The human immunodeficiency virus (HIV) that causes the disease known as aids selectively infects helper T cells (CD4+).
This retrovirus also infects macrophages and dendritic cells. When CD4+ T cell numbers decrease below a critical level (due to the killing of this cells with different mechanisms), cell-mediated immunity is lost. As a result, the body becomes progressively more susceptible to infections, leading to the development of AIDS.
<span> HIV can be transmitted only via body fluids like blood, semen, pre-seminal fluid, rectal fluids, vaginal fluids, and breast milk, which means that people usually get or transmit HIV through sexual behaviours and use of the needle. For HIV infection, these fluids must come in direct contact with a mucous membrane or damaged tissue. Another way is to be directly injected into the bloodstream (from a needle for example).</span>
D. It expands and contrasts
Hope this helps!!
The system that controls and coordinates
the body through hormones is the <span>endocrine system.</span>
<span>Endocrine system produces hormones and then these hormones
transmit the messages to various cells within the body. Hormones have great
importance in our body system and even our body is functioning due to hormones.
If hormones are disturbed it can lead to
many diseases.</span>
