Unit 6.3 - Defence against infectious disease

Question 1

What is a pathogen

Answer 1

pathogen is an organism or virus that causes disease.

Question 2

Barriers to infection

Answer 2

Skin and mucous membranes are primary defence against pathogens by forming a barrier preventing entry

Question 3

How does the skin work as a barrier

Answer 3

outer layers of skin are tough and for a physical barrier. Sebaceous glands in the skin secrete lactic acid and fatty acids which make surface of skin acidic preventing growth of most bacteria

Question 4

How does the mucous membrane work as a barrier

Answer 4

soft areas of skin that are kept moist with mucus. found in the nose, trachea, vagina and urethra. Although they do not form strong physical barrier - many bacteria killed by lysozyme (enzyme in the mucus). In trachea, pathogens get caught in the sticky mucus - cilia then push the mucus and bacteria up and out of the trachea

Question 5

Phagocytes

Answer 5

ingest pathogens by endocytosis - pathogens are then killed and digested inside the cell by enzymes in the lysosomes. Phagocytes can ingest pathogens in the blood and can also squeeze through the walls of blood capillaries and move through tissues to sites of infection. They then ingest the pathogens causing infection - large number of phagocytes forms pus

Question 6

Non specific immunity

Answer 6

Phagocytes give us whats called non specific immunity to disease as a phagocyte does not distinguish between pathogens

Question 7

Blood clotting

Answer 7

When the skin is cut and blood escapes from blood vessels - semi solid clot is formed from liquid blood to seal up the cut and prevent entry of pathogens

Question 8

What is the role of platelets

Answer 8

have an important role in clotting - small cell fragments that circulate with red and white blood cells in blood plasma.

Question 9

What is the clotting process (beginning with platelets)

Answer 9

Clotting begins with the release of clotting factors from damages tissue cells or platelets. These clotting factors set off a cascade of reactions in which each product is the catalyst in the next reaction.

Question 10

What is the role of fibrinogen ?

Answer 10

makes it a very rapid process. Fibrinogen, a soluble plams protein altered by removal of sections of polypeptides that have many negative charges. Allowing for the polypeptides to bind to others forming long proteins called fibrin. Fibrin forms a mesh of fibres across the wounds and blood cells are subsequently stuck

Question 11

Blood clots in coronary arteries

Answer 11

deposits of plaque in the arteries rupture, blood clots form (coronary thrombosis) which may block the artery. The consequence is that an area of cardiac muscle receives no oxygen and so stops beating in a coordinated way (leads to heart attack). Uncoordinated control = fibrillation, sometimes it will start beating again but sometimes this is not the case.

Question 12

Production of Antibodies

Answer 12

1) Antibodies are made by lymphocytes (white blood cell) - antigens are foreign substances that stimulate the production of antibody lymphocytes
2) A lymphocyte can only make one type of antibody ( may different ones are needed) - each lymphocyte puts some of the antibody that it can make into its cell surface membrane with antigen projecting outwards
3) When a pathogen enters the body - antigens bind to the antibodies in the cell of one type of lymphocyte
4) When antigens bind to the antibodies on the surface - lymphocyte becomes active and divides by mitosis to produce a clone of many identical cells
5) The cells produced by mitosis are plasma cells = produce large quantities of antibodies (antibody bind to antigens on surface of the pathogen and stimulates destruction)

Question 13

What is antibodies involved in

Answer 13

specific immunity because different antibodies are needed to defend against different pathogens. After an infection has been cleared from the body, most of the lymphocytes produced disappear but some persist as memory cells.

Question 14

HIV and the immune system

Answer 14

HIV infects a type of lymphocyte that plays a vital role in antibody production. Over a period of years, these lymphocytes gradually destroyed. Without lymphocytes, antibodies cannot be produced (AIDS) - leads to death if untreated.
HIV does not survive for long outside the body and cannot easily pass through the skin - transmission due to exchange of bodily fluids.

Question 15

How is HIV transmitted

Answer 15

1) Through small cuts or tears in the vagina penis mouth or intestine during vaginal, oral or anal sex
2) In traces of blood on hypodermic needles shared by intravenous drug abuse
3) Across the placenta from a mother to a baby (cuts during childbirth)
4) In transferred blood products such as Factor Vill (used to treat haemophiliacs)

Question 16

Antibiotics

Answer 16

chemicals produced by microorganisms to kill or control the growth of other organisms. work by blocking processes that occur in prokaryotic cells but not eukaryotic

Question 17

Viruses

Answer 17

lack a metabolism and instead rely on a host cell such as a human cell to carry out metabolic processes. Not possible to block these using an antibiotic without also harming human cells

Question 18

Bacterial diseases in humans

Answer 18

most can be treated successfully with antibiotics (some strains have acquired genes that confer resistance and some strains of bacteria now have multiple resistance

Question 19

Testing penecillin

Answer 19

Penecillin was developed as antibiotics by Florey and Chain in late 1930’s. First test was on eight mice that caused fatal pneumonia - all of the treated mice recovered but untreated mice dies.

Question 20

Florey and Chain

Answer 20

Work would not be regarded as safe today = extensive animal testing must be done first to prevent side effects - after small and then larger doses tested on healthy individuals and then on affected patients