6.3 Syllabus
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U1. ​The skin and mucous membranes form a primary defense against pathogens that cause infectious disease.

  • Skin and mucous membrane are physical barriers against infection from pathogens
  • Skin is constantly replacing its outermost epidermal layer of skin. These dead cells provide effective protection against foreign pathogens
  • Skin also secretes a substance called sebum to lubricate the skin. The sebum also lowers the pH of the skin, which effectively helps inhibit bacterial growth
  • Mucous membranes line the surfaces of the nasal cavity, trachea, bronchi, and bronchioles (surfaces that are exposed to the outside environment) 
  • Mucous traps foreign particles and pathogens contained in the air before they reach the lungs
  • Mucous contains lysozymes that can damage and kill pathogens
  • Trapped pathogens can also be expelled through the mouth or nose, or swallowed and destroyed by the high acidity of the stomach
  • Skin and mucous membranes are examples of non-specific immunity 
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U2. ​Cuts in the skin are sealed by blood clotting.

  • Blood clotting is the process in which cuts or broken blood vessels are repaired and sealed to prevent excessive blood loss
  • When a blood vessel is broken or cut, blood platelets collect at the site of the damaged blood vessel forming a platelet plug
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U3. Clotting factors are released from platelets.

  • The platelets and the damaged tissue release chemical factors called clotting factors 
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U4. The cascade results in the rapid conversion of fibrinogen to fibrin by thrombrin.

  • The clotting factors convert the clotting protein prothrombin to its active form thrombin (enzyme)
  • The enzyme thrombin converts clotting protein fibrinogen into the insoluble fibrous protein fibrin
  • Fibrin forms a mesh at the point of the broken vessel further trapping other platelets sealing up the damaged vessel and forming a stable clot
  • Once the damaged vessel has fully healed, the blood clot dissolves in the blood
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U5. ​Ingestion of pathogens by phagocytic white blood cells gives non-specific immunity to diseases.

  • Another type of non-specific immunity (not antigen specific and response is immediate) occurs when phagocytic leucocytes ingest and destroy foreign pathogens
  • The main type of phagocytic leucocytes are called macrophages. When pathogens get past the physical barriers, macrophages will engulf foreign pathogens through endocytosis
  • Pathogens are recognized as non-self cells by the structure of their protein coat
  • Once the pathogen is engulfed, lysosomes within the macrophage contain hydrolytic enzymes that will digest and destroy the foreign pathogens
  • Macrophages are the large white blood cell and involved in no-specific immune response. 
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U6. Production of antibodies by lymphocytes in response to particular pathogens gives specific immunity.

  • When a pathogen enters the blood, the specific antigen on the surface of the membrane is identified as being foreign or non-self
  • This stimulates a specific immune response in which antibodies are produced that are specific for that particular antigen
  • B-lymphocytes are white blood cells that produce antibodies that bind to the antigen on the invading pathogen
  • Each lymphocyte is able to produce one type of antibody; however, we have a vast diversity of lymphocytes that are able to respond to millions of foreign antigens. 
  • Once an antigen has been encountered the B-lymphocytes are stimulated to divide to produce a large amounts of clones of themselves. 
  • The active B-lymphocytes that are produced are called plasma cells which will begin to produce antibodies
  • The plasma cells created, produce and release mass amounts of anitbodies into the bloodstream. 
  • These antibodies surround and bind to the antigens on the foreign pathogens
  • Through a variety of different methods of pathogens are destroyed by the antibodies and other white blood cells. 
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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. 

  • Some of these divisions also produce B-cells called memory cells, which stay in the blood in case of a second infection to provide a quick response to the new infection
  • The primary response is the production of antibodies to the initial challenge by the invading antigen. 
  • The secondary response which is much quicker because memory cells are still in the blood occurs after a subsequent challenge y the same antigen. 

-Antigens
  • Chemicals that induce an immune response inside the body
  • Antigens are actually proteins, glycoproteins or other macromolecules on the surface of the cell membrane of the pathogen that are recognized by a specific antibody, to stimulate the immune response

-Antibodies
  • Protein molecules produced by B-lymphocytes that recognize and bind to the antigens on the foreign pathogens
  • Each antibody is specific to each type of antigen
  • Antibodies make the pathogen more recognizable to macrophages so that they are easily engulfed and destroyed
  • Antibodies also stop viruses from spreading by binding to host cells preventing the viruses from entering 
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U7. ​ANTIBIOTIC BLOCKS PROCESSES THAT OCCUR IN PROKARYOTIC CELLS BUT NOT IN EUKARYOTIC CELLS.

  • Antibiotics are a type of drug or chemical that inhibits the growth of microorganisms; mainly bacteria
  • Antibiotics block cellular processes such as DNA replication, transcription, translation, and cell wall formation
  • The first antibiotic discovered was identified as penicillin.
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U8. Some strains of bacteria have evolved with genes that confer resistance to antibiotics and some strains of bacteria have multiple resistance.

  • Some viruses lack their own metabolism, they have to use the chemical processes of a cell from a host that they infect
  • They are unable to reproduce on their own and cannot perform protein synthesis, transcription and other metabolic functions
  • Antibiotics work by blocking these vital processes in bacteria, killing the bacteria, or stopping them from multiplying
  • Since viruses do not perform their own metabolic reactions antibiotics such as penicillin and streptomycin, are ineffective in treating viral infections. 
  • Therefore treating viruses with antibiotics is not only useless and ineffective, it can also create antibiotic resistance in bacteria strains. 
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A3. ​Effects of HIV on the immune system and methods of transmission

  • HIV is a retrovirus that causes AIDS, which is a condition in humans where the immune system fails and is susceptible to life-threatening opportunistic infections
  • HIV targets helper- T cells because HIV can bind to proteins on the T cells
  • Helper- T cells play an important role in the production of clonal B lymphocyte cells, which produce antibodies for immune response
  • Therefore the reduction of T cells will reduce the amount of antibodies produced needed to fight off infection from invading pathogens
  • This inability to fight off disease is what eventually causes the person to die
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