There are five quarts of blood in the adult human
body, and the entire blood supply makes a complete circuit of the
heart, lungs, blood vessels, and back to the heart every 60
seconds.
There are four major blood groups, O, A, B and AB. Nearly half
the population is Type O, and they can donate blood to people with
all other blood groups but can only receive group O blood. The
rarest blood type, AB, is present in about 4 percent of the
population. These people can receive all types of blood.
There are about 50 to 75 trillion cells in the body, about half
of these are red blood cells. An individual red blood cell contains
about 250 million molecules of the iron-containing protein called
hemoglobin, which is capable of picking up four molecules of oxygen.
As a result, a single red blood cell can deliver up to 1 billion
molecules of oxygen.
Laid end-to-end, the arteries, capillaries and veins would
stretch for about 60,000 miles in the average child and would be
about 100,000 miles in an adult - enough to wrap around the world
nearly four times.
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At about 11 inches long and nearly 6 inches wide,
the lungs are your largest organ but together only weigh about
two pounds. They contain about 1 1/2 gallons of air.
The inside of your lungs is covered with 600 million
tissue-thin sacks called alveoli. Oxygen passes easily through
the 1/6,000th-of-an-inch-thick walls of the alveoli into the
capillaries that surround them. Stretched out flat, the
alveoli would cover a tennis court.
Each day, the average adult inhales about 4,250 gallons of
air, containing about 40 billion trillion molecules of oxygen.
Along with it comes about 20 billion particles of dirt and
other foreign matter.
When you cough, the air rushing out of your lungs hits
speeds of up to 600 mph - close to the speed of sound.
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The nose traps and filters up to 70
percent of the 20 billion dust particles that we inhale
each day. It also changes the temperature of the
incoming air to between 77 and 95 degrees F and
regulates humidity to between 35 percent and 80
percent.
Each year, people living in the United States catch
almost 1 billion colds. That's as many as six colds per
person per year. The reason: There are 110 different
rhinoviruses, the most common cold-causer, plus about 90
other kinds of cold-causing viruses.
The fastest sneeze ever recorded was clocked at just
over 100 mph.
Your nose contains 20 types of odor-detecting cells.
With these, you can distinguish up to 10,000 different
smells.
The tongue has 10,000 taste buds, but they can detect
only four basic taste sensations - sweet, sour, bitter
and salty.
The mouth produces about a quart of saliva each
day.
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Despite its diminutive name, the
small intestine is actually the longest part of
the digestive tract, stretching some 22 feet in
length. The large intestine, however, is just 5
feet long.
When full, the stomach holds between a quart
and a quart and a half of food and liquids. And it
takes about four hours for the stomach to fully
digest a meal and pass it along to the small
intestine. Food passes through the small intestine
in just two hours, zipping along at 0.002 mph.
Inside the large intestine, it takes about 14
hours, traveling at a more leisurely rate of
0.00007 mph.
The inside of the small intestine, which
absorbs the digested proteins, sugars and fats
from food, is covered with a fur-like layer of
tiny projections called villi and microvilli. This
food-absorbing "fur" boosts the surface area by
600 times, compared to what a smooth interior
surface would provide. If the interior of the
small intestine were smooth, it would have to be 2
1/4 miles long to provide the same food absorbing
power as its present 22 feet.
Each day, about three gallons of food, liquids
and digestive juices gurgles its way through the
digestive tract. Only about half a cup emerges as
feces.
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Most of your body is muscle. There
are 650 muscles, and they make up between 40
percent and 50 percent of the total body weight
in men and 30 percent to 40 percent of women's
weight.
The biggest muscle in the body is the gluteus
maximus - the butt. Each of the two cheeky
muscles tips the scales at about two pounds (not
including the overlying fat layer). The tiniest
muscle, the stapedius of the middle ear, is just
one-fifth of an inch long.
Most cells in the body are microscopic in
size, but muscle cells, also called muscle
fibers, can be up to 1 foot long and visible to
the naked eye
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The adult brain contains 100
billion neurons - more than the number of stars
in the Milky Way galaxy. Each of the brain's
neurons connects to as many as 100,000 other
neurons.
At three pounds, the brain makes up only 2
percent of total body weight but consumes 25
percent of the energy used by the entire
body.
Nerve impulses are not electrical; instead,
they are passed along by rapid chemical changes
in nerve fibers. While the light from your
computer screen streams at you at 186,000 miles
per second, the nerve impulses carrying images
from your eyes to your brain, for instance,
saunter along at a mere 250 mph.
When you're born, you have 300
bones. But an adult has only 206 bones. What
happens? Many bones, such as those that make up
the skull and spine, fuse together as we
grow.
Most people have 12 pairs of ribs, but about
5 percent of the population has an extra
pair.
The tiniest bone in the body is the stirrup
bone in the ear, which is just one-eighth of an
inch long. The longest bone is the femur, which
varies in length from person to person but is
about one-fourth of a person's overall
height.
Hand over foot: There are 54 bones in all in
your wrists, hands and fingers but only 52 in
both feet, ankles and toes.
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