Keeping microbes out
We are constantly surrounded by pathogens and other microbes that we need to defend ourselves against. The first line of defence against infection stops the pathogens from entering the body. These first lines of defence are called non-specific defences as they are general defences, not designed to fight a particular type of pathogen.
| Type of defence | Example | How they help protect the body |
| Physical | Skin in humans, cuticle and cell walls in plants, mucus | Provides a barrier to pathogens |
| Chemical | Stomach acid, antimicrobial substances, enzymes in body secretions such as tears and saliva | Damages or destroys pathogens and stops them reproducing |
| Bacterial | Bacteria on the skin and in the gut | Adapted to living on the body so competes against invading pathogens |
| Type of defence | Physical |
|---|---|
| Example | Skin in humans, cuticle and cell walls in plants, mucus |
| How they help protect the body | Provides a barrier to pathogens |
| Type of defence | Chemical |
|---|---|
| Example | Stomach acid, antimicrobial substances, enzymes in body secretions such as tears and saliva |
| How they help protect the body | Damages or destroys pathogens and stops them reproducing |
| Type of defence | Bacterial |
|---|---|
| Example | Bacteria on the skin and in the gut |
| How they help protect the body | Adapted to living on the body so competes against invading pathogens |
Skin
The skin covers almost all parts of the body and acts as a physical barrier to prevent infection from pathogens.
If it is cut or grazed, it immediately begins to heal itself, often by forming a scab, which prevents infection:
- A blood vessel is damaged, leaving rough edges.
- Blood exits the wound. Delicate The part of blood that clots to form a scab. in the blood are broken open by the rough edges.
- Chemicals are released into the blood which causes a series of reactions.
- This makes the blood clot and later form a scab.
Parts of the body that do not have skin have developed other ways to prevent infection. For example, the eyes produce tears, which contain A protein which catalyses or speeds up a chemical reaction., and these are chemical barriers.
Nose
The nose has internal hairs, which act as a physical barrier to infection. Cells in the nose produce Slimy white protein, which lines the respiratory tract and alimentary canal.. This traps pathogens before they can enter the lungs. When the nose is blown, mucus is removed and any pathogens are trapped within it. Any remaining mucus, and the trapped pathogens, are broken down by acid in the stomach.
Trachea and bronchi
The The windpipe, the tube that leads from the mouth towards the lungs. runs from the nose towards the lungs. The cells that line the trachea also have hairs called Tiny hair-like projections from a cell that usually allow it to move a substance past the cell (for example, in the bronchioles in the lungs)., which are much smaller than those in the nose. These are called Cells with tiny hair-like structures on their surface are said to be ciliated.. The ciliated cells waft their hairs and move mucus and pathogens upwards towards the throat where it is swallowed into the Muscular organ in the digestive system that produces hydrochloric acid and protease enzymes.. Other cells called Cells in the lining of the airways that produce mucus to trap dust and pathogens. create mucus in order to trap pathogens. The production of mucus in the airways is a physical barrier.
Stomach
Stomach acid benfits the digestive system as it helps in the breaking down of food. Additionally, It is part of the body's non-specific first line of defence. It is hydrochloric acid and, while it does us no harm, it is strong enough to kill any pathogens that have been caught in mucus in the airways or consumed in food or water. Stomach acid is a chemical barrier against infection.
Learn more about human defence systems against infection with Dr Alex Lathbridge.
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Learn more about human defence systems against infection with Dr Alex Lathbridge.