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What organ gets smaller with age?

Low birthweight

Low birthweight is when a baby is born weighing less than 5 pounds, 8 ounces. Some babies with low birthweight are healthy, even though they’re small. But having a low weight at birth can cause serious health problems for some babies. A baby who is very small at birth may have trouble eating, gaining weight and fighting off infections. Some may have long-term health problems, too. About 1 in 12 babies (about 8 percent) in the United States is born with low birthweight.

What causes a baby to have a low birthweight?

There are two main reasons:

  • Preterm birth.
  • Fetal growth restriction (also called intrauterine growth restriction or small for gestational age). This means a baby doesn’t gain the weight they should before birth. Some babies may have low birthweight simply because their parents are small. Others may have low birthweight because something slowed or stopped their growth during pregnancy. Your health care provider measures your belly and uses ultrasound to help track your baby’s growth during pregnancy. Ultrasound uses sound waves and a computer screen to show a picture of your baby while you’re pregnant.

If your provider thinks your baby’s growth is being restricted, you may have ultrasounds more often (every 2 to 4 weeks) to track your baby’s growth. Your provider also may do other tests such as heart rate monitoring and tests to check for infections or birth defects. Babies who have birth defects are more likely to be born too early.

Are you at risk of having a low-birthweight baby?

Some things may make you more likely than others to have a low-birthweight baby. These are called risk factors. Having a risk factor doesn’t mean you’ll definitely have a low-birthweight baby, but it may increase your chances. Talk with your health care provider about what you can do to reduce your risk.

Medical risk factors for having a low-birthweight baby

  • Preterm labor. This is labor that starts too soon, before 37 weeks of pregnancy.
  • Chronic health conditions. These are health conditions that last for a long time or that happen again and again over a long period of time. Chronic health conditions need to be treated by a health care provider. Chronic health conditions that may lead to having a baby with low birthweight include high blood pressure, diabetes and heart, lung and kidney problems.
  • Taking certain medicines to treat health conditions, such as high blood pressure, epilepsy and blood clots. Tell your provider about any prescription medicine you take. You may need to stop taking a medicine or switch to one that’s safer during pregnancy.
  • Infections. Certain infections, especially infections of the internal reproductive organs during pregnancy, can slow a baby’s growth in the womb. These include cytomegalovirus, rubella, chickenpox, toxoplasmosis and certain sexually transmitted infections.
  • Problems with the placenta. The placenta grows in the uterus and supplies the baby with food and oxygen through the umbilical cord. Some problems in the placenta can reduce the flow of oxygen and nutrients to the baby, which can limit the baby’s growth.
  • Not gaining enoughweight during pregnancy. Pregnant people who don’t gain enough weight during pregnancy are more likely to have a low-birthweight baby than those who gain the right amount of weight. If you have an eating disorder or have been treated for an eating disorder, tell your provider. Your provider can check on you and your baby carefully throughout pregnancy to help prevent complications and make sure you’re both healthy.
  • Having a baby who was born too early or who had low birthweight in the past.
  • Being pregnant with multiples(twins, triplets or more). More than half of multiple birth babies have low birthweight.
  • Smoking,drinking alcohol, using street drugs and abusing prescription drugs. Pregnant people who smoke are more than 3 times as likely to have a baby who weighs too little at birth than people who don’t smoke. Smoking, drinking alcohol, using street drugs, and abusing prescription drugs during pregnancy can slow the baby’s growth in the womb and increase the risk for preterm birth and birth defects.
  • Exposure to air pollution orlead
  • Being a member of a group that experiences the effects of racism andhealth disparities.
  • Domestic violence. This is when your partner hurts or abuses you. It includes physical, sexual and emotional abuse.
  • Age. Being a teen (especially younger than 15) or being older than 35 makes you more likely than other parents to have a low-birthweight baby.

Rates of low birthweight in the United States

Black babies are more likely than others to weigh less than they should at birth. The rates of low birthweight among different ethnic groups are:

  • About 1 in 7 Black babies (about 13 percent)
  • About 1 in 12 Asian babies (about 8 percent)
  • About 1 in 13 Native American or Alaska Native babies (about 8 percent)
  • About 1 in 14 Latinx babies (about 7 percent)
  • About 1 in 14 White babies (about 7 percent)

March of Dimes recognizes that racism and its effects are factors in the health disparities in pregnancy outcomes and babies’ health. We must work together to bring fair, just and full access to health care for all moms and babies.

Does a low birth weight cause problems for the baby?

Yes. Babies who weigh less than they should at birth are more likely than babies whose weight is normal to have health problems. Some need special care in a hospital’s newborn intensive care unit (also called NICU) to treat medical problems. These include:

  • Breathing problems, such as respiratory distress syndrome (also called RDS). Babies with RDS don’t have a protein called surfactant that keeps small air sacs in a baby’s lungs from collapsing. Treatment with surfactant helps these babies breathe more easily. Babies who have RDS also may need oxygen and other breathing help to make their lungs work.
  • Bleeding in the brain (also called intraventricular hemorrhage or IVH). Most brain bleeds are mild and go away on their own. More severe bleeds can cause pressure on the brain that can cause fluid to build up in the brain. This can cause brain damage. In some cases, a surgeon may insert a tube into the baby’s brain to drain the fluid.
  • Patent ductus arteriosus. Patent ductus arteriosus is when an opening between 2 major blood vessels leading from the heart does not close properly. This can cause extra blood to flow to the lungs. In many babies who have patent ductus arteriosus, the opening closes on its own within a few days after birth. Some babies need medicine or surgery to close the opening.
  • Necrotizing enterocolitis. This is a problem in a baby’s intestines. The intestines are long tubes that are part of the digestive system. The digestive system helps the body break down food. Necrotizing enterocolitis can be dangerous for a baby and can cause feeding problems, swelling in the belly, and other complications. Babies who have necrotizing enterocolitis are treated with antibiotics and fed through an intravenous, or IV, tube. Some babies need surgery to remove damaged parts of intestine.
  • Retinopathy of prematurity. This eye disease is what happens when a baby’s retinas don’t fully develop in the weeks after birth.
  • Jaundice. This is a condition that makes a baby’s eyes and skin look yellow. It’s caused when there’s too much of a substance called bilirubin in the blood.
  • Infections. The immune system protects the body from infection. In a baby who is born too early, the immune system may not be fully developed and may not be able to fight off infection.

Does a low weight at birth cause problems later in life?

Babies who are born weighing too little may be more likely than others to have certain health conditions later in life, including:

  • Diabetes
  • Heart disease
  • High blood pressure
  • Intellectual and developmental disabilities
  • Metabolic syndrome
  • Obesity

If you’ve had a baby who weighed less than they should have at birth, talk with their health care provider about what you can do to help your baby be healthy. As your child grows, make sure they eat healthy food, stay active and go to all their health care checkups. Regular checkups can help your baby’s provider spot health conditions that may cause problems as your baby grows older. These checkups also help make sure that your child gets all the vaccinations they need to stay protected from certain harmful diseases.

If my baby has developmental delays, do they need early intervention services?

Yes. If your baby has developmental delays, it’s important to get early intervention services as soon as possible. Developmental delays are when your child doesn’t reach developmental milestones when expected. Early intervention services can help improve your child’s development. They can help children from birth through 3 years old learn important skills. Services include therapy to help a child talk, walk, learn self-help skills and interact with others.

The CDC program Learn the signs. Act early offers tools and information for parents who think their child may have developmental delays. You can find your state’s contact information for early intervention services. You don’t need a doctor’s referral or a medical diagnosis to ask for a free screening.

Last reviewed: June, 2021

Are Telomeres the Key to Aging and Cancer

Inside the nucleus of a cell, our genes are arranged along twisted, double-stranded molecules of DNA called chromosomes. At the ends of the chromosomes are stretches of DNA called telomeres, which protect our genetic data, make it possible for cells to divide, and hold some secrets to how we age and get cancer.

Telomeres have been compared with the plastic tips on shoelaces, because they keep chromosome ends from fraying and sticking to each other, which would destroy or scramble an organism’s genetic information.

Yet, each time a cell divides, the telomeres get shorter. When they get too short, the cell can no longer divide; it becomes inactive or «senescent» or it dies. This shortening process is associated with aging, cancer, and a higher risk of death. So telomeres also have been compared with a bomb fuse.

Fluoresence-stained chromosomes

What are telomeres?

What are Telomeres

Like the rest of a chromosome, including its genes, telomeres are sequences of DNA — chains of chemical code. Like all DNA, they are made of four nucleic acid bases: G for guanine, A for adenine, T for thymine, and C for cytosine.

Telomeres are made of repeating sequences of TTAGGG on one strand paired with AATCCC on the other strand. Thus, one section of telomere is a «repeat» made of six «base pairs.»

In white blood cells, the length of telomeres ranges from 8,000 base pairs in newborns to 3,000 base pairs in adults and as low as 1,500 in elderly people. (An entire chromosome has about 150 million base pairs.) Each time it divides, an average cell loses 30 to 200 base pairs from the ends of its telomeres.

Cells normally can divide only about 50 to 70 times, with telomeres getting progressively shorter until the cells become senescent or die.

Telomeres do not shorten in tissues where cells do not continually divide, such as heart muscle.

Why do chromosomes have telomeres?

Without telomeres, the main part of the chromosome — the part with genes essential for life — would get shorter each time a cell divides. So telomeres allow cells to divide without losing genes. Cell division is necessary for growing new skin, blood, bone, and other cells.

Without telomeres, chromosome ends could fuse together and corrupt the cell’s genetic blueprint, possibly causing malfunction, cancer, or cell death. Because broken DNA is dangerous, a cell has the ability to sense and repair chromosome damage. Without telomeres, the ends of chromosomes would look like broken DNA, and the cell would try to fix something that wasn’t broken. That also would make them stop dividing and eventually die.

Broken DNA

Why do telomeres get shorter each time a cell divides?

Before a cell can divide, it makes copies of its chromosomes so that both new cells will have identical genetic material. To be copied, a chromosome’s two DNA strands must unwind and separate. An enzyme (DNA polymerase) then reads the existing strands to build two new strands. It begins the process with the help of short pieces of RNA. When each new matching strand is complete, it is a bit shorter than the original strand because of the room needed at the end for this small piece of RNA. It is like someone who paints himself into a corner and cannot paint the corner.

Painted Into Corner

Telomerase counteracts telomere shortening

An enzyme named telomerase adds bases to the ends of telomeres. In young cells, telomerase keeps telomeres from wearing down too much. But as cells divide repeatedly, there is not enough telomerase, so the telomeres grow shorter and the cells age.

Telomerase remains active in sperm and eggs, which are passed from one generation to the next. If reproductive cells did not have telomerase to maintain the length of their telomeres, any organism with such cells would soon go extinct.

TERT

Telomeres and cancer

As a cell begins to become cancerous, it divides more often, and its telomeres become very short. If its telomeres get too short, the cell may die. Often times, these cells escape death by making more telomerase enzyme, which prevents the telomeres from getting even shorter.

Many cancers have shortened telomeres, including pancreatic, bone, prostate, bladder, lung, kidney, and head and neck.

Measuring telomerase may be a way to detect cancer. And if scientists can learn how to stop telomerase, they might be able to fight cancer by making cancer cells age and die. In one experiment, researchers blocked telomerase activity in human breast and prostate cancer cells growing in the laboratory, prompting the tumor cells to die. But there are risks. Blocking telomerase could impair fertility, wound healing, and production of blood cells and immune system cells.

Telomeres and aging

Geneticist Richard Cawthon and colleagues at the University of Utah found shorter telomeres are associated with shorter lives. Among people older than 60, those with shorter telomeres were three times more likely to die from heart disease and eight times more likely to die from infectious disease.

While telomere shortening has been linked to the aging process, it is not yet known whether shorter telomeres are just a sign of aging — like gray hair — or actually contribute to aging.

If telomerase makes cancer cells immortal, could it prevent normal cells from aging? Could we extend lifespan by preserving or restoring the length of telomeres with telomerase? If so, would that increase our risk of getting cancer?

Scientists are not yet sure. But they have been able to use telomerase in the lab to keep human cells dividing far beyond their normal limit, and the cells do not become cancerous.

If we used telomerase to «immortalize» human cells, we may be able to mass produce cells for transplantation, including insulin-producing cells to cure diabetes, muscle cells for treating muscular dystrophy, cartilage cells for certain kinds of arthritis, and skin cells for healing severe burns and wounds. An unlimited supply of normal human cells grown in the laboratory would also help efforts to test new drugs and gene therapies.

Dr. Richard Cawthon

Listen to Dr. Richard Cawthon discuss his research on telomeres and aging.

How big is the role of telomeres in aging?

Some long-lived species like humans have telomeres that are much shorter than species like mice, which live only a few years. Nobody knows why. But it’s evidence that telomeres alone do not dictate lifespan.

Cawthon’s study found that when people are divided into two groups based on telomere length, the half with longer telomeres lives an average of five years longer than those with shorter telomeres. This study suggests that lifespan could be increased five years by increasing the length of telomeres in people with shorter ones.

People with longer telomeres still experience telomere shortening as they age. How many years might be added to our lifespan by completely stopping telomere shortening? Cawthon believes 10 years and perhaps 30 years.

After age 60, the risk of death doubles every 8 years. So a 68-year-old has twice the chance of dying within a year compared with a 60-year-old. Cawthon’s study found that differences in telomere length accounted for only 4% of that difference. And while intuition tells us older people have a higher risk of death, only 6% is due purely to chronological age. When telomere length, chronological age, and gender are combined (women live longer than men), those factors account for 37% of the variation in the risk of dying over age 60. So what causes the other 63%?

A major cause of aging is «oxidative stress.» It is the damage to DNA, proteins, and lipids (fats) caused by oxidants, which are highly reactive substances containing oxygen. These oxidants are produced normally when we breathe, and also result from inflammation, infection, and consumption of alcohol and cigarettes. In one study, scientists exposed worms to two substances that neutralize oxidants, and the worms’ lifespan increased an average 44%.

Another factor in aging is «glycation.» It happens when glucose, the main sugar we use as energy, binds to some of our DNA, proteins, and lipids, leaving them unable to do their jobs. The problem becomes worse as we get older, causing body tissues to malfunction, resulting in disease and death. Glycation may explain why studies in laboratory animals indicate that restricting calorie intake extends lifespan.

Most likely oxidative stress, glycation, telomere shortening, and chronological age — along with various genes — all work together to cause aging.

factors in aging

Telomeres and other diseases

People with a disease named dyskeratosis congenita have telomeres that get short much more quickly than normal. These people endure premature aging and death. They face a higher risk of life-threatening infections, leukemia and other blood cancers, intestinal disorders, cirrhosis of the liver, and pulmonary fibrosis, a deadly stiffening of lung tissue. They also are more likely to endure gray hair, balding, poor wound healing, spots on the skin, intestinal disorders, softening of the bones, and learning disabilities. The implication is that telomeres may play a role in all those conditions, because they all involve tissues in which cells divide often. There also is some evidence linking shortened telomeres to Alzheimer disease, hardening of the arteries, high blood pressure, and type 2 diabetes.

telomere length declines with aging

What are the prospects for human immortality?

Human lifespan has increased considerably since the 1600s, when the average lifespan was 30 years. By 2012, the average US life expectancy was nearly 79. Reasons for the increase include sewers and other sanitation measures, antibiotics, clean water, refrigeration, vaccines and other medical efforts to prevent children and babies from dying, improved diets, and better health care.

Some scientists predict average life expectancy will continue to increase, although many doubt the average will ever be much higher than 90. But a few say vastly longer lifespans are possible.

Cawthon says that if all processes of aging could be eliminated and oxidative stress damage could be repaired, «one estimate is people could live 1,000 years.»

Facts about Microcephaly

Microcephaly is a birth defect where a baby’s head is smaller than expected when compared to babies of the same sex and age. Babies with microcephaly often have smaller brains that might not have developed properly.

Microcephaly comparison

Typical Head Size, Microcephaly and Severe Microcephaly Comparison

Microcephaly comparison

The images are in the public domain and thus free of any copyright restrictions. As a matter of courtesy we request that the content provider (Centers for Disease Control and Prevention, National Center on Birth Defects and Developmental Disabilities) be credited and notified in any public or private usage of this image.

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What is microcephaly?

Microcephaly is a condition where a baby’s head is much smaller than expected. During pregnancy, a baby’s head grows because the baby’s brain grows. Microcephaly can occur because a baby’s brain has not developed properly during pregnancy or has stopped growing after birth, which results in a smaller head size. Microcephaly can be an isolated condition, meaning that it can occur with no other major birth defects, or it can occur in combination with other major birth defects.

What is severe microcephaly?

Severe microcephaly is a more serious, extreme form of this condition where a baby’s head is much smaller than expected. Severe microcephaly can result because a baby’s brain has not developed properly during pregnancy, or the brain started to develop correctly and then was damaged at some point during pregnancy.

Other Problems

Babies with microcephaly can have a range of other problems, depending on how severe their microcephaly is. Microcephaly has been linked with the following problems:

  • Seizures
  • Developmental delay, such as problems with speech or other developmental milestones (like sitting, standing, and walking)
  • Intellectual disability (decreased ability to learn and function in daily life)
  • Problems with movement and balance
  • Feeding problems, such as difficulty swallowing
  • Hearing loss
  • Vision problems

These problems can range from mild to severe and are often lifelong. Because the baby’s brain is small and underdeveloped, babies with severe microcephaly can have more of these problems, or have more difficulty with them, than babies with milder microcephaly. Severe microcephaly also can be life-threatening. Because it is difficult to predict at birth what problems a baby will have from microcephaly, babies with microcephaly often need close follow-up through regular check-ups with a healthcare provider to monitor their growth and development.

How Many Babies are Born with Microcephaly?

Microcephaly is not a common condition. Researchers estimate that about 1 in every 800-5,000 babies is born with microcephaly in the United States.

Causes and Risk Factors

The causes of microcephaly in most babies are unknown. Some babies have microcephaly because of changes in their genes. Other causes of microcephaly, including severe microcephaly, can include the following exposures during pregnancy:

  • Certain infections during pregnancy, such as rubella, toxoplasmosis, or cytomegalovirus
  • Severe malnutrition, meaning a lack of nutrients or not getting enough food
  • Exposure to harmful substances, such as alcohol, certain drugs, or toxic chemicals
  • Interruption of the blood supply to the baby’s brain during development

Some babies with microcephaly have been reported among mothers who were infected with Zika virus while pregnant. CDC scientists announced that enough evidence has accumulated to conclude that Zika virus infection during pregnancy is a cause of microcephaly and other severe fetal brain defects.

CDC continues to study birth defects, such as microcephaly, and how to prevent them. If you are pregnant or thinking about becoming pregnant, talk with your doctor about ways to increase your chances of having a healthy baby.

Zika Virus and Pregnancy

For information about the effects of Zika virus infection during pregnancy, visit CDC’s Zika and Pregnancy web page.

Diagnosis

Microcephaly can be diagnosed during pregnancy or after the baby is born.

During Pregnancy

During pregnancy, microcephaly can sometimes be diagnosed with an ultrasound test (which creates pictures of the body). To see microcephaly during pregnancy, the ultrasound test should be done late in the 2nd trimester or early in the third trimester. For more information about screening and confirmatory tests during pregnancy, visit CDC’s birth defects diagnosis web page.

After the Baby is Born

To diagnose microcephaly after birth, a healthcare provider will measure the distance around a newborn baby’s head, also called the head circumference, during a physical exam. The provider then compares this measurement to population standards by sex and age. Microcephaly is defined as a head circumference measurement that is smaller than a certain value for babies of the same age and sex. This measurement value for microcephaly is usually more than 2 standard deviations (SDs) below the average. The measurement value also may be designated as less than the 3rd percentile. This means the baby’s head is extremely small compared to babies of the same age and sex.

Head circumference growth charts for newborns, infants, and children up to age 20 years in the United States can be found on CDC’s growth charts website. Head circumference growth charts based on gestational age at birth (in other words, how far along the pregnancy was at the time of delivery) are also available from INTERGROWTH 21st . CDC recommends that health care providers use the WHO growth charts to monitor growth for infants and children ages 0 to 2 years of age in the United States.

Microcephaly can be determined by measuring head circumference (HC) after birth. Although head circumference measurements may be influenced by molding and other factors related to delivery, the measurements should be taken on the first day of life because commonly-used birth head circumference reference charts by age and sex are based on measurements taken before 24 hours of age. The most important factor is that the head circumference is carefully measured and documented. If measurement within the first 24 hours of life is not done, the head circumference should be measured as soon as possible after birth. If the healthcare provider suspects the baby has microcephaly, he or she can request one or more tests to help confirm the diagnosis. For example, special tests like like magnetic resonance imaging can provide critical information on the structure of the baby’s brain that can help determine if the newborn baby had an infection during pregnancy. They also can help the healthcare provider look for other problems that might be present .

Webinar on Surveillance

Microcephaly Webinar Thumbnail

Treatments

Microcephaly is a lifelong condition. There is no known cure or standard treatment for microcephaly. Because microcephaly can range from mild to severe, treatment options can range as well. Babies with mild microcephaly often don’t experience any other problems besides small head size. These babies will need routine check-ups to monitor their growth and development.

For more severe microcephaly, babies will need care and treatment focused on managing their other health problems (mentioned above). Developmental services early in life will often help babies with microcephaly to improve and maximize their physical and intellectual abilities. These services, known as early intervention , can include speech, occupational, and physical therapies. Sometimes medications also are needed to treat seizures or other symptoms.

Other Resources

The views of these organizations are their own and do not reflect the official position of CDC.

Mother To Baby (on behalf of the Organization of Teratology Information Specialists)
This website provides comprehensive information to mothers, healthcare professionals, and the general public about exposures during pregnancy.

References

  1. National Birth Defects Prevention Network. Major birth defects data from population-based birth defects surveillance programs in the United States, 2006-2010. Birth Defects Research (Part A): Clinical and Molecular Teratology. 2013;97:S1-S172.
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