AIDS wasn't discovered until the early 1980s, when doctors in the United States noticed clusters of patients suffering from highly unusual diseases. First seen in gay men in New York and California, these illnesses included Kaposi's sarcoma, a rare skin cancer, and a type of lung infection carried by birds.
Soon cases were also detected in intravenous drug users and recipients of blood transfusions. By 1982 the illness had a name—acquired immune deficiency syndrome. AIDS has since killed around 25 million people worldwide, orphaning 12 million children in Africa alone.
AIDS is triggered by a virus acquired through direct contact with infected body fluids. The virus causes an immune deficiency by attacking a type of white blood cell that helps to fight infections. Because this leads to various diseases, not a single illness, AIDS is referred to as a syndrome.
The virus is called HIV (human immunodeficiency virus).
Unprotected sex is HIV's main route into humans, where it targets the white blood cell known as CD4. The virus replicates inside, eventually bursting out and flooding the body in the billions. The immune system then kicks in, and the body and the virus wage all-out war. During the height of battle billions of CD4 cells can be destroyed in a single day. As the cell count drops, the immune system begins to fail and opportunistic infections such as tuberculosis take hold.
Ape Origins
AIDS is thought to have originated in Africa, where monkeys and apes harbor a virus similar to HIV called SIV (simian immunodeficiency virus). Scientists believe the illness first jumped to humans from wild chimpanzees in central Africa.
How the disease crossed the species barrier remains a puzzle. The leading theory is that it was picked up by people who hunted or ate infected chimpanzees. Researchers have dated the virus in humans to about 1930 using scientific estimates of the time it's taken for different strains of HIV to evolve.
AIDS today is a global pandemic affecting every country. In 2006, an estimated 39.5 million people had HIV/AIDS. Almost three million of them died.
The region most devastated by the disease is sub-Saharan Africa. It accounts for two-thirds of the world's HIV cases and nearly 75 percent of deaths due to AIDS. Infection rates vary, with southern African countries worst affected. In South Africa, an estimated 29 percent of pregnant women have HIV. Infection rates in Zimbabwe's adult population exceed 20 percent, while in Swaziland a third of adults are HIV-positive. Poverty, inadequate health care and education, and promiscuity have all been highlighted to explain Africa's AIDS nightmare.
Treatments But No Cure
Efforts to prevent the spread of AIDS focus on sex education and the use of condoms. Other measures, such as male circumcision, may also help to cut the risk of sexually transmitted infection.
There is no cure for AIDS, but treatments are available that combat its onset. Antiviral drugs work by slowing the replication of HIV in the body. These drugs need to be used in combination because the virus readily mutates, creating new and often drug-resistant strains. Such treatments are expensive, however, and are still denied to millions of people in the developing world.
In the future, the hope is for an AIDS vaccine that would prevent HIV infection. Researchers are currently working on more than 30 potential candidates.
© 1996-2009 National Geographic Society.
All rights reserved.
Making sense of the brain's mind-boggling complexity isn't easy. What we do know is that it's the organ that makes us human, giving people the capacity for art, language, moral judgments, and rational thought. It's also responsible for each individual's personality, memories, movements, and how we sense the world.
All this comes from a jellylike mass of fat and protein weighing about 3 pounds (1.4 kilograms). It is, nevertheless, one of the body's biggest organs, consisting of some 100 billion nerve cells that not only put together thoughts and highly coordinated physical actions but regulate our unconscious body processes, such as digestion and breathing.
The brain's nerve cells are known as neurons, which make up the organ's so-called "gray matter." The neurons transmit and gather electrochemical signals that are communicated via a network of millions of nerve fibers called dendrites and axons. These are the brain's "white matter."
The cerebrum is the largest part of the brain, accounting for 85 percent of the organ's weight. The distinctive, deeply wrinkled outer surface is the cerebral cortex, which consists of gray matter. Beneath this lies the white matter. It's the cerebrum that makes the human brain—and therefore humans—so formidable. Whereas animals such as elephants, dolphins, and whales have larger brains, humans have the most developed cerebrum. It's packed to capacity inside our skulls, enveloping the rest of the brain, with the deep folds cleverly maximizing the cortex area.
The cerebrum has two halves, or hemispheres. It is further divided into four regions, or lobes, in each hemisphere. The frontal lobes, located behind the forehead, are involved with speech, thought, learning, emotion, and movement. Behind them are the parietal lobes, which process sensory information such as touch, temperature, and pain. At the rear of the brain are the occipital lobes, dealing with vision. Lastly, there are the temporal lobes, near the temples, which are involved with hearing and memory.
Movement and Balance
The second largest part of the brain is the cerebellum, which sits beneath the back of the cerebrum. It is responsible for coordinating muscle movement and controlling our balance. Consisting of both grey and white matter, the cerebellum transmits information to the spinal cord and other parts of the brain.
The diencephalon is located in the core of the brain. A complex of structures roughly the size of an apricot, the two major sections are the thalamus and hypothalamus. The thalamus acts as a relay station for incoming nerve impulses from around the body that are then forwarded to the appropriate brain region for processing. The hypothalamus controls hormone secretions from the nearby pituitary gland. These hormones govern growth and instinctual behavior such as eating, drinking, sex, anger, and reproduction. The hypothalamus, for instance, controls when a new mother starts to lactate.
The brain stem, at the organ's base, controls reflexes and crucial, basic life functions such as heart rate, breathing, and blood pressure. It also regulates when you feel sleepy or awake.
The brain is extremely sensitive and delicate, and so requires maximum protection. This is provided by the surrounding skull and three tough membranes called meninges. The spaces between these membranes are filled with fluid that cushions the brain and keeps it from being damaged by contact with the inside of the skull.
© 1996-2009 National Geographic Society.
All rights reserved.
All this comes from a jellylike mass of fat and protein weighing about 3 pounds (1.4 kilograms). It is, nevertheless, one of the body's biggest organs, consisting of some 100 billion nerve cells that not only put together thoughts and highly coordinated physical actions but regulate our unconscious body processes, such as digestion and breathing.
The brain's nerve cells are known as neurons, which make up the organ's so-called "gray matter." The neurons transmit and gather electrochemical signals that are communicated via a network of millions of nerve fibers called dendrites and axons. These are the brain's "white matter."
The cerebrum is the largest part of the brain, accounting for 85 percent of the organ's weight. The distinctive, deeply wrinkled outer surface is the cerebral cortex, which consists of gray matter. Beneath this lies the white matter. It's the cerebrum that makes the human brain—and therefore humans—so formidable. Whereas animals such as elephants, dolphins, and whales have larger brains, humans have the most developed cerebrum. It's packed to capacity inside our skulls, enveloping the rest of the brain, with the deep folds cleverly maximizing the cortex area.
The cerebrum has two halves, or hemispheres. It is further divided into four regions, or lobes, in each hemisphere. The frontal lobes, located behind the forehead, are involved with speech, thought, learning, emotion, and movement. Behind them are the parietal lobes, which process sensory information such as touch, temperature, and pain. At the rear of the brain are the occipital lobes, dealing with vision. Lastly, there are the temporal lobes, near the temples, which are involved with hearing and memory.
Movement and Balance
The second largest part of the brain is the cerebellum, which sits beneath the back of the cerebrum. It is responsible for coordinating muscle movement and controlling our balance. Consisting of both grey and white matter, the cerebellum transmits information to the spinal cord and other parts of the brain.
The diencephalon is located in the core of the brain. A complex of structures roughly the size of an apricot, the two major sections are the thalamus and hypothalamus. The thalamus acts as a relay station for incoming nerve impulses from around the body that are then forwarded to the appropriate brain region for processing. The hypothalamus controls hormone secretions from the nearby pituitary gland. These hormones govern growth and instinctual behavior such as eating, drinking, sex, anger, and reproduction. The hypothalamus, for instance, controls when a new mother starts to lactate.
The brain stem, at the organ's base, controls reflexes and crucial, basic life functions such as heart rate, breathing, and blood pressure. It also regulates when you feel sleepy or awake.
The brain is extremely sensitive and delicate, and so requires maximum protection. This is provided by the surrounding skull and three tough membranes called meninges. The spaces between these membranes are filled with fluid that cushions the brain and keeps it from being damaged by contact with the inside of the skull.
© 1996-2009 National Geographic Society.
All rights reserved.
On usually, man's brain are 9% larger than woman's. According to a 2006 review by the National Intitute of Mental Health. The reports authors stresses that this defference does not mean that men are more intelligent than women.
By WK April 09''
What to do now? No idea.....
How to drive? Which one is real?
Call bomba.....
Haizzzzzzzz.... My god! Going to crazy...Prepared by WK April 09''
Photo form METACAFE
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