Lymphatic System and
Immunity
Chapter 16
Functions of Lymphatic System
1. Draining interstitial fluid
2. Transporting dietary lipids
3. Protection
Lymphatic Vessels
• Begin as closed ended lymph capillaries in
tissue spaces between cells
• NOT A CIRCULATING FLUID
• Interstitial fluid drains into lymphatic
capillaries, forming lymph.
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Lymph capillaries merge to form lymphatic
vessels
Lymphatic vessels carry lymph into and out
of lymph nodes
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• and finally back to the vascular system.
Lymphatic capillaries
• Made of a single layer of squamous
epithelial cells
• Slightly larger than blood capillaries
• Cells overlap and act as one-way valves
• Opened by pressure of interstitial fluid
• Anchoring filaments attach cells to
surrounding tissue
Lymphatic vessels
• Resemble veins (same 3 layers)
• Found throughout body except:
– Avascular tissues
– Central nervous system
– Splenic pulp
– Bone marrow
Lymphatic vessels join to form lymphatic trunks.
Lymphatic trunks join to form :
Thoracic duct (3/4 of body)
Right lymphatic duct (drains right arm,
and right side of head, neck and upper torso)
These empty into subclavian veins at junction
with internal jugular vein.
Formation of lymph:
Fluid leaves capillaries by diffusion and
filtration
Escaped proteins
If lymph flow blocked = tissue swelling or
edema
Specialized lymphatic capillaries in vili of
small intestine transport lipids - they are called
lacteals, and the fluid is called chyle.
Lymphatic Organs
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Red bone marrow
Thymus gland
Lymph nodes
Lymph nodules
Spleen
Primary organs
Secondary organs
Lymph Nodes
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Lymph is filtered through lymph nodes
Found in clusters
“Waste water treatment plants”
Vary in size
Principal groupings in cervical, axillary and
inguinal regions.
• Provide biological filtration
• Site of cancer growth and metastasis
• Vessels enter node on convex side
• Lymph passes through irregular channels
called sinuses
• Leaves node through one or two efferent
vessels at the hilum or hilus
• Capsule, cortex and medulla
• Cortex contains lymph nodules
• Follicular dendritic cells
• Germinal centers – B cells proliferate
Lymph nodules are also found singly or in
groups throughout the mucous membranes of
the respiratory, urinary, reproductive and
digestive tracts.
MALT – mucosa associated lymphoid tissue
Peyer’s patches in ileum
Tonsils
Some in appendix
Tonsils – lymphoid tissue under the mucous
membranes of the throat
palatine tonsils
pharyngeal tonsil – adenoid
lingual tonsils
First line of defense
Tonsillectomy
Thymus gland
• in mediastinum above the heart
• largest at age 10-12 then begins to atrophy
• Pre - T cells come from bone marrow and
develop into T cells
• T cells then go to other lymphatic tissues
• Thymus produces hormone thymosin - aids
maturation of T cells elsewhere in body
Spleen
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Largest lymphoid organ
In upper left quadrant of abdomen
Has a hilum and a capsule
Sinuses contain blood instead of lymph
White pulp:
little islands, mostly B cells
Red pulp:
Venous sinuses
Splenic cords – RBCs, macrophages,
lymphocytes, plasma cells and
granulocytes
Functions of Spleen
• Blood formation –
– All blood cells in fetus
– Only lymphocytes and monocytes after birth
• Blood filtration
– Removes bacteria, particles, worn out RBCs
and platelets (recycles iron)
• Blood storage
– Can contain over one pint of blood
Nonspecific Resistance
The ability to ward off disease is called
resistance.
Lack of resistance is susceptibility.
Nonspecific resistance refers to a wide variety
of body responses against a wide range of
pathogens. A pathogen is any microorganism
that causes disease.
Immunity
Immunity involves activation of specific
lymphocytes to combat a specific foreign
agent.
Nonspecific Resistance
Species (Inborn) Resistance – certain
species contract certain diseases, while
other species do not.
Mechanical Barriers
• Skin and mucous membranes :
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First line of defense
Physical barrier
Shedding of dead cells
Mucus
Hairs
Cilia
Coughing and sneezing, production of tears, saliva,
urine, defecation and vomiting physically remove
harmful substances
Chemical Protection
Sebaceous glands produce sebum – fatty
acids inhibit growth of bacteria and fungi
Lactic acid further decreases skin pH
Accumulation of salt
Vaginal secretions are also slightly acidic
Gastric juice – acid, enzymes and mucus
Lysozyme in tears, perspiration, saliva and
tissue fluids
Normal Microbiota – bacteria living on skin
inhibit the growth of pathogens by
producing antibiotics
Antimicrobial Substances
Transferrins are proteins that tie up the free
iron in the blood and interstitial fluid.
Interferon – “Paul Revere Chemical” – a
glycoprotein produced by virus infected cells
that cause neighboring cells to produce
anti-viral proteins. These also enhance
phagocytosis and can suppress growth of
tumor cells.
The Complement System:
10- 20 normally inactive proteins
When activated, they “complement” or
enhance certain immune, allergic and
inflammatory reactions.
1.Activation of inflammation
2. Opsonization – enhances phagocytosis
3.Cytolysis – membrane attack complex
Fever :
Causes liver and spleen to sequester iron
Increases phagocytosis
Inhibits growth of microbes
Speeds up body repair
Inflammation:
Characterized by:
Heat, swelling, redness, and pain
(and sometimes loss of function)
calor, tumor, rubor and dolor
Stages of inflammation
1. Vasodilation and increased permeability
of blood vessels
2. Phagocyte migration
1. Neutrophils come first
2. Followed by macrophages
3. Tissue Repair
Phagocytosis
Three phases:
1. Chemotaxis
2. Adherence
3. Ingestion
Natural Killer Cells
• Next line of defense (with phagocytes)
• Lymphocytes – but do not respond to
specific antigens
• Can kill a variety of microbes plus tumor
cells.
• May release perforins, or attack directly
• Cell may not display correct MHC antigens
Immunity
• Specific resistance to disease involving
the production of a specific lymphocyte or
antibody against a specific antigen.
• An antigen is any substance that elicits an
immune response. Best antigens are:
– Large
– Complex
– Recognized as foreign
Haptens are molecules that are small, foreign
and complex. To elicit an immune response,
they must piggy-back on a larger molecule,
often blood proteins.
Epitopes: a foreign protein may result in
several different antibodies. Each antibody
recognizes a different portion of the protein.
These regions are called epitopes.
Two forms of immunity:
Humoral or antibody mediated immunity
B cells (mature in bone) make
antibodies: specific proteins that bind to
specific antigens
OR
Cell-mediated immunity
Tcytoxic lymphocytes attack virus
infected or tumor cells directly
“The Story”
• Macrophage destroys a bacterium
• Takes bacterial antigen and fuses it with
MHC II complex
• MHC II complex and antigen are placed on
cell membrane.
• Displays antigen (like a proud cat) – so it
is called an antigen presenting cell.
It shows antigen to helper T cells, until it finds
one that has a receptor that matches the
antigen complex.
The helper T cell binds to the antigen complex,
and the macrophage is stimulated to produce
the cytokine Interleukin -1
A cytokine is a protein hormone which
regulates normal cell functions, like growth and
differentiation.
Every step needs 2 signals to proceed.
IL-1 binds to receptors on the helper T cell,
causing helper T-cell to clone itself and
produce IL-2.
IL-2 causes lymphocytes to multiply.
These steps are common to both humoral
and cell-mediated immunity.
Humoral or Antibody mediated
immunity
In order for B cells to become activated
and make antibodies against an
antigen, two things must happen:
1. B cell must encounter the antigen
2. IL-2 produced by helper T cell must
be present.
When both signals are present (the antigen
and IL-2). The B cell becomes activated
and forms two types of cells: plasma cells
and memory cells.
Plasma cells produce large quantities of
their specific antibody into the blood.
Memory cells lie in wait for the next
infection.
Antibodies
“Y” shaped proteins – gamma globulins
have a variable region that matches a
specific antigen (Fab region)
Have a constant region – activates
complement (Fc region)
The first antibodies produced are IgM.
Pentamers – with ten combining sites –
very effective in opsonization and
activating complement
Several days later, IgG is produced –
single unit antibodies, abundant in serum,
cross the placenta, and have the longest
half-life.
Cell mediated immunity
A virus is a core of nucleic acid wrapped in
a protein.
To reproduce, it must make use of a host
cell to replicate the viral nucleic acids and
proteins and assemble new viruses.
Infected cells put viral proteins on their
membranes.
This antigen is processed by macrophages.
Antibodies can’t get at viruses inside a cell,
so we need something different : a Tcytotoxic
or Tc Cell.
The Tc encounters the viral antigen with the
MHC -1 complex on the infected cell.
Now needs the second stimulus – IL-2 from
the helper T cell.
Tc cell clones itself, and makes activated
Tc cells and memory cells.
Tc Cells bind to antigens on infected cells
and release:
Perforins – punch holes in cell membrane.
Lymphotoxins- activate the cell’s own selfdestruct mechanism
Tc Cells are effective against bacteria
which are intracellular parasites,
viruses, fungi, cancer cells associated
with viral infections, and transplanted
cells.
Immune Response
The first time you encounter an antigen, you
have few B cells or Tc cells against that
antigen = primary response
The next time, you have many memory
cells, so response is much quicker, so you
don’t come down with the disease =
secondary response
HIV/AIDS
Human immunodeficiency virus
Attacks helper T cells
Without production of IL-2, there is no
second signal, and humoral and cell
mediated immunity are shut off.
See increase in rare diseases:
TB, Kaposi sarcoma, etc.
Hypersensitivity
“The immune system gone bad.”
Delayed Hypersensitivity
A type of cell mediated immunity.
Td cell – requires usual two signals
Second time antigen is encountered, Td cell
produces several cytokines that attract and
activate macrophages, resulting in an
inflammatory reaction.
Examples: poison ivy (urushiol), TB skin test
Immediate Type Hypersensitivity
• Exposure to certain antigens (allergens)
results in the formation of IgE antibodies
• IgE antibodies bind to mast cells by the Fc
end.
• When the antigen is encountered again,
binding with the antibody causes mast cell
to release histamine granules.
May be able to desensitize individual by
giving allergen to stimulate IgG
antibodies. These tie up antigen before
they can bind with IgE.
Acquired immunity
Active = person makes own antibodies
Passive = person receives antibodies from
someone else
Natural = “just happens”
Artificial = caused by man (often using a
needle)
Natural active acquired immunity:
person comes down with measles
Artificial active acquired immunity:
person is immunized with a vaccine
Artificial passive acquired immunity:
Person receives serum with antibodies
Natural passive acquired immunity:
Baby receives antibodies with mother’s
milk - colostrum