6.3 Defense Against Infectious Disease

UNDERSTANDINGS

The skin and mucous membranes form a primary defense against pathogens that cause infectious disease.

Cuts in the skin are sealed by blood clotting.

Clotting factors are released by platelets.

The cascade results in the rapid conversion of fibrinogen to fibrin by thrombin.

Ingestion of pathogens by phagocytic white blood cells gives non-specific immunity to diseases.

Production of antibodies by lymphocytes in response to particular antigens gives specific immunity.

Antibiotics block processes that occur in prokaryotic cells but not in eukaryotic cells.

Viruses lack a metabolism and cannot therefore be treated with antibiotics. Some strains of bacteria have evolved with genes the confer resistance to antibiotics, and some strains of bacteria have multiple resistance.

APPLICATIONS AND SKILLS

A: Causes and consequences of formation in coronary arteries.

A: Florey and Chain’s experiments to test penicillin on bacterial infections in mice.

A: Effects of HIV on the immune system.

Guidance:

-Diagrams of skin are not required.

-Subgroups of phagocyte and lymphocyte are not required but students should be aware that some lymphocytes act as memory cells and can quickly reproduce to form a clone of plasma cells if a pathogen carrying a specific antigen is re-encountered.

-The effects of HIV on the immune system should be limited to a reduction in the number of active lymphocytes and a loss of the ability to produce antibodies, leading to the development of AIDS.

Primary Defense

Skin- Two primary layers- Dermis

- Alive - Has sweat glands, capillaries, sensory cells- Has dermal cells for structure and strength

- Epidermis- Mainly dead cells- Constantly being replaced by underlying dermal cells

http://images.emedicinehealth.com/images/emedicinehealth/illustrations/skin.jpg

Primary Defense

Mucous Membranes

- Line entry points not covered by skin- Produce and secrete mucous to trap

pathogens- Some also have cilia

- Movement of cilia moves trapped pathogens up and out

S. aureus trapped in mucous being moved by cilia

http://www.microbiologyonline.org.uk/themed/sgm/img/slideshows/3.3.2_immune_4.png

Blood Clotting

Plasma proteins involved in clotting- Prothrombin

- Converts to thrombin (enzyme that converts fibrinogen into fibrin)

- Fibrinogen

Red blood cell

Platelets- Form in bone marrow- Made from one large

molecule that breaks into many smaller ones

- Live 8-10 days

Fibrin- Insoluble fibrous protein- Forms mesh-like network that traps

cellular debris to form a stable clotPrevents further blood loss and entry of pathogens

http://www.uphs.upenn.edu/news/News_Releases/jun05/Weisel_image1.jpg

Immune Response

Primary- First encounter with the pathogen- Takes a week or more to be successful- Experience symptoms while the body is fighting the pathogen

http://cliparts.co/cliparts/8c6/okA/8c6okAKzi.png

Secondary- Quicker, more intense- Rarely have associated symptoms

Macrophages

- Large leucocytes - Able to change shape- Can recognize if a cell is “self” or “not

self”- If not self, macrophage will engulf it by

phagocytosis - Breaks down with lysosomes

Specific Immunity

- Antibodies are pathogen specific- Pathogens have proteins on their outer

surface called antigens- Antibodies bind to antigens at the

binding site and becomes attached.

Y-shaped antibody protein

http://4.bp.blogspot.com/-jBbIGtBmxGQ/Ta3UesLcLnI/AAAAAAAABMo/Xwvi5Tfn6OA/s1600/monoclonal+antibodies.jpg

Steps for Primary Immune Response

1- Specific antigen identified2- Specific plasma cell is identified that can produce antibody that will bind to the antigen3- Plasma cell reproduces in order to rapidly increase the number of that type of plasma cell4- Plasma cells begin antibody production5- Antibodies circulate in the bloodstream and find their antigen match6- Antibodies help eliminate the pathogen7- Some of the cloned plasma cells remain in the bloodstream and provide immunity. These are memory cells.8- Memory plasma cells respond quickly if the same antigen is encountered again

- Human immunodeficiency virus

- Target cells are lymphocyte cells involved in immune response

- Person will eventually lose ability to produce antibodies

- AIDS (acquired immune deficiency syndrome) = specific immune response capability is lost

- Infected person can no longer fight off pathogens

Common modes of transmission- Having unprotected sex with an

infected person- Sharing needles- It is also possible for an HIV+

mother to pass it to her child during pregnancy, labor, delivery, or breastfeeding

https://s.yimg.com/fz/api/res/1.2/xuU.i9xr00t92nrMuAh68A--/YXBwaWQ9c3JjaGRkO2g9MjQ1O3E9OTU7dz0zNDc-/http://www.corrections.com/system/article/image/31668/HIV-AIDS.jpg?1350680429

http://scienceillustrated.com.au/blog/wp-content/uploads/2011/05/hiv.jpg

Antibiotics

- Work by blocking pathways in bacteria that aren’t used by eukaryotic cells

- Category of antibiotic depends on the chemical pathway being targeted

- Ex: May block production of a new cell wall (inhibits binary fission)

http://www.nature.com/nm/journal/v19/n5/images/nm.3198-I1.jpg

Why don’t antibiotics work on viruses? - Viruses are acellular- Use host’s cells to reproduce- A chemical that inhibits this would also damage host cells

Antibiotic Resistance

MRSA= methicillin resistant Staphylococcus aureus

http://learn.chm.msu.edu/vibl/content/differential/images/trypticsoy_s.aureus.jpg

- Within a population of bacteria, there is likely to be some with resistance to an antibiotic

- When an infection is treated with antibiotics, the ones that lack resistance will be eliminated

- What remains are the few that are resistant- They reproduce and quickly form a population

entirely composed of resistant bacteria

https://s.yimg.com/fz/api/res/1.2/2O7R6OWbNDvJsmPiA3vPrA--/YXBwaWQ9c3JjaGRkO2g9MzAwO3E9OTU7dz0zMDA-/http://mathbitsnotebook.com/Algebra1/FunctionGraphs/expdecay2.jpg

HomeworkVOCAB

Pathogen, antibiotic, quarantine, dermis, epidermis, mucous membrane, cilia, plasma proteins, prothrombin, fibrinogen, platelets, erythrocytes, leucocytes, clotting factor, thrombin, fibrin, immune response, primary immune response, secondary immune response, macrophage, antibodies, antigens, binding site, plasma cells

TOK pg 289

Summarize Nature of Science on pg 290

Exercises 7-10 pg 291

Read “Monitoring ventilation in humans at rest and after mild and vigorous exercise” on pg 294 (lab next class- dress comfortably for being outside)