The Lymphatic System And Body Defenses

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The Lymphatic System And Body Defenses
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The Lymphatic System

• Lymphatic vessels
• Lymphoid tissues and organs
• Lymphatic system functions
• Transport fluids back to the blood
• Play essential roles in body defense and
  resistance to disease

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How Lymph Moves

• One way system toward the heart
• No pump
• Milking action of skeletal muscle
• Peristalsis in vessel walls

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Lymphatic Pathways
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Lymphatic Ducts

• Lymph is delivered into one of two large ducts
• Right lymphatic duct drains the right upper arm
  and the right side of the head and thorax
• Thoracic duct arises from the cisterna chyli and
  drains the rest of the body
• Each empties lymph into venous circulation at the
  junction of the internal jugular and subclavian
  veins on its own side of the body

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Internal jugular veins
Right jugular trunk
Esophagus
Right lymphatic duct
Trachea
Right subclavian trunk
Left subclavian trunk
Right subclavian vein
Left jugular trunk
Right broncho- mediastinal trunk
Left subclavian vein
Brachiocephalic veins
Entrance of thoracic duct into vein
Superior vena cava
Left bronchomediastinal trunk
Azygos vein
Ribs
Thoracic duct
Hemiazygos vein
Cisterna chyli
Right lumbar trunk
Left lumbar trunk
Inferior vena cava
Intestinal trunk
(b) Major lymphatic trunks and ducts in relation
to veins and surrounding structures.
Anterior view of thoracic and abdominal wall.
Figure 20.2b
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Lymphatic Vessels
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Lymphatic Vessels

• Collects lymph from lymph capillaries
• Carries lymph to and away from lymph nodes
• Returns fluid to circulatory veins near the heart
• Lymph Functions absorption of dietary fats,
  delivers fats to bloodstream, collection of
  excess interstitial fluids, delivers excess
  fluids to bloodstream, delivers foreign particles
  to lymph nodes

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Lymphatic Capillaries

• Similar to blood capillaries, except
• Very permeable (take up cell debris, pathogens,
  and cancer cells)
• Endothelial cells overlap to form one-way
  minivalves
• Absent from bones, teeth, bone marrow and the CNS
• Lacteals specialized lymph capillaries present
  in intestinal mucosa
• Absorb digested fat and deliver fatty lymph
  (chyle) to the blood

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Filaments anchored to connective tissue
Endothelial cell
Flaplike minivalve
Fibroblast in loose connective tissue
(b) Lymphatic capillaries are blind-ended tubes
in which adjacent endothelial cells overlap
each other, forming flaplike minivalves.




Figure 20.1b
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Lymph

• Materials returned to the blood
• Water
• Blood cells
• Proteins
• Harmful materials that enter lymph vessels
• Bacteria
• Viruses
• Cancer cells
• Cell debris

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Lymph Nodes

• Filter lymph before it is returned to the blood
• Defense cells within lymph nodes
• Macrophages
• Lymphocytes
• Most are kidney-shaped, less than 1 inch long
• Cortex collections of lymphocytes
• Medulla phagocytic macrophages

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Other Lymphoid Organs

• Spleen, Thymus, Tonsils, Peyers patches
• Spleen Filters blood, Destroys worn out blood
  cells, Forms blood cells in the fetus, Acts as a
  blood reservoir.
• Thymus Located low in the throat, overlying the
  heart, Functions at peak levels only during
  childhood, Produces hormones (like thymosin) to
  program lymphocytes. Maturation of T-Cells
• Tonsils Trap and remove bacteria and other
  foreign materials, Tonsillitis is caused by
  congestion with bacteria
• Peyers Patches Capture and destroy bacteria in
  the intestine

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Diaphragm
Spleen
Adrenal gland
Left kidney
Splenic artery
Pancreas
(c) Photograph of the spleen in its normal
position in the abdominal cavity, anterior
view.
Figure 20.6c
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Immunity

• Resistance to disease
• Immune system has two intrinsic systems
• Innate (nonspecific) defense system
• Adaptive (specific) defense system

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Surface barriers Skin Mucous membranes
Innate defenses
Internal defenses Phagocytes NK cells
Inflammation Antimicrobial proteins Fever
Humoral immunity B cells
Adaptive defenses
Cellular immunity T cells
Figure 21.1
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Lets Play Defense

• The body has two defense systems for foreign
  materials
• Nonspecific defense system
• Mechanisms protect against a variety of invaders,
  Responds immediately to protect body from foreign
  materials
• Specific defense is required for each type of
  invader, Also known as the immune system

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Nonspecific Body Defenses

• The skin
• Stomach mucosa
• Saliva and lacrimal fluid contain lysozyme
• Mucus

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Defensive Cells

• Natural Killer Cells lyse or kill viral infected
  cells and cancer cells. Tend to be non-specific
  in their chemical use of perforins.
• Macrophages Free or Fixed (microglial)
• Neutrophils phagocytic levels rise and fall
• Dendritic Cells Carry foreign bodies to lymph
  nodes
• How Phagocytosis works
• Opsonization helps them adhere
• Engulf via phagocytosis
• Destroy with lysosomal enzymes

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Innate defenses
Internal defenses
(a) A macrophage (purple) uses its
cytoplasmicextensions to pull spherical bacteria
(green) toward it. Scanning electron micrograph
(1750x).
Figure 21.2a
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Innatedefenses
Internaldefenses
Inflammatorychemicalsdiffusingfrom
theinflamed siteact as chemotacticagents.
Chemotaxis.Neutrophilsfollow chemicaltrail.
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Capillary wall
Basementmembrane
Endothelium
Leukocytosis.Neutrophils enter bloodfrom
bone marrow.
Margination.Neutrophils clingto capillary
wall.
1
2
3
Diapedesis.Neutrophils flatten andsqueeze
out of capillaries.
Figure 21.4
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Chemical Defense

• interferons- are proteins that are secreted by
  viral infected cells that bond to healthy cells
  and prevent virus from bonding.
• Complement- 20 proteins that when activated can
  punch holes in infected cells literally blowing
  them up.
• Collectins- are proteins that recognize foreign
  structure or sugar arrangement and stick

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Innate defenses
Internal defenses
Virus
1
Virusenters cell.
New viruses
Viral nucleic acid
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Antiviralproteins blockviralreproduction.
2
Interferongenes switch on.
DNA
Nucleus
mRNA
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Interferonbindingstimulates cell toturn
on genes forantiviral proteins.
3
Cell producesinterferonmolecules.
Interferon
Host cell 2Binds interferon from cell 1
interferon induces synthesis ofprotective
proteins
Host cell 1Infected by virusmakes
interferonis killed by virus
Figure 21.5
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Alternative pathway
Classical pathway
Spontaneous activation
Antigen-antibody complex


Stabilizing factors (B, D, and P)

complex
No inhibitors on pathogen surface
Enhances inflammation
Opsonization
stimulates histamine release, increases blood
vessel permeability, attracts phagocytes by
chemotaxis, etc.
coats pathogen surfaces, which enhances
phagocytosis
Insertion of MAC and cell lysis (holes in target
cells membrane)
Pore
Complement proteins (C5bC9)
Membrane of target cell
Figure 21.6
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Cont..

• Fever
• Caused by pyrogens released from macrophages
• High temperatures inhibit the release of iron and
  zinc from liver and spleen needed by bacteria
• Fever also increases the speed of tissue repair
• Inflammatory response.
• chemical signals of the inflamatory response is
  histamine. basophils and mast cells
• triggers both dilation and increased permeability
  of nearby capillaries.

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Inflammation
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Immunity (Specific)

• Antigen specific----Pathogen?
• Systemic
• Has memory
• Distinguish self from non-self
• Humoral immunity Antibody-mediated.
• B-cells
• Cellular immunity Cell-mediated immunity,
• T-cells

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Cont.

• Allergies haptens or incomplete antigens) are
  not antigenic alone, but link up with our own
  proteins
• The immune system may recognize and respond to a
  protein-hapten combination
• Ex. Poison Ivy, Detergents, Pollen
• Cells Lymphocytes- Originate from
  hemocytoblasts in the red bone marrow and B
  lymphocytes become immunocompetent in the bone
  marrow T lymphocytes become immunocompetent in
  the thymus.

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Antigen Receptor Diversity

• Lymphocytes make up to a billion different types
  of antigen receptors
• Coded for by 25,000 genes
• Gene segments are shuffled by somatic
  recombination
• Genes determine which foreign substances the
  immune system will recognize and resist

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Cont

• Each antigen has a particular molecular shape and
  stimulates certain B cells to secrete antibodies
  that interact specifically with it
• B and T cells recognize specific antigens through
  their plasma membrane-bound antigen receptors
• single T or B lymphocyte bears about 100,000
  receptors for antigen, all with exactly the same
  specificity
• Although it encounters a large repertoire of B
  cells and T cells, a microorganism interacts only
  with lymphocytes bearing receptors specific for
  its various antigenic molecules

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B - Cells

• Plasma cells
• secrete about 2,000 antibody molecules per second
  over the cells 4- to 5-day life span
• Memory cells
• Clonal selection
• This 1st encounter is called the Primary Immune
  Response

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Cont

• Secondary immune responsestronger then the 1st
• response is faster (only 2 to 7 days), of greater
  magnitude, and more prolonged
• immunological memorythe basis of the vaccine

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Cell Mediated Immunity

• B cells and T cells mature in the bone marrow and
  thymus, their antigen receptors are tested for
  potential self-reactivity
• failures of self-tolerance can lead to autoimmune
  diseases
• T cells do have a crucial interaction with one
  important group of native molecules whereas
  B-Cells do not
• cell surface glycoproteins encoded by a family of
  genes called the major histocompatibility complex
  (MHC) mark body cells as self

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Cont

• Class I MHC molecules- found on almost all
  nucleated cells
• Class II MHC molecules macrophages, B cells,
  activated T cells, and those inside the thymus
• numerous possible alleles for each class I and
  class II MHC gene it is unlikely that any two
  people, except identical twins, will have exactly
  the same set of MHC molecules---Think transplant
• MHC Molecules are antigen presenters
• 2 main types of T cells, and each responds to one
  class of MCH molecule.
• Cytotoxic T cells (TC) class I MHC molecules.
• Helper T cells (TH) class II MCH molecules

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Cytoplasm of any tissue cell
Cisternae ofendoplasmicreticulum (ER)
Endogenous antigenpeptides enter ER
viatransport protein.
2
Endogenousantigen is degradedby protease.
1
Endogenousantigen peptide isloaded onto
classI MHC protein.
3
Endogenous antigenself-protein or
foreign(viral or cancer) protein
Loaded MHC proteinmigrates in vesicle
tothe plasma membrane,where it displays
theantigenic peptide.
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Transportprotein(ATPase)
Antigenic peptide
Plasma membrane of a tissue cell
Extracellular fluid
(a) Endogenous antigens are processed and
displayed on class I MHC of all cells.
Figure 21.17a
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Cytoplasm of APC
1a
Class II MHC issynthesized in ER.
Invariant chain prevents class II MHC from
binding to peptides in the ER.
Cisternae ofendoplasmicreticulum (ER)
Plasma membrane of APC
Extracellular fluid
(b) Exogenous antigens are processed and
displayed on class II MHC ofantigen-presenting
cells (APCs).
Figure 21.17b, step 1a
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Antigen Presentation
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Cell Mediated Response
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Overview
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Immunity Acquisition
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Antibodies

• Y shaped proteins that are completely specific
  and have many uses for immunity and science. Also
  known as immunoglobulin (Igs)
• secreted by B cells (plasma cells)
• Carried in blood plasma
• Capable of binding specifically to an antigen
• 5 main types made of 4 amino acids chains linked
  by di-sulfide bonds.

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Antigen-binding site
Heavy chain variable region
Hinge region
Heavy chain constant region
Stem region
Light chain variable region
Light chain constant region Disulfide bond
(a)
Figure 21.14a
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Immunoglobulin Structure
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Types

• IgG
• activates complement
• defends against bacteria, viruses, and toxins
• IgA
• defends against bacteria and viruses
• IgM
• reacts with naturally occurring antigens on RBCs
  following certain blood transfusions
• activates complement
• IgD
• plays a role in B cell activation
• IgE
• promotes inflammation and allergic reactions

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Review
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Grafts
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Autoimmunity

• The immune system does not distinguish between
  self and nonself
• The body produces antibodies and sensitized T
  lymphocytes that attack its own tissues

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Disorders
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Allergic Reactions

• Type I immediate-reaction allergy, hives, hay
  fever, asthma, eczema, gastric disturbances,
  anaphylactic shock- penicillin, or stings
• Type II antibody-dependent cytotoxic reaction
• takes 1-3 hours to develop
• transfusion reaction
• Type III immune-complex reaction
• antibody complexes cannot be cleared from body
• damage of body tissues
• Type IV
• delayed-reaction allergy