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Defenses Overview & Barriers

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Defenses & Barriers Objectives

  • Describe how the integumentary system, cardiovascular system, skeletal system, and lymphatic system play a role in defense.
  • List the two non-specific innate defenses and the two specific acquired defenses.
  • Provide examples of barriers that keep pathogens and parasites out of the body.
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.
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.

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

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.

The next section provides an overview of inflammation, another non-specific defense.
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Check your knowledge.  Can you:
  • describe how the integumentary system, cardiovascular system, skeletal system, and lymphatic system play a role in defense?
  • list the two non-specific innate defenses and the two specific acquired defenses?
  • provide examples of barriers that keep pathogens and parasites out of the body?

Go back to the Defense Systems Guide Overview

Go forward to the Inflammation Page

Defense Systems Lecture Guide Contents

The material from this guide and corresponding lecture is assessed on the weekly quiz.

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Defense Systems

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