Unit 12: Diseases and Infection
D: Understand how the human body responds to diseases and infections
The immune system
The immune system has the role of defending the body against infection as it is a complex
network of proteins and cells. It fights germs and substances that are harmful to the body,
such as the digestive system and through the skin. The specific immune system fights germs
that the body has already come into contact with by making antibodies.
Non-specific
The non-specific defence mechanism does not distinguish between one type of pathogen and
another, but instead responds to all of them in the same way. They act immediately, and take
2 forms: phagocytosis and barrier of entry. The first line of defence for non-specific is the
mechanical barriers. Those of which include; the mucus membrane, the secretion of mucus
membrane and the skin. The skin acts as a physical barrier where the acidic pH inhibits
bacterial growth. Microorganisms are trapped by the mucus membrane. The second line of
defence for non-specific is the internal defences. Tissues release two type of chemicals which
are kinins and histamine. They act to prevent further injury by activating pain receptors, it
allows fluid to flow into the injured area by causing blood vessels to dilate. Neutrophils also
enter the diapedesis and macrophages follow after.
Before microbes reach the tissues that are vulnerable to infection; physical barriers prevent
this from happening. To prevent invaders from crossing onto the deeper tissues, the barriers
consist of cells at the cellular level to stop this from happening. Microbes are blocked from
entering the bloodstream due to the endothelial cells that have very tight cell junctions.
Different types of cell junctions can be found in tissues in numerous parts of the body, for
example places like gap junctions, tight junctions, and desmosomes. This is further
highlighted in figure 1. Cell junctions connect with extracellular matrix as they contain cell
membrane proteins.
[Reference 1]i
1
D: Understand how the human body responds to diseases and infections
The immune system
The immune system has the role of defending the body against infection as it is a complex
network of proteins and cells. It fights germs and substances that are harmful to the body,
such as the digestive system and through the skin. The specific immune system fights germs
that the body has already come into contact with by making antibodies.
Non-specific
The non-specific defence mechanism does not distinguish between one type of pathogen and
another, but instead responds to all of them in the same way. They act immediately, and take
2 forms: phagocytosis and barrier of entry. The first line of defence for non-specific is the
mechanical barriers. Those of which include; the mucus membrane, the secretion of mucus
membrane and the skin. The skin acts as a physical barrier where the acidic pH inhibits
bacterial growth. Microorganisms are trapped by the mucus membrane. The second line of
defence for non-specific is the internal defences. Tissues release two type of chemicals which
are kinins and histamine. They act to prevent further injury by activating pain receptors, it
allows fluid to flow into the injured area by causing blood vessels to dilate. Neutrophils also
enter the diapedesis and macrophages follow after.
Before microbes reach the tissues that are vulnerable to infection; physical barriers prevent
this from happening. To prevent invaders from crossing onto the deeper tissues, the barriers
consist of cells at the cellular level to stop this from happening. Microbes are blocked from
entering the bloodstream due to the endothelial cells that have very tight cell junctions.
Different types of cell junctions can be found in tissues in numerous parts of the body, for
example places like gap junctions, tight junctions, and desmosomes. This is further
highlighted in figure 1. Cell junctions connect with extracellular matrix as they contain cell
membrane proteins.
[Reference 1]i
1
