1. 6.3 Defence against infectious disease
(Defence = defense)

2. Primary defence is to keep pathogens out.
U6.3.1 The skin and mucous membranes form a primary defence against pathogens that cause infectious disease
Primary defence is to keep pathogens out.
Pathogens: microbes that cause disease
Skin is a physical barrier –
Epidermis: tough outer layer which is constantly being replaced.
Dermis: underneath layer containing sweat glands, capillaries, sensory receptors and dermal cells which give structure and strength to the skin.
Mucous membranes: thinner and softer type of skin

3. Skin is a physical barrier (cont.)–
U6.3.1 The skin and mucous membranes form a primary defence against pathogens that cause infectious disease
Skin is a physical barrier (cont.)–
Mucous membranes: thinner and softer type of skin found in nasal passages and other passageways.
Secrete lining of glycoproteins (sticky mucous that contains the anti-bacterial enzyme - lysozyme) to trap pathogens. Either swallowed or expelled.
Some lined with cilia(hair-like projections that have wave-like movement) to move pathogens out
Goblet cells
Secrete mucus

4. The locations of mucus membranes
U6.3.1 The skin and mucous membranes form a primary defence against pathogens that cause infectious disease
The locations of mucus membranes
Area with a mucus membrane
What it is and does
Trachea
Tube that carries air to and from the lungs.
Nasal Passages
Tubes that allow air to enter the nose and then the trachea
Urethra
Tube that carries urine from the bladder to the outside
vagina
Reproductive tract leading from the uterus to the outside.
According to NIH (National institute of Health) bacteria outnumbered their human hosts by about 10 to 1 cells. In typical human adult, bacteria would account for about 2 % of his or her body mass.

5. U6.3.2 Cuts in the skin are sealed by blood clotting
Cut skin => severed blood vessels- capillaries, arterioles and venules
Clotting causes bleeding to stop
Blood goes from liquid to a semi-solid gel sealing the wound.
Prevents pathogens from being able to enter the system until new tissue is grown.
Prevents blood loss.

6. U6.3.3 Clotting factors are released from platelets
Clotting involves cascade of reactions with each producing a catalyst for the next reaction
Blood clots very rapidly
Clotting must be under strict control
Platelets release clotting factors

7. U6.3.4 Cascade results in the rapid conversion of fibrinogen to fibrin by thrombin
Thrombin is an enzyme that is produced as a result of the cascade of reactions released by the clotting factors from platelets.
Thrombin converts the soluble protein fibrinogen into the insoluble fibrin
Fibrin forms a mesh in cuts that traps more platelets and blood cells.
The clot begins as gel mesh and turns into a hard scab as exposed to air.

8. U6. 3. 3 Clotting factors are released from platelets U6. 3
U6.3.3 Clotting factors are released from platelets U6.3.4 Cascade results in the rapid conversion of fibrinogen to fibrin by thrombin
Platelets form plug over tear
Collagen comes into contact with blood
Tear in blood
vessel
Plasma proteins are activated
Damaged cell membrane release phospholipids
Prothrombin
Thrombin
Soluble fibrinogen in
plasma
Insoluble
fibrin
Forms network of fibres to cover the tear

9. Application: Causes and consequences of blood clot formation in coronary arteries
Thrombosis: blood clot.
Coronary thrombosis: blood clot in the heart’s coronary arteries.
Heart becomes deprived of nutrients and oxygen and therefore can’t produce sufficient ATP by aerobic respiration which leads to irregular and uncoordinated contractions called fibrillations. Can be fatal.
Atherosclerosis causes occlusions( blockage) by atheroma “plaque – fat, cholesterol, calcium, etc.) in the arteries. Artery wall becomes hardened and can rupture leading to the risk of coronary thrombosis.

10. Many different types of White blood cells
U6.3.5 Ingestion of pathogens by phagocytic white blood cells gives non-specific immunity to diseases
White blood cells – leukocytes - are the next line of defence after skin.
Phagocytes: type of cell capable of engulfing and absorbing bacteria and other small cells
Many different types of White blood cells
Some are macrophages that are phagocytes that squeeze out through pores in the walls of capillaries due to their ability to change shape and go to infection sites
use endocytosis to engulf the foreign bodies
digest them with the enzymes from lysosomes.
Large amounts of phagocytes result in the formation of a white liquid called pus
VIDEO of Macrophages (3:14)

11. Antigen : any chemical that stimulates an immune response.
U6.3.6 Production of antibodies by lymphocytes in response to particular pathogens gives specific immunity
Antigen : any chemical that stimulates an immune response.
Antibodies: the specific immune response to a particular pathogen. The antibodies bind to an antigen on that pathogen. Each pathogen will have its own antibody.
Lymphocytes: produce antibodies.
A pathogen causes small number of lymphocytes already in body to use cell division to create more lymphocytes in order to fight the pathogen. A large clone of lymphocytes is called plasma cells and are produced within a few days. This allows for the secretion of more antibodies to fight the pathogen.

12. Antibodies have 2 functional regions
U6.3.6 Production of antibodies by lymphocytes in response to particular pathogens gives specific immunity
Antibodies have 2 functional regions
hypervariable region (part of the variable region): binds to a specific antigen
Constant region: helps the body to fight the pathogen in one of a number of ways including:
Making a pathogen more recognizable to phagocytes.
Preventing viruses from docking to host cells so that they cannot enter the cells.
Antibodies only stay in the body for a few weeks or months. Plasma cells are also gradually lost.
Some of the lymphocytes produced during an infection are actually memory cells that are very long lived. They remain inactive unless the same pathogen infects the body again.

13. Applications: Effects of HIV on the immune system and methods of transmission
HIV and AIDS Explanation Video
Make sure you know facts from video
HIV positive means that antibodies can be detected.
HIV is a retrovirus that has genes made of RNA and uses reverse transcriptase to make DNA copies of its genes once it enters host cell.
HIV makes antibody production so ineffective that opportunistic infections strike and kill. Often they are very rare such as Kaposi’s sarcoma and are considered markers for the later stages of HIV infection.
AIDS: Acquired immune deficiency syndrome is when an HIV infected person has several diseases or conditions (syndrome)

14. U6.3.7 Antibiotics block processes that occur in prokaryotic cells but not in eukaryotic cells
Antibiotic: a chemical that inhibits the growth of microorganisms. Most are antibacterial.
Block processes that occur in prokaryotes (bacteria) but not eukaryotes (us). Can block:
Bacterial DNA replication
Transcription
Translation
Ribosome function
Cell wall formation
Used saprotrophic fungi which competes with saprotrophic bacteria to discover antibacterial antibiotics. One example is penicillin which is produced by Penicillium fungus.

15. Application: Florey and Chains experiments to test penicillin on bacterial infections in mice
HOMEWORK: READ TESTING PENICILLIN AND COME UP WITH TWO QUESTIONS FROM EACH PARAGRAPH (10 QUESTIONS)

16. U6.3.8 VIRAL DISEASES CANNOT BE TREATED USING ANTIBIOTICS BECAUSE THEY LACK A METABOLISM
Viruses are non-living and can only produce when inside living cells.
Use host cells chemical processes instead of their own metabolism.
This means these processes can’t be targeted because it would damage or kill the host.
Antibiotics should therefore only be used against bacteria and misuse leads to antibiotic resistance
Antivirals are used against viruses but only a few have been discovered.

17. U6.3.9 Some strains of bacteria have evolved with genes which confer resistance to antibiotics and some strains of bacteria have multiple resistance
The biggest concern is with bacteria that has developed multiple resistances
Methicillin-resistant Staphylococcus aureus (MRSA) has infected blood or surgical wounds of hospital patients and resists all commonly used antibiotics
Multidrug-resistant tuberculosis (MDR-TB) : the WHO has reported more than 300,000 cases worldwide per year.
How to prevent:
Doctors prescribing antibiotics only for serious bacterial infections
Patients completing courses of antibiotics to eliminate infections
Hospital staff maintaining high standards of hygiene to prevent cross-infection
Farmers not using antibiotics in animal feeds to stimulate growth
Pharmaceutical companies developing new types of antibiotic – no new types have been introduced since the 1980s.

18. The END