lymphatics Flashcards
Main function of lymphatic system
returns fluid that leaked from blood vessels back to blood
3 parts of lymphatic system
- network of lymphatic vessels
- Lymph (fluid in vessels)
- Lymph nodes (cleanse lymph)
Function of lymphoid organs/tissues and examples
- provide structural basis of immune system and house pagocytic cells/ lymphocytes
e. g. spleen, thymus, tonsils, lymph nodes
Lymphatic vessels
- function
- how much per day
- when is interstitial fluid considered lymph
- where AREN”T they found
return interstitial fluid and leaked plasma proteins back into the blood
- 3L/ day
- considered lymph once it enters lymphatics
- bones, teeth, bone marrow, and CNS
Lacteals
specialized lymph capillaries present in intestinal mucosa
-absorb digested fat and deliver fatty lymph (chyle) to blood
list the Structure of lymphatic vessels
- one way flow towards heart
- lymphatic capillaries, collecting lymphatic vessels, lymphatic trunks/ducts
Lymphatic capillaries
-similar to blood capillaries, but are super permeables (prots, cell debris, pathogens, cancer cells)
- endothelial cells loosly overlap to form one-way minivalves
- anchored by collagen filaments preventing collapse -> ECF opens minivalves
-Pathogens travel through body via lymphatics
Lymphatic Collecting Vessels
- what
- where
- how does it get nutrients?
similar to veins, but with thinner walls, more valves, and more anastomoses
- collecting vessels in skin travel with superficial veins
- deep vessels travel with arteries
- nutrients supplied from branching vasa vasorum
Lymphatic ducts
Lymph is delivered to one of two big ducts:
Right lymphatic duct drains right upper extremity and right side of head and thorax
Thorasic duct arises as cisterna chyli and drains the rest of the body
Both dump lymph into venous circulation at junction of internal jugular and subclavian veins
What propels lymph?
- milking action of skeletal muscles
- pressure changes in thorax from breathing
- valves preventing backflow
- pulsations of nearby arteries
- contractions of smooth muscle in walls of lymphatics
Main Lymphoid cells
-Lymphocytes = warriors of immune system arising in red bone marrow –> protect against antigens
T cells: manage immune response and attack/destroy infected cells
B cells: produce plasma cells which secrete antibodies (antibodies mark antigens for destruction by phagocytosis or not)
Other cells of lymphatic system
- Macrophages: phagocytize foreign substances and activate T cells
- Dendritic cells: capture antigens and deliver them to lymph nodes and activate T cells
Reticular cells: make reticular fiber stroma that supports other cells in lymphoid organs
Lymphoid Tissue
- function
- composition
-houses and provides proliferation site for lymphocytes; also is surveillance vantage point for lymphocytes and macrophages
Mostly reticular CT (loose):
- Diffuse lymphoid tissue
- lymphoid follicles
Diffuse lymphoid tissue
- made of lymphoid cells and reticular fibers
- in almost every body organ
- bigger collections in lamina propria of mucous membranes
lymphoid follicles
- solid, spherical bodies of tightly packed lymphoid cells and reticular fibers
- Germinal centers of proliferating B cells (if no B cells, then no follicles)
- may form part of bigger lymphoid organs
- in Peyer’s patches and appendix
lymph nodes: where?
main lymphoid organ of body
- embedded in CT in clusters along lymphatic vessels
- near body surface in inguinal, axillary, and cervical regions of body
Lymph node functions
- filter lymph: macrophages destroy microorganisms and debris
- Immune system activation: lymphocytes activated and mount attack against antigens
lymph node structure
- vary, but usually bean shaped
- external fibrous capsule
- trabeculae extend inward and divide node into compartments
- cortex
- medulla
Lymph node cortex
contains follicles with germinal centers, heavy with dividing B cells
- dendritic cells nearly encapsulate follicles
- deep cortex houses T cells in transit
- T cells circulate continuously among blood, lymph nodes, and lymph
lymph node medulla
medullary cord extends inward from cortex and contains B cells, T cells, and plasma cells
-Lymph sinuses contain macrophages
circulation in lymph nodes
lymph enters convex side through afferent lymphatic vessels –> travels through large subcapsular sinus and smaller sinuses to medullary sinuses –> exits concave side a hilum through efferent vessels
Fewer efferent than afferent, so flow is somewhat stagnant, allowing lymphocytes and macrophages time to function
spleen
- description
- main func
biggest lymphoid organ
-served by splenic artery and vein which enter and exit at the hilum
encased by fibrous capsule
-has lymphocytes, macrophages, and lots of erythrocytes
Func:
- site of lymphocyte proliferation and immune surveillance and response
- cleanses blood of aged cells and platelets (macrophages remove debris)
Spleen
-secondary function
- stores breakdown products of RBCs for later
- stores blood platelets and monocytes
- may be site of fetal erythrocyte production
Two areas of the spleen
White pulp: around central arteries–> mostly lymphocytes on reticular fibers –> involved in immune function
-Red pulp: in venous sinuses and splinic cords –> rich in RBCs and macrophages for disposal of RBCs and blood pathogens –> made of splenic cords and sinusoids
Thymus
- where?
- aging
- anterior, inferior neck –> extends into mediastinum –> partially overlies heart
- increases in size and most active during childhood, but stops growing during adolescence and gradually atrophies –> still produces immunocompetent cells super slowly
goes from 70g in infants to 3g in old age
Thymus structure
- lobes contain outer cortex and inner medulla
- most thymic cells are lymphocytes (cortex has rapidly dividing lymphocytes and scattered macrophages)
- medulla has fewer lymphocytes and thymic corpuscles involved in regulatory T cell development
How is thymus different from other lymphoid organs?
- has no follicles because it lacks B cells
- doesn’t directly fight antigens –> T cell maturation only –> keeps isolated via blood thymus barrier
-has stroma of epithelial cells (not reticular fibers) –> provide environment in which T lymphocytes become immunocompetent
Thymus cortex
- lots of T cells
- immature t cells migrate here from red bone marrow where they proliferate and begin to mature
- dendritic cells derived from monocytes assist in t cell maturation
- specialized epithelial cells help educate t cells through positive selection
- only 25% survive; the rest are eaten by macrophages
Thymus medulla
more mature t cells migrate here from corte
-more epithelial cells, dendritic cells, and macrophages
Mucosa associated lymphoid tissue (MALT)
lymphoid tissues in mucous membranes throughout body
- protects from pathogens
- biggest collections of malt in tonsils, peyer’s patches, and appendix
- also occurs in mucosa of respiratory and genitourinary organs and the digestive tract
Tonsils
- simplest lymphoid organ
- forms ring of lymphatic tissue around pharynx
palatine tonsils (posterior oral cavity) lingual tonsils (grouped at base of tongue) Phryngeal tonsil (posterior wall of nasopharynx) tubal tonsils (around openings of auditory tubes into pharynx)
gather and reove pathogens from food or air
tonsil structure
have follicles with germinal centers
-not fully encapsulated
overlying epithelium invaginates forming tonsillar crypts :
- trap and destroy bacteria/particulate matter
- allow immune cells to build memory for pathogens
Aggregates of lymphoid follicles
Peyer’s patches
- clusters of lymphoid follicles in wall of distal portion of small intestine
- similar structures in appendix, but Peyer’s patches are only on one side of intestinal wall
Peyer’s patches and appendix
- destroy bacteria, preventing them from breaching intestinal wall
- generate memory lymphocytes
