Chapter 20 The Lymphatic System.doc

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Chapter 20: The Lymphatic System
-the lymphatic system consists of 3 parts:
1) lymphatic vessels
2) lymph: the fluid contained in lymphatic vessels
3) lymph nodes: cleanse the lymph as it passes through it
-lymph organs and tissues include the spleen, thymus, tonsils etc.
-they have phagocytic cells and lymphocytes
-play an important role in the body's defence mechanisms
Lymphatic Vessels
-leaked fluids and plasma proteins that escape from the bloodstream is carried back to the
blood to ensure the cardiovascular system has sufficient blood volume to operate properly
-lymphatic vessels (lymphatics) are made up of drainage vessels that collect the interstitial
fluid and return it into the blood stream
-when interstitial fluid enters the lymphatics, it is called lymph
-they function to:
1) return excess tissue fluid to the bloodstream
2) return leaked proteins to the blood
3) carry absorbed fat from the intestine to the blood through lacteals
Distribution and Structure of Lymphatic Vessels
-lymphatic vessels form a one-way system where lymph is transported to the heart
-transport system begins with microscopic, blind-ended lymphatic capillaries
-capillaries weave between tissue cells and blood capillaries
-absent from bones, teeth, bone marrow, and the central nervous system
-very permeable
-permeability is due to 2 unique structural modifications:
1) endothelial cells forming the walls of lymphatic capillaries are not tightly
joined; the edges of adjacent cells overlap loosely, forming flaplike minivalves
that are easily opened
2) collagen filaments anchor the endothelial cells to surrounding structures; an
increase in interstitial fluid volume opens the minivalves, rather than causing the
lymphatic capillaries to collapse
-when fluid pressure in the interstitial space is greater than the pressure in the
lymphatic capillary, the minivalve flaps open, allowing fluid to enter the
lymphatic capillary
-when the pressure is greater inside the lymphatic capillary, the endothelial
minivalve flaps are close, preventing lymph from leaking out as pressure moves it
along the vessel
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-proteins in the interstitial space are unable to enter blood capillaries but can enter
lymphatic capillaries easily
-during inflammation, lymphatic capillaries develop openings that permit uptake of larger
particles (i.e.: cell debris, pathogens, cancer cells, etc.)
-lacteals (specialized lymphatic capillaries) are present in fingerlike villi of the intestinal
-lacteals absorb digested fats from the intestine and the lymph drainage is milky
-fatty lymph is called chyle and is delivered to blood via the lymphatic system
-lymphatic collecting vessels have the same 3 tunics as veins but the walls are thinner ;
they have more internal valves and more anastomoses
-lymphatics in the skin travel along superficial veins
-deep lymphatic vessels travel with deep arteries
-lymphatic trunks are formed by the union of the largest collecting vessels and drain fairly
large areas of the body
-include the paired lumbar trunks, bronchomediastinal trunks, subclavian trunks,
jugular trunks, and the single intestinal trunk
-right lymphatic duct drains lymph from the right upper limb, the right side of the head,
and the right side of the thorax
-the thoracic duct receives lymph from the rest of the body
-arises as the cisterna chyli
-collects lymph from the 2 large lumbar trunks that drain the lower limbs and the
intestinal trunk that drains digestive organs
-receives drainage from the left side of the thorax, left upper limb, and the head
-each terminal duct empties its lymph into venous circulation at the junction of the internal
jugular vein and subclavian vein on its own side of the body
Lymph Transport
-lymphatic vessels are low pressure systems
-the same mechanisms that promote venous return in blood vessels act on lymphatic
vessels as well
-the milking action of skeletal muscles, pressure changes in the thorax during
breathing, and valves to prevent backflow are important
-lymphatics are bundled together in connecive tissues along with blood vessels and
pulsations of nearby arteries promote lymph flow
-smooth muscle in the walls of lymphatic trunks and thoracic ducts help pump lymph
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