Download Topic 6: Human health and physiology

Topic 6.3: Defense against infectious disease
Key facts
Defense against infectious disease
39. A pathogen is an organism or virus that causes a disease.
40. Antibiotics are ineffective against viruses since viruses do not have their own metabolic pathways.
41. Antibiotics are effective against bacteria because they block the bacterium’s metabolic pathways.
42. Because human cells are different from bacterial cells, antibiotics do not harm human cells.
43. The skin and mucous membranes provide a barrier against pathogens.
44. Skin has sebaceous glands that secrete lactic acid and fatty acids. These secretions make the surface of the
skin acidic, thereby controlling the growth of most pathogens.
45. Mucous membranes occur in the soft areas of the skin including the nose, trachea, vagina, and urethra.
Mucous membranes produce an enzyme called lysozyme that kills many bacteria.
46. Some mucous membranes produce so much sticky mucus that they trap pathogens.
47. The blood contains white blood cells, some of which are called phagocytes. Phagocytes are able to identify
pathogens and ingest them by phagocytosis.
48. Once the pathogens are inside the phagocytes, lysosomes release enzymes that kill and hydrolyze them.
49. Phagocytes are able to squeeze out of the capillaries to attack pathogens at the site of infection.
50. Antigens are foreign substances that do not belong in the body and thus stimulate the production of
antibodies.
51. Antibodies are proteins that recognize and bind to antigens, thus destroying them.
52. Antibodies are quite specific. Since there are large numbers of different antigens, there are large numbers of
different antibodies.
53. Antibodies are produced by a specific type of white blood cell called lymphocytes. Lymphocytes are quite
specific so there is a different lymphocyte for every antibody produced.
54. Each type of lymphocyte puts some of its antibody on its plasma membrane. These lymphocytes have
antigen-combining sites on their surface. When a pathogen enters the body, its antigens bind to the antibody
specific for it which is on the surface of a circulating lymphocyte.
55. When the antigen binds to the antibody the lymphocyte is stimulated to produce copies of clones of it.
These clones of cells produce large amounts of the specific antibody necessary to disable the incoming
pathogen.
56. AIDS is known as a syndrome because it consists of a set of symptoms that are bound together. Ultimately
AIDS decreases the ability of one’s immune system to function, thus weakening the body and eventually
causing death.
57. HIV or human immunodeficiency virus is the pathogen that causes AIDS. This virus specifically attacks a
lymphocyte known as a T-lymphocyte to cause the syndrome.
Weakening and death is due to the death of the lymphocytes with the resulting inability to produce antibodies.
58. HIV can only survive very briefly outside the body and cannot easily pass through the skin.
59. Its transmission involves the transfer of body fluids from one infected person to an uninfected person.
Means of transmission include skin breaks or cuts in the vagina, penis, mouth or intestine during vaginal, anal
or oral sex.
60. HIV may also be transmitted via blood on hypodermic needles that are shared. It may also be transmitted
via blood transfusions.
61. HIV may cross the placenta from mother to baby. It may also pass to the baby from mother during breastfeeding.
62. Social implications of AIDS include
 Grief suffering by family and friends
 Financial stress
 Difficulty of AIDS patients in getting employment, housing, etc
 Affecting sexual activity due to fear of the disease
63. Most feel there is a moral obligation of those with technology and financial resources to help those without
such whom are suffering from AIDS. Africa, especially the southern region is highly affected by the disease.
64. State the difference between an antigen and an antibody.
65. Explain antibody production.
66. Explain how the skin and mucous membranes prevent entry of pathogens into the body
67. Explain why antibiotics are used to treat bacterial but not viral diseases.
68. State one use of monoclonal antibodies in diagnosis and one use in treatment.
Diagnosis:
Treatment:
69. Explain how antibiotic resistance develops in bacteria
70. Describe the transmission of malaria.