Download Lymphatic system Lecture #2

Lymphatic System
Lecture #2
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
Function of Lymph Nodes

1.
2.
2 basic functions
Filtration – macrophages destroy
microorganisms and debris
Immune system activation – monitor for
antigens and mount attack against them!
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

1.
2.
3.
Size and activity level vary with age:
Largest and most active during childhood
Stops growing during adolescence and
slowly starts to shrink
May disappear entirely in old age –
replaced by fibrous fatty tissue
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

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

Stores breakdown products of RBCs for
later reuse
– Spleen macrophages salvage and store iron
for later use by bone marrow

Stores blood platelets
Remember This!
Spleen cleanses the blood
 Lymph nodes cleanse the lymph
 Together they keep circulating body fluids
relatively free of damaged cells and
microorganisms

Red Bone Marrow

Origin of all blood cells red & white
– Present in skull, sternum, ribs clavicle, pelvis
& spinal column & ends of femur & humerus
White bc function in immunity
 5 types – 13.4 on page 255

Chief lymphatic cells & function

T cells and B cells protect the body
against antigens
– 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
– 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