Functional
Anatomy of
Lymphatic
System
Lymphatic System
 protects body against foreign material
 assists in circulation of body fluids between
cells and bloodstream
 transports dietary fats
Lymphatic System
(cont.)
 Consists of:
- lymph
- network of vessels
- lymph nodes and nodules
- tonsils
- spleen
- thymus gland
- bone marrow
Lymph
(lympha = clear fluid)
 derived from tissue fluid
 contains more white blood cells than plasma
 enters node through afferent lymphatic vessels
 flows through node in one direction
Lymph
(cont.)
 flows through sinuses in lymph node cortex
and then into the medulla
 exits the lymph node through efferent
lymphatic vessels
 must be returned to blood stream to maintain
blood volume and pressure
Lymph Capillaries




microscopic closed-ended vessels
located next to blood capillaries in tissue spaces
larger diameter than blood capillaries
are very permeable and collect tissue fluid and
proteins
 lymph capillaries merge to form larger lymph
vessels
Lymph Vessels
 resemble veins but have thinner walls and
more valves
 ends of endothelial cells overlap
- act as one-way valves allowing interstitial
fluid to flow in but not out
 attached to surrounding tissue by anchoring
filaments
Lymph Vessels
(cont.)
 no pump for lymph
 Lymph is kept moving by:
- constriction of vessels
- skeletal muscle pump
- respiratory pump
 at intervals along vessels lymph flows into
lymph nodes
 lymphatic vessels unite to form lymph trunks
Lymph Trunks
 formed by lymphatic vessels uniting
 large tubes
 empty their lymph into lymphatic ducts
Lymphatic Ducts
 Lymph empties into two conducting ducts:
- the thoracic duct (left lymphatic duct)
- the right lymphatic duct
Lymph from these ducts enters the blood
stream via the left subclavian vein and the
right subclavian vein
Thoracic Duct
(left lymphatic duct)
 about 15-18 inches (38-45 cm) in length
 begins as a dilation called the cisterna chyli
 main collecting duct of lymphatic system
 receives lymph from lower body and upper
left quadrant
 empties into the left subclavian vein
Cisterna Chyli
 large lymph vessel
 formed by the union of lymph vessels from
lower body
 located anterior to the second lumbar
vertebra
 continues superiorly as thoracic duct
Right Lymphatic Duct
 about 0.5 inches (1.5 cm) in length
 receives lymph from upper right quadrant
 empties into the right subclavian vein
Lymph Nodes
 oval or bean-shaped
 masses of lymphatic tissue
 aid in defense and white blood cell formation
 located along length of lymphatic vessels
 scattered throughout the body usually in clusters
Lymph
Nodes
 covered by a capsule
(cont.)
 contain capsular extensions called
trabeculae (form partitions within node)
 internal to capsule are reticular fibers and
fibroblasts
- form framework of a lymph node
 Two main regions of a lymph node:
- cortex
- medulla
arteriole
vein
germinal
center
lymphatic vessel
valve
cortex
trabeculae
medulla
Cortex
 outer region directly beneath the capsule
 contains densely packed lymphocytes
arranged in masses called follicles
- outer rim of follicle contains T cells,
macrophages, and follicular dendritic
cells (aid in T cell activation)
Medulla
 inner region
 lymphocytes are arranged in strands called
medullary cords
- contain macrophages and plasma cells
Biological Filtration
 as lymph passes through a node bacteria and
other foreign materials are trapped by
reticular fibers within the node
- bacteria are then phagocytized by
macrophages
Biological Filtration
(cont.)
 plasma cells produce antibodies to antigens
in the lymph
 antibodies, lymphocytes, and monocytes are
eventually returned to the blood via
subclavian veins
Major Lymph Nodes
 cervical
 axillary
 inguinal
 mesenteric
Cervical
 located in neck area
 filter lymph from head and neck
Axillary
 located in armpits
 filter lymph from hand, arm, breast
Inguinal
 located in groin area
 filter lymph from lower extremities and
external genital organs
Mesenteric
 located in abdominal peritoneum
 aid in infection control after abdominal
surgery
 filter lymph from abdominal cavity
Metastasis
 process by which bacteria or body cells are
spread from one body part to another
through lymphatic or circulatory systems
 cancer cells migrate to nearby nodes, eg.
breast cancer to axillary nodes chemotherapy is necessary once metastasis
occurs
Diffuse Lymphatic Tissue
 not enclosed by a capsule
 consists of reticular connective tissue that
contains lymphatic nodules
 Found in:
- small amounts in almost every organ,
especially mucous membranes that line tracts
of body
Isolated Lymphatic Nodules
(B cells)
 oval-shaped concentrations of lymphatic tissue
 most are solitary, small, and discrete
 Scattered in lamina propria of mucous
membranes of:
- gastrointestinal tract
- respiratory airways
- urinary and reproductive tract
Isolated Lymphatic Nodules
(B cells)
(cont.)
 when activated by antigens they differentiate
into plasma cells and produce antibodies
against specific antigens
 plasma cells secrete IgA antibodies
- provide protection against bacterial and
viral infections in lumen of tracts
Isolated Lymphatic Nodules
(B cells)
(cont.)
 located in mucus membranes of
gastrointestinal tract
 Examples:
- tonsils
- ileum of small intestine (Peyer’s patches)
- appendix
Tonsils
 aggregations of large lymphatic nodules
 embedded in mucous membrane
 located beneath epithelium of pharynx and
oral cavities
 protect nasal and oral cavities
 Three types:
- nasopharyngeal tonsils
- palatine tonsils
- lingual tonsils
Nasopharyngeal Tonsils
 commonly called adenoids
 Located:
- behind nose
- on roof of posterior wall of pharynx
- posterior opening of nasal cavity
Palatine Tonsils
 usually referred to as the “tonsils”
 Location:
- back of mouth
- lateral walls of pharynx
 most commonly removed - tonsillectomy
Lingual Tonsils
 base of tongue
 first line of defense from exterior
Spleen
 largest lymphatic organ
 located in upper left abdominal quadrant
 between fundus of stomach and diaphragm
 5-6 inches long, 2-3 inches wide
 resembles a large lymph node
 filters blood
Structure of Spleen
 capsule
- covering of dense connective tissue
 hilum
- depression on medial surface
- nerves and arteries enter spleen, veins and
lymphatic vessel exit
Structure of Spleen
(cont.)
 trabeculae
- extensions of capsule, form partitions
within the spleen
 pulp
- tissue inside
- divided into red and white
White Pulp
 consists of lymphatic tissue
 mostly lymphocytes arranged around central
arteries
Red Pulp
 Consists of:
- venous sinuses filled with blood
- cords of splenic tissue
consists of red blood cells, macrophages,
lymphocytes, plasma cells, and granulocytes
Functions of Spleen
 phagocytosis of bacteria and worn out or
damaged red blood cells and platelets
 stores and releases blood in times of demand,
e.g., hemorrhage
 functions in immunity as a site of B cell
proliferation into plasma cells
 does not filter lymph because it has no afferent
lymphatic vessels or lymph sinuses
Thymus Gland
 two-lobed organ
 located in upper part of chest along trachea
 inferior to thyroid gland, posterior to sternum
 largest and most active during prenatal
period and infancy
 after puberty it decreases in size
Thymus Gland
(cont.)
 composed of lymphatic tissue
 subdivided into lobules
 immature T cells originating in the bone
marrow migrate to thymus via blood
 in thymus, cells develop into mature T
cells for release into circulation
 thymic hormones aid in maturation of T cells
Thymus Gland
(cont.)
 mature T cells travel to lymph nodes, spleen,
and diffuse lymphatic tissues where they
reside
 responsible for cell-mediated immune
responses
Removal of Thymus
(thymectomy)
 can be removed but decreased T-cell
production results
 possible acute susceptibility to infection
Removal of Spleen
(splenectomy)
 can be removed
 other organs, e.g. the liver and bone marrow
can compensate for it
 increased susceptibility to disease may result