth and maturity to produce an average adult total of 206. Bone counts vary according to the method used to count them, because some systems treat as multiple bones a structure that other systems treat as a single bone with multiple parts.

How many muscles are in the human body?
There are about 656 muscles in the body, although some authorities make this figure even as high as 850 muscles.

Why do we become sore when we exercise?
If muscles are worked too hard, the cells run out of oxygen. This starts a fermentation process that produces lactic acid. The build-up of lactic acid in the muscles causes soreness and stiffness.

How many muscles does it take to produce a smile and a frown?
There are 17 smiling muscles. The average frown needs 43.

What is the largest nerve in the body?
The sciatic nerve is the largest in the human body – about as thick as a lead pencil – 0.78 inches (1.98 centimeters). It is a broad, flat nerve composed of nerve fibers, and it runs from the spinal cord down the back of each leg.

What is the largest organ in the human body?
The largest and heaviest human organ is the skin, with a total surface area of about 20 square feet (1.9 square meters).

What is the basic unit of the brain?
Neurons are the nerve cells that are the major constituent of the brain. At birth the brain has the maximum number of neurons – 20 billion to 200 billion neurons. Thousands are lost daily, never to be replaced and apparently not missed, until the cumulative loss builds up in very old age.

How does the heart work?
The heart squeezes out about 2½ ounces (70.8 grams) of blood at every beat. It daily pumps at least 2,500 gallons (9,450 liters) of blood, which weighs 20 tons (18,144 kilograms). On the average the adult heart beats 70 to 75 times a minute. At birth the heart of a baby can beat as fast as 130 times per minute.

Are the lungs identical?
No, the right lung is shorter than the left by 1 inch (2.5 centimeters); however, its total capacity is greater. The right lung has three lobes, the left lung has two. The maximum capacity of the lung averages about 6,500 cubic centimeters or about 1.7 gallons (6.4 liters).

Which gland is the largest?
The liver is the body’s largest gland and it’s the second-largest organ, after the skin.

How much blood is in the average human body?
A man weighing 154 pounds (69.8 kilograms) would have about 5.5 quarts of blood. A woman weighing 110 pounds (49.8 kilograms) would have about 3.5 quarts.

How many miles of blood vessels are contained in the body?
If they could be laid end to end, human blood vessels would extend about 60,000 miles (97,000 kilometers).

What blood types are most common in the United States?
In the world, the preponderance of one blood group varies greatly by locality. Group O is generally the most common (46%), but in some areas Group A predominates. O+ (37.4%), O- (6.6%), A+ (35.7%), A- (6.3%), B+ (8.5%), B- (1.5%), AB+ (3.4%), AB- (0.6%).

Which blood type is the rarest?
The rarest blood type is Bombay blood (subtype h-h), found only in a Czechoslovakian nurse in 1961 and in a brother and sister named Jalbert living in Massachusetts in 1968.

How much skin does an average person have?
The average human body is covered with about 20 square feet or 2 square meters of skin. Weighing almost 6 pounds (2.7 kilograms).

How many hairs does the average person have on his or her head?
The amount of hair covering varies from one individual to another. An average person has about 100,000 hairs on their scalp. Most redheads have about 90,000 hairs, blonds have about 140,000, and brunettes fall in between these two figures. Most people shed between 50 and 100 hairs daily.

Do the nails and hair of a dead person continue to grow?
Between 12 and 18 hours after death, the body begins to dry out. That causes the tips of the finger and the skin of the face to shrink, creating the illusion that the nails and hair have grown.

How fast do finger nails grow?
Healthy nails grow about 0.8 inches (2 centimeters) each year. The middle fingernail grows the fastest, because the longer the finger, the faster its mail growth. Fingernails grow four times as fast as toenails.

What are floaters that move around the eye?
Floaters are semi-transparent specks perceived to be floating in the field of vision. Some originate with red blood cells that have leaked out of the retina. The blood cells swell into spheres, some forming strings, and float around the areas of the retina. Others are shadows cast by the microscopic structures in the vitreous humor, a jellylike substructure located behind the retina.

How often does the human eye blink?
The rate of blinking varies, but on the average the eye blinks once every five seconds or 17,000 times each day or 6¼ million times a year.

20/20 vision defined:
Many people think that with 20/20 vision the eyesight is perfect, but it actually means that the eye can see clearly at 20 feet what a normal eye can see clearly at that distance. Some people can see even better – 20/15, for example. With their eagle eyes, they can view objects from 20 feet away with the same sharpness that a normal-sighted person would have to move in to 15 feet to achieve.

Why do all newborn babies have blue eyes?
The color of the iris gives the human eye its color. The amount of dark pigment, melanin, in the iris is what determines its color. In newborns the pigment is concentrated in the folds of the iris. When a baby is a few months old, the melanin moves to the surface of the iris and gives the baby his or her permanent eye color.