CIE IGCSE Biology: 复习笔记:16.1.6 Sexually Transmitted Infections

CIE IGCSE Biology: 复习笔记:16.1.6 Sexually Transmitted Infections



  • Unprotected sexual intercourse can lead to the transfer of pathogens via exchange of body fluids
  • Infections passed on in this way are known as sexually transmitted infections (STIs)
  • An example of an STI is HIV (Human Immunodeficiency Virus), the virus that usually leads to the development of acquired immunodeficiency disease (AIDS)
  • HIV can also be spread via sharing needles with an infected person, blood transfusions with infected blood and from mother to fetus through the placenta and mother to baby via breastfeeding



How HIV Affects the Immune System


  • Immediately after infection, people often suffer mild flu-like symptoms
  • These symptoms pass and for a period of time infected people might not know they are infected
  • The virus infects a certain type of lymphocyte of the body's immune system
  • Normally lymphocytes seek out and destroy pathogens that enter the body, producing antibodies that attach to pathogens, enhancing phagocytic activity
  • However HIV avoids being recognised and destroyed by lymphocytes by repeatedly changing its protein coat
  • It then infects a certain type of lymphocyte and uses the cells’ machinery to multiply
  • This reduces the number of lymphocytes of the immune system, and also the number of antibodies that can be made
  • This decreases the body’s ability to fight off infections, eventually leading to AIDS (Acquired immunodeficiency)


How-HIV-affects-lymphocytesHow HIV affects lymphocytes


Controlling the Spread of STIs


  • The spread of STIs such as HIV are best controlled by:
    • Limiting the number of sexual partners an individual has
    • Not having unprotected sex, but making sure to always use a condom
    • Getting tested if unprotected sex or sex with multiple partners has occurred
    • Raising awareness by education programmes