Transcript Slide 1 - buechner

Lymphatic & Immune
System
Lymph: Definition
Lymph is excess tissue fluid contained in
lymphatic vessels
Consists of (mostly) water and plasma
proteins that have leaked out of the
capillaries
Semi-independent parts of the
lymphatic system
1. Meandering network of lymphatic vessels
2. Lymphoid tissues and organs scattered
throughout the body
Functions of the lymphatic system
1. Lymphatic vessels return interstitial fluid
and leaked plasma proteins back to the
blood
2. Lymphatic capillaries (lacteals) absorb
fats/fat soluble vitamins at intestinal villi
and transport to the blood
3. The lymphatic system helps defend the
body against disease
Lymphatic vessels: 3 types
1. Blind-ended capillaries
2. Lymphatic collecting vessels
3. Trunks and ducts
Blind-ended Capillaries
1.
2.
3.
4.
Specially adapted:
Highly permeable
One-way valves (similar to veins) so
lymph only flows towards the heart
Valves resist interstitial pressure to
remain open
Can absorb cell debris, pathogens,
cancer cells
Collecting Vessels
Similar to veins but have thinner walls and
more internal valves
Lots of branching networks

Anastomose = dividing/branching
Travel with the superficial veins in skin
Deep vessels travel with arteries
Vasa vasorum (vessels of the vessels)
supply nutrients to cells
Collecting Vessels
Capillaries consist of a single layer of cells
and are the only blood vessels that can
exchange materials with the interstitial
fluid
Cells will die if they are not within 1 or 2
cell widths of a capillary
The lymphatic system removes excess
fluid
Trunks & Ducts
Capillaries join to form vessels that merge
in the thoracic cavity before entering one
of two ducts:
Thoracic duct & right lymphatic duct
Trunks are formed by joining of the largest
collecting ducts and are classified by the
regions served
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Paired lumbar, subclavian, jugular, intestinal
Trunks & Ducts cont’d
Lymph is delivered into one of the two
large trunks (ducts)
1. Right lymphatic duct
1.
Drains right upper arm, the right side of the
head and thorax
2. Thoracic duct
1.
Drains the rest of the body
Lymph Transportation
Every region of the body has extensive
lymphatic vessels
Structural walls are similar to veins (but
are thinner) and contain valves
Movement is dependent on muscular
contraction (skeletal) – when muscles
contract lymph is squeezed past a valve
that closes and prevents backwash
Chief lymphatic cells & function
T cells and B cells protect the body
against antigens
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T for thymus origin
B for bone origin (red marrow)
T lymphocytes (T cells) mature in the
thymus (along trachea atop heart) and are
“tested” if they react against “self” they die,
if they have potential to attack foreign cells
they leave the thymus
T cells cont’d
Responsible for cell-mediated immunity
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Depends on actions of several types of T cells
Antibodies are not produced, instead they
directly attack foreign cells that carry antigens
Other T cells release proteins to coordinate
other actions of the immune response: T cells,
B cells and macrophages
Protects against parasites, bacteria, fungi,
cancerous cells – anything “foreign”
Chief lymphatic cells & function
cont’d
B lymphocytes (B cells) are responsible for
antibody-mediated immunity

B cells produce antibodies – proteins that bind
with and neutralize specific antigens
Growing within the bone marrow B cells
develop unique surface receptors that
allow them to recognize specific antigens

Protects against viruses, bacteria and foreign
molecules soluble in blood and lymph
Lymph nodes
Round bean-shaped structures found at
certain points along lymphatic vessels
A fibrous capsule divided into nodules
containing sinuses (open spaces) filled
with macrophages and lymphocytes.
Two distinct regions: cortex & medulla
As lymph passes through the sinuses in
the nodules it is cleansed of infectious
organisms and debris
Lymph node
Lymph nodes cont’d
Nodules are mainly in the lymph nodes but
can also be single or in groups
(aggregations)
Aggregations are found near the body
surface in inguinal (groin), axillary
(armpits) and cervical (neck) regions
Function of Lymph Nodes (12)
2 basic functions
1. Filtration – macrophages destroy
microorganisms and debris
2. Immune system activation – monitor for
antigens and mount attack against them!
Tuberculosis and leukemia can
cause the spleen to enlarge
Spleen and its functions
Upper left abdominal cavity just beneath
the diaphragm (fist-sized)
Similar structure to a lymph node: outer
connective tissue divides it into sinuscontaining lobules BUT in the spleen
sinuses are filled with blood NOT lymph

Blood reservoir if needed in times of low
pressure or extra oxygen is required
Spleen and its functions cont’d
Spleen lobules contain red pulp and white
pulp
Red pulp – rbc, lymphocytes and
macrophages
White pulp – contains only lymphocytes
and macrophages
Fxns: purify blood that passes through
spleen = quality control (removal of
damaged rbc and invaders)
Spleen’s 2 main functions
Quality control of circulating rbc by
removing old damaged ones – cleansed
blood stored in red pulp
Helps fight infection – white pulp –
primarily lymphocytes
Other spleen functions (14)
Stores breakdown products of RBCs for
later reuse
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Spleen macrophages salvage and store iron
for later use by bone marrow
Stores blood platelets
Important!
Spleen cleanses the blood
Lymph nodes cleanse the lymph
Together they keep circulating body fluids
relatively free of damaged cells and
microorganisms
Thymus and its function
Located in lower neck behind sternum,
just above the heart
Bilobed organ that secretes 2 hormones:
1. Thymosin
2. Thymopoietin
These cause certain lymphocytes to mature
and become active in body defense
Thymus cont’d
Size and activity level vary with age:
1. Largest and most active during childhood
2. Stops growing during adolescence and
slowly starts to shrink
3. May disappear entirely in old age –
replaced by fibrous fatty tissue
Tonsils and their function
Masses of lymphatic tissue near the
entrance to the throat
Gather and filter microorganisms that
enter the throat through air and food
Familiar tonsils @ back of throat largest &
most often infected = tonsilitis
Adenoids (pharyngeal tonsils) lie at the
back of the nasal passages – usually
shrink by 5 years old & gone by puberty
Enlarged tonsils
Adenoids cont’d
Can enlarge and obstruct air passages –
causing mouth breathing and nasal voice
& snoring
Sometimes removed