Good. In tomorrow's lesson I'll get you to presernt up to the section concerning defence barriers. You also need to tell us about the cinditions under which an organism is considered a pathogen..... are staph, HIV and yeast always pathogens e

​​ " What are pathogens and how can we control their spread? "

What is a Pathogen?

A pathogen is a biological agent that causes illness or disease to its host

Pathogens of particular concern may include bacteria, viruses and protozoa.
The term pathogen most commonly refers to infectious organisms, these include: bacteria (such as staph,) viruses (such as HIV), and fungi (such as yeast).


How do Pathogens Cause Disease?

Different pathogens act in different ways. Some produce toxins, while others invade cells or tissues and then produce toxins. Even when localized in the body, such infections can have systemic effects. Symptoms are often a result of the body over-reacting in its own defence. For instance, inflammation is an important part of the body's natural reaction to pathogens and is a response to a signal that there is a problem in a certain area. Defences are sent to increase the exposure of a pathogen to the body's own antimicrobial factors.


Defence Barriers to Prevent the Entry of Pathogens:

Pathogens can enter the human body in common cases such as:

· Inhaled into the lungs; e.g. Influenza
· Enter into the gut as consumables; e.g. Salmonella
· Enter through breaks in skin; e.g. Bacteria causing Tetanus
· Pass to a foetus from its’ mother; e.g. Rubella
· Transmitted between people during sexual contact; e.g. Bacteria causing Syphilis

To prevent the entry of pathogens, the body implements the following defences:

Line of defence
What it does
Skin continuously grows by new cells being produced from below. Cells fit tightly together to form a protective layer covered by dead cells.
When unbroken, skin prevents the entry of pathogens. Oil glands in the skin secrete substances that kill bacteria.
Mucous Membrane
Cells lining the respiratory tract and openings of the urinary and reproductive systems that secrete a protective layer of mucus
Mucus is sticky and traps pathogens and other particles. When there are many pathogens more mucus is produced to flush them out.
Hair-like projections from cells lining the air passages
Move with a wavelike motion to push pathogens from the lungs up to the throat.
Chemical Barriers
Acidic pH in the stomach . Alkali in the small intestine. Lacrimal glands in the eyes secrete the enzyme lysozyme.
Stomach acid destroys or inhibits the growth of pathogens, including those that are carried to the throat by cilia and then swallowed. Alkali destroys acid resistant pathogens and allows various bacteria to reside there normally, preventing pathogens from living there. Lysozyme is and enzyme secreted from the Lacrimal glands in the eyes which is bactericidal and dissolves the cell membranes of bacteria.

Other body secretions
Secretions from sweat glands and oily secretions from glands in hair follicles
Contain chemicals that destroy or weaken bacteria and fungi.
An antigen is a substance capable of inducing a specific immune response.
When the body detects an antigen, the adaptive immune system produces B & T lymphocytes with antigen receptors on their surface of specific shape to bind with, and destroy that antigen. In vaccinations, dead or weakened antigens are introduced into the body, which then produces lymphocytes to deal with it & any future invasions by that antigen, giving the person immunity.

What Defensive Adaptations Does the Body Have to Counteract Pathogens?
To counteract the spread of pathogens, the body has the following defensive adaptations:

· Inflammation Response
· Phagocytosis
· Lymph System
· Cell Death to Seal Off Pathogen

Inflammation Response
· Inflammation occurs when blood vessels around an infected area are supplied with extra blood. This makes the area swollen and red. The release of histamines by the damaged tissue increases the permeability of the blood vessels, which allows white blood cells to leave the blood vessels and move into the damaged tissue.
· e.g. the inflamation response is the protective attempt by the organism to remove injurous stimuli as well as initiate the healing process for the tissue.

· Some white blood cells, called macrophages and neutrophils, can very easily change their shape so that they flow around particles and completely enclose them within their cell, where they are broken up by cell enzymes. This is called phagocytosis.
· //
· e.g. white blood cell engulfing a large, liquid protein droplet.

Lymph System
· The lymph system returns intercellular fluid to the blood system, filters cell debris and produces white blood cells responsible for the immune response.
· The ducts of the lymphatic system provide transportation for proteins, fats, and other substances in a medium called lymph.

Cell Death to Seal off Pathogen
· For some pathogens, macrophages and lymphocytes completely surround a pathogen so that it is enclosed in a cyst. The white cells involved die, so that the pathogen is isolated from its food supply and also dies.
· e.g. apoptosis is the process of programmed cell death that may occur in multicellular organisms.

How to Prevent the Spread of Pathogens

One of the primary pathways by which food or water become contaminated is from the release of untreated sewage into a drinking water supply or onto cropland, with the result that people who eat or drink contaminated sources become infected. In developing countries most sewage is discharged into the environment or on cropland; even in developed countries there are periodic system failures resulting in a sanitary sewer overflow.

The most common methods of preventing the spread of pathogens include:

§ Receiving Vaccinations
§ Using General First Aid i.e. Covering any open sores with bandages
§ Keeping General Hygeine
§ Using Antibiotics
§ Washing your hands properly and frequently
§ Maintaining immunizations
§ Observing good nutrition
§ Filtration and addition of chemical to water sources (e.g. chlorine)

Source List:

· html
· If%20I%20Ruled%20the%20World%20lesson%201.doc


1. DESCRIBE the conditions under which an organism is considered a pathogen.
2. THE body has three lines of defence against disease. List each and evaluate their effectiveness at protecting the body against disease (the specific defences itemised in the table above can be categories into three broader groupd. You'll need to do this in order to answer this question).