Topic 11 Immunity.

Question 1

Define the following terms:
- Immunity.
- Immune system.
- Immune Response.

Answer 1

• Immunity is the body’s ability to fight off infections.
• The immune system is the body’s defense network against infections, involving cells, tissues, and organs that detect and destroy pathogens.
• An immune response is the body’s defense mechanism against non-self antigens.

Question 2

What is a pathogen?

Answer 2

A pathogen is a disease causing organism.

Question 3

What is a transmissible disease?

Answer 3

A transmissible disease is a disease in which the pathogen can be passed from one host to another.

Question 4

What are the lines of defence against disease?

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Answer 4

1. First line of defence: External.
2. Second line of defence: Internal and involves phagocytes.
3. Third line of defence: Internal and involves lymphocytes.

Question 5

What is the external defence system?

Answer 5

The external defense system is the body’s first line of protection against pathogens through physical, cellular and chemical barriers:

• Physical Barriers:
  Structures like skin and epithelial cells lining the mucous membranes (trap dirt and pathogens) that prevent pathogens from entering the body.
  Blood clotting that stops the loss of blood and prevents the entry of pathogens through wounds in the skin.
• Cellular Barriers:
  Phagocytes such as macrophages and neutrophils, which engulf and destroy pathogens that breach physical barriers.
• Chemical Barriers:
  Substances like hydrochloric acid in the stomach that kills bacteria that we ingest.

Question 6

What is the internal defence system?

Answer 6

The internal defense system is the body’s secondary line of protection against pathogens that have breached the external barriers. It includes:

• Immune cells such as white blood cells (e.g., macrophages, neutrophils) that identify and destroy pathogens.
• Inflammatory response that involves swelling, redness, and heat to isolate and eliminate pathogens and promote healing.
• Adaptive immune response with lymphocytes (B cells and T cells) that recognize and specifically target pathogens, and create memory cells for long-term protection.

Question 7

What is an antigen?

Answer 7

An antigens are large, complex macromolecules on cell surfaces, such as proteins, polysaccharides, glycoproteins, and glycolipids that are recognized as foreign to the body and stimulates an immune response.

There are two types of antigen: self and non-self antigens.

Question 8

What is the difference between self and non-self antigens?

Answer 8

Non-self antigens are molecules that originate from outside the body and are recognized by the immune system as foreign. The immune system triggers an immune response to eliminate them,

Self antigens are molecules produced by the body itself and does not trigger an immune response.

Question 9

What is the immune response?

Answer 9

The immune response is the body’s defence mechanism against non-self antigens.
It involves white blood cells that are made in the bones marrow:
They can be divided into two main types:
- Phagocytes for example neutrophils and monocytes (which mature into macrophages) which engulf and destroy pathogens.
- Lymphocytes for example B-lymphocytes and T-lymphocytes.

Reference to Chapter 8 (Transport in Mammals for more information on White Blood Cells).

Question 10

Describe the structure of:
- White blood cells.

Answer 10

• White blood cells all have a nucleus.
• Most white blood cells are larger than red blood cells, although one type, lymphocytes, may be slightly smaller.
• White blood cells are either spherical or irregular in shape, not a biconcave disc.

Question 11

Answer the following questions:
- Where are white blood cells made?
- What is the main purpose of white blood cells?
- What are the two types of white blood cells?

Answer 11

• White blood cells are made in the bone marrow.
• The main purpose of white blood cells is fighting disease.
• They can be divided into two main types:
  - Phagocytes.
  - Lymphocytes.

Question 12

What are phagocytes and what are the two types of phagocytes?

Answer 12

Phagocytes are cells that destroy invading microorganisms or pathogens by phagocytosis.

The two types of phagocytes are:

• Neutrophils: which is the most common type of phagocyte and can be recognised by its lobed nucleus and granular cytoplasm.
• Monocytes: are cells that can develop into a different type of phagocyte called a macrophage.

Question 13

Describe the function of the following white blood cell:
- Monocytes.

Answer 13

Monocytes are large phagocytic white blood cells with a large oval-shaped nucleus. They circulate in the bloodstream and can differentiate into macrophages when they migrate from the blood into tissues.
Their primary functions include* detecting pathogens as they have recepetor proteins on their cell surface that can detect non-self antigens* and destroying pathogens through phagocytosis as well as antigen presentation.

Question 14

What is a macrophage?

Answer 14

A type of phagocytic white blood cell found in tissues throughout the body and they act as antigen-presenting cells.

Question 15

What is antigen presentation?

Answer 15

Antigen presenting involves the display of antigens on the surface of specialized cells known as antigen-presenting cells (such as macrophages). This process is essential for the activation of T cells (a type of lymphocyte).

Question 16

How do macrophages work as antigen-presenting cells?

Answer 16

Macrophages are long-lived cells that help start immune responses. Instead of completely destroying pathogens, they break them down using the hydrolytic enzymes in their lysozymes and display pieces of them (antigens) on their surface. This allows lymphocytes to recognize and respond to these antigens.

Question 17

Describe the function of the following white blood cell:
- Neutrophils.

Answer 17

Neutrophils are a type of white blood cell containing a lobed nucleus and a granular cytoplasm. Neutrophils have receptor proteins on their membranes to identify pathogens as non-self.

Neutrophil’s cell surface membrane engulfs the pathogens and traps them within a phagocytic vacuole in a process called endocytosis. Lysosomes fuse with the phagocytic vacuoles releasing enzymes that breakdown the pathogens.

When there is an infection, large numbers of neutrophils are released from the bone marrow and accumulate at the site of infection. However, they are short-lived and die after digesting pathogens causing the formation of pus.

Question 18

What is phagocytosis?

Answer 18

Phagocytosis is the process by which a cell engulfs and ingests large particles, such as pathogens or dead cells. During phagocytosis, the cell’s membrane of a neutrophil surrounds the pathogen, forming a vesicle called a phagosome, and then digests the contents using enzymes.

Question 19

Describe the function of the following white blood cell:
- Lymphocytes.

Answer 19

Lymphocytes are a type of white blood cell that circulates in the blood and lymph when matured with a large round nucleus that almost fills the cell and only a small amount of cytoplasm. They destroy pathogens through the secretion of chemicals called antibodies (meaning that they only respond to specific non-self antigens) which attach to antigens and destroy the invading pathogens.

There are two types of lymphocytes:
- B-lymphocytes (B-cells).
- T-lymphocytes (T-cells).