هل تعرف وظائف اعضاء جسمك؟ سلسلة تعريفية بدون تعقيدات اكاديمية

Quote: I Am Jean's breast I am one of the most visible signs of womanliness. But today many think of me as little more than a cosmetic appurtenance, a prop for the female ego. I am considerably more than that. My real reason for being is that I am capable of baffling, almost miraculous chemical conversions. I change blood into milk. I am Jane’s left breast (As in most women, the left is slightly larger than the right.) At one time, the very survival of the human race depended on me. For Jane’s primitive women ancestors, pregnancy was the normal state; baby followed baby. Breasts produced milk almost continuously during the childbearing years and even after those years were over. A granny could put to her breast the infant of a woman who had died, and soon there would be milk. In actuality, I am nothing more than a modified, and infinitely complex, sweat gland. For the first few days after Jane was born I functioned. Hormones from her mother stimulated me into producing a few droplets of "witch's milk". (So, when he was born, did Joe's breasts.) Then the hormones' effect wore off and I went to sleep. Until Jane was about 12 I was dormant. Then the magic wand of the hormones was waved. Her ovaries matured, and under the pod of their hormones I rted developing. (Breasts start developing among Jane’s friends as early as eight years or as late as 18 years.) Fat deposits I am mostly fat were laid down. I swelled. My nipple grew, and my areola, the halo around it, took on a heavier pigmentation. My glandular structure is by far my most interesting component I have 17 independent milk-producing units. Some women have more, some fewer. Each is shaped something like a berry bush. The berries are my tens of thousands of microscopic alveoli. The invisible droplets of milk they produce feed into the benching ducts and finally into the main stem. The 17 stems terminate in my nipple. My fat coat provides protection and insulation for these delicate structures. I also contain connective tissue to bind me together; strands of this attach to Jane’s chest wall--a kind of internal bra. I am under almost total control of hormones. Prior to menstruation, they make me swell and I become more sensitive. My really big moment came, with Jane’s first pregnancy, when hormones from the placenta--which links baby and womb awakened me. The hormone estrogen stimulated growth of my milk-duct system, and progestin prodded development an proliferation of my berry like alveoli. Blood vessels, too, expanded their networks; Blue veins on my surface became visible. My weight doubled. As birth neared, I began a big housecleaning job. Und then my alveoli had been filled with hard cellular material. It was necessary to dissolve this and make room for milk. When Jane’s baby was born, a new hormone came into production: prolactin, manufactured by the pituitary gland on the underside of Jane’s brain. This remarkable hormone starts my milk on its way. For the first four days after birth, I secreted a yellowish, watery fluid: colostrums. There was very little nourishment here for Jane’s baby. He last weight, and Jane fretted. But I knew what I was doing. The colostrum helped clear the baby’s digestive tract of mucus and other debris. Further, in my case, it was rich in antibodies to protect the newborn from diseases that might be deadly--such things as measles, whooping cough, scarlet fever, which Jane had as a child. By the fifth day, Jane’s baby had been cleansed internally and was ready for real nourishment. And I was ready with the perfect food. Initially, my partner and I produced about half a liter of milk a day. To achieve this, we needed many liters of blood circulating through us each day. From the blood my alveoli plucked glucose, or blood sugar, which my enzymes, the most talented of all chemists, changed into lactose and other sugars acceptable to the infant body. It was the same with amino acids, building block, for casein and other complex milk proteins that the baby would need for growth and tissue repair. Fats went through other transformations. From the passing blood my alveoli plucked minerals, particularly calcium for one building, and vitamins essential to health. Jane feared that her infant’s sucking might "ruin" my contours. Her fears were groundless. Nursing would have no effect whatever on stretching the ligaments of my internal bra. She noted that my areola darkened and thickened; new lubricating fat glands had grown here to prevent painful cracking of the nipple. My nipple is composed of erectile tissue. When she put her baby to breast, this tissue hardened, providing a better grip for the hungry little mouth. The sucking brought instant response, thanks to an interesting feature of my architecture. Just under my nipple the stalks of my milk trees widen to make little cisterns - instant milk to assuage hunger pangs. This tiny supply was soon exhausted. But my nipple is richly laced with sensory nerves. Via them, word was communicated to Jane’s faraway pituitary. Within 30 seconds the pituitary responded, emptying the hormone oxytocin into her bloodstream once this substance reached my alveoli, gossamer muscular walls squeezed shut, forcing milk out. From now on, the baby did not really have to suck-he could simply drink. The milk that I produced is exactly tailored to infant needs, and that is why we breasts wish women would nurse their infants if they can. Cow’s milk can be modified to approximate the needs of this stage of life. But it on never be quite the same. Nursing has other pluses. It stimulates Jane’s womb into rhythmic contraction. This helped shrink it back from an envelope large enough to enclose a baby to its normal pear size. Contractions also reduced danger of hemorrhage, and gave Jane a mild sense of sexual pleasure. At the beginning of lactation, my companion and I produced under half a liter a day-ample for a three-kilo baby. But as baby grew, so did our production--in some women up to one and a half liters a day. The composition of my milk changed, too. As more calcium was needed for building bone and blood, the calcium con- tent of my milk soared. Finally, after about two months, Jane tired of nursing, though I could have carried on for six months without her baby needing a supplementary diet, except for some vitamins and iron. With no stimulus from a hungry little mouth, my glandular components drifted off to sleep again, and I resumed my normal weight. What ailments am I prey to? Not many. Perhaps the commonest source of worry is breasts that are either too large or too small. Fortunately, Jane has neither of these problems. My usual weight is 170 grams. Although Jane is 42 years old, I am still firm and erect. Had she not been so blessed, she could have sought the help of a surgeon. But if I were too small, virtually any reputable surgeon would have refused to implant the liquid silicone Jane hears about. However, silicone implants are being used to augment breasts in appropriate patients. Correcting gross enlargement is difficult, major surgery. Then, excess fat and skin are trimmed away - often many kilos of it. The breast is reshaped, and the nipple transplanted to proper position over the fourth rib. The biggest danger I face is cancer. I am more susceptible to this disease than any other organ in Jane's body, and the most likely cause of cancer death in women. Fortunately, Jane can do a great deal to avoid this disaster. She has heard a lot about self-examination of breasts. With a little practice she can become expert at this examination, detecting lumps so small as to be missed by most doctors. She could lie down; a pillow under her left shoulder, and with the flats of three fingers on her right hand examine her left breast thoroughly. Next, she should put one pillow under her right shoulder and examine the right breast with her left hand. This should be done once a month on some set date-say, two days after menstruation ceases. Further, she should watch for any depression in either breast; cancer tissue, because of its effect on other structures of the breast, can cause a slight hollowing. Any twisting of my nipple from normal position is also signal to watch for. And any abnormal discharge from the nipple should be considered something to be checked into. Should Jane detect a lump, she should not panic. Chances that it is cancerous are less than one in three. But she should get to a doctor instantly-not wait, as some women do. If cancer is present and detected early, there are several possible operations that offer a survival rate of at least five years for 85 percent of patients Jane will soon be going through menopause. Then the things that happened to me in puberty will be reversed. I will lose some but not all of my fat deposits. My glandular structure will wither, and nearly disappear. I will shrink. That about wraps up my story. I was put on earth for an active, productive life, and it makes me rather sad whenever I am considered primarily a decoration--however greatly admired. So I am pleased to report that there is a strong revival of interest in breast-feeding on the part of many of today's young mothers. More power to them!

Quote: One of my major tasks is cleaning and conditioning the air for Joe's lungs. Each day I must process about 500 cubic feet of air--a small roomful. Joe may be skiing on a frigid, dry day, but his lungs are not interested in dry, zero air. They want about what one would find on a humid summer day--75 to 80 percent saturated, temperature in the 90s. They demand air almost totally free of bacteria, and cleansed of grit, smoke and other irritants. The air conditioner for a medium-sized mom is as large as a small trunk. My air-conditioning system is compressed into a tiny area only a few centimeters long. For the humidifying job I secrete about a liter of moisture a day. Mostly this is sticky mucus, produced by the spongy, red membrane that lines my passages. While the rough cleaning job is done by hairs in Joe's nostrils, it is the mucus that does the major work, acting as a kind of flypaper to trap bacteria and particles that get past the hairs. Naturally, I cannot permit this film of mucus to stagnate. In a few hours there would be total pollution. So every 20 minutes I produce a clean new mucous blanket. To remove the old mucus, I have an army of microscopic brooms--cilia. These minute hairs rapidly whip the film back to the throat for swallowing and then slowly settle back to their original positions. Strong stomach acid destroys most swallowed bacteria. My tireless little cilia make about ten sweeping stroke a second. Joe, of course, is unaware of this activity, which goes on day and night. But on a cold day he becomes aware of it, since cold partially paralyses my cilia and causes overproduction of mucus. Then, instead of being swept back to the throat, the moisture dribbles out the front.

(عدل بواسطة احمد سيد احمد on 09-21-2014, 11:43 AM)
(عدل بواسطة احمد سيد احمد on 09-21-2014, 06:57 PM)