The Lymphatic and Immune System
Lymphatic System
Lymphatic System Functions
The lymphatic system has three main functions:
i. lymphatic vessels return excess tissue fluid to the bloodstream
ii. lacteals receive and transport lipoproteins
iii. lymphatic organs work with the immune system to combat disease
The walls of lymphatic capillaries consist mostly of simple squamous (scaled) epithelium
Lymphatic Vessels
Small, lymphatic capillaries join to
form lymphatic vessels.
The lymphatic vessels collect fat
molecules at the intestinal villi and
excess tissue fluid at blood
capillaries; they carry lymph to the
subclavian veins.
The fluid inside lymphatic vessels
is called lymph.
Lymphatic Ducts
Lymphatic vessels merge before
entering one of two ducts:
i. Thoracic Duct: collects and
returns lymph from below the
thorax, left arm, and left side of
head and neck; leads to the left
subclavian vein
ii. Right Lymphatic Duct: collects
and returns lymph from right
arm and right side of head and
neck; returns to right subclavian vein
, Note: the thoracic duct is bigger than the right lymphatic duct
Lymph Vessels
Lymph vessels are similar in structure to cardiovascular veins:
have one way valves
dependent upon muscle contraction
Edema is the retention of fluids in the tissues (failure of lymphatic system to drain them)
Lymphatic Organs
Lymphoid organs, which contain large numbers of lymphocytes, are separated into primary (the red
bone marrow and the thymus gland) and secondary (lymph nodes and spleen).
Lymphocytes, which are produced and mature in the primary lymphatic organs, accumulate in the
cortex of these organs.
Recall: the two types of lymphocytes are B-lymphocytes and T-lymphocytes
Red Bone Marrow produces stem cells that become blood cells. It is only found in certain locations in
adults. B-lymphocytes mature here.
The thymus gland is divided into lobes and it is the site of T-lymphocyte maturation.
Secondary Lymphatic Organs
In secondary lymphatic organs, lymphocytes encounter and bind to antigens, after which they
proliferate and engage foreign material in the body.
Blood is cleansed of pathogens and their toxins in the larger spleen.
Lymph Nodes
Lymph nodes are small ovoid structures found near lymph vessels which cleanse lymph.
This organ is made of many nodules. Each nodule contains a sinus.
Macrophages filter lymph in sinuses by engulfing pathogens.
T-lymphocytes fight infections and attack cancerous cells.
Lymphatic System
Lymphatic System Functions
The lymphatic system has three main functions:
i. lymphatic vessels return excess tissue fluid to the bloodstream
ii. lacteals receive and transport lipoproteins
iii. lymphatic organs work with the immune system to combat disease
The walls of lymphatic capillaries consist mostly of simple squamous (scaled) epithelium
Lymphatic Vessels
Small, lymphatic capillaries join to
form lymphatic vessels.
The lymphatic vessels collect fat
molecules at the intestinal villi and
excess tissue fluid at blood
capillaries; they carry lymph to the
subclavian veins.
The fluid inside lymphatic vessels
is called lymph.
Lymphatic Ducts
Lymphatic vessels merge before
entering one of two ducts:
i. Thoracic Duct: collects and
returns lymph from below the
thorax, left arm, and left side of
head and neck; leads to the left
subclavian vein
ii. Right Lymphatic Duct: collects
and returns lymph from right
arm and right side of head and
neck; returns to right subclavian vein
, Note: the thoracic duct is bigger than the right lymphatic duct
Lymph Vessels
Lymph vessels are similar in structure to cardiovascular veins:
have one way valves
dependent upon muscle contraction
Edema is the retention of fluids in the tissues (failure of lymphatic system to drain them)
Lymphatic Organs
Lymphoid organs, which contain large numbers of lymphocytes, are separated into primary (the red
bone marrow and the thymus gland) and secondary (lymph nodes and spleen).
Lymphocytes, which are produced and mature in the primary lymphatic organs, accumulate in the
cortex of these organs.
Recall: the two types of lymphocytes are B-lymphocytes and T-lymphocytes
Red Bone Marrow produces stem cells that become blood cells. It is only found in certain locations in
adults. B-lymphocytes mature here.
The thymus gland is divided into lobes and it is the site of T-lymphocyte maturation.
Secondary Lymphatic Organs
In secondary lymphatic organs, lymphocytes encounter and bind to antigens, after which they
proliferate and engage foreign material in the body.
Blood is cleansed of pathogens and their toxins in the larger spleen.
Lymph Nodes
Lymph nodes are small ovoid structures found near lymph vessels which cleanse lymph.
This organ is made of many nodules. Each nodule contains a sinus.
Macrophages filter lymph in sinuses by engulfing pathogens.
T-lymphocytes fight infections and attack cancerous cells.
