lymphatic system

traberculae

fibrous extenstions of capsule. septa subdivide thymic lobes into lobules.

T lymphocytes

formed elements move from red bone marrow into blood following hemopoiesis. unlike the other formed elements, T lymphocytes must migrate to thymus to complete maturation. T lymphocytes originates from requirement of these cells to complete their maturation in thymus.

hilum

hilus. Lymph drained via the efferent lymphatic vessel from this region of lymph node.

medulla

inner

primary lymphatic structures

involved in formation and maturation of lymphocytes. both red bone marrow and thymus are considered primary lymphatic structures.

secondary lymphatic structures

not involved in lymphocyte formation, but instead serve to house both lymphocytes and other immune cells following their formation. secondary lymphatic structures provide site where an immune response is initiated. major secondary lymphatic structures include lymph nodes, spleen, tonsils, lymphatic nodules and MALT.

cortex

outer

peyer patches

MALT very prominent in mucosa of small intestine, primarily in the ileum. there collections of lymphatic nodules ... can become quite large and bulge into the gut lumen.

characteristics of lymph

approx. 15% of fluid that enters the interstitial space surrounding cells is not reabsorbed back into the blood capillaries during capillary exchange. this interstitial fluid amounts to about 3 liters daily and is normally absorbed into lymphatic capillaries.

thymus

bilobed organ that is located in superior mediastinum and functions in T lymphocyte maturation. in infants and young children, thymus is quite large and extends into anterior mediastinum as well. thymus continues to grow until puberty, when it reaches a maximum weight of 30-50 grams. cells within thymus begin to regress after it reaches size. thereafter, much of thymic tissue is replaced by adipose connective tissue.

afferent lymphatic vessels

bring lymph to lymph node.

lymphatic system

composed of lymph vessels and lymphatic tissues and organs. lymph is fluid transported w/in lymph vessels. Lymph originates as interstitial fluid surrounding tissue cells; it moves passively into the lymphatic capillaries due to pressure gradient. lymphatic capillaries merge to form larger lymph vessels.

movement of lymph into lymphatic capillaries

driving force to move fluid into lymphatic capillaries is an increase in hydrostatic pressure w/in interstitial space. interstitial hydrostatic pressure rises as additional fluid is filtered from blood capillaries. an increase in pressure at margins of lymphatic capillary endothelial cells " pushes" interstitial fluid into the lymphatic capillary lumen. the higher the interstitial fluid pressure, the greater amount of fluid that enters lymphatic capillary. the anchoring filaments extending between the lymphatic capillary cells and surrounding tissue prevent the collapse of lymphatic capillaries as pressure exerted by interstitial fluid increases.

MALT (mucosa associated lymphatic tissue)

located in lamina propria of mucosa of GI, respiratory, genital, and urinary tracts. the lymphatic cells in MALT help defend against foreign substances that come in contact w. mucosal membranes.

right lymphatic duct

located near right clavicle. receives lymph from lymphatic trunks that drain following: 1) right side of head and neck 2) right upper limb 3) right side of thorax. returns lymph into junction of right subclavian vein and right internal jugular vein. thus, right lymphatic duct drains lymph from upper right quadrant of body.

lymphatic vessels

lymphatic capillaries merge to form larger structures. superficial lymphatic vessels are generally positioned adjacent to superficial veins of the body; in contrast, deep lymphatic vessels are next to deep arteries and veins.

lacteals

lymphatic capillaries within gastrointestinal tract, allow for absorption of lipid soluble substances from GI tract.

lymphatic nodules

lymphatic follicles are small oval clusters of lymphatic cells with some extracellular matrix that are not completely surrounded by a connective tissue capsule. scattered lymphatic nodules are referred to as diffuse lymphatic tissue. this tissue can be found in every body organ and w/in the wall of appendix helping to defend against infections in these structures. however, in some areas of the body, many lymphatic nodules group together to form larger structures, such as MALT.

lymphatic ducts

lymphatic trunks drain into largest lymph vessels. there are two lymphatic ducts: the right lymphatic duct and thoracic duct. both of these convey lymph back into venous blood circulation.

lymphatic trunks

lymphatic vessels feed into .. on both right and left side of body. each lymphatic trunk removes lymph from a specific major body region: - jugular trunks drain lymph from both head and neck. - subclavian trunks remove lymph from upper limbs. - bronchomediastinal trunks drain lymph from deep thoracic structures. - intestinal trunks drain lymph from most abdominal structures. - lumbar trunks remove lymph from lower limbs, abdominopelvic wall and pelvic organs.

valves

lymphatic vessels resemble small veins between both contain all three vessel tunics (intima, media, externa) and have valves w/in lumen. valves are required to prevent lymph from pooling in vessel and help prevent lymph backflow b/c lymphatic vessel network is a low pressure system, these valves are especially important in areas where lymph flow is against direction of gravity such as in lower limbs.

lymphedema

recognized as an accumulation of interstitial fluid that occurs due to interference with lymphatic drainage in a part of body. interstitial fluid accumulates and affected area both swells and becomes painful. if lymphedema is left untreated, the protein rich interstitial fluid may interfere w/ wound healing and can even contribute to an infection by acting as a growth medium for bacteria.

lymph nodes

small, round or oval encapsulated structures located along pathways of lymph vessels, where they serve as main lymphatic organ. lymph nodes function in the filtering of lymph and removal of unwanted substances.

lymphatic capillaries

smallest lymph vessels. lymphatic capillaries are microscopic, closed ended vessels that absorb interstitial fluid. they are interspersed throughout areolar connective tissue among most capillary networks, except those within the red bone marrow and central nervous system. note that lymphatic capillaries are absent within avascular tissues such as epithelia.

lobules

subdivided thymic lobes.

capsule

surround thymic lobes through connective tissue.

thymic lobes

thymus when in its prime, consists of two fused .. each surrounded by connective tissue capsule.

efferent lymphatic vessels

typically only one ... which originates at the involuted portion of the lymph node.