lymphatic system anatomy

Lymph

Interstitial fluid contained inside lymphatic cells, does not go out

Lymphatic capillaries

small closed-end vessels that collect and carry away excess fluid, in spaces between tissue cells, intertwined with blood capillaries

lymphatic vessels

similar to veins but with thinner walls, not influenced by pumping of the heart

lymphatic valves

prevent backflow of lymph, more quantity than veins to ensure undirectional flow

Minivalves

Endothelial cells

lymphatic collecting vessels

lymph node

• Widely distributed in the body in clusters and groups

• There are superficial and deep lymph nodes

• Small and encapsulated bean-shaped organs about 1mm-2cm in length

• Along lymphatic vessels, help filter out foreign substances and killing bacteria

• Lymph enters via afferent lymphatic vessels and exit through 1-2 efferent lymphatic vessels at the hilum

right lymphatic duct

• short duct (1 cm)

• drains from right upper part of body

• accounts for ¼ of lymph drainage

thoracic duct

• long duct

• between thoracic aorta and argygos vein

• drains from right lower part and all of left part of body

• cisterna chyli at 1st and 2nd lumbar level

cisterna chyli

azygos vein

thoracic aorta

right subclavian vein

left subclavian vein

left internal jugular vein

right internal jugular vein

lacteals

• specialized lymphatic vessels in small intestine

• important for absorption/transport of lipids/chylomicrons

• empties into nearby lymph nodes

• if lymph in lacteals are fatty enough it turns white

intestinal villus

primary section

red bone marrow and thymus

maturation of lymphocytes

B cells mature in bone marrow

T cells mature in thymus

secondary section

tonsils, lymph nodes, spleen, lymphatic nodules

capsules

provide support and form paths for blood vessels and nerves to course through

thymus

• Bi-lobed organ with lumpy surface

• Between sternum and upper part of heart

• T cells that are produced in bone marrow are developed into mature T cells in thymus

  • Immature T cells populate outer cortex (densely packed) and move to inner medulla to mature

    • In medulla there are Hassall’s corpuscles, formed by flattened epithelial cells

  • Mature T cells continue to travel via blood to other lymphatic organs

• Active in youth and degenerates slowly after puberty

  • Fat accumulates inside and turns yellow at old age

red bone marrow

tonsils

spleen

• Largest lymphatic organ in the body

• In upper left abdomen close to diaphragm

• Smooth and convex, dark-purplish color

• Holds a lot of blood that comes from celiac trunk of aorta to splenic artery to spleen

• Where aged, damaged, and broken RBC are broken down and recycled

• Blood reserve, can pump up to 100mL into circulation

lymphatic nodules

medulla

Thymus cortex

hassall’s corpuscles

red pulp

• Blood-filled splenic sinuses and cords

• Houses macrophages, lymphocytes, plasma cells, and others

white pulp

• Lymphoid tissue formed by clumps of lymphocytes around central arteries (branches of splenic artery)

• Allow for rapid immune response against antigens in blood transported to spleen

central ateries

tail of pancreas

diaphragm

stomach

left kidney

left colic fixture

splenic sinuses

splenic cords

Lymph node cortex

• has superficial and deep (paracortical) layers

  • Deep layer contains mostly T cells

Lymphatic nodule

contain B-cells and macrophages

Lymph node medulla

has cords of lymphatic tissue containing B-cells, macrophages, antigen presenting cells, and plasma cells

Trabeculae:

supportive fibers between nodules

Reticular meshwork

composed of reticular cells and fibers

Lymph node medullary cord

Subcapsular sinus

Trabecular sinus

Lymph node medullary sinus

Superficial layer

Deep layer

Afferent lymphatic vessels

Efferent lymphatic vessels

hilum

macrophages

can expose fragment of antigen on surface

release helper T-cells which will trigger B-cells (via interleukin-2) to divide into plasma and memory B-cells

plasma cells

produce antibodies that bind to antigens, attracting macrophages to engulf them

Helper T-cells

trigger cytotoxic T-cells to attack antigen cells directly by creating pores, causing apoptosis

Pharyngeal tonsil/adenoid

roof of pharynx posterior to nasal cavity

Tubal tonsils

slightly below adenoid, behind 2 eustachian tube openings

Palatine tonsils

• lie on the lateral pharyngeal wall directly behind mouth and palate

• Largest and most often infected in childhood

Tonsillectomy

surgical removal of tonsils

Lingual tonsils

posterior surface of the tongue

Tonsils

• Group of lymphoid organs in pharyngeal region at top of the throat

• mucosal swellings deep to the epithelium of pharyngeal wall

• Inside swellings are spherical lymphoid nodules with lymphocytes

Tonsillar crypts

help trap bacteria and foreign matter, which activates the lymphocytes

lymphoid nodule

• High concentration can be found in ileum of small intestine and appendix because small intestine always attacked by bacteria in swallowed food

• generate a diverse range of memory lymphocytes from sampling different antigens, important in immune response

Peyer’s patches

lymphatic nodules aggregated in ileum, large densely stained spherical structures

lymphocyte nuclei

appendix

ileum