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Negative selection

survival of T cells depends upon not recognizing self-antigen

Functions of lymphatic system

assist cardiovascular system by returning excess fluid to the blood to maintain fluid balance; assist immune system

Hepatic portal system

digested fats are transferred from the GI system to the liver and then must go to the circulation; fluid in the interstitium is recaptured and put back into the cardiovascular system

Lymphatic system and immunity

transports and houses lymphocytes and other immune cells that help the immune system defend against foreign substances or pathogens


fluid similar to plasma without plasma proteins or RBCS

Lymphatic ducts and trunks

lymph is transported through progressively larger and larger lymph vessels, including lymphatic capillaries, vessels, trunks, and ducts; lymphatic ducts drain lymph into venous circulation

Lymphatic vessels

provide a conduit from the peripheral tissues to the venous system; drain into lymph nodes

Lymphatic organs

bone marrow, lymph nodes, spleen, thymus, etc.

Lymphatic cells

lymphocytes, phagocytes, APCs, etc.

Closed system

fluid and dissolved molecules enter and leave small vessels - net fluid flow is OUT

Lymphatic vessel structure

begin as a blind ended tube; larger lumens and thinner walls than capillaries; endothelial cells are loosely bound together with overlaps or openings; acts as a one-way valve


movement of cancerous cells from the point of origin via the lymphatic vessels to new sites


parasitic filarial worms live, breed, and block the lymphatic vessels; mosquitoes are the vector

Bone marrow

site of maturation for all formed elements except T-cells

Antigen presenting cells (APCs)

cells that phagocytose a foreign component, digest most of the molecules but present parts of the component on its cell surface

Education of lymphocytes

occurs in bone marrow and B lymphocytes leave; occurs in thymus and T lymphocytes leave

Migration of lymphocytes

occurs via blood or lymphatic vessels to occupy CT as free cells or in lymphatic nodules; in lymph nodes; and in spleen

Naive B lymphocytes

educated by presenting with self-antigens; if they recognize self-antigens, they are killed

Naive T lymphocytes

leave bone marrow and migrate to the thymus; education occurs in thymus in the presence of epithelial reticular cells

Primary lymphatic structures

bone marrow and thymus; sites of cell formation and education

Secondary lymphatic structures

lymph nodes, spleen, tonsils, lymph nodules (MALT); sites of cell activation and proliferation

Lymph nodules

collections of lymphocytes (MALT, GALT, BALT); germinal center mostly B cells; marginal zone T cells; macrophages everywhere

Lymph nodes

located along lymphatic vessels; all lymph fluid must pass through to be cleaned by lymphocytes and returned to the blood

Afferent lymphatic vessels

carry lymph from peripheral tissues into lymph node

Efferent lymphatic vessels

carry lymph to venous circulation

Lymph flow from subscapular space

contains macrophages and dendritic cells (APCs)

Lymph flow through outer cortex

contains B cells within germinal centers

Lymph flow through paracortex

dominated by T cells

Lymph flow through core/medulla

contains B cells and plasma cells, organized into medullary cords

Lymph flow

from subscapular space; through outer cortex; through paracortex; through core/medulla; into hilum and efferent lymphatics

Blood flow in the spleen

blood enters via arteries and percolates through the white pulp and red pulp where it is monitored and cleaned; blood can move in and out of sinusoidal capillaries; eventually exits via the venous system

Spleen functions

white pulp filters blood; red pulp removes old (senescent) RBCs and platelets

White pulp

nodules containing APCs, B and T cells, and macrophages destroy antigens

Red pulp

macrophages digest RBCs; iron from RBCs is stored and reused

Spleen anatomy

arteries branch out through the spleen and discharge blood at sinusoidal capillaries; collections of lymphocytes serve to detect and remove pathogens; clean blood collected back into venues and returned to circulation


site of T-cell maturation and education; located in mediastinum

Positive selection

survival of T cels depends upon ability to bind to MHC

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