BIOL 3542 Lecture Notes - Lecture 4: Aids, Immunodeficiency, Diabetes Mellitus Type 1
26 Jun 2018
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Human Physiology II
Chapter 24: The Immune System
Overview
immune system major functions:
1. Recognizes, removes abnormal “self” cells
created with normal cell growth, development go wrong
2. Removes dead/damaged cells
and old red blood cells
3. Protects body from pathogens
almost all exogenous molecules/cells have potential to elicit immune response
Immunogens: substances that trigger immune response
Antigens: immunogens that react with products of immune response
3 categories of immune system pathogens:
1. Incorrect responses
Autoimmune Disease: immune system attacks body’s normal cells
ex. Type 1 Diabetes Mellitus
2. Overactive responses
immune system creates response out of proportion to threat posed by antigen
ex. allergies
3. Lack of response
Immunodeficiency Disease: some component of immune system fails
Primary Immunodeficiency: family of genetically inherited disorders
Acquired Immunodeficiencies: result of infection, side effect of drug, radiation therapy
ex. acquired immunodeficiency syndrome (AIDS) caused by human immunodeficiency
virus (HIV)
Pathogens of the Human Body
parasites can be introduced to human body by insect bites (ex. malaria), contaminated food/
water, inhaled (ex. valley fever, histoplasmosis), burrowed through skin (blood fluke)
microbes, parasites may enter host cells to evade immune system of stay in extracellular
compartment
Bacteria and Viruses Require Different Defense Mechanisms
1. Structure
bacteria are cells, viruses aren’t (capsid, envelope, viral spikes/proteins)
viruses made of nucleic acid (DNA or RNA)
2. Living conditions and reproduction
most bacteria can survive, reproduce outside host
viruses must use intracellular machinery of host to replicate
3. Susceptibility to drugs
bacteria killed by antibiotics, viruses cannot be
some viruses killed by antiviral drugs
Viruses Can Replicate Only inside Host Cells
virus binds to membrane receptors triggering endocytosis of entire virus particle or virus
envelope fuses with host cell membrane, allowing viral core to enter cytoplasm
viral nucleic acid takes over host cell resources to make new viral nucleic acid and proteins
virus can rupture cell, releasing new virions, or new virions surround themselves with layer
of host cell membrane then bud off from cell surface
viruses may disrupt cell metabolism so cell dies
ex. Herpes simplex type 1 (cold sores), varicellazoster virus (chicken pox)
some viruses hide out in host cell, replicate sporadically
some viruses incorporate their DNA into host DNA
ex. HIV, oncogenic viruses (cancer)
The Immune Response
2 lines of defense:
1. physical and chemical barriers try to keep pathogens out of internal environment
2. internal immune response
4 steps in internal immune response:
1. detection and identification of foreign substance
2. communication with other immune cells to rally organized response
3. recruitment of assistance, coordination of response among participants
4. destruction/suppression of invader
Cytokines: protein messengers released by one cell that affect growth/activity of another cell
Antibodies: proteins secreted by certain immune cells, bind antigens and make them more visible
to immune system
human immune response divided into 2 categories: non-specific innate immunity and specific
acquired immunity
Innate Immunity: present from birth; non-specific immune response
membrane receptors that mediate innate immunity have broad specificity, allow some
immune cells to respond to molecular signals unique and common to pathogenic
microorganisms
begins within minutes to hours
Inflammation: red, warm swollen area on skin; hallmark of cytokine-mediated innate immunity
Acquired Immunity: directed at certain invaders; specific immune response
membrane receptors highly specific, distinguish between pathogens
response to first exposure can take days
secondary responses more rapid
divided into 2 types:
1. Cell-mediated immunity: immune cell binds through receptors to target cell
2. Humoral immunity/antibody-mediated immunity: antibodies carry out immune response
communication, coordination among all pathways vital for max. protective effect
sometimes, body can only control damage and keep pathogen from spreading
ex. tuberculosis bacteria, malaria parasite, herpes virus
Lymphoid Tissues Are Everywhere
primary lymphoid tissues are thymus gland, bone marrow
sites where immune cells form, mature
some immune cells don’t specialize until their first pathogen encounter
Naïve Cells: mature, unspecialized immune cells
mature immune cells interact with pathogens in secondary lymphoid tissues
divided into encapsulated tissues (spleen, lymph nodes) and unencapsulated tissues
encapsulated tissues have outer wall formed from fibrous collagenous capsules
spleen contains immune cells that monitor blood for pathogens and phagocytic cells that
destroy old red blood cells
filtered fluid from blood capillaries picked up by lymph capillaries, passes through
encapsulated lymph nodes where immune cells look for pathogens
Diffuse Lymphoid Tissues: unencapsulated; aggregates of immune cells that appear in other
organs
include tonsils, gut-associated lymphoid tissue (GALT) located under epithelium of
esophagus, intestines, and clusters of lymphoid tissue associated with skin and respiratory,
urinary, reproductive tracts
immune system positioned wherever pathogens are most likely to enter body
Leukocytes Mediate Immunity
Leukocytes (a.k.a. white blood cells): primary cells responsible for immune response
most circulate in blood
usually leave capillaries, function extravascularly (outside vessels)
some types can live in tissues for months; others hours to days
6 types:
1. basophils in blood, mast cells in tissues
2. eosinophils
3. neutrophils
4. monocytes and derivative macrophages
5. lymphocytes and derivative plasma cells
6. dendritic cells (not usually found in blood)
Immune Cell Names
Granulocytes: leukocytes whose cytoplasm contains prominent granules
Degranulation: granule contents released from cell by exocytosis
Phagocytes: neutrophils, macrophages, monocytes (macrophage precursors)
Cytotoxic Cells: kill cells they attack
includes eosinophils, some lymphocytes
Antigen-Presenting Cells: macrophages, monocytes, one type of lymphocyte, dendritic cells
Mononuclear Phagocyte System: macrophages in tissues and parent monocytes in blood
Basophils
rare in circulation
large, dark blue granules in cytoplasm
similar to mast cells of tissues (both release mediators that contribute to inflammation)
Document Summary
Overview immune system major functions: recognizes, removes abnormal self cells. Created with normal cell growth, development go wrong: removes dead/damaged cells. And old red blood cells: protects body from pathogens. Almost all exogenous molecules/cells have potential to elicit immune response. Antigens: immunogens that react with products of immune response. Autoimmune disease: immune system attacks body"s normal cells. Immune system creates response out of proportion to threat posed by antigen. Immunodeficiency disease: some component of immune system fails. Primary immunodeficiency: family of genetically inherited disorders. Acquired immunodeficiencies: result of infection, side effect of drug, radiation therapy. Ex. acquired immunodeficiency syndrome (aids) caused by human immunodeficiency virus (hiv) Pathogens of the human body parasites can be introduced to human body by insect bites (ex. malaria), contaminated food/ water, inhaled (ex. valley fever, histoplasmosis), burrowed through skin (blood fluke) Microbes, parasites may enter host cells to evade immune system of stay in extracellular compartment. Bacteria and viruses require different defense mechanisms: structure.
