[Unit 5.1] | Defense Mechanisms

Question 1

What is a pathogen?

Answer 1

A disease causing micro-organism.

Question 2

What 2 types of non-specific and 2 types of specific defense mechanism exist?

Answer 2

• NS: Physical Barriers
• NS: Phagocytosis

• S: Cell-Mediated Response (B-Cells)
• S: Humoral Response (T-Cells)

Question 3

How do lymphocytes distinguish self and non-self cells?

Answer 3

• Proteins

with enormous variety and highly specific tertiary structures on cell surfaces.

Question 4

List 4 examples of non-self cells.

Answer 4

• Pathogens
• Non-self cells from organisms of the same species
• Toxins from pathogens
• Abnormal body cells (ie. cancer)

Question 5

Why are transplated organs often rejected by the body?

Answer 5

• The antigens cause lymphocytes to recognise them as non-self cells.

Question 6

How do lymphocytes recognise self cells?

Answer 6

• There are around 10 million lymphocytes present at any time, each with a different tertiary structure.

• In the fetus, infection is rare (due to the placenta) and therefore lymphocytes only collide with self-cells.
• Lymphocytes with receptors that fit these self-cells are destroyed, leaving only the ones that recognise foreign material.

• The same happens in adult bone marrow.
• Any lymphocytes with tertiary shapes that complement self-antigens undergo apoptosis (cell death) and only those that respond to non-self cells remain.