Unit 3 Lymphatics Flashcards
lymphatic functions
- return interstitial fluid to the blood
- filtration of lymph
- filtration of blood
- defense of body from invasion and damage by microorganisms and foreign substances
lymphatic components
organs, tissue, nodes, vascular system
primary lymph components
bone marrow (lymphocytes) thymus (maturation of T lymphocytes)
secondary lymph components
lymph nodes
spleen
tonsils
lymph vascular system
capillaries (close ended)
vessels (interrupted by lymph nodes)
trunks (empty into subclavian veins)
lymphoid tissue function
- houses and provides proliferation sites for lymphocytes
2. offers surveillance vantage points for lymphocytes and macrophages as they filter through lymph
lymphoid tissue components
reticular connective tissue
a. macrophages live on reticular fibers
b. spaces between fibers offer a place for lymphocytes to occupy when they return form patrolling the body
reticular cells of thymus
- derived from endoderm
- called epithelial-reticular cells
- do not produce reticular fibers
- participate in maturation of T lymphocytes
reticular cells of other lymphatic tissues
- mesenchymal (mostly mesoderm)
2. produce reticular fibers (type III collagen)
lymphocytes
cells involved in adaptive (specific) immunity
B lymphocytes
responsible for humoral immunity, differentiate into plasma cells, form nodules
T lymphocytes
responsible for cell mediated immunity
multiple classes:
helper, suppressor (regulatory), cytotoxic (cytolytic), memory T cells do not form nodules
lymph nodules
cells responding to antigen, proliferating differentiating into plasma cells
primary lymph nodules
uniformly densely stained, cells have not been exposed to antigen
secondary lymph nodules
contain lightly stained central region (germinal center)
unencapsulated (mucosa associated) lymphoid tissue (MALT)
- lymphoid tissues in mucous membranes throughout body
- protects from pathogens trying to enter body
- largest collections of MALT is in tonsils, Peyer’s patches, appendix
- also in mucosa of respiratory and genitourinary organs; rest of digestive tract
tonsils
incompletely encapsulated in contact with epithelium
palatine tonsils
a. paired
b. lateral wall of oral pharynx
c. epithelium is stratified squamous NK with crypts
pharyngeal
a. single
b. superior-posterior portion of pharynx
c. epithelium is PCCE
d. hypertrophy produces adenoids
lingual
a. numerous
b. base of Tonge
c. epithelium is stratified squamous NK
lymph nodes
in line filters of lymph; has afferent and efferent lymphatics
lymph node stroma
a. hilum (AN enter, VL exit)
b. capsule and trabecular of CT
c. sub capsular sinus and peritrabecular sinuses
d. reticular cells and fibers
lymph node parenchyma
a. cortex (nodules of B cells)
b. paracortex (accumulations of T cells)
c. medulla: cords (mostly B cells, some plasma) and sinuses (partially lined with macrophages and reticular cells)
lymph circulation
- afferent lymphatics
- subcapsular sinus
- peritrabecular sinuses
- medullary sinuses
- efferent lymphatics
blood circulation
- arteries enter at hilum
- branch into stroma
- capillaries in cortex
- postcapillary venules in paracortex – lymphocytes exit blood to
- reside in node
- veins exit at hilum
thymus
- lobulated; no nodules, no sinuses
- size varies with age
- capsule with trabeculae delineates lobules
- each lobule has cortex and medulla
thymus stroma
- epithelial-reticular cells
- no reticular fibers
- cellular processes create framework supporting lymphocytes
- secrete thymosin – necessary for differentiation of T cells
thymus parenchyma cortex
- thymocytes: immature T cells; not yet immunocompetent
2. macrophages phagocytize many thymocytes
thymus parenchym medulla
- higher concentration of epithelial-reticular cells
- larger lymphocytes
- Hassall’s corpuscles – unique to thymus; function unknown
thymus vascularization
capillaries in cortex surrounded by sheath of epithelial reticular cells; blood-thymus barrier
spleen
- largest lymphoid organ
- filters blood
- destroys old erythrocytes
- produces activated lymphocytes in response to blood-borne antigens
spleen stroma
- capsule – dense connective tissue
- trabeculae – carry nerves and arteries from hilum to splenic pulp; carries veins and efferent lymphatics from pulp to hilum
- reticular connective tissue
spleen parenchyma
aka splenic pulp
a. white pulp – lymphoid tissue surrounding central arteries
b. periarterial lymphatic sheath (PALS) composed of T cells
c. splenic nodules – B cells
red pulp
splenic cords
sinusoids
splenic cords
aka cords of Billroth
a. reticular cells and fibers
b. macrophages, lymphocytes, blood cells
splenic sinusoids
a. elongated endothelial cells
b. transversely arranged reticular fibers
c. macrophages between endothelial cells
d. incomplete basal lamina
marginal zone (spleen)
a. between red and white pulp
b. lymphocytes – mostly B cells
c. macrophages act as antigen presenting cells
d. lymphocytes exit blood and enter white pulp
splenic blood supply
a. trabecular arteries
b. central arteries – surrounded by lymphocytes
c. penicillar arteries (arterioles)
d. arterial capillaries arterial capillaries
splenic closed circulation
arterial capillaries empty directly into sinusoids of red pulp
splenic open circulation
- arterial capillaries end in splenic cords and blood must pass through wall of sinusoids to reenter circulation
- old RBCs lose flexibility and cannot squeeze past
- endothelial cells
- sinusoids
- red pulp veins
- trabecular veins
- splenic vein