The Immune System Flashcards
Define the term ‘non-specific defence mechanism’ and state two examples
Immediate and the same for all pathogens
-Physical barrier
-Phagocytosis
Define the term ‘specific defence mechanism’ and state two examples
Slower and pathogen specific
-Cell-mediated response (T lymphocytes )
-Humoral response (B lymphocytes)
Describe four ways in which non-specific defence mechanisms stop pathogens from entering
Skin- tough / dry outer layer has sebum oil which repels pathogens + forms scabs to prevent pathogens from entering
Trachea/ bronchi/ nose- goblet cells produce sticky mucus + mucus traps bacteria which is carried away by cilia
Eyes- produce antiseptic tears which contain enzymes (lysozymes) which hydrolyse pathogens
Stomach- contains HCl which hydrolyses pathogens on food or in swallowed mucus
Define the term ‘pathogen’
A microorganism which causes infectious disease e.g. bacteria, virus, fungi or protist
Define the term ‘infection’
The body’s response to a pathogen
Define the term ‘immunity’
Resistance to infectious disease
Define the term ‘antigen’
A protein molecule on the cell surface of pathogens that stimulate an immune response
They can be glycoproteins, polysaccharides, lipids or nucleic acids
Explain, what do antigens allow the immune system to identify?
-Pathogens (bacteria, fungi or viruses e.g. HIV)
-Non-self material (transplanted cells)
-Toxins (some pathogens release toxins into blood)
-Abnormal body cells
Lymphocytes must distinguish between body cells (self) and non-self material. Explain what would happen if the body could not distinguish.
-The immune system would not combat pathogens
-Lymphocytes would destroy your own tissues
Explain, are lymphocytes produced in response to an infection?
-No
-They already exist (10 million different types/ not many of each type)
Explain the role of lymphocytes when a pathogen enters the body
-A lymphocyte will have a protein molecule on its cell surface that is complimentary to the antigens on the pathogens surface
-The lymphocyte will ‘recognise’ the pathogen
-The complimentary lymphocyte has to increase in number (clonal selection)
Define the term ‘lag time’
-Produces many copies of a specific lymphocyte which have protein molecule on its surface that are complimentary to the antigens on the pathogens surface
-This takes time (lag time)
-Pathogens multiply so we get symptoms
Explain why there is a huge variety of antigens
-Large range of amino acids (20) which allows for a huge variety of protein molecules
-Have a highly specific tertiary structure
-This gives them a variety of specific 3D structures
-This allows one cell to be distinguished from another
What is clonal selection of lymphocytes?
-Produces many copies of a specific lymphocyte which have protein molecule on its surface that are complimentary to the antigens on the pathogens surface
-This takes time (lag time)
-Pathogens multiply so we get symptoms
-When enough lymphocytes are produce we start to recover and combat infection
What is the role of fetal lymphocytes?
Fetal lymphocytes collide almost exclusively with self cells
Why are infections before birth rare?
Due to the placenta and the mothers defences
In adults, where are lymphocytes produced?
Bone marrow
In adults, lymphocytes produced in the bone marrow initially only encounter what type of molecule?
-Initially only encounter self-antigens
-Any lymphocytes that produce an immune response to self antigens undergo apoptosis
-This must happen before they differentiate into mature lymphocytes
-This prevents any appearing in the blood
Explain two ways to minimise the risk of rejection of transplanted cells and tissues
-Donor tissues are closely matched with the recipient
-Family member if possible
-Immunosuppressant medications are given to reduce the immune response
State two types of white blood cells
Phagocytes (non-specific)
Lymphocytes (specific)
Describe the process of phagocytosis
- Phagocyte engulfs the pathogen and phagosome forms around the pathogen inside the phagocyte
- Phagocyte contains lysosomes which fuse with the phagosome and releases lysozymes (lytic enzymes) which hydrolyse the pathogen
- The products of hydrolysis are absorbed by the phagocyte and the antigens from the pathogen are presented on the phagocytes cell membrane
4.Lymphocytes recognise the antigens and produce specific antibodies which will form some immunity if the same pathogen re-enters
Explain how a change in the pH changes the effectiveness of enzymes in the immune response?
-A change in the pH could alter the charge on the active site of the enzymes which hydrolyses the pathogen when it is inside the phagosome
-This means the pathogen would not be hydrolysed by the lysozymes and the antigens would not be present on the surface
-The immune system would struggle to combat the infection
Explain how phagocytes lead to inflammation at the site of infection
-Swelling contains hydrolysed pathogens and phagocytes
-Inflammation is caused by histamine
-Histamine causes dilation of the blood vessels
-This speeds up the delivery of phagocytes to the site of infection
State the type of lymphocytes involved in the cellular response (cell mediated immunity)
T lymphocytes (T cells)
Where do T cells mature?
Thymus gland
What is the role of T cells?
-The receptors on each T cell respond to a single antigen
-On a phagocyte
What do the receptor proteins on the cell surface of T cells allow T cells to identify?
-Phagocytes
-Body cells invaded by a virus (presents viral antigens on their cell surface- distress signal)
-Abnormal body cells
-Transplanted cells
Explain why the cell mediated response is described as ‘specific’
T cells only respond to antigens on the surface of antigen presenting cells (not antigens detached from cells or within bodily fluids such as the blood)
Describe the cell-mediated response
- Phagocyte engulfs the pathogen and antigens are presented on the cell surface. This is now an APC
- Helper T cells have specific receptors on their surface which attach to antigens on the APC
- Once attached, this activates helper T cells to divide by mitosis to replicate and a large number of clones are made
- Cloned helper T cells differentiate into different cells:
-Some remain helper T cells and activate B lymphocytes
-Some stimulate phagocytes to engulf pathogens by phagocytosis
-Some develop into memory cells that circulate in the blood and tissue fluid (these have specific protein receptors on their surface that are complimentary to the antigens present on the cell surface membrane if the same pathogen re-enters)
-Some become cytotoxic T cells
State four types of cell that T lymphocytes can develop into in the cell-mediated response
-Some remain helper T cells and activate B lymphocytes
-Some stimulate phagocytes to engulf pathogens by phagocytosis
-Some develop into memory cells that circulate in the blood and tissue fluid (these have specific protein receptors on their surface that are complimentary to the antigens present on the cell surface membrane if the same pathogen re-enters)
-Some become cytotoxic T cells
What are cytotoxic T cells?
-Attack abnormal or infected body cells
-Produce the protein perforin which makes holes in the cell surface membrane
-This makes the cell freely permeable, causing cell death
State the first phase of the specific response
Clonal selection of complimentary T cells
-Some T cells stimulate B cells to divide
-B cells are involved in the next phase of the specific response: humoral immunity
Where do B lymphocytes mature?
Bone marrow
What is the role of B lymphocytes?
-Respond to antigens in the humor (tissue fluid)
-Approximately 10 million different B cells
-Each type has a specific antibody on its surface
-This antibody binds to a specific antigen
Describe the activation of B cells (humoral response)
- Antigens in the blood collide with their complimentary antibody on a B cell
- B cell takes in the antigen by endocytosis and presents it on its cell surface membrane
