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NOTES: The Lymphatic /
Immune Immune System
(Ch 12, part 1)
The lymphatic system is closely
associated with the cardiovascular
system.
Functions of the Lymphatic
System:
● transports excess fluid to the bloodstream
● absorbs fats
● helps defend the body against disease-causing agents
LYMPHATIC PATHWAYS
Lymphatic capillaries
● microscopic, closed-end
tubes that extend
into intercellular spaces
● receive LYMPH through ● receive LYMPH through
their thin walls
(LYMPH = the fluid of the lymphatic system… more later!)
● lymphatic capillary networks parallel blood capillary networks
Lymphatic vessels:
● have walls similar to
those of veins, but thinner,
and have valves to
prevent backflow of
lymph
● become larger and lead to LYMPH NODESand then merge into LYMPHATIC TRUNKS
Lymphatic Trunks and Collecting Ducts:
● lymphatic trunks lead to two collecting ducts:
-THORACIC DUCT
� larger and longer duct;
� receives lymph from the lower limbs,
abdominal regions, left upper limb, left side of
thorax, head, and neck
-RIGHT LYMPHATIC DUCT
� receives lymph from the R side of the head &
neck, R upper limb, R thorax
● collecting ducts join the SUBCLAVIAN VEINS
Tissue Fluid & Lymph:
● LYMPH is essentially tissue fluid that has entered a lymphatic capillary
● tissue fluid originates from blood plasma and is composed of:
-water-water
-dissolved substances that leave blood capillaries (small molecules, nutrients, gases, hormones)
**NOT present are larger plasma proteins (too large to pass through capillary walls)
Functions of lymph:
1) returns to the bloodstream small proteins that leaked out of blood capillaries
2) transports foreign particles, such as 2) transports foreign particles, such as bacteria or viruses, to lymph nodes
Lymph Movement● lymph, like venous blood,
is under low pressure and may not flow readily
● movement of lymph is ● movement of lymph is affected
by skeletal muscle
contraction and pressure
changes associated
with breathing
**if lymph movement is impaired, it may
accumulate within the intercellular
spaces and produce EDEMA, or
swelling
(example: after surgery, the lymphatic vessels and lymph nodes around the wound may be damaged, causing fluid to wound may be damaged, causing fluid to accumulate around the surgery site and lead to swelling)
Lymph Nodes:
Structure of a Lymph Node:
● lymph nodes are subdivided into nodules
● nodules contain
masses of
lymphocytes
and macrophages
Locations of Lymph Nodes:
● lymph nodes aggregate in groups or chains along the paths of larger lymphatic vessels
Functions of Lymph Nodes:
● filter potentially harmful foreign particles from lymph
● are centers for the production of lymphocytes(attack invading viruses, bacteria, parasites, etc.)etc.)
● contain phagocytic cells
(engulf and destroy foreign
substances, damaged
cells, cellular debris)
THYMUS AND SPLEEN
Thymus:
● located anterior to aorta
and posterior to upper
part of sternum
● shrinks slowly after puberty● shrinks slowly after puberty
● contains large numbers of
LYMPHOCYTES which
mature into T CELLS (T lymphocytes) –important in providing immunity (more on these later…)
Spleen:
● largest lymphatic organ
● located in upper left portion of abdominal cavity (just inf. to diaphragm and lat./post. to stomach)to stomach)
● resembles a large lymph node (divided into lobules)
Spleen:
● spaces within splenic
lobules are filled with blood
● contains many macrophages, which destroy/remove foreign which destroy/remove foreign particles and damaged RBCs from the blood
**the spleen filters blood as the lymph nodes filter lymph!**