Functional Anatomy of Lymphatic System

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Functional Anatomy of Lymphatic System
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Lymphatic System

• protects body against foreign material
• assists in circulation of body fluids between
  cells and bloodstream
• transports dietary fats

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Lymphatic System (cont.)

• Consists of
• - lymph
• - network of vessels
• - lymph nodes and nodules
• - tonsils
• - spleen
• - thymus gland
• - bone marrow

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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

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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

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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

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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

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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

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Lymph Trunks

• formed by lymphatic vessels uniting
• large tubes
• empty their lymph into lymphatic ducts

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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

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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

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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

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Right Lymphatic Duct

• about 0.5 inches (1.5 cm) in length
• receives lymph from upper right quadrant
• empties into the right subclavian vein

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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

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Lymph Nodes (cont.)

• covered by a capsule
• 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

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lymphatic vessel
arteriole
vein
valve
germinal center
cortex
trabeculae
medulla
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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)

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Medulla

• inner region
• lymphocytes are arranged in strands called
  medullary cords
• - contain macrophages and plasma cells

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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

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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

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Major Lymph Nodes

• cervical
• axillary
• inguinal
• mesenteric

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Cervical

• located in neck area
• filter lymph from head and neck

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Axillary

• located in armpits
• filter lymph from hand, arm, breast

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Inguinal

• located in groin area
• filter lymph from lower extremities and external
  genital organs

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Mesenteric

• located in abdominal peritoneum
• aid in infection control after abdominal surgery
• filter lymph from abdominal cavity

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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

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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

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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

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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

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Isolated Lymphatic Nodules (B cells)
(cont.)

• located in mucus membranes of gastrointestinal
  tract
• Examples
• - tonsils
• - ileum of small intestine (Peyers patches)
• - appendix

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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

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Nasopharyngeal Tonsils

• commonly called adenoids
• Located
• - behind nose
• - on roof of posterior wall of pharynx
• - posterior opening of nasal cavity

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Palatine Tonsils

• usually referred to as the tonsils
• Location
• - back of mouth
• - lateral walls of pharynx
• most commonly removed - tonsillectomy

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Lingual Tonsils

• base of tongue
• first line of defense from exterior

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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

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Structure of Spleen

• capsule
• - covering of dense connective tissue
• hilum
• - depression on medial surface
• - nerves and arteries enter spleen, veins and
  lymphatic vessel exit

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Structure of Spleen (cont.)

• trabeculae
• - extensions of capsule, form partitions within
  the spleen
• pulp
• - tissue inside
• - divided into red and white

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White Pulp

• consists of lymphatic tissue
• mostly lymphocytes arranged around central
  arteries

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Red Pulp

• Consists of
• - venous sinuses filled with blood
• - cords of splenic tissue
• consists of red blood cells, macrophages,
  lymphocytes, plasma cells, and granulocytes
  

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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

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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

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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

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Thymus Gland (cont.)

• mature T cells travel to lymph nodes, spleen, and
  diffuse lymphatic tissues where they reside
• responsible for cell-mediated immune responses

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Removal of Thymus(thymectomy)

• can be removed but decreased T-cell production
  results
• possible acute susceptibility to infection

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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