Defense against infectious disease Topic 6.3

Exposure may not lead to disease Pathogen: any living organism or virus that is capable of causing disease viruses, bacteria, protozoa, fungi, and various worms Exposure may not lead to disease

Preventing Invasion of Pathogens Barrier to infection Epidermis (top) Constantly being replaced as dermal cells die and move upwards  good barrier against most pathogens Dermis (underneath) – alive Sweat glands, capillaries, sensory receptors, dermal cells Intact skin  we are protected

Mucus Other entry method: breathing (nasal or mouth) Cells of mucous membranes produce/secrete lining of sticky mucus Cilia lined tissue Move trapped pathogens up and out mucous-lined tissues Traps incoming pathogens Secretes lysozyme Chemically damage many pathogens

Area with mucous membrane What it is and does Trachea Tube which carries air to and from the lungs Nasal passages Tubes which allow air to enter the nose and then the trachea Urethra Tube which carries urine from bladder to the outside Vagina Reproductive tract leading from uterus to the outside

Blood Clotting Bruising Braking small blood vessels (capillaries, arterioles, venules) allowing blood to escape the closed circulatory system Allows entry point for pathogens Clots Seals damaged blood vessels Prevents excessive blood loss and entering pathogens

Blood Clotting Damaged blood vessel Prothrombin (clotting protein) Chemicals (clotting factors) which convert Chemicals released Platelets adhere to damaged area Thrombin (enzyme) one large cell breaks into many fragments Soluble Fibrinogen (clotting protein) Insoluble Fibrin (forms mesh) Short life span

Discuss causes of blood clotting in coronary arteries. What would be a consequence of this?

Production of more antibodies in less time

Immune System Respose Leucocytes – white blood cells Fight off pathogens that pass our primary barriers Macrophage: Large WBC Able to change cellular shape to surround invading cell – process called phagocytosis Ability to move in/out of blood vessels to fight infections

Macrophage Recognizes ‘self’ (normal cells) from ‘not-self’ (invading cells) Based on protein molecules of surface of all cells/viruses ‘Self’ cells not ingested, ‘not-self’ cells are ingested via phagocytosis Contain lots lysosomes to chemically digest foreign body Non-specific response – identity of pathogen not known

Antigens: All cellular invaders (viruses included) have protein receptors (antigens) embedded on membranes – identifies cells as ‘not-self’ Can have several antigens on surface, triggers production of several different antibodies Antibodies: Protein molecules produced in response to specific type of pathogen

Antibodies: Is a protein that is Y shaped At end of forks of the Y is a binding site Where antibody attaches itself to antigen B Lymphocytes (Plasma Cell) Antibody producing leucocytes One B lymphocyte, one antibody

Immune Response A specific antigen type is identified A specific plasma cell is identified that can produce an antibody which will bind to the antigen Plasma cellclone themselves (mitosis) to rapidly increase the number of identical B cells Begin antibody production Released antibodies circulate in bloodstream, find their antigen match Various mechanisms, antibodies helps eliminate pathogen Some plasma cells remain in bloodstream for second infection (memory cells).

Viruses Find a cell type that matches their own proteins in a complementary way Allows them to enter host cell for replication Causes damage to those particular cells, and not others Example: Cold Virus (Rhinovirus) Proteins match mucous membrane cells, causes inflammation of those cells only

Targets Helper T Cells Functions as communicator cell in bloodstream Which cells need to undergo the cloning process and begin antibody production Latency period Infection occurs, but cells remain alive Infection Helper T Cells start to die, antibody production does not occur results in set of symptoms collectively call acquired immunodeficiency syndrome (AIDS)

Transmission Person to person through bodily fluids Sex Sharing of needles Blood transfusions Pregnancy, labor, delivery, breastfeeding

Antibiotics are chemicals – take advantage of biochemical differences between pro- and eu-karyotic cells Inhibits production of new cell wall Block DNA replication Why not Viruses? Selectively block protein synthesis Viruses make use of our own cells metabolism  do not have their own Any chemical that could inhibit their processes would affect our cells as well

Antibiotics are very specific Due to large bacterial numbers  variation occurs in population Antibiotic resistant bacterial strains