Immune system Flashcards
What is a communicable disease?
Diseases caused by foreign organisms invading the body and multiplying there. They can be transmitted from one person to another.
What is a pathogen?
Disease causing organisms
Contagious communicable diseases
Passed on by direct contact with a person suffering from the disease
Vectors
spread the disease from person to person trough intermediate hosts of the pathogen, such as mosquitos or fleas
Types of pathogens
- Bacteria
- Viruses
- Fungi
- Animal parasites
What are bacteria?
- Many are non-pathogenic and harmless to humans
- Consists of a single cell
- Cell shape is used to clarify bacteria
Examples of bacteria
- Chlamydia
- Meningitis (bacterial)
- Tetanus
- Whooping cough
What are viruses?
- Molecule of DNA or RNA surrounded by a coat of protein
- When a virus infects a living cell, the DNA or RNA induces the cell to manufacture more virus particles
- The new virus particles leave the host cell to infect other cells
What are bacteriophages?
Viruses that multiply in bacterial cells, causing death of the bacterium
Examples of viruses
- HIV/AIDS
- Chicken pox
- Colds
Examples of fungi
- Ring worms
- Thrush
- Tinea
Examples of animal parasites?
- Tape worms
- Thrush
- Ticks
6 ways pathogens can be transmitted?
- Transmissions by contact
- Transfer of body fluids
- Infection by droplets
- Ingestion
- Airborne transmission
- Transmission by vectors
Transmission by contact
- Through direct (touching an infected person) or indirect means (toughing an object that has been touched by an infected person)
Transfer of body fluids
- Such as blood, semen, or breast milk
- HIV, hepatitis B and C are spread this way
Infection by droplets
- Emitted when breathing, sneezing or coughing
- Spreads diseases such as measles, mumps, colds and influenza
Airborne transmission
- Can cause infection when inhaled
Transmission by vectors
- Transfer of pathogens by other animals, such as insects, ticks or mice
What are non-specific defences?
Work against all pathogens
What are specific defences?
Directed at particular pathogens
What is the purpose of the first line of defence?
- Prevents pathogens from entering and multiplying inside the body
The skin
- Provides a tough impervious barrier
- Oily secretions called sebum (produced in the oil glands) contain substances that kill some pathogenic bacteria
- Sweat also contains salts and fatty acids that prevent the growth of many micro-organisms
Mucous membranes
- Line body cavities that open to the exterior
- Secrete mucous which inhibit the entry of micro-organisms to organs of the body
- EG. in the digestive, urinary and reproductive tracts
Hairs and cilia
- EG. nose cavity and ears
- Trap microbes
- The beating of the cilia moves mucous containing trapped particles and micro-organisms towards the throat
- It is then coughed up or swallowed
Acids
- Gastric juices and vaginal secretions are acidic
- Inhibit or destroy microbes
- Sweat is slightly acidic
Lysozyme
- An enzyme that kills bacteria
- It is in our tears, saliva, sweat and nose secretions
- Our eyes are protected by the flushing actions of our tears, which contains this enzyme
Cerumen
- Traps microbes and debris
- Slightly acidic and contains lysozyme
Flushing action
- Urine flows from the urethra
- Has a cleansing action
- Flushes microbes out of the body
- Prevents bacteria growth and helps to stop bacteria from reaching the bladder and kidneys
- Tears, sweat and saliva are also involved in flushing out microbes
Protective reflexes
helps to protect the body from injury or infection
- Sneezing
- Coughing
- Vomiting
- Diarrhoea
Second line of defence
Non-specific and occurs if a pathogen gets past our external defences
The immune system consists of:
- The lymph nodes
- Lymph vessels
- Lymphoid tissues (scattered throughout organs)
- Many different leucocytes circulating throughout the body
Where does the lymphatic system drain fluid?
Drains intercellular fluid back to the heart at the vena cava
What are phagocytes?
Cells that can engulf and digest micro-organisms and cell debris
What are leucocytes?
- White blood cells
- Able to leave blood capillaries and migrate through the tissues to places of infection or injury
Types of non-specific immunity?
- Inflammatory response
- Phagocytosis
- Fever
What is the inflammatory response?
The response to an damage to the tissues
Purpose of the inflammatory response?
- Reduce the spread of pathogens
- Remove damaged tissues and cell debris
- Begin repair of the damaged tissues
Signs of inflammation?
Redness, swelling, heat and pain
Steps in the inflammatory response
- When cell damage occurs, mast cells release histamine and heparin into inter-cellular fluid
- Histamine increases blood flow through the area and causes the walls of the blood capillaries to become more permeable so that fluid is filtered from the blood
- This causes heat, redness and swelling
- Heparin prevents immediate clotting
- The chemicals released attract phagocytes. Macrophages and leucocytes actively consume micro-organisms and debris via phagocytosis
- Abnormal conditions stimulate pain receptors
- The dead phagocytes and tissue fluid form a yellow liquid called pus
- New cells are produced by mitosis and repair of the damaged tissues takes place
What is a fever?
- Change in body temperature due to a resetting of the body’s thermostat
- Controlled by the hypothalamus
- Believed to inhibit the growth of some bacteria and viruses
What temperature does the human body usually sit at?
The human body usually sits at 37.5°C
What happens when infection occurs (fever)?
When infection occurs, the bodies thermostat increases to about 38-39°C
- This is caused when the white blood cells combating the infection release chemicals called pyrogens
- Pyrogens cause the hypothalamus to increase body temperature
What is the result of an increased thermostat?
Increases thermostat means that at normal body temperature (37.5°C) you start to feel cold
Body responds by:
- Shivering
- Piloerection
- Vasoconstriction of the blood vessels in the skin
This conserves heat and increases heat production
What do these heat production and heat conservation actions cause?
The body temperature to increase to meet the new set point
What is it called when the infection is over?
The fever has broken
What does no pyrogens cause?
The hypothalamus will re-set the set point back to 37.5°C
The body then feels too hot and needs to cool down
- Vasodilation
- Increased sweating
Specific resistance to infection
Third line of defence
Directed at a particular pathogen
What are lymphocytes?
- Type of white blood cells involved in both specific and non-specific defences
- Produced in the bone marrow, as well as in lymphoid tissues
What are macrophages?
- Also involved in specific and non-specific defences
- Large phagocytic cells that develop from a type of white blood cell
- Able to consume foreign substances and micro-organisms by phagocytosis (non-specific)
- Alert the immune system of the presence of foreign materials (specific)
What are the two types of specific immunity?
- Humoral or antibody mediated immunity
2. Cell mediated
What are B-cells and T-cells?
- Types of lymphocytes
- Both produced in the bone marrow
- B-cells mature in the bone marrow
- T-cells mature in the thymus gland/lymphoid tissue
- When these cells react it is called an immune response
How do both aspects of the immune response involve lymphoid tissue?
- Occurs in the lymph nodes, but also occurs in other parts of the body , such as the spleen, thymus gland and tonsils
What is an antigen?
Any substance capable of causing a specific immune response
proteins,
This includes: carbohydrates, lipids, whole microbes, flagella, cell walls, viruses, cell structures from other individuals, pollen grains and egg whites
What is a self-antigen?
- Materials recognised by the immune system as belonging to the organism
- Do not cause an immune response
What is a non-self-antigen?
- Materials recognised by the immune system as not belonging to the organism
- Stimulates an immune response
When does an autoimmune disease occur?
When the body’s cells are not recognised and therefore, there is an immune response
What is an antibody?
A specialised protein produced in response to a non-self-antigen. They belong to a group of proteins called immunoglobulins (Ig)
5 classes of immunoglobulins
- IgA
- IgD
- IgE
- IgG
- IgM
What is an antigen-antibody complex?
Occurs when the antibody produced in response to an antigen combines with that antigen
What is the humoral response?
Provides resistance to viruses, bacteria and bacterial toxins before these micro-organisms enter the body’s cells (pathogens that are outside cells)
Steps to the humoral response?
- Antigen comes in contact with a B-cell
- It becomes sensitised, then enlarges and divides (clones)
- 75% of the B-cells become plasma cells
- Plasma cells secrete specific antibodies capable of attaching to the active site of the antigen
- These antibodies circulate in the blood, lymph and extracellular fluid to reach the site of the invading micro-organism or foreign material
- 25% of the B-cells become memory cells
- These memory cells spread to all body tissues to allow the response to occur more rapidly should the antigen enter the body again
What is the primary response?
- The immune response on the first exposure to the antigen
- It is relatively slow and takes several days to build up a large amount of antibodies (it takes time for B-cells to multiply and differentiate)
- Leaves the immune system with a memory of that particular antigen
What is the secondary response?
- Occurs with the re-exposure to the same antigen
- Occurs much faster due to the activity of the memory cells
- Plasma cells are able to form quickly, increasing antibody levels rapidly
Antibodies may…
- Combine with bacterial/viral toxins/enzymes and inhibit them
- Bind to the surface of viruses and prevent them from entering cells
- Coat bacteria so that the bacteria are more easily consumed by phagocytosis
- Cause particles such as bacteria, viruses or foreign blood cells to clump together (this is known as agglutination)
- Dissolve organisms
- React with soluble substances to make them insoluble and thus more easily consumed by phagocytosis
What is cell mediated immunity?
Provides resistance to the intracellular phase of bacterial and viral infections
What is cell mediated important for?
- Fighting bacterial and viral infections
- Resistance to fungi and parasites
- Organ rejection in transplants
- Fighting cancer cells
What cells are responsible for cellular immunity?
T-cells
Steps to cell mediated immunity
- A B-cell or a macrophage encounters the foreign antigen and travels to the nearest lymph node and presents it to a T-cell
- The T-cell becomes sensitised, it then enlarges and divides, giving rise to cloned T-cells
- Some of the cells of the clone remain in the lymphoid tissue as memory cells, which are able to recognise the original invading antigen, should re-exposure occur
- The remaining T-cells develop further, developing into three types of T-cells: Killer T-cells, helper T-cells and suppressor T-cells
What are killer T-cells?
- Migrate to the site of infection
- Attach to the invading cells and secrete a substance that will destroy the antigen
- They then go and search for more antigens
What are helper T-cells?
- Plays an important role in both humoral and cellular immunity
- Secrete substances that:
• Cause lymphocytes at the infection site to become sensitised, thus intensifying the response
• Attract macrophage to the place of infection so that macrophages can destroy the antigens by phagocytosis
• Intensify the phagocytic activity of macrophages
What are suppressor T-cells?
- Act when the immune activity becomes excessive or the infection has been dealt with successfully
- Release substances that inhibit B-cell and T-cell activity
- Slow down the immune response
What is immunity?
Resistance to infection by invading micro-organisms. It can be natural or artificial, passive or active.
What is natural immunity?
Occurs without human intervention
What is artificial immunity?
Results from giving people an antibody an antigen
What is passive immunity?
- Occurs when a person is given antibodies produced by someone else
- The individual’s body plays no part in the production of antibodies
- Short lived and only lasts until the antibodies are broken down and excreted
Example of natural passive
When antibodies from the mother pass across the placenta to a developing foetus or through breast milk
Example of artificial passive
When a person is injected with antibodies to combat a particular infection so that immunity is established immediately
What is active immunity?
- Occurs when the body is exposed to a foreign antigen and manufactures antibodies in response to that antigen
- Immunity is prolonged at first, although should a subsequent infection occur (same antigen), the appropriate antibodies can be produced very quickly
- Immunity can last for many years, often for life.
Example of natural active
Can result from an actual attack of the disease
Example of artificial active
An injection of the antigens associated with the disease
What is immunisation?
Involves programming the immune system so that the body can respond rapidly to infecting micro-organisms
What is a vaccination?
The artificial introduction of the antigen of the pathogenic organism so that the ability to produce the appropriate antibodies is acquired without the person having to suffer from the disease
Vaccinations can be given as:
- Injections
- Orally
- Nostril sprays
- Skin patches
What is a vaccine?
The antigen preparation used in artificial immunisation
Types of vaccines?
- Contain living attenuated micro-organisms
- Contain dead micro-organisms
- Made from filtrates of bacterial cultures containing toxins
- Sub-unit vaccine
Living attenuated micro-organism?
- Micro-organisms of reduced virulence
- Reduced ability to produce disease symptoms
- Immunised person does not contract the disease but still manufactures antibodies against the antigen
- Used to protect against: measles, mumps, rubella, rabies, tuberculosis and yellow fever
Dead micro-organism
manufactures antibodies against the antigen
- Used to protect against: measles, mumps, rubella, rabies, tuberculosis and yellow fever
Bacterial cultures containing toxins
- Toxins can be inactivated
- Therefore, they do not make the person ill
- Inactive toxins are called toxoids
- They are used to immunise against diphtheria and tetanus
Sub-unit vaccine
- A fragment of the organism is used to provoke the immune response
- Used to vaccinate against human papilloma virus and hepatitis B
When was the last case of small pox recorded?
1977 in Somalia
What is herd immunity?
Occurs when a high proportion of a population is immune to a disease meaning that there is less change of the disease being transmitted between them
How can herd immunity be lost?
People can become complacent about diseases that they don’t see. This results in a failure to vaccinate and a loss of herd immunity.
There can be breakouts of diseases with previously low incidence rates, such as whooping cough and polio (in some Dutch regions)
Risks to vaccinations
- Allergic reactions (usually to the medium in which the antibody is held in)
- Cross species contamination
- Dangerous chemicals used in manufacture
Ethical concerns
- How the vaccine was manufactured
- Testing on animals
- Risks to health
