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Wonderfully Made Humans
In order to transmit information from one part of the body to the other, the body makes use of specialized cell known as neurons or nerve cells which communicate with one another by electrical or chemical means. There are an estimated 13 billion neurons in the human body.
The Psalmist declares that he offers praises to God because he is fearfully and wonderfully made (Psalm 139: 14; New International Version); another rendition (New Living Translation) puts it this way: Thank you for making me so wonderfully complex! Whichever version one chooses to read, the simple fact is that the human body is a phenomenal piece of work, the most complex that is known to man; and the more that we learn about it, the more wonderfully complex it shows itself to be.
Stages in embryo development
Starting from the point of conception, every embryo is superficially identical; only when the embryo reaches the age of 8-10 weeks does the differentiation, whether it will grow to be male or female, begin to manifest. Whether an embryo turns out to be male or female is a factor that is determined by the chromosomes that the embryo has inherited from its parents.
Chromosomes are rod-like structures that are found in the nucleus of a cell, and they are made up of continuous strands of deoxyribonucleic acid, DNA, and they are the means by which hereditary information is passed on from one generation to another. The chromosomal pattern that an embryo inherits from its parents that determine the sex of the ensuing baby. This pattern is defined by the letters “X” and “Y”, and each chromosome contains at least two of the letters. An “XX” pattern denotes a female whilst an “XY” pattern denotes a male. Each parent contributes one letter from his or her chromosomal base to the makeup of the child; thus, mothers, being “XX”, contribute an “X” whilst fathers, being “XY”, contributes either an “X” or a “Y”.
The father’s contribution is the determining factor whether the ensuing child is male or female, for it is the chromosomal pattern that determines whether testes or ovaries will develop. Where the pattern is “XY”, the presence of the “Y” chromosome causes the secretion of the hormones testosterone and AMH (anti-Müllerian hormone) which hormones suppress further development of the Müllerian ducts, named for the German physiologist Johannes Peter Müller (1801-1858), which would otherwise develop into the female reproductive organs, i.e. the Fallopian tubes, the uterus and the vagina. Simultaneously, the “Y” chromosome stimulates the Wolffian ducts, named for the German-born embryologist Kasper Freidrich Wolff (1733-1794), which ducts go on to develop into the male reproductive organs.
The Human Brain
Of all the organs that make up the human body, the brain is by far the most important, and it can be likened to the Central Command Center of a large army. Although the brain constitutes just about 3% of the total average adult body weight, its importance is shown by the amount of energy that it consumes. Using 20% of all the oxygen that the body uses, 20% of all the calories the body consumes in food, and 15% of the entire blood supply, the brain is a veritable energy guzzler; but it’s all in a good cause: keeping all else going that keeps the body going.
Pump and Pipelines
But if the brain acts as Central Command, there are other organs that also have major parts to play in keeping the body shipshape. The heart, that workaday pump, it is that has the duty of keeping the brain supplied with the enormous amounts of blood that it requires; it is also the heart’s duty to keep every other part of the body supplied with blood. The heart does its job in exemplary fashion; beating more than 2 billion times in an average lifespan, the heart pumps some half billion liters (110 million gallons) of blood in that time. Even when a person is asleep and the heart’s workload is reduced, this phenomenal pump continues to pump some 350 liters (75 gallons) of blood each and every hour; enough blood, if motor cars were powered by blood, to fill the gas tank of an average car every 7 or so minutes! In going about its work, the human heart generates enough power, each and every day, to lift an average motor car some 15 meters (50 feet) off the ground.
Of course, it would be absolutely useless, all this pumping, if there were not an adequate delivery system, and the human body is provided with a more than adequate one. 100,000 kilometers (60,000 miles) of arteries (conveying the blood from the heart to the parts that require it), veins (conveying the blood back to the heart after use) and subsidiary blood vessels provide a more than first class delivery system. What this combination of pump and pipelines means is that the body’s entire blood supply, some 4.5 liters (8 pints) on average, washes through the lungs about once a minute - almost 1,500 times every day.
The Human Lungs
The lungs! It is the function of the lungs to keep the body’s blood supply in a fit state for the body’s needs. As blood moves about the body, the various parts of the body extract the oxygen and nutrients that the require from it, at the same time disposing of the waste products that come from their utilization of these supplies into the blood. If the levels of waste in the blood become too high, then the whole body is threatened; the waste products that enter the blood stream must be removed promptly and efficiently, and the lungs are a part of the cleaning facilities with which the body is provided. Gaseous waste, mostly in the form of carbon dioxide resulting from the body’s utilization of oxygen, is filtered out in the lungs and replaced with the healthful oxygen that the body depends upon. In order to do this, the lungs employ some 300 billion, yes, 300 billion, or so capillaries, tiny blood vessels which, if laid out, end to end, would stretch some 2,400 kilometers (1,500 miles).
But although blood is absolutely vital for life, not every part of the body is actually connected to the blood supply. There is a portion of the inner ear whose work it is to convert sound vibrations to to nerve impulses; the cells in this part of the body are not connected to the blood supply, instead they are fed by a constant non-blood fluid bath. The reason is simple: if the blood coursing through the rest of the body went there, the nerves which transfer sound vibrations would be deafened by the body’s pulse.
Bones of the human hand
Bones of the human foot.
Stronger than concrete!
The entire human body is held up by a skeletal structure that is made up mainly of bone. Adults have a total of 206 bones in their bodies, about half of which are to be found in the hands and feet. 206 might seem a large number, but between birth and adulthood the numbers of bones in the body has actually reduced! At birth, humans have 300 bones, of which 94 fuse together during childhood.
The bony skeletal structure upon which the rest of the body depends is certainly up to the task to which it is called. Human bone is extremely strong; as strong as granite when it comes to supporting weight. A block of human bone the size of an average matchbox can support up to 9 tonnes; a similar block made of concrete supports just about 2.5 tonnes!
A Little Waste-disposal
Whilst the lungs are busy cleaning out the gaseous waste from the bloodstream, there are other wastes that have entered into the bloodstream. These wastes come as a result of the process of digestion, which separates the nutrients that the body requires from the foods consumed from the waste that it does not. The digestive process is facilitated in the stomach by acids which break down the food we consume so that nutrients can be extracted. In fact, the acids that aid digestion are so concentrated that they can dissolve zinc! The reason why the acids do not eat through the body tissues is simply that the cells that make up the lining of the stomach are renewed with such rapidity, some half million cells per minute and the entire stomach lining every 3 or so days, that under normal circumstances the acids never have the chance to eat through the lining!
Liquid waste is handled by the kidneys. Humans are born with two, but so efficient are these organs that one can live a perfectly normal life on just one. Each kidney comes equipped with about a million individual filters and, between them, both kidneys filter an average of 1.3 liters (2.2 pints) of blood per minute and removing an average of 1.4 liters (2.5 pints) of waste per day in the form of urine.
Providing a cover for all these intricate working parts is the body’s largest organ, the skin. Ranging from an average size of 1.6 m2 (17 square feet) for women to about 1.9 m2 (20 square feet) for men the skin is constantly being denuded and replaced with new tissue. On average, the entire skin is replaced about 7 times a year, about once every 50 days. In the course of a lifetime, one can expect to have shed some 18 kilograms (40 lbs) of skin; not a bad way to loose weight!
Then, of course, there are the muscles, of which the heart is one. Even setting aside the heart, it is difficult to imagine a human race without muscles. There are 639 named muscles in the human body the largest of which is the gluteus maximus, the buttock muscle which helps to keep us upright and fights against gravity when we climb, then there is the sartorius, the thigh muscle, and longest muscle in the body, that allows humans to sit in a cross-legged position. When it comes to raw power, the strongest muscle in the body is the masseter, the jaw muscle that allows us to chew; the masseter can cause the incisors to bring to bear a force equivalent to about 25kilograms (55 lbs) and for the molars a force equivalent to about 90 kilograms (200 lbs). The smallest muscle in the human body is the stapedius, a mere 1mm (0.05 in) length, which controls the stapes, a small bone located in the middle ear.
This brings us neatly to the eyes. The muscles that control the focusing function in our eyes are the most active muscles in the body, bar none, moving more than 100,000 times each day. In order to exercise the leg muscles to a similar degree, one would have to take an 80 kilometer (50 mile) walk every single day! But they do have to do all that work; if not, how would we be able to put the 130 million rod cells (for black and white vision) and 7 million cone cells (for color vision) that are set upon our 650mm2 (1 square inch) retina to use to enjoy the beauty that surrounds us?
But, what makes it all up?
Good question. Well,................................water; your simple, everyday, ever friendly H2O! The body of an average adult is 65% composed of water by weight. Then, in addition to the water, there is a bit of this and a bit of that, some bits more and some bits less. There is as much carbon as one would get from about 12 kilograms (26.5 lbs) of coke; enough limestone to whitewash a small shed; enough phosphorus to make somewhat more than 2,000 match heads; a spoonful of sulfur; some iron, enough to make a 25mm (1 in) nail; and about 30 grams (1 oz) of sundry other metals. Like I said, a bit of this and a bit of that. I give you Psalm 139: 14.