7a1 Defense Systems

Defense Systems Multiple Organ Systems Battle Pathogens

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Defense Systems Objectives

  • Explain how the integumentary system, cardiovascular system, skeletal system, and lymphatic system play a role in defense.
  • Describe the two non-specific innate defenses and the two specific acquired defenses.
  • Sketch and label the processes of inflammation as well as the two specific defenses, cell-mediated and antibody-mediated immunity.

The body’s defenses against pathogens are often called the “immune system.”  However, there is no single immune system like the other organ systems we have been covering in this course.   The body has multiple defenses against pathogens, involving multiple organ systems.

Our defenses are complex, to say the least.  It will take us two webpages to go through the basics.  This will enable us to address what the body needs to do to defend us against pathogens like SARS-CoV-2 (COVID).

This video provides an overview of the human defenses against pathogens and parasites.

Here are four organ systems involved in the response against pathogens.

Skin and secretions like tears and urine are a barrier against pathogens. Mucus-membranes line the trachea to trap and move pathogens up and out of the respiratory system.

Integumentary System

Skin and secretions like tears and urine are a barrier against pathogens. Mucus-membranes line the trachea to trap and move pathogens up and out of the respiratory system.
The bone marrow produces white blood cells and each cell can destroy pathogens in different ways.

Skeletal System

The bone marrow produces white blood cells and each cell can destroy pathogens in different ways.
Some white blood cells travel through the blood to distant locations like the thymus and lymph nodes, while others patrol the blood in search of pathogens.

Cardiovascular System

Some white blood cells travel through the blood to distant locations like the thymus and lymph nodes, while others patrol the blood in search of pathogens.
Some white blood cells monitor pathogens that may have accumulate in the lymph (extracellular fluid). Lymphocytes wait in lymph nodes, prepared to pounce on pathogens.

Lymphatic System

Some white blood cells monitor pathogens that may have accumulate in the lymph (extracellular fluid). Lymphocytes wait in lymph nodes, prepared to pounce on pathogens.

These organ systems form four lines of defense

Two non-specific and two specific defenses.

Barriers

skin, mucus membranes, and secretions keep pathogens out of the body.

Inflammation

permeable blood vessels bring in platelets and white blood cells.

Cell-mediated Immunity

white blood cells seek out and destroy cells infected with specific pathogens.

Antibody-mediated Immunity

white blood cells produce antibodies that stick to specific pathogens.

This is a quick look at the four basic defenses, two that are non-specific (barriers and inflammation) and two that are specific involving T Lymphocytes (T cells) killing infected cells and B lymphocytes (B cells) producing antibodies.

For this Guide’s first journal assignment (next webpage), you will be sketching and labeling the four lines of defense.  We will go through them one-by-one.

Two lines of defense are non-specific, pre-programmed and similar responses to any potential pathogen.
Structures and chemicals keep pathogens from entering the body.

Barriers

Structures and chemicals keep pathogens from entering the body.
Wounded cells release chemicals that dilate blood vessels and bring in blood to clean the wounded area. The next section describes inflammation in detail.

Inflammation

Wounded cells release chemicals that dilate blood vessels and bring in blood to clean the wounded area. The next section describes inflammation in detail.

Barriers (non-specific defense)

The skin is a very effective barrier, but even shallow abrasions to the epidermis could lead to an infection.

Mucus is a critical barrier secretion in the respiratory system, but excessive mucus can result in a variety of disorders, including sinusitis.

Inflammation (non-specific defense)

Innate inflammation and the two acquired forms of immunity (cell-mediated and antibody-mediated) involve white blood cells.  This video recalls the five basic types of wbcs.

The role of white blood cells in the inflammation is discussed in the next two videos.
For the quiz question from this page, you will be asked to explain each step of inflammation from wounded cells to clean-up by the white blood cells. You can submit a written story response, but many people prefer to make a labeled sketch.  You can work on either of these while watching the videos.

This poster summarizes the non-specific defenses of barriers and inflammation.  It also adds antimicrobial proteins that are often released during inflammation responses.

Wounded cells secrete chemicals that start the inflammation response. Vessels dilate, blood flushes out the wound, platelets form a clot, and the white blood cells arrive.
Wounded cells secrete chemicals that start the inflammation response. Vessels dilate, blood flushes out the wound, platelets form a clot, and the white blood cells arrive.
Natural Killer lymphocytes, the same type that kill cancer cells, start killing damaged cells, leaving room for new, healthy cells to take their place.
Natural Killer lymphocytes, the same type that kill cancer cells, start killing damaged cells, leaving room for new, healthy cells to take their place.
Neutrophils become phagocytes which means "eating cells," and they eat up the debris, including the mess left by the natural killer cells.
Neutrophils become phagocytes which means “eating cells,” and they eat up the debris, including the mess left by the natural killer cells.
Monocytes turn into macrophages or "big eaters," and they eat up the large debris the neutrophils can't handle. Monocytes also play a role in both types of specific immunity.
Monocytes turn into macrophages or “big eaters,” and they eat up the large debris the neutrophils can’t handle. Monocytes also play a role in both types of specific immunity.
Which suffix is added to a word to indicate an inflammatory disease? -____
List as many inflammatory diseases as you can remember from the course so far.  There have been quite a few!

Two forms of Specific Immunity

Now it gets personal!  

To recognize a pathogen, specific types of lymphocytes have to be able to recognize antigens, surface molecules that are distinctly different than the molecules on our own individual cells.

Two Specific (Acquired) Lines of Defense
A type of lymphocyte called the "cytotoxic T cell" learns what antigens on a pathogen look like and kills cells infected with that pathogen. We are covering this specific defense in this section.

Cell-Mediated Immunity

A type of lymphocyte called the “cytotoxic T cell” learns what antigens on a pathogen look like and kills cells infected with that pathogen. We are covering this specific defense in this section.
A type of lymphocyte called the "plasma B cell" learns to produce antibodies that stick to the antigens on the surface of pathogens. This will be covered in the next section.

Antibody-Mediated Immunity

A type of lymphocyte called the “plasma B cell” learns to produce antibodies that stick to the antigens on the surface of pathogens. This will be covered in the next section.

Cell-Mediated Immunity (specific defense)

In this section we are focusing on cell-mediated immunity.

This poster summarizes the cell-mediated immune response.

Specific Cell-Mediated Immunity

Here are the details of how lymphocytes can kill cells infected by a specific pathogen.

Helper T cells that have communicated with the antigen-presenting macrophages tell naive (uneducated) T cells what to to seek out and destroy.
Helper T cells that have communicated with the antigen-presenting macrophages tell naive (uneducated) T cells what to to seek out and destroy.
Most of the naive T cells that are educated become cytotoxic T cells that seek out cells infected with the target pathogen and destroy them.
Most of the naive T cells that are educated become cytotoxic T cells that seek out cells infected with the target pathogen and destroy them.
The cytotoxic T cells have chemicals that dissolve the infected cell's plasma membrane. This is similar to how natural killer cells destroy damaged cells, but more specific in targeting cells that harbor a certain pathogen.
The cytotoxic T cells have chemicals that dissolve the infected cell’s plasma membrane. This is similar to how natural killer cells destroy damaged cells, but more specific in targeting cells that harbor a certain pathogen.
Some of the educated T cells hold back and are called memory T cells. If the pathogen attacks again, the memory T cells start undergoing mitosis and become large numbers of cytotoxic T cells that attack cells infected by the pathogen.
Some of the educated T cells hold back and are called memory T cells. If the pathogen attacks again, the memory T cells start undergoing mitosis and become large numbers of cytotoxic T cells that attack cells infected by the pathogen.

Antibody-Mediated Immunity (specific defense)

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Antibodies are proteins that adhere to the antigens on the surface of a pathogen.  This is a specific fit, like a key in a lock.

The previous section focused on cell-mediated immunity.  This section focuses on the other acquired and specific response: antibody-mediated immunity.

This poster summarizes the antibody-mediated response.

Specific Antibody-Mediated Immunity

Here are the details of how lymphocytes can produce antibodies to attack specific pathogens.

Helper T cells tell naive (uneducated) B cells what to make antibodies against. Some B cells can also activate directly when they come in contact with a pathogen.
Helper T cells tell naive (uneducated) B cells what to make antibodies against. Some B cells can also activate directly when they come in contact with a pathogen.
Most of the naive B cells that are educated become plasma B cells that pump out large quantities of antibodies.
Most of the naive B cells that are educated become plasma B cells that pump out large quantities of antibodies.
Antibodies attach to the antigens on the surface of pathogens. This traps the pathogens in place and they can be consumed and destroyed by the phagocytes, including the macrophages.
Antibodies attach to the antigens on the surface of pathogens. This traps the pathogens in place and they can be consumed and destroyed by the phagocytes, including the macrophages.
Some of the educated B cells hold back and are called memory B cells. If the pathogen attacks again, the memory B cells become Plasma B cells and start producing antibodies against them quickly.
Some of the educated B cells hold back and are called memory B cells. If the pathogen attacks again, the memory B cells become Plasma B cells and start producing antibodies against them quickly.
In news related to COVID-19, there is mention of a “cytokine storm.”  From the videos, why are cytokines important?  A cytokine storm indicates that the body’s reaction against SARS-CoV-2 is so strong, there can be an excessive immune response that may itself be damaging.

Antibody tests may indicate whether a person has responded to SARS-CoV-2.  It does not indicate whether they have sufficient memory cells to have a rapid response if they re-encounter the virus.  Research is ongoing as to how effectively memory cells are formed against the coronavirus.

The following vocabulary list may assist in understanding this guide’s material as well as the continuing COVID-19 news stories that emerge as researchers study the disease.

Vocabulary

Pathogen: a virus, bacterium, or protist that can cause disease.

Antigen: molecules on a surface of a pathogen that are different than the markers on all of your own cells.

Infected Cell: a cell being attacked by a pathogen.  For example, a respiratory epithelial cell that is infected by the influenza virus.

Chemical Signals: a variety of molecules communicate information between cells.  Wounded and infected cells releases chemical signals that trigger the inflammation process.  White blood cells also communicate with chemical signals.

Macrophage: a monocyte that has become a “big eater,” consuming debris and pathogens.  The macrophage can remove the antigens from the surface of a pathogen and “present” these antigens to the helper T cell.

Helper T cell: a cell with the ability to recognize an antigen and communicate its structure through chemical signals to other T cells and B cells, educating them on what to destroy.

Cytotoxic (killer) T cell: once educated by the helper T cell, immature/naive T cells can seek out and destroy cells infected with that specific pathogen.

Memory T cell: some educated T cells hold back and do not turn cytotoxic until the pathogen re-enters the body at a later date.

Plasma B cell: immature (naive) B cells can be activated by helper T cells or by directly encountering a pathogen.  Many turn into Plasma B cells that pump out antibodies that attach to specific antigens.

Antibody: a small Y-shaped molecule that attaches to the antigens on the surface of a specific pathogen.  These antibodies can stick the pathogen into a ball that is consumed by the macrophage.

Memory B cell: some educated B cells hold back and do not turn into plasma B cells until the pathogen re-enter the body.

Suppressor T cell: a group of cells, also called regulatory T cells, that slow down the white blood cells response once the pathogen has been eliminated.

With so many critical steps in our defenses, there are many things that can go wrong.  The next section summarizes this page and introduces immune disorders.
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Check your knowledge.  Can you:

  • explain how the integumentary system, cardiovascular system, skeletal system, and lymphatic system play a role in defense?
  • describe the two non-specific innate defenses and the two specific acquired defenses?
  • sketch and label the processes of inflammation as well as the two specific defenses, cell-mediated and antibody-mediated immunity?
7a1 Defense Systems

Go back to the Defenses Guide Page

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Go forward to the Immunity Page

Defenses Guide Contents

Complete all four of these sections before taking the quiz and submitting your two journal pages.
Defense Systems - YOU ARE HERE

Defense Systems - YOU ARE HERE

Immunity

Immunity

Eliminating Diseases

Eliminating Diseases

Persistent Threats

Persistent Threats

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