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)
