gradient. It is the sodium ion concentration gradient rather than ATP directly that powers the
movement of glucose and amino acids into the cell. This makes it an indirect rather than
direct form of active transport.
Chapter 5: Cell Recognition and the immune system
5.1: Defense mechanisms
● Any infection is in effect an interaction between the pathogen and the body’s
defence mechanisms.
● When the body’s defence mechanism overwhelms a pathogen the body’s defenses
are better prepared for a second infection. This is immunity.
Defence mechanisms
● The range of defence in the human body is there to protect itself from pathogens.
Some are general like the skin: forming a barrier to entry of pathogens. Others are
more specific, less rapid but longer-lasting.
● These include:
→ cell-mediated responses involving T-lymphocytes
→ humoral responses involving B-lymphocytes
Recognising your cells
● In order not to destroy the organism's tissues, lymphocytes must be able to
distinguish the body’s cells.
● Each cell has a specific molecule on its surface to identify it. The molecules can be a
variety of types but protein is the most important.
● These protein molecules usually allow the immune system to identify:
1. Pathogens
2. Non-self materials such as cells from other organisms
3. Toxins
4. Abnormal body cells
● Although this response is advantageous to the organisms, it has implications for
humans who have transplants
● Specific lymphocytes are not produced in response to an infection but they already
exist in all 10 million types.
, How lymphocytes recognise cells belonging to the body
● In the foetus, lymphocytes are constantly colliding with other cells.
● Infection in the foetus is rare because it is from the outside
● Lymphocytes are constantly colliding so they will collide exclusively with the body’s
self
● Some of the lymphocytes will have receptors that exactly fit those of the body's cells.
These are suppressed.
● In adults lymphocytes produced in the bone marrow initially only encounter
self-antigens.
5.2: Phagocytosis
● If any pathogen can enter the body, then the next defence is the white blood cells.
● There are two types:
1. Phagocytes
2. Lymphocytes
Phagocytes ingest and destroy pathogens by a process called phagocytosis before they can
cause harm. Lymphocytes are involved in immune responses.
Phagocytosis
● Is the process in which white blood cells engulf pathogens thus destroying them
Process:
1. Phagocytes are attached to the pathogen by chemical products. It is more
towards the pathogen along a concentration gradient
2. The phagocyte has several receptors on its cell surface membrane that attach
to chemicals on the surface of the pathogen
3. Lysosomes within the phagocyte migrate towards the phagosome formed by
engulfing the bacterium
4. Lysosomes release their lysozymes into the phagosome where they hydrolyse
the bacterium
5. The hydrolysis products of the bacterium are absorbed by the phagocyte and
presented on the surface.
movement of glucose and amino acids into the cell. This makes it an indirect rather than
direct form of active transport.
Chapter 5: Cell Recognition and the immune system
5.1: Defense mechanisms
● Any infection is in effect an interaction between the pathogen and the body’s
defence mechanisms.
● When the body’s defence mechanism overwhelms a pathogen the body’s defenses
are better prepared for a second infection. This is immunity.
Defence mechanisms
● The range of defence in the human body is there to protect itself from pathogens.
Some are general like the skin: forming a barrier to entry of pathogens. Others are
more specific, less rapid but longer-lasting.
● These include:
→ cell-mediated responses involving T-lymphocytes
→ humoral responses involving B-lymphocytes
Recognising your cells
● In order not to destroy the organism's tissues, lymphocytes must be able to
distinguish the body’s cells.
● Each cell has a specific molecule on its surface to identify it. The molecules can be a
variety of types but protein is the most important.
● These protein molecules usually allow the immune system to identify:
1. Pathogens
2. Non-self materials such as cells from other organisms
3. Toxins
4. Abnormal body cells
● Although this response is advantageous to the organisms, it has implications for
humans who have transplants
● Specific lymphocytes are not produced in response to an infection but they already
exist in all 10 million types.
, How lymphocytes recognise cells belonging to the body
● In the foetus, lymphocytes are constantly colliding with other cells.
● Infection in the foetus is rare because it is from the outside
● Lymphocytes are constantly colliding so they will collide exclusively with the body’s
self
● Some of the lymphocytes will have receptors that exactly fit those of the body's cells.
These are suppressed.
● In adults lymphocytes produced in the bone marrow initially only encounter
self-antigens.
5.2: Phagocytosis
● If any pathogen can enter the body, then the next defence is the white blood cells.
● There are two types:
1. Phagocytes
2. Lymphocytes
Phagocytes ingest and destroy pathogens by a process called phagocytosis before they can
cause harm. Lymphocytes are involved in immune responses.
Phagocytosis
● Is the process in which white blood cells engulf pathogens thus destroying them
Process:
1. Phagocytes are attached to the pathogen by chemical products. It is more
towards the pathogen along a concentration gradient
2. The phagocyte has several receptors on its cell surface membrane that attach
to chemicals on the surface of the pathogen
3. Lysosomes within the phagocyte migrate towards the phagosome formed by
engulfing the bacterium
4. Lysosomes release their lysozymes into the phagosome where they hydrolyse
the bacterium
5. The hydrolysis products of the bacterium are absorbed by the phagocyte and
presented on the surface.
