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With each heartbeat, blood is sent throughout our bodies, carrying oxygen and nutrients to every cell. Each day, 2,000 gallons of blood travel many times through about 60,000 miles of blood vessels that branch and cross, linking the cells of our organs and body parts.
About the Heart and Circulatory System
The circulatory system is composed of the heart and blood vessels, including arteries, veins, and capillaries. Our bodies actually have two circulatory systems: The pulmonary circulation is a short loop from the heart to the lungs and back again, and the systemic circulation (the system we usually think of as our circulatory system) sends blood from the heart to all the other parts of our bodies and back again.
The heart is the key organ in the circulatory system. As a hollow, muscular pump, its main function is to propel blood throughout the body. It usually beats from 60 to 100 times per minute, but can go much faster when necessary. It beats about 100,000 times a day, more than 30 million times per year, and about 2.5 billion times in a 70-year lifetime.
The heart gets messages from the body that tell it when to pump more or less blood depending on an individual's needs. When we're sleeping, it pumps just enough to provide for the lower amounts of oxygen needed by our bodies at rest. When we're exercising or frightened, the heart pumps faster to increase the delivery of oxygen.
The heart has four chambers that are enclosed by thick, muscular walls. It lies between the lungs and just to the left of the middle of the chest cavity. The bottom part of the heart is divided into two chambers called the right and left ventricles, which pump blood out of the heart. A wall called the interventricular septum divides the ventricles.
The upper part of the heart is made up of the other two chambers of the heart, the right and left atria. The right and left atria receive the blood entering the heart. A wall called the interatrial septum divides the right and left atria, which are separated from the ventricles by the atrioventricular valves. The tricuspid valve separates the right atrium from the right ventricle, and the mitral valve separates the left atrium and the left ventricle.
Two other cardiac valves separate the ventricles and the large blood vessels that carry blood leaving the heart. These are the pulmonic valve, which separates the right ventricle from the pulmonary artery leading to the lungs, and the aortic valve, which separates the left ventricle from the aorta, the body's largest blood vessel.
Arteries carry blood away from the heart. They are the thickest blood vessels, with muscular walls that contract to keep the blood moving away from the heart and through the body. In the systemic circulation, oxygen-rich blood is pumped from the heart into the aorta. This huge artery curves up and back from the left ventricle, then heads down in front of the spinal column into the abdomen. Two coronary arteries branch off at the beginning of the aorta and divide into a network of smaller arteries that provide oxygen and nourishment to the muscles of the heart.
Unlike the aorta, the body's other main artery, the pulmonary artery, carries oxygen-poor blood. From the right ventricle, the pulmonary artery divides into right and left branches, on the way to the lungs where blood picks up oxygen.
Arterial walls have three layers:
1. The endothelium is on the inside and provides a smooth lining for blood to flow over as it moves through the artery.
2. The media is the middle part of the artery, made up of a layer of muscle and elastic tissue.
3. The adventitia is the tough covering that protects the outside of the artery.
As they get farther from the heart, the arteries branch out into arterioles, which are smaller and less elastic.
Veins carry blood back to the heart. They're not as muscular as arteries, but they contain valves that prevent blood from flowing backward. Veins have the same three layers that arteries do, but are thinner and less flexible. The two largest veins are the superior and inferior vena cavae. The terms superior and inferior don't mean that one vein is better than the other, but that they're located above and below the heart.
A network of tiny capillaries connects the arteries and veins. Though tiny, the capillaries are one of the most important parts of the circulatory system because it's through them that nutrients and oxygen are delivered to the cells. In addition, waste products such as carbon dioxide are also removed by the capillaries.
What the Heart and Circulatory System Do
The circulatory system works closely with other systems in our bodies. It supplies oxygen and nutrients to our bodies by working with the respiratory system. At the same time, the circulatory system helps carry waste and carbon dioxide out of the body.
Hormones — produced by the endocrine system — are also transported through the blood in the circulatory system. As the body's chemical messengers, hormones transfer information and instructions from one set of cells to another. For example, one of the hormones produced by the heart helps control the kidneys' release of salt from the body.
One complete heartbeat makes up a cardiac cycle, which consists of two phases:
1. In the first phase, the ventricles contract (this is called systole), sending blood into the pulmonary and systemic circulation. To prevent the flow of blood backwards into the atria during systole, the atrioventricular valves close, creating the first sound (the lub). When the ventricles finish contracting, the aortic and pulmonary valves close to prevent blood from flowing back into the ventricles. This is what creates the second sound (the dub).
2. Then the ventricles relax (this is called diastole) and fill with blood from the atria, which makes up the second phase of the cardiac cycle.
A unique electrical conduction system in the heart causes it to beat in its regular rhythm. The sinoatrial or SA node, a small area of tissue in the wall of the right atrium, sends out an electrical signal to start the contracting of the heart muscle. This node is called the pacemaker of the heart because it sets the rate of the heartbeat and causes the rest of the heart to contract in its rhythm.
These electrical impulses cause the atria to contract first, and then travel down to the atrioventricular or AV node, which acts as a kind of relay station. From here the electrical signal travels through the right and left ventricles, causing them to contract and forcing blood out into the major arteries.
In the systemic circulation, blood travels out of the left ventricle, to the aorta, to every organ and tissue in the body, and then back to the right atrium. The arteries, capillaries, and veins of the systemic circulatory system are the channels through which this long journey takes place.
Once in the arteries, blood flows to smaller arterioles and then to capillaries. While in the capillaries, the bloodstream delivers oxygen and nutrients to the body's cells and picks up waste materials. Blood then goes back through the capillaries into venules, and then to larger veins until it reaches the vena cavae.
Blood from the head and arms returns to the heart through the superior vena cava, and blood from the lower parts of the body returns through the inferior vena cava. Both vena cavae deliver this oxygen-depleted blood into the right atrium. From here the blood exits to fill the right ventricle, ready to be pumped into the pulmonary circulation for more oxygen.
In the pulmonary circulation, blood low in oxygen but high in carbon dioxide is pumped out the right ventricle into the pulmonary artery, which branches off in two directions. The right branch goes to the right lung, and vice versa.
In the lungs, the branches divide further into capillaries. Blood flows more slowly through these tiny vessels, allowing time for gases to be exchanged between the capillary walls and the millions of alveoli, the tiny air sacs in the lungs.
During the process called oxygenation, oxygen is taken up by the bloodstream. Oxygen locks onto a molecule called hemoglobin in the red blood cells. The newly oxygenated blood leaves the lungs through the pulmonary veins and heads back to the heart. It enters the heart in the left atrium, then fills the left ventricle so it can be pumped into the systemic circulation.
Problems of the Heart and Circulatory System
Problems with the cardiovascular system are common — more than 64 million Americans have some type of cardiac problem. But cardiovascular problems don't just affect older people — many heart and circulatory system problems affect children and teens, too.
Heart and circulatory problems are grouped into two categories: congenital (problems present at birth) and acquired (problems developed some time after birth).
Congenital heart defects. These abnormalities in the heart's structure are present at birth. Approximately 8 out of every 1,000 newborns have congenital heart defects ranging from mild to severe. These defects occur while the fetus is developing in the mother's uterus and it's not usually known why they occur. Some congenital heart defects are caused by genetic disorders, but most are not. What all congenital heart defects have in common, however, is that they involve abnormal or incomplete development of the heart.
A common sign of a congenital heart defect is a heart murmur — an abnormal sound (like a blowing or whooshing sound) that's heard when listening to the heart. Usually a heart murmur is detected by a doctor who's listening to the heart with a stethoscope during a routine exam. Murmurs are very common in children and can be caused by congenital heart defects or other heart conditions.
Arrhythmia. Cardiac arrhythmias, also called dysrhythmias or rhythm disorders, are problems in the rhythm of the heartbeat. They may be caused by a congenital heart defect or they may be acquired later. An arrhythmia may cause the heart's rhythm to be irregular, abnormally fast, or abnormally slow. Arrhythmias can occur at any age and may be discovered during a routine physical examination. Depending on the type of rhythm disorder, an arrhythmia may be treated with medication, surgery, or pacemakers.
Cardiomyopathy. This chronic disease causes the heart muscle (the myocardium) to become weakened. Usually, it first affects the lower chambers of the heart, the ventricles, and then progresses and damages the muscle cells and even the tissues surrounding the heart. In its most severe forms, it can lead to heart failure and even death. Cardiomyopathy is the #1 reason for heart transplants in children.
Coronary artery disease. The most common heart disorder in adults, coronary artery disease is caused by atherosclerosis. Deposits of fat, calcium, and dead cells, called atherosclerotic plaques, form on the inner walls of the coronary arteries (the blood vessels that supply the heart) and interfere with the smooth flow of blood. Blood flow to the heart muscle may even stop if a thrombus, or clot, forms in a coronary vessel, which may cause a heart attack. In a heart attack (or myocardial infarction), the heart muscle becomes damaged by lack of oxygen, and unless blood flow returns within minutes, muscle damage increases and the heart's ability to pump blood is compromised. If the clot can be dissolved within a few hours, damage to the heart can be reduced. Heart attacks are rare in kids and teens.
Hypercholesterolemia (high cholesterol). Cholesterol is a waxy substance that's found in the body's cells, in the blood, and in some foods. Having too much cholesterol in the blood, also known as hypercholesterolemia, is a major risk factor for heart disease and can lead to a heart attack.
Cholesterol is carried in the bloodstream by lipoproteins. Two kinds — low-density lipoproteins (LDL) and high-density lipoproteins (HDL) — are the most important. High levels of LDL cholesterol (the bad cholesterol) increase a person's risk for heart disease and stroke, whereas high levels of HDL cholesterol (the good cholesterol) can protect against these.
A blood test can indicate if someone's cholesterol is too high. A child's cholesterol level is borderline if it's 170 to 199 mg/dL, and it's considered high if it's above 200 mg/dL.
About 10% of teens between 12 and 19 have high cholesterol levels that put them at increased risk of cardiovascular disease.
High blood pressure (hypertension). Over time, high blood pressure can damage the heart, arteries, and other body organs. Symptoms can include headache, nosebleeds, dizziness, and lightheadedness. Infants, kids, and teens can have high blood pressure, which may be caused by genetic factors, excess body weight, diet, lack of exercise, and diseases such as heart disease or kidney disease.
Kawasaki disease. Also known as mucocutaneous lymph node syndrome, Kawasaki disease affects the mucous membranes (the lining of the mouth and breathing passages), the skin, and the lymph nodes (part of the immune system). It can also lead to vasculitis, an inflammation of the blood vessels. This can affect all major arteries in the body — including the coronary arteries. It can also cause inflammation of the heart muscle, called myocarditis. When coronary arteries become inflamed, a child can develop aneurysms, which are weakened and bulging spots on the walls of arteries. This increases the risk of a blood clot forming in this weakened area, which can block the artery, possibly leading to a heart attack. In addition to the coronary arteries, the heart muscle, lining, valves, or the outer membrane that surrounds the heart can become inflamed. Arrhythmias or abnormal functioning of some heart valves can occur. Kawasaki disease has surpassed rheumatic fever as the leading cause of acquired heart disease in children in the United States.
Rheumatic heart disease. Usually the complication of an untreated strep throat infection, rheumatic fever can lead to permanent heart damage and even death. Most common in kids between 5 and 15 years of age, it begins when antibodies the body produces to fight the strep infection begin to attack other parts of the body. They react to tissues in the heart valves as though they were the strep bacteria and cause the heart valves to thicken and scar. Inflammation and weakening of the heart muscle may also occur. Usually, when strep throat infections are promptly treated with antibiotics, this condition can be avoided.
Stroke. Strokes occur when the blood supply to the brain is cut off or when a blood vessel in the brain bursts and spills blood into an area of the brain, causing damage to brain cells. Children or infants who have experienced stroke may be suddenly numb or weak, especially on one side of the body, and they may experience a sudden severe headache, nausea or vomiting, and difficulty seeing, speaking, walking, or moving. During childhood, strokes are rare.
Getting plenty of exercise, eating a nutritious diet, maintaining a healthy weight, and getting regular medical checkups are the best ways to help keep the heart healthy and avoid long-term problems like high blood pressure, high cholesterol, and heart disease.
"I pray that this article empowers you to Get A L.I.F.E."
Friday, May 27, 2011
Saturday, May 21, 2011
The Female Reproductive System
About Human Reproduction
All living things reproduce. Reproduction — the process by which organisms make more organisms like themselves — is one of the things that sets living things apart from nonliving matter. But even though the reproductive system is essential to keeping a species alive, unlike other body systems, it's not essential to keeping an individual alive.
In the human reproductive process, two kinds of sex cells, or gametes, are involved. The male gamete, or sperm, and the female gamete, the egg or ovum, meet in the female's reproductive system to create a new individual.
Both the male and female reproductive systems are essential for reproduction. The female needs a male to fertilize her egg, even though it is she who carries offspring through pregnancy and childbirth.
Humans, like other organisms, pass certain characteristics of themselves to the next generation through their genes, the special carriers of human traits. The genes that parents pass along are what make their children similar to others in their family, but also what make each child unique. These genes come from the male's sperm and the female's egg.
Most species have two sexes: male and female. Each sex has its own unique reproductive system. They are different in shape and structure, but both are specifically designed to produce, nourish, and transport either the egg or sperm.
Components of the Female Reproductive System
Unlike the male, the human female has a reproductive system located entirely in the pelvis. The external part of the female reproductive organs is called the vulva, which means covering. Located between the legs, the vulva covers the opening to the vagina and other reproductive organs located inside the body.
The fleshy area located just above the top of the vaginal opening is called the mons pubis. Two pairs of skin flaps called the labia (which means lips) surround the vaginal opening. The clitoris, a small sensory organ, is located toward the front of the vulva where the folds of the labia join. Between the labia are openings to the urethra (the canal that carries urine from the bladder to the outside of the body) and vagina. Once girls become sexually mature, the outer labia and the mons pubis are covered by pubic hair.
A female's internal reproductive organs are the vagina, uterus, fallopian tubes, and ovaries.
The vagina is a muscular, hollow tube that extends from the vaginal opening to the uterus. The vagina is about 3 to 5 inches (8 to 12 centimeters) long in a grown woman. Because it has muscular walls, it can expand and contract. This ability to become wider or narrower allows the vagina to accommodate something as slim as a tampon and as wide as a baby. The vagina's muscular walls are lined with mucous membranes, which keep it protected and moist.
The vagina serves three purposes:
1. It's where the penis is inserted during sexual intercourse.
2. It's the pathway that a baby takes out of a woman's body during childbirth, called the birth canal.
3. It provides the route for the menstrual blood (the period) to leave the body from the uterus.
A thin sheet of tissue with one or more holes in it called the hymen partially covers the opening of the vagina. Hymens are often different from female to female. Most women find their hymens have stretched or torn after their first sexual experience, and the hymen may bleed a little (this usually causes little, if any, pain). Some women who have had sex don't have much of a change in their hymens, though.
The vagina connects with the uterus, or womb, at the cervix (which means neck). The cervix has strong, thick walls. The opening of the cervix is very small (no wider than a straw), which is why a tampon can never get lost inside a girl's body. During childbirth, the cervix can expand to allow a baby to pass.
The uterus is shaped like an upside-down pear, with a thick lining and muscular walls — in fact, the uterus contains some of the strongest muscles in the female body. These muscles are able to expand and contract to accommodate a growing fetus and then help push the baby out during labor. When a woman isn't pregnant, the uterus is only about 3 inches (7.5 centimeters) long and 2 inches (5 centimeters) wide.
At the upper corners of the uterus, the fallopian tubes connect the uterus to the ovaries. The ovaries are two oval-shaped organs that lie to the upper right and left of the uterus. They produce, store, and release eggs into the fallopian tubes in the process called ovulation. Each ovary measures about 1½ to 2 inches (4 to 5 centimeters) in a grown woman.
There are two fallopian tubes, each attached to a side of the uterus. The fallopian tubes are about 4 inches (10 centimeters) long and about as wide as a piece of spaghetti. Within each tube is a tiny passageway no wider than a sewing needle. At the other end of each fallopian tube is a fringed area that looks like a funnel. This fringed area wraps around the ovary but doesn't completely attach to it. When an egg pops out of an ovary, it enters the fallopian tube. Once the egg is in the fallopian tube, tiny hairs in the tube's lining help push it down the narrow passageway toward the uterus.
The ovaries are also part of the endocrine system because they produce female sex hormones such as estrogen and progesterone.
What the Female Reproductive System Does
The female reproductive system enables a woman to:
produce eggs (ova)
have sexual intercourse
protect and nourish the fertilized egg until it is fully developed
give birth
Sexual reproduction couldn't happen without the sexual organs called the gonads. Although most people think of the gonads as the male testicles, both sexes actually have gonads: In females the gonads are the ovaries. The female gonads produce female gametes (eggs); the male gonads produce male gametes (sperm). After an egg is fertilized by the sperm, the fertilized egg is called the zygote.
When a baby girl is born, her ovaries contain hundreds of thousands of eggs, which remain inactive until puberty begins. At puberty, the pituitary gland, located in the central part of the brain, starts making hormones that stimulate the ovaries to produce female sex hormones, including estrogen. The secretion of these hormones causes a girl to develop into a sexually mature woman.
Toward the end of puberty, girls begin to release eggs as part of a monthly period called the menstrual cycle. Approximately once a month, during ovulation, an ovary sends a tiny egg into one of the fallopian tubes.
Unless the egg is fertilized by a sperm while in the fallopian tube, the egg dries up and leaves the body about 2 weeks later through the uterus — this is menstruation. Blood and tissues from the inner lining of the uterus combine to form the menstrual flow, which in most girls lasts from 3 to 5 days. A girl's first period is called menarche.
It's common for women and girls to experience some discomfort in the days leading to their periods. Premenstrual syndrome (PMS) includes both physical and emotional symptoms that many girls and women get right before their periods, such as acne, bloating, fatigue, backaches, sore breasts, headaches, constipation, diarrhea, food cravings, depression, irritability, or difficulty concentrating or handling stress. PMS is usually at its worst during the 7 days before a girl's period starts and disappears once it begins.
Many girls also experience abdominal cramps during the first few days of their periods caused by prostaglandins, chemicals in the body that make the smooth muscle in the uterus contract. These involuntary contractions can be either dull or sharp and intense.
It can take up to 2 years from menarche for a girl's body to develop a regular menstrual cycle. During that time, her body is adjusting to the hormones puberty brings. On average, the monthly cycle for an adult woman is 28 days, but the range is from 23 to 35 days.
Fertilization
If a female and male have sex within several days of the female's ovulation, fertilization can occur. When the male ejaculates (when semen leaves a male's penis), between 0.05 and 0.2 fluid ounces (1.5 to 6.0 milliliters) of semen is deposited into the vagina. Between 75 and 900 million sperm are in this small amount of semen, and they "swim" up from the vagina through the cervix and uterus to meet the egg in the fallopian tube. It takes only one sperm to fertilize the egg.
About a week after the sperm fertilizes the egg, the fertilized egg (zygote) has become a multicelled blastocyst. A blastocyst is about the size of a pinhead, and it's a hollow ball of cells with fluid inside. The blastocyst burrows itself into the lining of the uterus, called the endometrium. The hormone estrogen causes the endometrium to become thick and rich with blood. Progesterone, another hormone released by the ovaries, keeps the endometrium thick with blood so that the blastocyst can attach to the uterus and absorb nutrients from it. This process is called implantation.
As cells from the blastocyst take in nourishment, another stage of development, the embryonic stage, begins. The inner cells form a flattened circular shape called the embryonic disk, which will develop into a baby. The outer cells become thin membranes that form around the baby. The cells multiply thousands of times and move to new positions to eventually become the embryo.
After approximately 8 weeks, the embryo is about the size of an adult's thumb, but almost all of its parts — the brain and nerves, the heart and blood, the stomach and intestines, and the muscles and skin — have formed.
During the fetal stage, which lasts from 9 weeks after fertilization to birth, development continues as cells multiply, move, and change. The fetus floats in amniotic fluid inside the amniotic sac. The fetus receives oxygen and nourishment from the mother's blood via the placenta, a disk-like structure that sticks to the inner lining of the uterus and connects to the fetus via the umbilical cord. The amniotic fluid and membrane cushion the fetus against bumps and jolts to the mother's body.
Pregnancy lasts an average of 280 days — about 9 months. When the baby is ready for birth, its head presses on the cervix, which begins to relax and widen to get ready for the baby to pass into and through the vagina. The mucus that has formed a plug in the cervix loosens, and with amniotic fluid, comes out through the vagina when the mother's water breaks.
When the contractions of labor begin, the walls of the uterus contract as they are stimulated by the pituitary hormone oxytocin. The contractions cause the cervix to widen and begin to open. After several hours of this widening, the cervix is dilated (opened) enough for the baby to come through. The baby is pushed out of the uterus, through the cervix, and along the birth canal. The baby's head usually comes first; the umbilical cord comes out with the baby and is cut after the baby is delivered.
The last stage of the birth process involves the delivery of the placenta, which at that point is called the afterbirth. After it has separated from the inner lining of the uterus, contractions of the uterus push it out, along with its membranes and fluids.
Problems of the Female Reproductive System
Some girls might experience reproductive system problems, such as:
Problems of the Vulva and Vagina
Vulvovaginitis is an inflammation of the vulva and vagina. It may be caused by irritating substances (such as laundry soaps or bubble baths) or poor personal hygiene (such as wiping from back to front after a bowel movement). Symptoms include redness and itching in the vaginal and vulvar areas and sometimes vaginal discharge. Vulvovaginitis also can be caused by an overgrowth of Candida, a fungus normally present in the vagina.
Nonmenstrual vaginal bleeding is most commonly due to the presence of a vaginal foreign body, often wadded-up toilet paper. It may also be due to urethral prolapse, in which the mucous membranes of the urethra protrude into the vagina and form a tiny, doughnut-shaped mass of tissue that bleeds easily. It also can be due to a straddle injury (such as when falling onto a gymnastics beam or bicycle frame) or vaginal trauma from sexual abuse.
Labial adhesions, the sticking together or adherence of the labia in the midline, usually appear in infants and young girls. Although there are usually no symptoms associated with this condition, labial adhesions can lead to an increased risk of urinary tract infection. Sometimes topical estrogen cream is used to help separate the labia.
Problems of the Ovaries and Fallopian Tubes
Ectopic pregnancy occurs when a fertilized egg, or zygote, doesn't travel into the uterus, but instead grows rapidly in the fallopian tube. A woman with this condition can develop severe abdominal pain and should see a doctor because surgery may be necessary.
Endometriosis occurs when tissue normally found only in the uterus starts to grow outside the uterus — in the ovaries, fallopian tubes, or other parts of the pelvic cavity. It can cause abnormal bleeding, painful periods, and general pelvic pain.
Ovarian tumors, although they're rare, can occur. Girls with ovarian tumors may have abdominal pain and masses that can be felt in the abdomen. Surgery may be needed to remove the tumor.
Ovarian cysts are noncancerous sacs filled with fluid or semisolid material. Although they are common and generally harmless, they can become a problem if they grow very large. Large cysts may push on surrounding organs, causing abdominal pain. In most cases, cysts will disappear on their own and treatment is unnecessary. If the cysts are painful, a doctor may prescribe birth control pills to alter their growth or they may be removed by a surgeon.
Polycystic ovary syndrome is a hormone disorder in which too many male hormones (androgens) are produced by the ovaries. This condition causes the ovaries to become enlarged and develop many fluid-filled sacs, or cysts. It often first appears during the teen years. Depending on the type and severity of the condition, it may be treated with drugs to regulate hormone balance and menstruation.
Ovarian torsion, or the twisting of the ovary, can occur when an ovary becomes twisted because of a disease or a developmental abnormality. The torsion blocks blood from flowing through the blood vessels that supply and nourish the ovaries. The most common symptom is lower abdominal pain. Surgery is usually necessary to correct it.
Menstrual Problems
A variety of menstrual problems can affect girls, including:
Dysmenorrhea is when a girl has painful periods.
Menorrhagia is when a girl has a very heavy periods with excess bleeding.
Oligomenorrhea is when a girl misses or has infrequent periods, even though she's been menstruating for a while and isn't pregnant.
Amenorrhea is when a girl has not started her period by the time she is 16 years old or 3 years after starting puberty, has not developed signs of puberty by age 14, or has had normal periods but has stopped menstruating for some reason other than pregnancy.
Infections of the Female Reproductive System
Sexually transmitted infections (STIs). These include infections and diseases such as pelvic inflammatory disease (PID), human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS), human papillomavirus (HPV, or genital warts), syphilis, chlamydia, gonorrhea, and genital herpes (HSV). Most are spread from one person to another by sexual contact.
Toxic shock syndrome. This uncommon illness is caused by toxins released into the body during a type of bacterial infection that is more likely to develop if a tampon is left in too long. It can produce high fever, diarrhea, vomiting, and shock.
If you think your daughter may have symptoms of a problem with her reproductive system or if you have questions about her growth and development, talk to your doctor — many problems with the female reproductive system can be treated.
"I pray that this article empowers you to Get A L.I.F.E."
All living things reproduce. Reproduction — the process by which organisms make more organisms like themselves — is one of the things that sets living things apart from nonliving matter. But even though the reproductive system is essential to keeping a species alive, unlike other body systems, it's not essential to keeping an individual alive.
In the human reproductive process, two kinds of sex cells, or gametes, are involved. The male gamete, or sperm, and the female gamete, the egg or ovum, meet in the female's reproductive system to create a new individual.
Both the male and female reproductive systems are essential for reproduction. The female needs a male to fertilize her egg, even though it is she who carries offspring through pregnancy and childbirth.
Humans, like other organisms, pass certain characteristics of themselves to the next generation through their genes, the special carriers of human traits. The genes that parents pass along are what make their children similar to others in their family, but also what make each child unique. These genes come from the male's sperm and the female's egg.
Most species have two sexes: male and female. Each sex has its own unique reproductive system. They are different in shape and structure, but both are specifically designed to produce, nourish, and transport either the egg or sperm.
Components of the Female Reproductive System
Unlike the male, the human female has a reproductive system located entirely in the pelvis. The external part of the female reproductive organs is called the vulva, which means covering. Located between the legs, the vulva covers the opening to the vagina and other reproductive organs located inside the body.
The fleshy area located just above the top of the vaginal opening is called the mons pubis. Two pairs of skin flaps called the labia (which means lips) surround the vaginal opening. The clitoris, a small sensory organ, is located toward the front of the vulva where the folds of the labia join. Between the labia are openings to the urethra (the canal that carries urine from the bladder to the outside of the body) and vagina. Once girls become sexually mature, the outer labia and the mons pubis are covered by pubic hair.
A female's internal reproductive organs are the vagina, uterus, fallopian tubes, and ovaries.
The vagina is a muscular, hollow tube that extends from the vaginal opening to the uterus. The vagina is about 3 to 5 inches (8 to 12 centimeters) long in a grown woman. Because it has muscular walls, it can expand and contract. This ability to become wider or narrower allows the vagina to accommodate something as slim as a tampon and as wide as a baby. The vagina's muscular walls are lined with mucous membranes, which keep it protected and moist.
The vagina serves three purposes:
1. It's where the penis is inserted during sexual intercourse.
2. It's the pathway that a baby takes out of a woman's body during childbirth, called the birth canal.
3. It provides the route for the menstrual blood (the period) to leave the body from the uterus.
A thin sheet of tissue with one or more holes in it called the hymen partially covers the opening of the vagina. Hymens are often different from female to female. Most women find their hymens have stretched or torn after their first sexual experience, and the hymen may bleed a little (this usually causes little, if any, pain). Some women who have had sex don't have much of a change in their hymens, though.
The vagina connects with the uterus, or womb, at the cervix (which means neck). The cervix has strong, thick walls. The opening of the cervix is very small (no wider than a straw), which is why a tampon can never get lost inside a girl's body. During childbirth, the cervix can expand to allow a baby to pass.
The uterus is shaped like an upside-down pear, with a thick lining and muscular walls — in fact, the uterus contains some of the strongest muscles in the female body. These muscles are able to expand and contract to accommodate a growing fetus and then help push the baby out during labor. When a woman isn't pregnant, the uterus is only about 3 inches (7.5 centimeters) long and 2 inches (5 centimeters) wide.
At the upper corners of the uterus, the fallopian tubes connect the uterus to the ovaries. The ovaries are two oval-shaped organs that lie to the upper right and left of the uterus. They produce, store, and release eggs into the fallopian tubes in the process called ovulation. Each ovary measures about 1½ to 2 inches (4 to 5 centimeters) in a grown woman.
There are two fallopian tubes, each attached to a side of the uterus. The fallopian tubes are about 4 inches (10 centimeters) long and about as wide as a piece of spaghetti. Within each tube is a tiny passageway no wider than a sewing needle. At the other end of each fallopian tube is a fringed area that looks like a funnel. This fringed area wraps around the ovary but doesn't completely attach to it. When an egg pops out of an ovary, it enters the fallopian tube. Once the egg is in the fallopian tube, tiny hairs in the tube's lining help push it down the narrow passageway toward the uterus.
The ovaries are also part of the endocrine system because they produce female sex hormones such as estrogen and progesterone.
What the Female Reproductive System Does
The female reproductive system enables a woman to:
produce eggs (ova)
have sexual intercourse
protect and nourish the fertilized egg until it is fully developed
give birth
Sexual reproduction couldn't happen without the sexual organs called the gonads. Although most people think of the gonads as the male testicles, both sexes actually have gonads: In females the gonads are the ovaries. The female gonads produce female gametes (eggs); the male gonads produce male gametes (sperm). After an egg is fertilized by the sperm, the fertilized egg is called the zygote.
When a baby girl is born, her ovaries contain hundreds of thousands of eggs, which remain inactive until puberty begins. At puberty, the pituitary gland, located in the central part of the brain, starts making hormones that stimulate the ovaries to produce female sex hormones, including estrogen. The secretion of these hormones causes a girl to develop into a sexually mature woman.
Toward the end of puberty, girls begin to release eggs as part of a monthly period called the menstrual cycle. Approximately once a month, during ovulation, an ovary sends a tiny egg into one of the fallopian tubes.
Unless the egg is fertilized by a sperm while in the fallopian tube, the egg dries up and leaves the body about 2 weeks later through the uterus — this is menstruation. Blood and tissues from the inner lining of the uterus combine to form the menstrual flow, which in most girls lasts from 3 to 5 days. A girl's first period is called menarche.
It's common for women and girls to experience some discomfort in the days leading to their periods. Premenstrual syndrome (PMS) includes both physical and emotional symptoms that many girls and women get right before their periods, such as acne, bloating, fatigue, backaches, sore breasts, headaches, constipation, diarrhea, food cravings, depression, irritability, or difficulty concentrating or handling stress. PMS is usually at its worst during the 7 days before a girl's period starts and disappears once it begins.
Many girls also experience abdominal cramps during the first few days of their periods caused by prostaglandins, chemicals in the body that make the smooth muscle in the uterus contract. These involuntary contractions can be either dull or sharp and intense.
It can take up to 2 years from menarche for a girl's body to develop a regular menstrual cycle. During that time, her body is adjusting to the hormones puberty brings. On average, the monthly cycle for an adult woman is 28 days, but the range is from 23 to 35 days.
Fertilization
If a female and male have sex within several days of the female's ovulation, fertilization can occur. When the male ejaculates (when semen leaves a male's penis), between 0.05 and 0.2 fluid ounces (1.5 to 6.0 milliliters) of semen is deposited into the vagina. Between 75 and 900 million sperm are in this small amount of semen, and they "swim" up from the vagina through the cervix and uterus to meet the egg in the fallopian tube. It takes only one sperm to fertilize the egg.
About a week after the sperm fertilizes the egg, the fertilized egg (zygote) has become a multicelled blastocyst. A blastocyst is about the size of a pinhead, and it's a hollow ball of cells with fluid inside. The blastocyst burrows itself into the lining of the uterus, called the endometrium. The hormone estrogen causes the endometrium to become thick and rich with blood. Progesterone, another hormone released by the ovaries, keeps the endometrium thick with blood so that the blastocyst can attach to the uterus and absorb nutrients from it. This process is called implantation.
As cells from the blastocyst take in nourishment, another stage of development, the embryonic stage, begins. The inner cells form a flattened circular shape called the embryonic disk, which will develop into a baby. The outer cells become thin membranes that form around the baby. The cells multiply thousands of times and move to new positions to eventually become the embryo.
After approximately 8 weeks, the embryo is about the size of an adult's thumb, but almost all of its parts — the brain and nerves, the heart and blood, the stomach and intestines, and the muscles and skin — have formed.
During the fetal stage, which lasts from 9 weeks after fertilization to birth, development continues as cells multiply, move, and change. The fetus floats in amniotic fluid inside the amniotic sac. The fetus receives oxygen and nourishment from the mother's blood via the placenta, a disk-like structure that sticks to the inner lining of the uterus and connects to the fetus via the umbilical cord. The amniotic fluid and membrane cushion the fetus against bumps and jolts to the mother's body.
Pregnancy lasts an average of 280 days — about 9 months. When the baby is ready for birth, its head presses on the cervix, which begins to relax and widen to get ready for the baby to pass into and through the vagina. The mucus that has formed a plug in the cervix loosens, and with amniotic fluid, comes out through the vagina when the mother's water breaks.
When the contractions of labor begin, the walls of the uterus contract as they are stimulated by the pituitary hormone oxytocin. The contractions cause the cervix to widen and begin to open. After several hours of this widening, the cervix is dilated (opened) enough for the baby to come through. The baby is pushed out of the uterus, through the cervix, and along the birth canal. The baby's head usually comes first; the umbilical cord comes out with the baby and is cut after the baby is delivered.
The last stage of the birth process involves the delivery of the placenta, which at that point is called the afterbirth. After it has separated from the inner lining of the uterus, contractions of the uterus push it out, along with its membranes and fluids.
Problems of the Female Reproductive System
Some girls might experience reproductive system problems, such as:
Problems of the Vulva and Vagina
Vulvovaginitis is an inflammation of the vulva and vagina. It may be caused by irritating substances (such as laundry soaps or bubble baths) or poor personal hygiene (such as wiping from back to front after a bowel movement). Symptoms include redness and itching in the vaginal and vulvar areas and sometimes vaginal discharge. Vulvovaginitis also can be caused by an overgrowth of Candida, a fungus normally present in the vagina.
Nonmenstrual vaginal bleeding is most commonly due to the presence of a vaginal foreign body, often wadded-up toilet paper. It may also be due to urethral prolapse, in which the mucous membranes of the urethra protrude into the vagina and form a tiny, doughnut-shaped mass of tissue that bleeds easily. It also can be due to a straddle injury (such as when falling onto a gymnastics beam or bicycle frame) or vaginal trauma from sexual abuse.
Labial adhesions, the sticking together or adherence of the labia in the midline, usually appear in infants and young girls. Although there are usually no symptoms associated with this condition, labial adhesions can lead to an increased risk of urinary tract infection. Sometimes topical estrogen cream is used to help separate the labia.
Problems of the Ovaries and Fallopian Tubes
Ectopic pregnancy occurs when a fertilized egg, or zygote, doesn't travel into the uterus, but instead grows rapidly in the fallopian tube. A woman with this condition can develop severe abdominal pain and should see a doctor because surgery may be necessary.
Endometriosis occurs when tissue normally found only in the uterus starts to grow outside the uterus — in the ovaries, fallopian tubes, or other parts of the pelvic cavity. It can cause abnormal bleeding, painful periods, and general pelvic pain.
Ovarian tumors, although they're rare, can occur. Girls with ovarian tumors may have abdominal pain and masses that can be felt in the abdomen. Surgery may be needed to remove the tumor.
Ovarian cysts are noncancerous sacs filled with fluid or semisolid material. Although they are common and generally harmless, they can become a problem if they grow very large. Large cysts may push on surrounding organs, causing abdominal pain. In most cases, cysts will disappear on their own and treatment is unnecessary. If the cysts are painful, a doctor may prescribe birth control pills to alter their growth or they may be removed by a surgeon.
Polycystic ovary syndrome is a hormone disorder in which too many male hormones (androgens) are produced by the ovaries. This condition causes the ovaries to become enlarged and develop many fluid-filled sacs, or cysts. It often first appears during the teen years. Depending on the type and severity of the condition, it may be treated with drugs to regulate hormone balance and menstruation.
Ovarian torsion, or the twisting of the ovary, can occur when an ovary becomes twisted because of a disease or a developmental abnormality. The torsion blocks blood from flowing through the blood vessels that supply and nourish the ovaries. The most common symptom is lower abdominal pain. Surgery is usually necessary to correct it.
Menstrual Problems
A variety of menstrual problems can affect girls, including:
Dysmenorrhea is when a girl has painful periods.
Menorrhagia is when a girl has a very heavy periods with excess bleeding.
Oligomenorrhea is when a girl misses or has infrequent periods, even though she's been menstruating for a while and isn't pregnant.
Amenorrhea is when a girl has not started her period by the time she is 16 years old or 3 years after starting puberty, has not developed signs of puberty by age 14, or has had normal periods but has stopped menstruating for some reason other than pregnancy.
Infections of the Female Reproductive System
Sexually transmitted infections (STIs). These include infections and diseases such as pelvic inflammatory disease (PID), human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS), human papillomavirus (HPV, or genital warts), syphilis, chlamydia, gonorrhea, and genital herpes (HSV). Most are spread from one person to another by sexual contact.
Toxic shock syndrome. This uncommon illness is caused by toxins released into the body during a type of bacterial infection that is more likely to develop if a tampon is left in too long. It can produce high fever, diarrhea, vomiting, and shock.
If you think your daughter may have symptoms of a problem with her reproductive system or if you have questions about her growth and development, talk to your doctor — many problems with the female reproductive system can be treated.
"I pray that this article empowers you to Get A L.I.F.E."
Saturday, May 14, 2011
The Eyes
We depend on sight more than any other of our senses to maneuver through the space around us. In a single glance, lasting a fraction of a second, our eyes work with our brains to tell us the size, shape, color, and texture of an object. They let us know how close it is, whether it's standing still or coming toward us, and how quickly it's moving. Every day, our eyes give us messages that help us understand the world around us.
Although the eyes are small compared with most of the body's other organs, their structure is incredibly complex. The eyes work together to perceive depth, enabling us to judge distance and the size of objects to help us move around them. Not only do the two eyes work together, they also work with the brain, muscles, and nerves to produce complicated visual images and messages. And our eyes constantly adapt to the changing environment — for example, they are able to adjust so that we can easily move around in a nearly dark room or bright sunlight.
To understand more about how the eyes work, it's important to know about the structures that make up the eye and about conditions and diseases that can interfere with vision.
How Eyes Work
Only part of the eye is visible in a person's face. The whole eye — the eyeball — is about the size and shape of a ping-pong ball.
The eye — both the parts that are visible and those that aren't — is extremely delicate. The body has several ways of protecting this vulnerable organ. The eyeball sits in the eye socket (also called the orbit) in a person's skull, where it is surrounded by bone. The visible part of the eye is protected by the eyelids and the eyelashes, which keep dirt, dust, and even harmful bright light out of the eye.
Our eyes are also protected by tears, which moisten the eyes and clean out dirt, dust, and other irritants that get past the defenses of our eyelashes and eyelids. Tears also help protect the eyes against infection.
Every time we blink, our eyelids spread a layer of mucus, oil, and tears over the cornea, which covers the eye. The lacrimal glands in the upper outer corner of each eye socket produce tears.
After they've done their job moistening the eyes, the tears flow into canals in the eyelids, which drain into the lacrimal sac, a pouch in the lower inner corner of each eye socket. Tears then exit through a passage which leads to the nose.
To see, the eye has to move. Six muscles, called extraocular muscles, surround the eyeball in the skull. These muscles act like the strings on a puppet, moving the eye in different directions. The muscles of each eye normally move together at the same time, allowing the two eyes to remain aligned.
The wall of a person's eyeball is made up of three layers, rather like the layers on an onion:
1. The sclera is the outermost protective layer. This tough, fibrous tissue surrounds the eyeball and attaches to the cornea, which is the clear front surface of the eye. What we see as the white of the eye is the sclera. Over the sclera lies the conjunctiva, a clear mucous membrane that protects the eye from becoming dry.
2. The choroid is the middle layer that contains blood vessels that deliver oxygen and nutrients to the retina.
3. The retina, the innermost of the three layers, lines the inside of the eyeball. The retina is a soft, light-sensitive layer of nervous system tissue. The optic nerve carries signals from the retina to the brain, which interprets them as visual images.
The space in the center of the eyeball is filled with a clear jelly-like material called the vitreous humor. This material allows light to pass through to the retina. It also helps the eye keep its round shape.
Vision is the process by which images captured by the eye are interpreted by the brain, and the visible part of the eye is where the process of sight begins. On the front surface of the eye is the see-through, circle-shaped cornea. You can't see a person's cornea the way you can see the colored part of the eye behind it — the cornea is like a clear window that focuses light into the eye. Behind the cornea is a watery fluid called the aqueous humor. The cornea and aqueous humor form an outer lens that refracts (bends) light on its way into the eye. This is where most of the eye's focusing work is done.
The colored circular membrane in the eye just behind the cornea is called the iris. The iris controls the amount of light entering the eye through the pupil, which is the opening in the center of the iris that looks like a tiny black circle. Like a camera, which controls the amount of light coming in to prevent both overexposure and underexposure, the iris becomes wider and narrower, changing the size of the pupil to control the amount of light entering the eye. The pupil gets bigger when more light is needed to see better and smaller when there's plenty of light.
The eye's lens sits just behind the iris. Just like a camera lens, the eye's lens focuses light to form sharp, clear images. Light that has been focused through the cornea and aqueous humor hits the lens, which then focuses it further, sending the light rays through the vitreous humor and onto the retina.
To focus on objects clearly at varying distances, the eye's lens needs to change shape. The ciliary body contains the muscular structure in the eye that changes the shape of the eye's lens. In people who have normal vision, the ciliary body flattens the lens enough to bring objects into focus at a distance of 20 feet or more. To see closer objects, this muscle contracts to thicken the lens. Young children can see objects at very close range; many people over 45 have to hold objects farther and farther away to see them clearly. This is because the lens becomes less elastic as we age.
The retina (the soft, light-sensitive layer of tissue that lines the back of the eyeball wall) is made up of millions of light receptors. These are called rods and cones. Rods are much more sensitive to light than cones. Each eye has about 125 million rods that help us see in dim light and detect shades of gray, but they cannot distinguish colors. In comparison, the 6 million cones in each eye allow us to see in bright light, and they also sense color and detail.
The macula is a small, specialized area on the retina. The macula helps our eyes see fine details when we look directly at an object. It contains mainly cones and few rods.
When focused light is projected onto the retina, it stimulates the rods and cones. The retina then sends nerve signals are sent through the back of the eye to the optic nerve. The optic nerve carries these signals to the brain, which interprets them as visual images. The portion of the brain that processes visual input and interprets the messages that the eye sends is called the visual cortex.
As in a camera, the eye's lens transmits light patterns upside down. The brain learns that the impulses received from the upper part of the retina are really from the lower part of the object we're seeing and vice versa.
Most people use both eyes to see an object. This is called binocular vision. Through binocular vision, images are formed on the retina of each eye. These images are slightly different, because the object is being viewed from slightly different angles. Nerve signals representing each image are sent to the brain, where they are interpreted as two views of the same object. Some of the nerve fibers from each eye cross, so each side of the brain receives messages from both eyes. Through experience, the brain learns to judge the distance of an object by the degree of difference in the images it receives from the two eyes. This ability to sense distance is called depth perception.
Vision is a fine-tuned process. All the parts of the eye — and the brain — need to work together so a person can see correctly. Because the eye's structure is so complex, though, a lot of things can go wrong.
Vision Problems
Some of the most common eye problems are refractive errors. These are the problems that eye doctors check for routinely in a vision test. Refraction means bending of light rays to focus the light coming from an image. Refractive errors are problems with the focusing of the eye, because of the way the eye is shaped, which causes the image you see to be blurred.
Refractive errors include:
Astigmatism. In astigmatism, there's a problem with the curve of the cornea. This causes part of the eye's image to be blurry. Corrective lenses such as contact lenses or glasses can usually correct vision in people with astigmatism.
Nearsightedness. Also called myopia or shortsightedness, nearsightedness occurs when the eye focuses the image of an object in front of the retina instead of directly on it. In most cases, people can't see well far away, but can see objects clearly close up. The condition tends to get somewhat worse through childhood and adolescence, but stabilizes in adulthood. People with this condition may need to wear glasses or contacts to correct their vision. Laser eye surgery is now commonly used in adults to correct nearsightedness permanently by changing the shape of the cornea. Laser surgery is not used in kids and teens because the eye may still be growing and the refractive error changing.
Farsightedness. Also called hyperopia or longsightedness, farsightedness occurs when the incoming image is not focused on the retina, but behind it. This makes it difficult to see close objects clearly, even though far-off objects can be seen clearly. Glasses or contact lenses can correct this problem in kids and teens. Most adults develop a form of farsightedness called presbyopia as they get older.
Some of the other eye problems that can affect children and teens include:
Blindness. This is the loss of useful sight. Blindness can be temporary or permanent and it has many causes. Birth defects or damage to any portion of the eye, the optic nerve, or the area of the brain responsible for vision can lead to blindness. The visual impairment cannot be corrected with surgery or corrective lenses, and the condition can make it difficult to perform everyday activities. Diabetes, problems with the macula, and eye changes because of aging account for most blindness in the United States.
Cataracts. Some children are born with cataracts, a cloudiness of the eye's lenses that prevent images from being seen clearly or at all. But cataracts are much more prevalent in the elderly among whom surgery to remove cataracts and correct vision is common. In infants and young children, cataracts must be treated to prevent permanent problems with development of vision.
Color blindness. Color blindness is caused by problems in the pigments of the cones in the retina. Most people who are color-blind can see some colors. In most cases, someone who is color-blind confuses some colors with others, usually red and green. People can be born color-blind or they may develop the condition over time. The most common form of color blindness is an inherited condition that affects boys much more often than girls. Color blindness cannot be corrected.
Conjunctivitis. Conjunctivitis refers to inflammation (redness, pain, and swelling) of the conjunctiva. One type of conjunctivitis is called pinkeye, a common contagious infection in which the eyes become pinkish red and watery, and pus may form. Pinkeye is usually treated with eyedrops. Conjunctivitis may also occur due to allergies or from a scratch on the surface of the eye.
Dacryostenosis. Dacryostenosis is a blockage of the tear drainage system of the eye occurring in the lower eyelid. This is a fairly common problem in infants, but often improves with time.
Eye injuries. Injuries to the eye are one of the most common preventable causes of blindness. Eye injuries may be caused by irritants such as sand, dirt, or other foreign bodies on the eye's surface. Chemicals or foreign bodies that become embedded in the eye can also cause pain and loss of vision. Forceful blows to the eye can cause bleeding inside the eye and damage to the cornea, retina, and other important eye structures.
Glaucoma. One of the leading causes of blindness in the United States, glaucoma is a disorder that causes fluid pressure to build up inside the eye, potentially causing damage to the optic nerve. Although it can occur in infants and children, it is much more common among older adults. Unless detected early by routine screening tests, it usually goes undiagnosed until some vision is lost.
Macular degeneration is an eye disease that mainly affects older people. But sometimes infants and children can develop it, too. When someone has macular degeneration, the middle area of the retina becomes scarred. This causes eyesight to deteriorate over many years. The cause of macular degeneration is unknown in most cases, but it tends to run in families, which indicates that genes and heredity are involved.
Retinoblastoma. This is a cancerous tumor in the eye that usually appears in the first 5 years of life. There may be permanent vision loss, and the affected eye(s) may have to be removed.
Retinopathy of prematurity. Premature babies sometimes have damage to the blood vessels in the eye's retina, a condition known as retinopathy of prematurity, which can lead to severe vision loss in some cases.
Strabismus. A condition in which the eyes appear crossed, strabismus is usually caused by a defect in the balance of the pull exerted by the muscles that help the eyes stay straight and move together properly. Surgery on the eye muscles can help realign the eyes. Permanent vision loss in the less-used eye (amblyopia) can occur if the condition is not treated in early childhood.
Sty. A sty is an infection of one of the follicles from which the eyelashes grow. Sties are treated by applying warm compresses and using antibiotics.
Proper care of your child's eyes includes having periodic eye exams at routine office checkups and by an eye specialist according to the schedule recommended by your doctor. Signs that a very young child may be having vision trouble include constant eye rubbing, tearing or redness, and trouble following an object. Older kids may squint or sit too close to the TV. Kids who are having trouble seeing might also complain of headaches at the end of the day.
"I pray that this article empowers you to Get A L.I.F.E."
Although the eyes are small compared with most of the body's other organs, their structure is incredibly complex. The eyes work together to perceive depth, enabling us to judge distance and the size of objects to help us move around them. Not only do the two eyes work together, they also work with the brain, muscles, and nerves to produce complicated visual images and messages. And our eyes constantly adapt to the changing environment — for example, they are able to adjust so that we can easily move around in a nearly dark room or bright sunlight.
To understand more about how the eyes work, it's important to know about the structures that make up the eye and about conditions and diseases that can interfere with vision.
How Eyes Work
Only part of the eye is visible in a person's face. The whole eye — the eyeball — is about the size and shape of a ping-pong ball.
The eye — both the parts that are visible and those that aren't — is extremely delicate. The body has several ways of protecting this vulnerable organ. The eyeball sits in the eye socket (also called the orbit) in a person's skull, where it is surrounded by bone. The visible part of the eye is protected by the eyelids and the eyelashes, which keep dirt, dust, and even harmful bright light out of the eye.
Our eyes are also protected by tears, which moisten the eyes and clean out dirt, dust, and other irritants that get past the defenses of our eyelashes and eyelids. Tears also help protect the eyes against infection.
Every time we blink, our eyelids spread a layer of mucus, oil, and tears over the cornea, which covers the eye. The lacrimal glands in the upper outer corner of each eye socket produce tears.
After they've done their job moistening the eyes, the tears flow into canals in the eyelids, which drain into the lacrimal sac, a pouch in the lower inner corner of each eye socket. Tears then exit through a passage which leads to the nose.
To see, the eye has to move. Six muscles, called extraocular muscles, surround the eyeball in the skull. These muscles act like the strings on a puppet, moving the eye in different directions. The muscles of each eye normally move together at the same time, allowing the two eyes to remain aligned.
The wall of a person's eyeball is made up of three layers, rather like the layers on an onion:
1. The sclera is the outermost protective layer. This tough, fibrous tissue surrounds the eyeball and attaches to the cornea, which is the clear front surface of the eye. What we see as the white of the eye is the sclera. Over the sclera lies the conjunctiva, a clear mucous membrane that protects the eye from becoming dry.
2. The choroid is the middle layer that contains blood vessels that deliver oxygen and nutrients to the retina.
3. The retina, the innermost of the three layers, lines the inside of the eyeball. The retina is a soft, light-sensitive layer of nervous system tissue. The optic nerve carries signals from the retina to the brain, which interprets them as visual images.
The space in the center of the eyeball is filled with a clear jelly-like material called the vitreous humor. This material allows light to pass through to the retina. It also helps the eye keep its round shape.
Vision is the process by which images captured by the eye are interpreted by the brain, and the visible part of the eye is where the process of sight begins. On the front surface of the eye is the see-through, circle-shaped cornea. You can't see a person's cornea the way you can see the colored part of the eye behind it — the cornea is like a clear window that focuses light into the eye. Behind the cornea is a watery fluid called the aqueous humor. The cornea and aqueous humor form an outer lens that refracts (bends) light on its way into the eye. This is where most of the eye's focusing work is done.
The colored circular membrane in the eye just behind the cornea is called the iris. The iris controls the amount of light entering the eye through the pupil, which is the opening in the center of the iris that looks like a tiny black circle. Like a camera, which controls the amount of light coming in to prevent both overexposure and underexposure, the iris becomes wider and narrower, changing the size of the pupil to control the amount of light entering the eye. The pupil gets bigger when more light is needed to see better and smaller when there's plenty of light.
The eye's lens sits just behind the iris. Just like a camera lens, the eye's lens focuses light to form sharp, clear images. Light that has been focused through the cornea and aqueous humor hits the lens, which then focuses it further, sending the light rays through the vitreous humor and onto the retina.
To focus on objects clearly at varying distances, the eye's lens needs to change shape. The ciliary body contains the muscular structure in the eye that changes the shape of the eye's lens. In people who have normal vision, the ciliary body flattens the lens enough to bring objects into focus at a distance of 20 feet or more. To see closer objects, this muscle contracts to thicken the lens. Young children can see objects at very close range; many people over 45 have to hold objects farther and farther away to see them clearly. This is because the lens becomes less elastic as we age.
The retina (the soft, light-sensitive layer of tissue that lines the back of the eyeball wall) is made up of millions of light receptors. These are called rods and cones. Rods are much more sensitive to light than cones. Each eye has about 125 million rods that help us see in dim light and detect shades of gray, but they cannot distinguish colors. In comparison, the 6 million cones in each eye allow us to see in bright light, and they also sense color and detail.
The macula is a small, specialized area on the retina. The macula helps our eyes see fine details when we look directly at an object. It contains mainly cones and few rods.
When focused light is projected onto the retina, it stimulates the rods and cones. The retina then sends nerve signals are sent through the back of the eye to the optic nerve. The optic nerve carries these signals to the brain, which interprets them as visual images. The portion of the brain that processes visual input and interprets the messages that the eye sends is called the visual cortex.
As in a camera, the eye's lens transmits light patterns upside down. The brain learns that the impulses received from the upper part of the retina are really from the lower part of the object we're seeing and vice versa.
Most people use both eyes to see an object. This is called binocular vision. Through binocular vision, images are formed on the retina of each eye. These images are slightly different, because the object is being viewed from slightly different angles. Nerve signals representing each image are sent to the brain, where they are interpreted as two views of the same object. Some of the nerve fibers from each eye cross, so each side of the brain receives messages from both eyes. Through experience, the brain learns to judge the distance of an object by the degree of difference in the images it receives from the two eyes. This ability to sense distance is called depth perception.
Vision is a fine-tuned process. All the parts of the eye — and the brain — need to work together so a person can see correctly. Because the eye's structure is so complex, though, a lot of things can go wrong.
Vision Problems
Some of the most common eye problems are refractive errors. These are the problems that eye doctors check for routinely in a vision test. Refraction means bending of light rays to focus the light coming from an image. Refractive errors are problems with the focusing of the eye, because of the way the eye is shaped, which causes the image you see to be blurred.
Refractive errors include:
Astigmatism. In astigmatism, there's a problem with the curve of the cornea. This causes part of the eye's image to be blurry. Corrective lenses such as contact lenses or glasses can usually correct vision in people with astigmatism.
Nearsightedness. Also called myopia or shortsightedness, nearsightedness occurs when the eye focuses the image of an object in front of the retina instead of directly on it. In most cases, people can't see well far away, but can see objects clearly close up. The condition tends to get somewhat worse through childhood and adolescence, but stabilizes in adulthood. People with this condition may need to wear glasses or contacts to correct their vision. Laser eye surgery is now commonly used in adults to correct nearsightedness permanently by changing the shape of the cornea. Laser surgery is not used in kids and teens because the eye may still be growing and the refractive error changing.
Farsightedness. Also called hyperopia or longsightedness, farsightedness occurs when the incoming image is not focused on the retina, but behind it. This makes it difficult to see close objects clearly, even though far-off objects can be seen clearly. Glasses or contact lenses can correct this problem in kids and teens. Most adults develop a form of farsightedness called presbyopia as they get older.
Some of the other eye problems that can affect children and teens include:
Blindness. This is the loss of useful sight. Blindness can be temporary or permanent and it has many causes. Birth defects or damage to any portion of the eye, the optic nerve, or the area of the brain responsible for vision can lead to blindness. The visual impairment cannot be corrected with surgery or corrective lenses, and the condition can make it difficult to perform everyday activities. Diabetes, problems with the macula, and eye changes because of aging account for most blindness in the United States.
Cataracts. Some children are born with cataracts, a cloudiness of the eye's lenses that prevent images from being seen clearly or at all. But cataracts are much more prevalent in the elderly among whom surgery to remove cataracts and correct vision is common. In infants and young children, cataracts must be treated to prevent permanent problems with development of vision.
Color blindness. Color blindness is caused by problems in the pigments of the cones in the retina. Most people who are color-blind can see some colors. In most cases, someone who is color-blind confuses some colors with others, usually red and green. People can be born color-blind or they may develop the condition over time. The most common form of color blindness is an inherited condition that affects boys much more often than girls. Color blindness cannot be corrected.
Conjunctivitis. Conjunctivitis refers to inflammation (redness, pain, and swelling) of the conjunctiva. One type of conjunctivitis is called pinkeye, a common contagious infection in which the eyes become pinkish red and watery, and pus may form. Pinkeye is usually treated with eyedrops. Conjunctivitis may also occur due to allergies or from a scratch on the surface of the eye.
Dacryostenosis. Dacryostenosis is a blockage of the tear drainage system of the eye occurring in the lower eyelid. This is a fairly common problem in infants, but often improves with time.
Eye injuries. Injuries to the eye are one of the most common preventable causes of blindness. Eye injuries may be caused by irritants such as sand, dirt, or other foreign bodies on the eye's surface. Chemicals or foreign bodies that become embedded in the eye can also cause pain and loss of vision. Forceful blows to the eye can cause bleeding inside the eye and damage to the cornea, retina, and other important eye structures.
Glaucoma. One of the leading causes of blindness in the United States, glaucoma is a disorder that causes fluid pressure to build up inside the eye, potentially causing damage to the optic nerve. Although it can occur in infants and children, it is much more common among older adults. Unless detected early by routine screening tests, it usually goes undiagnosed until some vision is lost.
Macular degeneration is an eye disease that mainly affects older people. But sometimes infants and children can develop it, too. When someone has macular degeneration, the middle area of the retina becomes scarred. This causes eyesight to deteriorate over many years. The cause of macular degeneration is unknown in most cases, but it tends to run in families, which indicates that genes and heredity are involved.
Retinoblastoma. This is a cancerous tumor in the eye that usually appears in the first 5 years of life. There may be permanent vision loss, and the affected eye(s) may have to be removed.
Retinopathy of prematurity. Premature babies sometimes have damage to the blood vessels in the eye's retina, a condition known as retinopathy of prematurity, which can lead to severe vision loss in some cases.
Strabismus. A condition in which the eyes appear crossed, strabismus is usually caused by a defect in the balance of the pull exerted by the muscles that help the eyes stay straight and move together properly. Surgery on the eye muscles can help realign the eyes. Permanent vision loss in the less-used eye (amblyopia) can occur if the condition is not treated in early childhood.
Sty. A sty is an infection of one of the follicles from which the eyelashes grow. Sties are treated by applying warm compresses and using antibiotics.
Proper care of your child's eyes includes having periodic eye exams at routine office checkups and by an eye specialist according to the schedule recommended by your doctor. Signs that a very young child may be having vision trouble include constant eye rubbing, tearing or redness, and trouble following an object. Older kids may squint or sit too close to the TV. Kids who are having trouble seeing might also complain of headaches at the end of the day.
"I pray that this article empowers you to Get A L.I.F.E."
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