Chapter 7

Question 1

Pathogen

Answer 1

Causative agent of disease

Question 2

First line of defence

Answer 2

Intact skin is our main physical barrier
Chemical barriers prevent pathogen growth
Natural flora compete with potential pathogens (harmless bacteria that live in our bodies, not controlled by immune system), found everywhere
Compete for space and nutrients
Inhibits growth of pathogenic bacteria

Question 3

Second line of defence

Answer 3

Complementary proteins kill bacteria directly or activate other components of the innate immune system to eliminate pathogen

Inflammatory response (basophil releases histamine, mast is similar but found in tissues)
• Release of histamine causing blood vessels to dilate allowing phagocytes to reach the site of infection. Also increases blood supply (because pathogens are taking over cells, less nutrients available)
Attracts phagocytes

Pus- dead phagocytes from engulfing too many bacteria

Phagocytic cells (neutrophil, monocyte-long lived in circulation, macrophage-long-lived in tissues)
	• phagocytes bind to target pathogen and engulfs it by endocytosis, phagosome forms and fuses with lysosome which release antimicrobial proteins to break down pathogens, waste is discharged, phagocyte displays bacteria antigen
	• engulf bacteria and operate in a positive feedback system (stops producing histamine to stop cycle bill, if not excessive swelling), and attracts other immune cells

Cytotoxic cells (eosinophil kills parasites (cellular pathogens), NK cell kill virus infected cells (non-cellular infected cells)
	• Release molecules that trigger apoptosis, do they inflammatory**

Dendritic cells
• Similar to phagocytic macrophage, present antigens to specific immune system

Interferons make uninfected cells more resistant

Question 4

Humoral response with reference to antibodies

Answer 4

B cells are activated by their complimentary raw antigen (clonal selection)
A specific T helper cell stimulate their proliferation through a secretion of cytokines(clonal expansion)
B cells divide to form plasma cells and memory cells:

Plasma cells make one unique antibody which is specific to one antigen (unique antigen-binding site which is effective)
Memory cells live for as long as we live, don’t secrete antibodies but give rise to plasma cells

Antibodies- ‘y-shaped proteins’, four polypeptide chains (two short, two long) that inactivate antigens and mark the pathogen to attract other immune cells

Defend against extracellular pathogens

Question 5

Cell mediated response

Answer 5

T cytotxic cells are activated by the antignes displayed on the MHC by infected cells
T helper cells stimulate the proliferation of T cytotoxic cells through a secretion of cytokines
T cytotoxic cells attack and induce apoptosis to the infected cell
Defend against intracellular pathogens
T helper cells are activated by the binding of a complimentary/specific antigen to its receptors through an APC. They then proliferate and stimulate the proliferation of B and T cells through cytokines