Defense Against Infectious Disease (6.3, 11.1) Flashcards
What is a pathogen?
A disease causing agent that disrupts the normal physiology of the infected organism. They can be cellular (eg. bacteria) or acellular (eg. viruses).
How do bacteria reproduce?
Binary fission (asexual reproduction). The bacterium divides into two identical daughter cells. It occurs quickly, thus allowing for a rapid rate of reproduction.
Give three diseases caused by bacteria
Meningitis (caused by droplet infection, affects the brain).
Tuberculosis (caused by droplet infection, affects the respiratory organs).
Salmonella (caused by ingesting contaminated food, affects the digestive system).
How do viruses reproduce?
The virus attaches to the host cell with its tail and injects its genetic material into the cell. It then hijacks the host cell and uses it to produce more viruses.
Give three viral diseases
Influenza (caused by droplet infection, affects the respiratory organs).
Smallpox (caused by droplet infection/contact, affects the skin/blood).
Ebola (caused by contact with body fluids, affects the immune system cells).
Why are antibiotics ineffective against viruses?
Because viruses do not undergo metabolic reactions.
How are infectious diseases spread?
- Direct contact (eg. sexual transmission)
- Insect bites
- Droplets
- Contaminated food/water
How do pathogens enter the body?
- Natural openings
- Untreated wounds
- Insect/animal bites
What are common symptoms of a disease?
Increased temperature (to kill the pathogen).
Inflammation (increased blood flow to infected area).
Swollen glands (white bloods cells fighting the pathogen in the glands).
Tiredness (energy is used to fight the pathogen).
Increased secretions/pus (to sweep pathogens out of the body).
The first line of defence.
Surface barriers that prevent the pathogens entry to the body.
Examples of the first line of defence.
The skin protects internal structures. It is waterproof and contains chemicals that are antimicrobial (sebum, earwax, sweat and tears).
Mucous membranes protect internal structures (externally accessible tubes such as the trachea). Mucus is an antiseptic sticky secretion that traps pathogens and dust. It contains lysozyme, an enzyme which is effective against bacteria. The cilia hairs sweep the mucus and trapped pathogens out of the respiratory system into the nose/mouth where physical actions such as coughing and sneezing remove the pathogens from the body entirely.
What is the function of clotting?
To prevent blood loss and limit pathogenic access to the bloodstream.
What are the components of blood clots?
Platelets and fibrin strands.
Describe the process of clotting.
This process is collectively called the coagulation cascade. It is stimulated by the release of clotting factors from damaged cells or platelets.
Clotting factors triggers the production of thrombin which catalyses the production of fibrin. Fibrin forms a mesh of fibres across the wound and traps blood cells to form a insoluble, temporary clot. When exposed to air the clot dries to form a protective scab.
When the wound has healed the enzyme plasmin is activated to dissolve the clot.
Haemophilia
A bleeding disorder where blood doesn’t clot normally. People with haemophilia have lower levels of clotting factors in their blood so the normal coagulation cascade is impaired and fibrin formation does not occur. This means a lasting blood clot does not form.
The second line of defence.
The innate immune system (phagocytes). It is non-specific in its response (i.e. it does not differentiate between different types of pathogens and responds to an infection the same way every time).
What are leucocytes?
A general term for white blood cells. There are two types: phagocytes and lymphocytes.