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examBoard: Pearson Edexcel
examType: IGCSE
lessonTitle: Phagocytes and Pathogens
When pathogens (disease-causing organisms) enter our bodies, we have several lines of defence to protect us. One of the most important defensive mechanisms involves special white blood cells called phagocytes. These cells are like the body's own "pac-men" - they hunt down, engulf and destroy invading microorganisms.
Key Definitions:
The human body has several types of phagocytes:
There are four main types of pathogens:
Phagocytosis is a remarkable process that helps keep us healthy. It involves several steps that work together to eliminate harmful invaders from our body.
Phagocytosis happens in a series of steps:
Phagocytes detect chemicals released by pathogens or damaged tissues. They move towards the infection site through a process called chemotaxis.
The phagocyte attaches to the pathogen. This is easier when the pathogen is coated with antibodies (a process called opsonisation).
The phagocyte extends pseudopodia (false feet) around the pathogen, eventually enclosing it in a vesicle called a phagosome.
Lysosomes (containing digestive enzymes) fuse with the phagosome, forming a phagolysosome. The enzymes break down the pathogen.
Waste materials from the digested pathogen are removed from the cell through exocytosis.
Some phagocytes present fragments of the pathogen to other immune cells, helping to develop immunity against future infections.
Pathogens are microorganisms that can invade our bodies and cause disease. They reproduce rapidly inside the body and produce toxins that damage our cells and tissues.
Pathogens cause harm in several ways:
Our body has multiple defence mechanisms:
The common cold is caused by rhinoviruses and other viruses that infect the upper respiratory tract. When these viruses enter your nose or mouth, they trigger an immune response. Phagocytes rush to the site of infection and begin engulfing the viruses. However, cold viruses reproduce quickly and can mutate, which is why we can catch colds repeatedly. Symptoms like runny nose, sneezing and coughing are actually caused by your immune system's response to the virus rather than by the virus itself. This case demonstrates how phagocytes work as part of a larger immune response to fight pathogens.
Different types of pathogens cause various diseases. Understanding these can help us appreciate the importance of our immune system, including phagocytes.
When tissues are damaged by injury or infection, a process called inflammation occurs. This is a crucial part of the body's defence system and phagocytes play a central role.
The classic signs of inflammation are redness, heat, swelling and pain. Here's how it works:
A single macrophage can engulf and digest more than 100 bacteria during its lifetime! These remarkable cells are constantly patrolling your body, looking for invaders. In fact, about 1% of your white blood cells are actively engaged in phagocytosis at any given moment, even when you're perfectly healthy. This ongoing surveillance helps prevent infections from taking hold.
Sometimes our phagocytes don't work properly, which can lead to various health problems:
These conditions highlight how crucial phagocytes are for our health and survival. Without these cellular defenders, even minor infections could become life-threatening.
While you can't directly control your phagocytes, you can support your immune system through healthy lifestyle choices:
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