Throughout your body, intricate delivery systems transport nutrients
and information for survival and action.Your body is an extraordinary organism, an electrical, chemical, and
mechanical marvel.
Your body is an extraordinary organism, an electrical, chemical, and
mechanical marvel. Its trillions of individual cells array themselves
in complex combinations to produce the physical wonder that is at once
uniquely you and at the same time like every other human being. Bodies
have more exciting bits and carry out more strenuous tasks than you’ve
probably ever imagined. For instance, although you’ve not likely
counted them, five million hairs sprout from the 36 to 60 square feet
(3.3 to 5.6 m²) of durable, waterproof covering you know as skin.
Beneath this living overcoat are three types of muscles, your “movers
and shakers,” more than 600 in all, which connect to, and are supported
by, the 206 bones forming your skeleton. This lightweight framework is
not only flexible, but also incredibly strong. Your thigh bones, for
example, are pound for pound stronger than reinforced concrete.
Throughout your body, intricate delivery systems transport nutrients
and information for survival and action. Every day your heart beats
100,000 times, pumping 300 quarts (273 l) of blood per hour through
90,000 miles (145,000 km) of blood vessels, keeping you warm,
nourishing your cells, removing waste, and destroying harmful
substances. Your internal communication network, the nervous system,
controls and coordinates most of your body’s activities with electrical
impulses that travel at speeds of up to 250 miles per hour (400 km/h).
Much slower and longer lasting are the chemical reactions governed by
your hormonal system which affect when and how you grow, the onset of
puberty, menopause, andropause, the density of your bones, and the
intensity of your sex drive.
Not only does your body keep you
functioning fairly smoothly throughout your allotted lifespan but it
also carries within the keys to ensure survival of future generations.
At birth a woman’s ovaries already cradle up to two million eggs, any
of which can mature to mate with one of the more than several hundred
million sperm a typical man produces daily. The result of this
passionate joining is a zygote that, although smaller than the head of
a pin, contains every bit of the genetic information needed to create a
new, one-of-a-kind human being.
All of this boisterous activity
requires energy derived from oxygen and food. In a lifetime, the
average person will breathe about 75 million gallons (280 million
litres) of air and consume up to 50 tons (45 tonnes) of food. Built-in
taste and aroma sensors entice you to feed your body. Nine thousand
taste buds adorn your tongue, beguiling you with five distinct flavors
and their thousands of combined permutations. The ten million olfactory
receptacles in your nose can distinguish 10,000 separate scents.
Your body is a sensory cornucopia. In addition to taste and smell,
sight, sound, and touch contribute to the wealth of sensate experience
available to you. Your eyes can identify ten million different colors.
Your ears can hear more than 400,000 unique sounds. Your skin has
thousands of miniscule, highly sensitive receptors that make it a
head-to-toe communication source more eloquent than words.
