Chapter21 - Lymphatic System Flashcards
Lymphatic system functions
- Aids immune system: produces, houses, and transports lymphocytes and other immune cells
- Aids circulatory system: balancing fluids, blood volume, and blood pressure.
Lymphatic system components
- lymph,
- lymphatics (vessels)
- lymphatic tissues and organs
Lymph
fluid composed of water, dissolved solutes, small amount of protein, cell debris, pathogens, or cancer cells.
Formation of lymph:
≈15% of fluid entering spaces does not get reabsorbed into the blood capillaries (about 3L daily).
-Moves passively into lymphatic capillaries due to the pressure gradient.
Pathway of Lymphatics
lymphatic capillaries lymphatic vessels lymphatic trunks lymphatic ducts veins
lymphatic capillaries
- smallest lymph vessels
- closed-ended, larger in diameter than blood capillaries
- Walls composed of only endothelial cells that overlap with one-way flaps
to allow fluid entrance
-Anchoring filaments
Anchoring filaments
attach endothelial cells to the nearby structures
lymphatic vessels
are structures formed from merged lymphatic capillaries.
- Three vessel tunics(intima, media, externa)
- Have valves (prevent lymph from pooling and backflow).
Because LS is without a pump it relies on several mechanisms to move lymph through the vessels:
- skeletal muscle pump
- respiratory pump in the torso
- pulsatile movement of blood in nearby arteries
- rhythmic contraction of smooth muscle in larger lymph vessel walls (contain pacemaker cells)
Lymphatic Trunks
fed into by lymphatic vessels; present on both sides of the body.
Lymphatic Ducts
-largest lymphatic vessels
(right lymphatic duct and thoracic duct)
convey lymph back into venous circulation (left and right jugular veins)
Lymphedema
accumulation of interstitial fluid due to interference w/ lymphatic drainage
Lymphatic Tissue & Organs
The major component of the lymphatic structures is the lymphatic tissue
-a type of loose connective tissue that contains an extensive matrix of thin collagen fibers (also called “reticular fibers”) that houses a variety of immune and supporting cells
Diffuse lymphatic tissue
– a loose arrangement of cells and reticular fibers
– is found in every body organ.
Nodular lymphatic tissue
-a compact arrangement of cells within the matrix of reticular fibers forming lymphatic nodules (=lymphatic follicles) of various size. -Can be part of a larger lymphatic organ (ex. lymph node) or scattered in the walls of other organs (ex. appendix).
Primary lymphatic structures are
involved in formation and maturation of lymphocytes.
Secondary lymphatic structures
- house immune cells,
- site of immune response initiation
Primary Lymphatic Structures:
Red Bone Marrow
Thymus
Red Bone Marrow
-the flexible tissue located within the spaces between the trabeculae in the sections of spongy bone and responsible for hemopeosis
-All formed elements leave the bone marrow and directly enter and circulate in the blood.
Exception: T-lymphocytes complete their maturation in the thymus.
Thymus location
superior mediastinum
Thymus function
T-lymphocyte maturation
Thymus size
grows until puberty, then is slowly replaced by adipose tissue
Thymus structure
consists of two fused thymic lobes covered with the capsule.
Trabeculae
Trabeculae
fibrous extensions of the capsule,
subdivide lobes into lobules.
T-lymphocytes in cortex & medulla
- each lobule with outer cortex (with immature T-lymphocytes)
- inner medulla (with mature T-lymphocytes)
Secondary Lymphatic Structures:
- Lymph Node
- Spleen
- Tonsils
- Mucosa-associated lymphatic tissue(MALT)
Lymph Node characteristics
- Small (1-25 mm), oval, encapsulated structures located along the pathways of lymphatic vessels. Total # 500-700
- F: Filter lymph and remove unwanted substances
Capsule
sends internal extension into it, trabeculae
2 regions of a lymph node:
Cortex & Medulla
Cortex
(outer)
contains lymphatic nodule with dividing immune cells
Medulla
(inner)
carries medullary cords, support strands of mature immune cells.
Sinuses
lined by macrophages (remove foreign debris)
If a lymphocyte encounters a foreign substance…
…immune response is generated, during which lymphocytes undergo rapid cell division (“swollen lymph nodes”)
Spleen
-large lymphatic organ located posterolaterally to the stomach.
Spleen is surrounded by connective tissue capsule with …
…trabeculae extending into the organ and subdividing the spleen
2 regions of the spleen
White pulp
Red pulp
White pulp
Contains a central artery + clusters of T- and B-lymphocytes and macrophages (immune function)
Red pulp
Has splenic sinusoids so that blood cells (erythrocytes, platelets) can easily enter and exit the vessel. Rich in macrophages that will dispose of the worn-out erythrocytes.
Spleen basic function
filters blood
IN
-> white pulp (lymphatic cells monitor blood for foreign materials and bacteria
…->red pulp (macrophages phagocytize bacteria, foreign debris, and old erythrocytes and platelets)
->OUT
Spleens 4 main function
- Body’s defense
- Removal and cycling of old and defective erythrocytes and throbocytes(platelets)
- Reservoirs of erythrocytes and thrombocytes
- Formation of RBC during fetal development.
Tonsil location
pharynx (throat)
Tonsil function
protection against foreign substances inhaled/ingested
Tonsil structure
Not completely encapsulated
- Tonsillar crypts
- Lymphatic nodules
Tonsillar crypts
(invaginations) increase surface area to trap material
Lymphatic nodules
might contain large number of activated B cells
Mucosa-associated lymphatic tissue (MALT)
- aggregation of lymphatic nodules in the mucosa in GI, respiratory, genital, and urinary tracts.
- Ex. Peyer’s patches in SI.
Lymphoma
- cancer of the lymph system (or lymphatic system), which is part of our immunity.
- characterized by the formation of solid tumors in the immune system.
- affects immune cells called lymphocytes, which are white blood cells.
