3. lymphatic system

primary lymphatic organs + tissues

• prod lymphocytes, which are immunocompetent cells, fundamental in adaptive/ acquired immunity

secondary lymphatic organs and tissues

• sites where mature lymphocytes (+ other immune cells) agglomerate and participate in immune response

• (become active + defend organ against pathogens)

lymphatic system (process)

1. primary lymphatic organs + tissues

2. secondary lymphatic organs + tissues

3. lymphatic vessels

lymphatic system (image)

fluid = lymph

sentinel lymph nodes

first nodes draining and filtering lymph from cancer

sentinel node biopsies useful for cancer staging and therapy planning

lymphadenopathy

• inflammation of nodes actively responding to primary local infection, autoimmune condition/ malignancy

• swollen superficial nodes can be easily palpable (visible)

(adeno = gland)

lymphedema

accumulation of fluid in interstitial spaces due to impaired lymphatic system

(edema = extra fluid)

lymphatic capillaries

• closed ended, > lumen than blood capillaries

• present in almost all vascularised tissues and organs of body

lacteals

lymphatic capillaries present in core of villi of small intestines

lymph formation

1. increased interstitial p

2. extremities of endothelial cells pushed inward

3. momentaneous formation of pores

4. interstitial fluid, large molecules and cells enter lumen of lymphatic capillary

5. pores close (valvular function)

(occurs in blood capillaries)

lymphatic vessels and plexuses structure

(plexuses = network of vessels)

lymphatic vessels and plexuses

• lymph drained by capillaries transported by lymphatic vessels that form plexuses

• mov of lymph facilitated by action of

  • smooth muscle in walls of lymphatic vessels

  • valves (promote unidirectional flow)

  • respiratory pump

  • muscular pump

  • vascular pump

• lymphatic vessels merge to form larger and terminal lymphatic trunks and ducts that tribute lymph to brachiocephalic veins (venous circulation)

lymphatic trunks and ducts

lymphatic trunks and ducts +veins

primary lymphatic organs

thymus + bone marrow

lymphocytes formed

red boen marrow

• specialised connective tissue (hematopoietic tissue) present inside bones

• generate blood cells, incl. immature lymphocytes

• b-cells = lymphocytes that mature in rbm

• ageing → substitution of rbm with yellow bone marrow (adipose tissue)

thymus

• soft bilobed (divided into 2 lobes) organ in mediastinum, anterior to pericardium and posterior to sternum

• t-cells = lymphocytes that mature in thymus

• ageing → considerable fibrofatty degeneration of thymus

  • (substituted with fat = immune function decrease)

secondary lymphatic organs

spleen

lymph node

MALT

spleen

• encapsulated solid organ in superior left quadrant of abdomen

• prenatally, spleen (+liver + rbm) = site of hematopoiesis (create new blood cells + platelets)

postnatally

1. becomes haemopoietic in certain pathological conditions

2. destroys defective rbc

3. responds to pathogens in blood

4. functions as blood reservoir

lymph node

• pea-sized encapsulated organ present along path of lymphatic vessels

• filters lymph before returned to venous circulations

(~600 lymph nodes in body that tend to form large clusters in diff regions of body, especially. adjacent to major blood vessels

mucosa-associated lymphatic tissue (MALT)

• agglomerations of non-encapsulated lymphoid tissue found adjacent to mucosa that lines hollow organs of respiratory, gastrointestinal, urinary and reproductive tracts

1. tonsils (Waldeyer’s ring) in mucosa of pharynx

2. Peter’s patches in mucosa of small intestine

3. lymphoid follicles in mucosa of large intestine, particularly in vermiform appendix

• prevent pathogens from invading internal environment