Human Body Defense Mechanisms

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Questions and Answers

What substance is contained in tears and saliva that helps to digest bacterial cell walls?

Hydrochloric acid

Phagocytes

Lysozyme (correct)

Mucus

The skin ceases to be an effective barrier only when it is punctured.

True

What is the role of mucus in the respiratory tract?

To trap pathogens and prevent them from penetrating the underlying membranes.

The process by which phagocytes engulf pathogens is called __________.

phagocytosis Signup and view all the answers

Match the following cells with their characteristics:

Polymorphs = Most common phagocytes that arrive first Macrophages = Develop from monocytes and can engulf larger pathogens Phagocytes = Cells that perform phagocytosis T cells = Involved in adaptive immunity Signup and view all the answers

What is the main function of hydrochloric acid in the stomach?

To kill most pathogens Signup and view all the answers

Phagocytes are specific immune cells that target only one type of pathogen.

False Signup and view all the answers

What happens to capillaries during an inflammatory response?

They become leaky, allowing plasma to seep into surrounding areas. Signup and view all the answers

What is the main function of antigen-presenting cells?

Present antigens to T-cells Signup and view all the answers

Suppressor T cells are responsible for enhancing the immune response.

False Signup and view all the answers

What type of cells do Killer T cells destroy?

Infected cells or abnormal cells Signup and view all the answers

Helper T cells secrete the protein __________ to limit virus replication.

interferon Signup and view all the answers

Which type of T cell is primarily involved in stimulating B cells?

Helper T cells Signup and view all the answers

Match the following types of T cells with their functions:

Killer T cells = Destroy infected cells Helper T cells = Stimulate other immune cells Suppressor T cells = Suppress immune response Memory T cells = Respond rapidly to future infections Signup and view all the answers

Memory T cells can respond quickly to previously encountered pathogens.

True Signup and view all the answers

What process is enhanced by Helper T cells to facilitate the clearance of pathogens?

Phagocytosis Signup and view all the answers

Study Notes

The First Line of Defence

The body’s first line of defence is the skin. It acts as a tough barrier that most pathogens have difficulty penetrating. This only ceases to work if the skin is punctured.
Lysozymes, present in tears, saliva, and sweat, are antibacterial enzymes that can hydrolyse bacterial cell walls.
The respiratory tract is lined with a mucous membrane that traps pathogens and prevents them from penetrating the lower respiratory system. Cilia sweep this mucous and trapped pathogens up the trachea.
Hydrochloric acid in the stomach kills most pathogens ingested by denaturing their enzymes due to its low pH.

Phagocytosis

Phagocytosis is a non-specific process whereby phagocytes engulf pathogens.
It is a relatively fast process, although it is not the primary mechanism for all pathogens.
Phagocytes include:
- Polymorphs: the most common type of phagocyte, arriving first at the site of infection.
- Macrophages: develop from monocytes in the blood, larger, and longer-lived than polymorphs. These can squeeze through capillary walls and engulf pathogens and cell debris.
During phagocytosis, the phagocyte moves towards the pathogen, attracted by chemicals it produces. The phagocyte’s membrane invaginates to enclose the pathogen. This forms a phagosome.
Lysosomes then fuse with the phagosome, releasing hydrolytic enzymes onto the pathogen, effectively destroying it.
The digested products are then absorbed into the cytoplasm of the phagocyte.

The Immune Response & T Cells

The immune response is stimulated by the body’s cells that have been altered due to the presence of non-self material (called antigens). These changed cells are known as antigen-presenting cells.
Types of antigen presenting cells include:
- Macrophages that have engulfed and broken down pathogens, presenting some of their antigens on their own cell surface membranes.
- Any type of body cell that has been infected by a virus, presenting some of the viral antigens on its cell surface membranes.
- Cancer cells, which often present abnormal antigens on their surface membranes.
These cells then activate a response that leads to the production of T cells. T cells differentiate into different types with specialized roles:

T Cell Types

Killer T Cells: These cells destroy infected or abnormal cells by directly attacking and destroying them with enzymes. They recognize infected cells by the presence of viral or abnormal antigens on the cell surface membrane.
Helper T Cells: These cells stimulate other cells involved in the immune response. For example, they:
- Stimulate B cells to divide and produce plasma cells, which produce antibodies.
- Promote phagocytosis by influencing phagocytes.
- Attach opsonins (proteins that tag pathogens) to pathogens, making them easier targets for phagocytes.
- Secrete interferon, a protein that helps limit the ability of viruses to replicate.
Suppressor T Cells (Regulatory T Cells): Suppress the immune response when necessary. These cells:
- Switch off the immune response after invading microbes and infected cells have been destroyed.
- Prevent autoimmune reactions by preventing the immune system from attacking healthy cells.
Memory T Cells: Circulate in the body fluids and can respond rapidly to future infection by the same pathogen. As these cells are already sensitised, they can quickly produce a large clone of T-lymphocytes if they encounter the same antigen again. This results in a much faster immune response to subsequent infections by the same pathogen.

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Description

Explore the first line of defense the body has against pathogens, including the role of the skin, lysozymes, and the respiratory tract. Understand the process of phagocytosis and the types of phagocytes involved in combating infections.