1. Describe how a human muscle is organized. How does the structure of the muscle reflect the function?
2. What changes take place in the immune system of a person infected with HIV, and how might that infection develop into AIDS?
Please be detailed in your explanations. It would be greatly appreciated! Thanks! Human Muscle
Muscle is composed of thousands of muscle fibers, each composed of a single muscle cell. As shown in Figure 1 , a muscle cell contains a series of ultramicroscopic filaments called myofibrils. Each myofibril is a muscle cell that contains units called sarcomeres. Sarcomeres contain thick microfilaments composed of the protein myosin. Sarcomeres also contain thin microfilaments composed of the protein actin. The actin and myosin filaments are arranged parallel to one another, with the myosin filaments' molecular 鈥渉eads鈥?protruding toward the actin filaments. In skeletal muscle, the overlapping actin and myosin filaments give the muscle fiber a banded, or striated, appearance. Hence the muscle is striated muscle.
Types of muscle
The human body has three major types of muscle. The muscle type discussed previously is striated muscle because the fibers' overlapping actin and myosin filaments give it a banded appearance (see Figure 1 ). This muscle is found in the limbs and is also called skeletal muscle. It operates under voluntary control and so is additionally known as voluntary muscle.
The second muscle type is smooth muscle, which has few actin and myosin filaments; therefore, it has few striations. Smooth muscle is found in the linings of the blood vessels, along the gastrointestinal tract, in the respiratory tract, and in the urinary bladder. Because it operates without voluntary control, it is sometimes called involuntary muscle.
The third muscle type is cardiac muscle, which is found in the heart. It has striations because it has multiple actin and myosin filaments, but it is involuntary muscle. The actin and myosin filaments in cardiac muscle exist as intertwined branches that form a conducting network for nerve impulses.
second answer:
AIDS is caused by a virus called HIV, the Human Immunodeficiency Virus. If you get infected with HIV, your body will try to fight the infection. It will make "antibodies" -- special molecules to fight HIV.
A blood test for HIV looks for these antibodies. If you have them in your blood, it means that you have HIV infection. People who have the HIV antibodies are called "HIV-Positive." Fact Sheet 102 has more information on HIV testing.
Being HIV-positive, or having HIV disease, is not the same as having AIDS. Many people are HIV-positive but don't get sick for many years. As HIV disease continues, it slowly wears down the immune system. Viruses, parasites, fungi and bacteria that usually don't cause any problems can make you very sick if your immune system is damaged. These are called "opportunistic infections." See Fact Sheet 500 for an overview of opportunistic infections.
How Do You Get AIDS?
You don't actually "get" AIDS. You might get infected with HIV, and later you might develop AIDS. You can get infected with HIV from anyone who's infected, even if they don't look sick and even if they haven't tested HIV-positive yet. The blood, vaginal fluid, semen, and breast milk of people infected with HIV has enough of the virus in it to infect other people. Most people get the HIV virus by:
* having sex with an infected person;
* sharing a needle (shooting drugs) with someone who's infected;
* being born when their mother is infected, or drinking the breast milk of an infected woman.
Getting a transfusion of infected blood used to be a way people got AIDS, but now the blood supply is screened very carefully and the risk is extremely low.
There are no documented cases of HIV being transmitted by tears or saliva, but it is possible to be infected with HIV through oral sex or in rare cases through deep kissing, especially if you have open sores in your mouth or bleeding gums. For more information, see the following Fact Sheets:
* 150: Stopping the Spread of HIV
* 151: Safer Sex Guidelines
* 152: How Risky Is It?
The Centers for Disease Control and Prevention (CDC) estimates that 1 million to 1.2 million U.S. residents are living with HIV infection or AIDS; about a quarter of them do not know they have it. About 75 percent of the 40,000 new infections each year are in men, and about 25 percent in women. About half of the new infections are in Blacks, even though they make up only 12 percent of the US population. In the mid-1990s, AIDS was a leading cause of death. However, newer treatments have cut the AIDS death rate significantly. For more information, see the U.S. Government fact sheet at www.niaid.nih.gov/factsheets/aidsstat.ht...
What Happens if I'm HIV Positive?
You might not know if you get infected by HIV. Within a few weeks after being infected, some people get fever, headache, sore muscles and joints, stomach ache, swollen lymph glands, or a skin rash for one or two weeks. Most people think it's the flu. Some people have no symptoms. Fact Sheet 103 has more information on the early stage of HIV infection.
The virus will multiply in your body for a few weeks or even mon |
