Aging and death are just as important as development and birth.
If animals did not age and eventually die, their increasing numbers would overwhelm the ability of the Earth to support life.
Multiple factors affect the aging process.
Scientists who study gerontology believe that aging is preprogrammed.
The idea is supported by the fact that children of long-lived parents live longer than children of short-lived parents.
Studies show that identical twins have the same life span as nonidentical twins.
The hypotheses of cellular aging and damage accumulate in this section.
The life span of the worms can be double if the activity of a hormone receptor similar to the insulin receptor is decreased.
Small-breed dogs, such as poodles and terriers, which may live 15 to 20 years, have lower levels of an analogous receptor compared to large-breed dogs that live 6 to 8 years.
Studies of the behavior of cells grown in the lab suggest a genetic influence on aging.
A limited number of differentiated cells can be divided.
Telomeres protect the ends of the chromosomes.
Cells with shorter telomeres tend to have fewer divisions.
Stem cells have an enzyme called telomerase, which replenishes the length of the telomeres and makes stem cells immortal.
Cancer cells are similar to stem cells in that they have an active telomerase enzyme which allows them to replicate continuously.
Stem cells and cancer cells have begun to close in on the genetic factors that cause cellular aging.
The powerhouses of the cell are the mitochondria.
Free radicals are created when the mitochondria harvest the energy contained in sugars and fats.
Free radicals have an extra electron.
To become stable, free radicals give an electron to another molecule.
The cell loses its internal functions as these molecules become unable to function.
This may cause cell death.
Scientists have found that a high-calorie diet increases the levels of free radicals.
Studies on model organisms have shown that a low-calorie diet can extend the life span.
It is possible to reduce the negative effects of free radicals by increasing one's consumption of natural antioxidants, such as those present in brightly colored and dark-green vegetables and fruits.
Chemicals in nuts, fish, shellfish, and red wine have been shown to reduce our exposure to free radicals and slow the aging process.
According to experts, genes account for 25% of what determines the length of life.
A set of hypotheses suggests that aging involves damage over time.
The average human life expectancy was 45 years in 1900.
A baby born in the US this year has a life expectancy of 78 years.
Most of the increase in life span is due to better medical care and the application of scientific knowledge about how to prolong our lives, because human genes have not changed much in such a short time.
There are two basic types of cellular damage.
The first type can be thought of as agents that are unavoidable.
The inability of the blood vessels, heart, and lungs to function as they once did may be explained by this cross-linking.
The first step in a cross-linking process is the attachment of glucose to any type of protein.
They are experimenting with drugs to prevent cross-linking.
Poor diet or exposure to the sun are some of the sources of cellular damage.
The average age of the human population is now older than ever before.
In the next 50 years, the number of people over the age of 65 will increase.
The effects of aging on the various body systems should be considered before discussing possible mechanisms behind the aging process.
The skin becomes thinner and less elastic as the number of elastic fibers decreases and the collagen fibers become cross-linked to each other.
Older people are more likely to feel cold because there is less fat in the body.
The changes result in sagging and wrinkling of the skin.
The sweat glands become less active as people get older.
The hair on the limbs is thin because there are fewer hair follicles.
Older people have a decrease in the number of melanocytes, which makes their hair gray and their skin pale.
Some of the remaining cells are larger and there are spots on the skin.
Problems with cardiovascular function are usually related to diseases.
Even with normal aging, the heart muscle may increase in size as it compensates for its decreasing strength.
It takes longer for the heart rate and blood pressure to return to normal after being stressed, even for the most fit older athlete.
The blood vessels are affected by aging.
The elastic fibers in the middle of the arteries become more cross-linked and rigid with time.
A gradual increase in blood pressure with age is caused by these changes and a decrease in the internal diameter of arteries.
More than 50% of older adults have chronic hypertension.
Changes are common in Western industrialized countries, but not in agricultural societies.
A sensible exercise program, along with a diet low in cholesterol and saturated fat, may help prevent age-related cardiovascular disease.
Many of the immune system's functions become compromised as people age.
Because a healthy immune system normally protects the entire body from infections, toxins, and at least some types of cancer, some investigators believe that losses in immune function can play a major role in the aging process.
Section decreasing in size and eventually becoming replaced by fat and connective tissue is an important site for T-cell maturation.
The ability of older people to generate T-cell responses decreases due to the fact that the thymus of a 60-year-old adult is less than that of a newborn.
Older animals have already responded to most of the antigens to which they will be exposed in their life and this may be the reason for this.
Other immune functions are affected by aging.
Most B-cell responses are dependent on T cells.
The elderly don't respond as well to vaccinations as young people do.
There are challenges in protecting older people against diseases that can be prevented with an annual vaccine.
Researchers may be able to learn more about immunity in the elderly by investigating how these cells remain active throughout a normal human life span.
The aging process affects other systems, but the digestive system is not.
More decay and periodontal disease can be caused by the decrease in saliva production.
Less efficient metabolism of drugs or toxins can be caused by reduced blood flow to the liver.
As a person gets older, less medication is needed to maintain the same level in the bloodstream.
Cardiovascular problems are often accompanied by respiratory disorders.
The elasticity of lung tissues is decreasing.
Unless the demand for oxygen increases, these effects will not be noticed.
The blood supply to the kidneys is reduced.
The kidneys become less efficient as they become smaller.
The elderly are more likely to get dehydrated than young people.
An enlarged urethra can cause frequent or difficult urination in men.
The brain loses 20% of its weight and volume between the ages of 20 and 90.
Reduced blood flow in narrowed blood vessels may be the cause of neuron death.
Recent studies using advanced techniques show that most age related brain function loss is not due to the loss of neurons.
Alterations in complex chemical reactions or increased inflammation in the brain may be the reason for decreased function.
Recent studies have shown that lifestyle factors can affect the aging brain.
There were fewer Alzheimer-like changes in the brains of animals on a restricted-calorie diet.
Other positive factors that may help maintain a healthy brain include lifelong learning, regular exercise, and getting enough sleep.
Aging requires more stimulation for taste, smell, and hearing.
The inability to detect smoke, gas leaks, or spoiled food can be a serious health hazard.
After age 50, most people lose the ability to hear higher frequencies and this can make it difficult to identify individual voices in a group.
Many people have to wear reading glasses as they get older.
Cataracts and other eye disorders become more common in old age.
In the twenties or thirties, muscle mass generally decreases due to decreases in both the size and the number of muscle fibers.
Most people have less muscle mass when they reach 90.
Regular exercise can slow the decline.
With age, bones shrink in size and density.
As we age, we lose height due to compression of the spine and changes in posture.
The decline in bone mass is a normal part of aging.
The loss of bone mass can be slowed by a proper diet and exercise program.
Many different organs of the body can be affected by the aging of the hormonal system.
The changes are complex with some hormones decreasing and others increasing.
A lower metabolism is caused by a decline in the activity of the thyroid gland.
After age 50, the cells become less sensitive to the effects of diabetes and the production ofinsulin by the pancreas will remain stable.
Human growth hormone levels decline with age, but it is not likely that taking injections will cure aging.
One study found that people with lower levels of HGH lived longer than those with higher levels.
Men in their twenties have the highest testosterone levels.
testosterone levels decrease after 30 years of age.
There is a link between low testosterone levels and a decrease in sex drive, excessive weight gain, osteoporosis, general fatigue, and depression.
The levels below which testosterone treatment should be started are controversial.
Testosterone replacement therapy, whether through injection, patches, or gels, is associated with a number of side effects such as enlargement of the prostrate, skin reactions, and the production of too many red blood cells.
The period in a woman's life during which the ovarian and uterine cycles cease is called menopause.
The hormones produced by the pituitary are no longer being produced by the ovaries.
As long as menstruation occurs, it is possible for a woman to have a baby.
The physical symptoms of menopause include hot flashes, dizziness, headaches, insomnia, and depression.
In 2002, a large clinical study showed that HRT caused more health problems than it prevented, so it was stopped.
Doctors no longer recommend long-term HRT for the prevention of postmenopausal conditions.
As a group, females live longer than males.
When women are younger, it is likely that they have protection against cardiovascular disorders.
In their forties, males suffer a marked increase in heart disease, but an increase is not noted in females until after menopause, when women lead men in the incidence of stroke.
Men are more likely to have a heart attack than women are.
The oocyte has only one sperm entering it.
The early stages of development in animals are cellular, tissue, and organ stages.
Organ formation is related to germ layers.
The neural tube in frog embryos is formed by the notochord.
The axes of the body are determined by some morphogen genes.
The concept of sequential sets of master genes code for the next set of master genes has emerged.
The homeodomain is the portion of theProtein that Binds to DNA.
Homeotic genes must have arisen early in the history of life because they have been found in a wide variety of organisms.
As the embryo moves toward the uterus, it undergoes fertilization in a uterine tube.
The blastocyst is the endometrium of the uterus.
Fetal and maternal blood is exchanged.
Neural tube and heart formation are the first stages of organ development.
There is a steady progression of organ formation.
The fetus adds weight during fetal development.
The aging process is important for the evolution of animals.
Every organ system of the human body is affected by aging.
Various hypotheses have been advanced to explain the aging process, which can be grouped into those suggesting that aging is genetically preprogrammed and those emphasizing the damage that occurs over time.
Pick the best answer for the question.
Only one sperm enters andfertilizes a human ovum.
Growth, differentiation, and morphogenesis are required for developmental changes.
Page 807 is about the development of another tissue.
The statement should be matched with the terms in the key.
This diagram shows the placement of the extraembryonic membranes, and should be labeled with a function for each one.
The start of menopause is due to a lack of ovarian follicles.
They have their own genetic material.
There are no contributions from the father when it comes to the genes of theMitochondrial.
Women can purchase fertility tests over the counter at drug stores.
As more women delay their first pregnancies until they are older, these tests are becoming more popular.
The hormones found in a woman's urine are the subject of many of these tests.
The Biological Systems feature suggests that women of childbearing age begin taking precautions to prevent birth defects.
Tall smokestacks in the Midwest caused acid rain in the Northeast.
The only way to solve an ecological problem is to stop the activity that caused it.
It needs to be dealt with head-on.
Today's ecology is also an experimental science, but it describes the portions of the sea, land, and air that contain living organisms.
Ecologists use the scientific process to figure out how the environment will respond to humans.
Ecologists use models to make predictions about future ecological changes.
One of the main goals of biology is to preserve species.
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