Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Definition: A sexually transmitted infection (STI) is an infection that is transmitted via body fluids through sexual contact. Examples include HIV, gonorrhea, and syphilis.
HIV (Human Immunodeficiency Virus): A retrovirus that targets the immune system, specifically the -helper cells (lymphocytes).
AIDS (Acquired Immunodeficiency Syndrome): The advanced stage of HIV infection where the immune system is so weakened (low -cell count) that the body can no longer fight off opportunistic infections or cancers.
Transmission Methods: HIV is transmitted through the exchange of body fluids such as blood, semen, vaginal secretions, and breast milk. This occurs via unprotected sexual intercourse, sharing of contaminated needles, or from mother to child during birth/breastfeeding.
Mechanism of Action: HIV infects lymphocytes and uses its reverse transcriptase enzyme to integrate its into the host's . The destruction of -helper cells leads to a decrease in the production of antibodies by -lymphocytes.
Prevention: Use of barrier contraception such as condoms ( mechanical barriers), screening of blood for transfusions, use of sterile needles, and pre-exposure prophylaxis ().
Treatment: There is no current cure, but Highly Active Antiretroviral Therapy () can suppress viral replication and maintain high counts.
📐Formulae
💡Examples
Problem 1:
Explain the biological reason why a person with advanced HIV () often dies from common infections like pneumonia or tuberculosis.
Solution:
The virus destroys -helper cells. In the absence of these cells, the immune system cannot effectively signal -lymphocytes to produce specific antibodies (, ).
Explanation:
Because the concentration of functional -cells falls below a critical threshold (typically ), the body loses its adaptive immune response, allowing opportunistic pathogens to proliferate.
Problem 2:
How does the use of a latex condom act as a preventative measure against the transmission of HIV during intercourse?
Solution:
A condom acts as a mechanical barrier that prevents the exchange of bodily fluids.
Explanation:
Since the virion is approximately in diameter, a continuous latex membrane prevents the virus-carrying fluids (semen or vaginal secretions) from crossing the barrier and entering the bloodstream of the partner.