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Lecture 22.docx

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Western University
Biology 1202B
Brenda Murphy

1 Immunology: Introduction (Chapter 43) Disease  Disease has plagued all organisms for billions of years  Humans evolved out of Africa 200,000 years ago o AIDS – 40 million people o Malaria – 500 million peope  World population 7,001,509,012 (March 19, 2011) What Causes Disease?  Pathogens o Viruses – Multicellular but can only reproduce inside of a plant, animal, or cell o Fungi – Multicellular but plant-like similar to tree fungus – takes nutrition from plant, tree, or animal o Protozoa – One-celled creatures – usually spread through water o Parasites - Actual complex of living organisms – can live in intestinal tract or blood stream o Protein – Multi-cellular but can only reproduce inside a plant, animal or person o Bacteria – Tiny, one-celled creatures, can live inside or outside the body Immunology  Study of the immune system o The collective name for the organs, tissues, and cells of the body that work to prevent and heal diseases 3 Lines of Defence Against Invasion 1. Physical Barrier  Prevent entry of pathogen  Many of the body cavities lined by mucus membranes have environments that are hostile to pathogens o Acid stomach kills most ingested bacteria & breaks down most viruses  If they survive, they are exposed to digestive enzymes & bile secreted into small intestine o Reproductive tract acidic prevents pathogen survival o Epithelium tissues secrete enzymes such as defensins or lysozymes that are lethal to many bacteria 2. Innate Immune System  Inherited mechanism that protect body in a non-specific mechanism  Reaction to the infection takes minutes  Generalized internal chemical, physical & cellular reactions against pathogens that have survived first line of defense 2  Immediate, nonspecific response targets invading pathogens & has no memory of prior exposure to that specific pathogen o Inflammation which creates an internal condition that inhibits or kills many pathogens o Specialized cells that engulf or kill pathogens or infected body cells 3. Adaptive (or Acquired) Immune System  Found only in vertebrates  Inherited mechanisms that lead to the synthesis of antibodies  Reaction to the infection takes several days  Most complex line of defence  Reaction is specific to foreign substances  Attack is to neutralize or eliminate pathogens  Reaction is triggered by specific molecules on the pathogen that are recognized as being foreign “non-self” to the body  Body retains a memory of the first exposure to that pathogen, enabling it to respond more quickly if the pathogen is encountered again in the future Bacterial Induction of Inflammation  A break in the skin introduces bacteria, which reproduces at the wound site o Pathogens have highly conserved molecular patterns present on their surface that are not on host cells, which allows for recognition of foreign material  Activated macrophages engulf the pathogens & secrete cytokines & chemokines  Activated mast cells release a histamine which dilate local blood vessels & increase their permeability o Monocytes (a type of leukocyte) enter the damaged tissue from the bloodstream through the endothelial wall of the capillary o Once in the damaged tissue the monocyte differentiates into macrophages (big eaters) o Macrophage receptors recognize & bind to surface molecules of the pathogens & initiate phagocytosis o If there is not enough macrophages, they will also secrete cytokines to attract other immune cells o Death of cells caused by pathogens at the infection site activates cells that are dispersed through the connective tissue (mast cells) o Cytokines also make the blood vessel wall sticky, causing neutrophils to attach  Chemokines (secreted by macrophages) attract neutrophils, which pass between cells of the blood vessel wall & migrate to the infection site  Neutrophils engulf the pathogens & destroy them o Neutrophils are starting in the capillary 3 o Because the capillary is opened up, they are moving from it and into the system and take
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