I'm kinda confused about the transmission of HIV into the blood stream. Everything that I've been reading states that any opening into the blood stream is an opening for HIV. But what does it take for HIV to "take hold" and survive. one cell or not? I'm not a med-major, just wondering if exposure to HIV means, you will get HIV. I know the "possible" to get HIV from one exposure, but what does it take for HIV to kick the hell out of your immune system?
Your question is complicated and is not an easy one to answer in this forum. Specifically why someone does or does not get infected at a particular moment when they are exposed to HIV is not very clear because we can't actually see it happen. Ideas about the actual mechanics of infection are based on animal and test tube studies. Most theories about the mechanics of infection in humans are extrapolated from these studies. Sexual contact in the real world will generally not mimic the controlled conditions of laboratory studies, making it difficult for anyone to truly "know" what happens.
HIV, like other viruses, needs a host to survive. The virus navigates and reproduces itself within the host by using the host's white blood cells, which comprise the immune system. Infection happens when HIV fuses with these cells, is carried to lymphatic tissue, and begins manufacturing copies of itself while simultaneously incapacitating the function of the cells that it uses. HIV can fuse with cells in the mucosal membranes that transport the virus to other cells in the body or through direct access to the bloodstream. Infection is probably determined by HIV's efficacy in initially fusing with cells.
The process of infection is complex and there is much more that we need to learn about the mechanics of HIV in humans.