Download Intro to the Lymphatic System

THE LYMPHATIC
SYSTEM
The Lymphatic System

Two Semi-Independent Parts
Lymphatics (vessels)
1.
 Collects
leaked plasma & proteins
from bloodstream (lymph)
 One way flow  toward heart
 Minivalves
Lymphoid tissues & organs
2.

Immune functions
Lymph Nodes


Contain macrophages
to digest bacteria
Contain lymphocytes
B cells that generate
plasma cells (antibodyreleasing cells)
 T cells that destroy
tumor cells


More afferent than
efferent vessels
Lymphoid Organs



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Spleen – filters worn
erythrocytes, bacteria,
viruses, & other debris
Thymus – Releases
hormone thymosin during
childhood to help T
lymphocytes mature
Tonsils – Trap foreign
pathogens entering throat
Peyer’s patches – capture
& destroy bacteria in the
small intestine
The Immune System

Two Types of Resistance:
Nonspecific Resistance
1.



General protection against many pathogens
Immediate
Present since birth (inherited)
Specific Resistance
2.

Develops in response to
contact with specific invaders
First Line of Defense: Barriers

Physical Barriers:
 Skin
 Hairs
 Mucous
Membranes





Digestive
Respiratory
Urinary
Reproductive
Cilia
First Line of Defense: Barriers

Chemical Barriers



Acid secretions –
skin, vagina, stomach;
kill bacteria
Sebum – oil of skin;
toxic to bacteria
Lysozyme –
enzymes in tears,
saliva, and urine that
destroys bacteria
Second Line of Defense: Cells
Nonspecific; Attack pathogens but don’t
“remember” for next time.
 Phagocytes – perform phagocytosis

 Neutrophils
– first to enter infected tissues; kill
bacteria
 Macrophages – slower; BIG eaters
Second Line of Defense: Cells

Natural Killer Cells (Killer T cells) –
 Kills
cancer cells
 Kills virus-infected body cells
 Lyses cell with perforin
Second Line of Defense:
Inflammatory Response


Triggered when tissues are injured
Four Signs:
 Redness
 Heat
 Swelling
 Pain
Second Line of Defense:
Inflammatory Response
First Step: Alarm
 Injured cells release histamine & kinins
causing:
– increases blood flow
 Leaky capillaries – causes edema
 Activated pain receptors – forces rest
 Chemotaxis – chemical gradient attracts
phagocytes and other white blood cells
 Vasodilation
Second Line of Defense:
Inflammatory Response


One hour later:
Neutrophils perform
diapedesis and start
clean-up
8-12 hours later:
Monocytes become
macrophages!
Second Line of Defense:
Inflammatory Response



Prevents the spread of infection
Disposes of cell debris & pathogens
Sets the stage for repair and healing
Second Line of Defense:
Antimicrobial Chemicals


Interferon –
protein
released by
virus-infected
cells to prevent
neighboring
cells from
reproducing
new viruses
Urine
Second Line of Defense:
Antimicrobial Chemicals

Complement System
 At
least twenty proteins always circulating
 Activated by foreign antigens
 Release chemicals:
 Vasodilators
 Chemotaxis
– cause foreign cell
membranes to become sticky (and
yummy)
 Opsonization
Second Line of Defense: Fever


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White blood cells secrete
pyrogens
Triggers hypothalamus to raise
body temperature
Inhibits bacterial growth
Stimulates phagocytosis
Causes liver & spleen to store
iron, reducing availability for
bacteria
Third Line of Defense:
The Immune System

Two parts (working simultaneously):
Immunity – (antibody-mediated),
antibodies present in the body fluids
 Cellular Immunity – (cell-mediated),
lymphocytes defend the body
 Humoral



Specific
Systemic
Has memory
Overview: Antigens


Nonself antigens
Self antigens – MHC
(major histocompatibility)
complex
Overview: Antibodies



AKA immunoglobulins (Igs)
Bind to specific antigen
Inactivates by:
 Activating
complement proteins = cell lysis
 Binds to toxic secretions, rendering them
harmless
 Agglutination
 Causes precipitation of soluble antigens
Effects of Antibodies
Cell Overview: Lymphocytes


Formed from hemocytoblasts in bone marrow
Mature by gaining immunocompetence (ability
to respond to specific antigen)
 In
Bone marrow = B cells
 In Thymus = T cells
Cell Overview: Macrophages


Antigen Presentation – present fragments of
the antigens they’ve eaten on cell surface, for
T cells to recognize
Secrete monokines, that further activate T
cells
Primary Humoral Response



Antigen binds to immature B lymphocyte
causing clonal selection
Helper T cells activate B cells
B cell makes clones!
 Plasma
 Make
cells (most)
antibodies
 Memory
cells (few)
 Remember
invader for
faster response in future
Clonal Selection/T cell activation
B cell cloning/Antibody Production
Secondary Humoral Response




Achieved by memory B Cells in response to
the old antigen
Faster
More prolonged
More effective
Active Immunity

Active immunity – activation of B Cells
– bacterial or viral infection
 Artificially – vaccine
 Naturally
 Spared
threat of the disease
 Still primes immune system for secondary response
Passive Immunity

Passive immunity – antibodies
are transferred into the body\
– from mother to baby
through placenta or breastmilk
 Artificially – antivenin (snake bites),
antitoxin (botulism, rabies, tetanus)
 Naturally


B cells are not challenged by
antigen
Immunological memory does not
occur
Cellular Immune Response:
Helper T cells



Recruit other immune cells to join fight
Cannot recognize free-floating antigen
Macrophages present antigens: double
recognition (self & non-self)
Cellular Immune Response:
Helper T cells

Activation of Helper T cells:
 Stimulates
B cells & Killer T cells to grow/divide
 Attracts other white blood cells to area
 Enhances macrophage ability to eat & destroy
 Releases lymphokines – chemicals that help
destroy antigens
Cellular Immune Response:
Other T cells



Suppressor T Cells – slows
or stops the activity of B and
T cells once the infection has
been conquered
Memory T Cells – same as
memory B cells
Killer T Cells (cytotoxic T
cells)