The Body's Defenses
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- Nonspecific defense mechanisms
- First line of defense:
- A) Skin
- B) Mucus membranes
- C) Secretions from both
- 2) Second line of defense:
- A) Phagocytic white blood cells
- B) Antimicrobial proteins
- C) Inflammatory response
Specific defense mechanisms
- Third line of defense (Immune System):
- A) Lymphocytes
- B) Antibodies
First Line of Defense (Skin and Mucus Membranes)
- Skin is barrier that cannot normally be penetrated by bacteria or viruses.
- - However, cuts or abrasions could allow entry.
- - Provide physical barriers but also produce secretions. (Examples: oil, sweat).
Skin and mucus membranes: secretions
- Secretions have lower pH (more acidic)
- - Secretions may contain antimicrobial proteins. (Example: lysozyme).
- - In tears and upper respiratory system.
- - Attacks cell walls of bacteria
Mucus (thick, viscous secretion), produced by mucus membranes, can trap microbes and particles. Example: Upper respiratory system
Second Line of Defense
- - Provide main internal mechanism of nonspecific defense.
- - Main phagocytic cells = Neutrophils
- - 60-70% of all white blood cells
- - attracted by chemical signals (Chemotaxis)
- - 5% of white blood cells
- - even more effective than Neutrophils
- - become Macrophages ("big eaters")
- - 1.5% of white cells
- - limited pagocytic activity
- - A group of > 20 proteins that act in cascade of activation steps to lyse invading microbes.
- - Produced by virus-infected cells.
- - Helps other cells resist infection.
- Localized Inflammation:
- - Inflammation = "setting on fire"
- - Tissue damage triggers vasodilation in small vessels increasing blood supply to damaged area.
- - Example: Histamine release from basophils and mast cells.
- - Example: Prostaglandin release by damaged tissue.
- - Vasodilation also delivers clotting elements.
- - Perhaps the most important aspect of vasodilation is phagocyte migration
- Release of large numbers of neutrophils from bone marrow.
- - Fever caused by pyrogens.
Third Line of Defense: Basic features
- - Recognize antigens
- - Produce antibodies
- 2) Diversity:
- - Immune system can respond to millions of kinds of invaders.
- - Stems from huge variety of lymphocytes.
Third Line of Defense: Basic features pt. 2
- Self/Non-Self Recognition:
- - Ability to distinguish body's own molecules.
- - Malfunctions can lead to autoimmune disorders.
- 4) Memory:
- - Acquired Immunity: remembers antigen seen before responds faster second time.
- i) Active Acquired Immunity:
- - Depends on person's own immune system.
- Examples: Plague, Vaccinations
- ii) Passive Acquired Immunity:
- - Pregnant woman's body passes antibodies to fetus or newborn
Immune System Has 2 subdivisions
- Humoral Immunity:
- - Results in antibody production by B lymphocytes.
- - Defends against toxins, bacteria and viruses that are free in body fluids
- Cell Mediated Immunity:
- - Depends on direct action T lymphocytes (T cells).
- - Defends against bacteria and viruses inside cells, and fungi, protozoans and worms.
- - Also attacks transplanted cells
B and T Lymphocytes
- All originate from stem cells in the bone marrow.
- - Maturation site determines identity.
- - Maturation in thymus gland = T lymphocytes.
- - If remain in bone marrow = B lymphocytes.
- - Mature B and T cells most concentrated in lymphatic organs.
B and T Lymphocytes
- Both B and T cells have antigenic receptors.
- - B Cells have bound antibodies
- - T Cells have receptors that recognize antigens.
- - Specificity of immune system depends on B and T cells being able to recognized specific antigens.
- - When antigen binds to receptors on B and T cells, these cells divide and give rise to effector cells.
Five Subclasses of Immunoglobulins
IgM and IgG
- IgM = pentamer
- a) first to arrive
- b) indicates current infection
- 2) IgG = monomer
- a) Most abundant
- b) crosses vessels easily
- c) protects against toxins viruses and bacteria
Five Subclasses of Immunoglobulins
IgA and IgD and IgE
- 3) IgA = dimer
- a) prevent viruses and bacteria from attaching to epithelial surfaces
- b) secretions (tears and colostrum)
- 4) IgD = monomer
- a) antigen receptor on surface of B cells
- 5) IgE = monomer
- a) on surface of basophils and mast cells
- b) Allergic reactions
- Lymphocytes not plastic in their abilities to respond to antigens.
- - Rather, specificity pedetermined during development.
- - If antigen binds to receptor on surface of lymphocyte, cell divisions result in clones.
- - Antigen-specific selection and cloning of lymphocytes called clonal selection.
Primary Immune Response
- 5 -10 days
- - T cells become Effector T cells and
- - B cells become plasma cells
secondary immune response
- Faster: 3-5 days
- - Response more prolonged
- - Antibodies more effective at binding
- •Ability to recognize antigen as previously encountered.
- - Memory cells produced along with short lived effector cells during
- primary immune response.
- A) They do not exist until after primary immune response
- B) Proliferate rapidly when re-exposed.
- - Confers immunity against diseases.
Lymphocytes with antigen receptors against self undergo apoptosis (i.e.,"commit suicide“ before birth, a form of programmed cell death).
- Major Histocompatibility complex (MHC):
- - Classes I & II
- - glycoproteins
- - 20 genes
- - bichemical fingerprint (except identical twins)
The Immune System works in close associatio with what?
the lymphatic system
- •Part of the circulatory system that collects fluids and proteins that have escaped from cells and returns them to the blood.
- •Phagocytic removal of cellular debris, and foreign matter (e.g., pathogens)
- •Effector cells directly defend body.
- From B cells: Plasma Cells.
- From T cells: Cytotoxic T Cells and Helper T Cells.
Cytotoxic T cells
destroy infeected cells and cancer
Helper T cells
stimulate humoral adn cell-mediated immunity
- usually protein or large polysaccharide (ex: on coat of bacterium)
- Antigen is anything that can elicit an immune response or allergy that can be bound to (3D structure)
Antibodies - Only recognizes a localized region on antigen called antigenic determinant or epitope. Belong to class of proteins called Immunoglobulins.
Structure of typical antibody
- Heavy and light chains
- - constant nd variable regions
- - antigen-binding sites
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