BC SCIENCE 8 ~ UNIT 1 Cells and Systems

CHAPTER 3 The Immune System Protects the Human Body

CHAPTER 3.1 The Immune System (pp )

We learned about red blood cells when we were studying the Respiratory & Circulatory systems. There are several other components of blood that have important roles in the immune system. The Components of Blood (from Ch. 2. 3)

a drop of healthy blood contains about 5,000 – 11,000 white blood cells white blood cells are much larger in size than red blood cells the number of white blood cells increases when you have an infection white blood cells fight infection and prevent the growth of cancer The Components of Blood (from Ch. 2. 3)

in a drop of blood there are about 200,000 – 400,000 platelets platelets are important for clotting blood when you get a cut, platelets stop the bleeding and seal the wound by thickening the blood so a scab can form over the cut The Components of Blood (from Ch. 2. 3)

Immune System The immune system’s purpose is to protect our cells from threats One type of threat is from pathogens, which are “germs” or disease-causing invaders These disease-causing organisms and substances are everywhere and can infect people with a range of infectious diseases

Methods of infection There are many different ways to contract infectious diseases. The majority of these can be grouped into 4 categories.

Four ways to transmit infectious diseases Transmission Method Example 1. Direct Contact Shaking hands or sharing drinking containers or bodily fluids with an infected person.

Four ways to transmit infectious diseases

Transmission Method Example 1. Direct Contact Shaking hands or sharing drinking containers or bodily fluids with an infected person. 2. Indirect Contact Being near an infected person who sneezes without covering his/her mouth. Pathogens can travel up to 5 m and infect people within that range.

Four ways to transmit infectious diseases

Transmission Method Example 1. Direct Contact Shaking hands or sharing drinking containers or bodily fluids with an infected person. 2. Indirect Contact Being near an infected person who sneezes without covering his/her mouth. Pathogens can travel up to 5 m and infect people within that range. 3. Water and Food Eating foods such as eggs and some meats, that are infected with Salmonella bacteria. Drinking water infected with E. coli bacteria can also result in serious illness.

Four ways to transmit infectious diseases

Transmission Method Example 1. Direct Contact Shaking hands or sharing drinking containers or bodily fluids with an infected person. 2. Indirect Contact Being near an infected person who sneezes without covering his/her mouth. Pathogens can travel up to 5 m and infect people within that range. 3. Water and Food Eating foods such as eggs and some meats, that are infected with Salmonella bacteria. Drinking water infected with E. coli bacteria can also result in serious illness. 4. Animal BitesBeing bitten by an animal carrying the rabies virus.

Four ways to transmit infectious diseases

First Line of Defence the first line of defence to infectious diseases is the skin and the linings of all internal body systems the skin is a physical barrier that stops most pathogens from entering the body sweat and oil from your skin are slightly acidic and also prevent some pathogens from growing on the surface of our body

First Line of Defence the mucus and cilia lining your nose prevent pathogens from entering your respiratory system

First Line of Defence another defence is the acidic gastric juice secreted by the stomach lining which can destroy pathogens such as bacteria that enter the stomach

Second Line of Defence your body produces an immune response to attack and destroy invaders that make it past the first line of defence this depends on your body’s ability to distinguish between cells that belong to it and cells that don’t

Second Line o f Defence the second line of defence includes two types of immune response 1. an innate immune response - a response all animals are born with 2. an acquired immune response - a response animals with backbones can mount

The Second Line of Defense Part 1: Innate Immune Response

Innate Immune Response this response is quick and general or non- specific the response is the same for anything the body recognizes as an invader

Innate Immune Response innate immune responses are mounted against invading bacteria and some viruses (both are pathogens) the first action is inflammation, which is a flow of fluid, cells, and dissolved substances from the blood to the site of infection this can cause a fever, swelling, and redness in the area

Inflammation

Innate Immune Response there is also an increase in types of white blood cells called phagocytes which fight infection these cells roam the body and search for invader cells and swallow them by increasing the number of phagocytes in an area the immune system can destroy pathogens

Inflammation

The Second Line of Defense Part 2: Acquired Immune Response

Acquired Immune Response this is a highly specific attack on a particular pathogen or antigen an antigen is any substance the body cannot recognize from a virus to a splinter

Pathogens and Antigens are different: a pathogen is a disease-causing organism or substance an antigen is a non-living particle or substance (often part of a pathogen)

Acquired Immune Response acquired immune responses involve types of white blood cells called B cells and T cells this response can take up to a week to develop because it needs time to develop a specific response to defeat the particular invader

B & T cells in action the process of an acquired immune response begins when a white blood cell (WBC) recognizes an antigen this WBC signals for other WBCs called T cells which in turn signal B cells

B & T cells in action when B cells recognize antigens present in the body they produce specific particles called antibodies antibodies can attach to and destroy both antigens and pathogens

In the figure below, a B cell has recognized the antigens on this pathogen and produced antibodies that bind to the antigens and completely cover the pathogen.

B & T cells in action the antibodies either prevent the pathogen from infecting body cells or mark it for destruction by other white blood cells at the same time, the body produces large numbers of similar B cells to fight other antigens in the body

B & T cells in action once the attack is over, some antibodies remain in the body to protect against future infections - this protection is known as immunity

B & T cells in action a second type of T cell is called the killer T cell these work independently and directly to destroy antigens or pathogens

Active Immunity all acquired immune responses help give you active immunity this means your body remembers which antibodies should be used to attack a pathogen that has infected it before this is why people get diseases like chickenpox only once

Active Immunity after the first infection, your body stores some of the specific antibodies on B cells these memory B cells can be reactivated if the antigen or pathogen reappears