ch 22 lymphatic

lymphatic system

protects us against disease → cells respond to environmental, toxins, abnormal body cells (such as cancers)

lymphocytes

part of the immune response; identify, attack and develop immunity to specific pathogens

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make up 20-40% of circulating leukocytes → most are stored, not circulating

components of lymphatic system

lymph, lymphatic vessels, lymphoid tissues and organs, lymphoid cells

lymph

a fluid similar to plasma but without plasma proteins

lymphatic vessels

carry lymph from lymph from peripheral tissues to veins

lymphoid tissues and organs

scattered throughout the body

lymphoid cells

lymphocytes, phagocytes and other cells

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immune system cells and supportive cells in lymphoid tissues

lymphocyte production

produced in primary lymphoid tissues and organs (red bone marrow and thymus)

lymphocyte activation

become activated in secondary lymphoid tissues and organs

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tonsils, MALT, lymph nodes and spleen

functions of lymphatic system

produce, maintain, and distribute lymphocytes and other lymphoid cells

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return excess fluid to bloodstream (maintain normal blood volume)

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transport hormones, nutrient, wastes

lymphatic capillaries

overlap of endothelial cells acts as one-way valve

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allows fluids, solutes, viruses, and bacteria to enter; prevents their return to intercellular spaces

vessels to lymphatics

some fluids (not red, no RBCs or heme), toxins and bacteria will leak out of capillaries into tissue → get pushed and absorbed into lymphatic vessels (bunch of one way valves so that bacteria/toxins don't return to blood) → passes through increasingly larger vessels (like venous side)

lacteals

special lymphatic capillaries in small intestine; transport lipids from digestive tract

deep lymphatics

larger vessels that accompany deep arteries and veins

lymphatic vessels

superficial lymphatics, deep lymphatics, join to form large lymphatic trunks that empty into 2 major collecting vessels

thoracic duct

base expands to form cisternae chili, which receives lymph from right and left lumbar trunks + intestinal trunk

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empties into left subclavian vein

right lymphatic duct

collects lymph from right jugular trunk, right subclavian trunk, right bronchomediastinal trunk

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empties into right subclavian vein

reentry of lymph

ducts drains into precava and reenter the blood

lymphedema

blockage of lymph drainage from a limb, causes severe swelling (when lymph vessels get blocked = build up of fluid in tissue)

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interferes with immune system function

venous vs. lymphatic system

no vasoconstriction in either, movement is based on muscle compression

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one-way valves

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fluid moves from smaller vessels to larger vessels

T cells

thymus dependent

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lymphocytes divide in cortex → migrate into medulla → mature in the thymus (like a rigorous training) then leave by medullary blood vessels

B cells

bone marrow-derived, mature in bone marrow

NK cells

natural killer cells

lymphoid tissues

connective tissues dominated by lymphocytes

lymphoid nodules

tissue with densely packed lymphocytes, germinal center contains dividing lymphocytes

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distributed in lymph nodes, spleen, respiratory tract (tonsils), along digestive/urinary/reproductive tracts

germinal center

area found within the lymph node that produces the lymphocytes

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bacteria thrown into a hoard of lymphocytes, any B cell that can recognize it will become active and start multiplying

tonsils

bigger lymph nodes found in wall of pharynx: pharyngeal tonsil (adenoid), left and right palatine tonsils, two lingual tonsils

tonsillitis

inflammation of tonsils, especially palatine tonsils

MALT

mucosa-associated lymphoid tissue (in the digestive tract)

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lymphoid tissues associated with digestive system and aggregated lymphoid nodules (Peyer's Patches) → clustered deep to intestinal epithelial lining

appendix

vermiform appendix; contains a mass of fused lymphoid nodules

lymphoid organs

include lymph nodes, thymus, spleen (only difference is size)

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separated from surrounding tissues by fibrous connective tissue capsule

trabeculae

bundles of collagen fibers, extend from capsule into interior of lymph node

hilum

shallow indentation where blood vessels and nerves reach lymph node

afferent lymphatics

carry lymph from peripheral tissues to lymph node

efferent lymphatics

leave lymph node at hilum, carry lymph to venous circulation

lymph flow

through nodes: from subcapsular space → outer cortex → medulla → efferent lymphatics at hilum

lymph node function

purify lymph before return to venous circulation by removing antigens

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antigens released due to infection → enter lymph and stimulate immune cells

lymphoid tissues/lymph nodes

monitor peripheral infections and respond before infections reach vital organs

antigens

target of the immune system (on a molecular level)

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antibodies released by B cells have very specific molecular patterns that bind to them

lymph nodes of gut, trachea, lungs, thoracic duct

protect against pathogens in digestive and respiratory systems

largest lymph nodes

in groin, axillary, base of neck

swell in response to infection (and may harden)

lymphadenopathy

chronic or excessive enlargement of lymph nodes; may indicate infections or cancer (lymphoma)

thymus

located in mediastinum (middle of chest area), divided into 2 thymic lobes, septa divide lobes in smaller lobules

thymic lobule

dense outer cortex and pale central medulla

thymosin

promotes development and maturation of T cells

spleen functions

1. removal of abnormal blood cells by phagocytosis
2. storage of iron recycled from red blood cells
3. initiation of immune responses by B and T cells in response to antigens in circulating blood

spleen location

attached to stomach, contracts diaphragm and left kidney

spleen histology

cellular components within capsule make up pulp

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red pulp contains many red blood cells, white pulp resembles lymphoid nodules