6.3 Defence against infectious disease Flashcards
What is the primary defence against infection?
Skin and mucous membranes!
The skin provides tough physical barrier and prevents pathogens from entering. Sebaceous glands are associated with hair follicles and they secrete a chemical called sebum, which maintains skin moisture and slightly lowers pH. The lower pH inhibits the growth of bacteria and fungi.
Mucous membranes are a thinner and softer type of skin that is found in areas such as the nasal passages and other airways. The mucus that these areas secrete is a sticky solution of glycoproteins. Mucus acts as a physical barrier; pathogens and harmful particles are trapped in it and either swallowed or expelled.
What do sebaceous glands do?
They are associated with hair follicles on the skin and secrete a chemical called sebum which maintains skin moisture and slightly lowers skin pH. The lower skin pH inhibits the growth of bacteria and fungi.
How does the body fix cuts?
Cuts in the skins are healed by blood clotting. The process starts by platelets in the blood releasing clotting factors, the platelets aggregate and stick together at the site of breakage and release clotting factors. The cascade of reactions that occurs after the release of clotting factors from platelets quickly results in the production of an enzyme called thrombin. Thrombin converts the soluble protein fibrinogen into the insoluble protein fibrin. The fibrin forms a mesh in cuts that traps more platelets and also blood cells, the resulting clot is a gel but exposed to air forms a hard scab.
What is thrombin?
Thrombin is an enzyme that converts the soluble protein fibrinogen to fibrin.
What is coronary thrombosis?
In patients with coronary heart disease sometimes blood clots form in the coronary arteries. If the coronary arteries become blocked by clots then part of the heart can be deprived of oxygen and glucose and therefore unable to produce ATP to perform it’s functions. The heart contractions become irregular and uncoordinated.
Thrombosis means clot.
What are phagocytes?
A type of white blood cell. Phagocytes squeeze out through the pores in the walls of the capillaries and move to sites of infection. There they engulf pathogens by endocytosis and digest them inside their cels with enzymes from lysosomes. When wounds become infected, large numbers of phagocytes are attracted resulting in the formation of a white liquid called pus.
What do lymphocytes?
When a foreign cell enters the body, the body will recognise the antigens on the surface of that cell as foreign and will stimulate an immune response. Each lymphocyte produces a different type of antibody, and that antigen will trigger cell division of that lymphocyte that deals with that antigen, and produces that type of antibody to destroy it.
When the antigen have disappeared, the antibodies do not persist but many of the lymphocytes do as memory cells so the immune response is faster next time. Then if the antigen comes in to the body again they can divide very rapidly to form plasma cells.
What do antibodies do?
Antibodies are large proteins that have two functional regions - a hyper variable region that binds to a specific antigen and another region that helps the body to fight the pathogen.
- Either they make a pathogen more recognisable to phagocytes so they are more readily engulfed, or they prevent viruses from docking to host cells so they they cannot enter the cells.
What is HIV?
HIV is the human immunodeficiency virus. It invades and destroys t-helper cells and the result is a progressive loss of the capacity to produce antibodies.
It is a retrovirus and is made of RNA and so uses reverse transcriptase to make DNA copies of itself.
This makes people very vulnerable to infection or other diseases that would be easily fought off by a normal immune system. When a syndrome of conditions due to HIV is present then the person is said to have AIDS.
What are antibiotics?
These are chemicals that inhibit growth of prokaryotic cells and stop processes such as bacterial DNA replication, transcription, translation, ribosome function and cell wall formation.
THEY DO NOT WORK ON EUKARYOTIC CELLS.
How was penicillin tested?
Penicillin is an antibiotic. Florey and Chain tested its effects on mice. They grew an organism that secreted penicillin.
They gave 8 mice diseases and then four were given penicillin, within 24 hours the 4 that were not were dead and the 4 that were, were healthy.
Give an example of drugs causing problems because they have not been tested properly?
Thalidomide - was prescribed to relieve pregnant women of morning sickness. But 10,000 babies were born with birth deformities.
How do we not treat viruses?
DO NOT TREAT VIRUS’S WITH ANTIBIOTICS
This is because antibiotics target and ruin metabolism which virus’s do not have, they do not have their own means of transcription and translation but rather they rely on the host’s cells for ATP synthesis etc.
If you did then it would build up resistance
Antibiotic resistance?
Some strains of bacteria have evolved with genes which confer resistance to anti-biotics and some strains of bacteria have multiple resistance.
How do we avoid antibiotic resistance?
- Doctors only prescribe antibiotics for serious bacterial infections
- Not for viruses
- Patients completing courses of antibiotics to kill it completely
- Hospital staff maintaining high standards of hygiene to prevent cross-infection.
- Farmers not using antibiotics in animal feeds to stimulate growth
