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3/28/2016
1
LYMPH AND LYMPHATIC VESSELS
Cardiovascular System
Lymphatic System
• Capillary system: outflow of fluid slightly
exceeds return
• Fluid is returned to the bloodstream via
lymphatic system
Figure 19.2Figure 19.2Figure 19.2Figure 19.2
Large veinsLarge veinsLarge veinsLarge veins(capacitance(capacitance(capacitance(capacitancevessels)vessels)vessels)vessels)
LargeLargeLargeLargelymphaticlymphaticlymphaticlymphaticvesselsvesselsvesselsvessels
ArteriovenousArteriovenousArteriovenousArteriovenousanastomosisanastomosisanastomosisanastomosis
LymphaticLymphaticLymphaticLymphaticcapillarycapillarycapillarycapillary
PostcapillaryPostcapillaryPostcapillaryPostcapillaryvenulevenulevenulevenule
SinusoidSinusoidSinusoidSinusoid
MetarterioleMetarterioleMetarterioleMetarteriole
Terminal arterioleTerminal arterioleTerminal arterioleTerminal arteriole
ArteriolesArteriolesArteriolesArterioles(resistance vessels)(resistance vessels)(resistance vessels)(resistance vessels)
Muscular arteriesMuscular arteriesMuscular arteriesMuscular arteries(distributing(distributing(distributing(distributingvessels)vessels)vessels)vessels)
Elastic arteriesElastic arteriesElastic arteriesElastic arteries(conducting(conducting(conducting(conductingvessels)vessels)vessels)vessels)
Small veinsSmall veinsSmall veinsSmall veins(capacitance(capacitance(capacitance(capacitancevessels)vessels)vessels)vessels)
LymphLymphLymphLymphnodenodenodenode
CapillariesCapillariesCapillariesCapillaries(exchange vessels)(exchange vessels)(exchange vessels)(exchange vessels)
Precapillary sphincterPrecapillary sphincterPrecapillary sphincterPrecapillary sphincterThoroughfareThoroughfareThoroughfareThoroughfarechannelchannelchannelchannel
LymphaticLymphaticLymphaticLymphaticsystemsystemsystemsystem
Venous systemVenous systemVenous systemVenous system Arterial systemArterial systemArterial systemArterial system
HeartHeartHeartHeart
Figure 20.2a
Cervical nodesEntrance of right
lymphatic duct into vein
Internal jugular vein
Entrance of thoracic
duct into vein
Thoracic duct
Cisterna chyli
Lymphatic
collecting vessels
Axillary nodes
Aorta
Inguinal nodes
Regional
lymph nodes:
(a) General distribution of lymphatic collecting vessels
and regional lymph nodes.
Drained by the right
lymphatic duct
Drained by the
thoracic duct
Lymphatic System
• Consists of three parts
– A network of lymphatic vessels carrying lymph
• Transports fluid back to CV system
– Lymph nodes
• Filter the fluid within the vessels
– Lymphoid organs
• Participate in disease prevention
Lymphatic System
• Functions
1. Returns interstitial fluid and leaked plasma proteins
back to the blood
2. Disease surveillance
3. Lipid transport from intestine via lacteals
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Figure 20.1
Lymphaticsystem:
Lymph duct
Lymph trunk
Lymph node
Lymphatic
capillary
Bloodcapillaries
Lymphatic
collecting vessels, with valves
HeartArterial systemVenous system
Tissue
fluid
Tissue cellBlood
capillariesLymphatic
capillaries
(a) Structural relationship between acapillary bed of the blood vascularsystem and lymphatic capillaries.
Filaments anchored
to connective tissue
Fibroblast in loose
connective tissue
Endothelial cell
Flaplike minivalve
(b) Lymphatic capillaries are blind-ended tubes in which
adjacent endothelial cells overlap each other,
forming flaplike minivalves.
Lymph
• Interstitial fluid which enters lymph capillaries
– Lower concentration of proteins than blood
– Electrolyte differences
• Hydrostatic and colloid osmotic pressure
regulate exchange
Lymphatic Vessels
• One-way system, lymph flows toward the heart
• Lymph vessels (lymphatics) include
– Lymphatic capillaries
– Lymphatic collecting vessels
– Lymphatic trunks and ducts
Lymphatic Capillaries
• Similar to blood capillaries, except…
– Dead end vessels
– No basement membrane = very permeable
• Take up cell debris, pathogens and cancer cells
– Endothelial cells overlap to form one-way mini-
valves
Figure 20.1b
Filaments anchored
to connective tissue
Fibroblast in loose
connective tissue
Endothelial cell
Flaplike minivalve
(b) Lymphatic capillaries are blind-ended tubes in which
adjacent endothelial cells overlap each other,
forming flaplike minivalves.
3/28/2016
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Lymphatics
• Collecting vessels
• Capillaries join to form larger vessels = lymphatics
– Empty into thoracic duct or right lymphatic duct
• Similar to veins, except
– Have thinner walls
– Anastomose more frequently
– More valves
– Occasionally modified to form nodes
Lymphatic Ducts
• Lymph is delivered into one of two large ducts
– Right lymphatic duct
• Drains the right upper arm & the right side of the head &
thorax
– Thoracic duct
• Arises from the cisterna chyli & drains the rest of the
body
• Connect with subclavian veins
Figure 20.2a
Cervical nodesEntrance of right
lymphatic duct into vein
Internal jugular vein
Entrance of thoracic
duct into vein
Thoracic duct
Cisterna chyli
Lymphatic
collecting vessels
Axillary nodes
Aorta
Inguinal nodes
Regional
lymph nodes:
(a) General distribution of lymphatic collecting vessels
and regional lymph nodes.
Drained by the right
lymphatic duct
Drained by the
thoracic duct
Lymphatics Lymph Transport
• No pump
• Lymph movement similar to venous return
– Valves
– Skeletal muscle contraction
– Thoracic pump
– Pressure gradients
– Contraction of nearby arteries & smooth muscle within vessels
– Movement is slow and sporadic
Edema
• Lymphedema
– Prevention of return of lymph to blood
• May be due to:
– Osmotic changes
– Blockage of lymph vessels
• Parasites
– Inflammation
– Surgery
Lymphatic Tissues
• Tissues house and provide a proliferation site
for lymphocytes
– Furnish a surveillance vantage point
• Mucosa-associated lymphatic (MALT)
– Respiratory, digestive, urinary, reproductive systems
– Peyer’s patches
• Junction of large and small intestine
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Lymph Nodes
• Solid, spherical, well-defined organs
– Distributed along course of lymphatic vessels
– Concentrated
• Cervical region
– Behind the ear, inferior mandible and lateral neck
• Axillary region
• Abdomen
– Along abdominal aorta and mesenteric arteries
• Inguinal region
Lymph Nodes
• Functions
1. Filter lymph
• Macrophages destroy microorganisms and debris
2. Immune system
• Lymphocytes are activated and mount an attack against
antigens
Lymph Nodes
• Structure
– Outer cortex
• Follicles with germinal centers, heavy with dividing B cells
– Inner medulla
• Medullary sinuses
– Macrophages
Lymphatic System Components
�Lymph
�Lymphatic vessels
�Lymph nodes
�Lymphatic tissues
• Lymphatic organs
Spleen
• Largest lymphoid organ
– Macrophages remove old RBC’s, platelets and
bacteria
– Production of RBC’s
• In fetus and severely anemic patients
– Splenic contraction
• May return 200-300 mls of blood to circulation from
sinuses
Figure 20.6a,b
Arterioles and
capillaries
Capsule
Trabecula
Venous sinuses
Red pulp
Splenic cords
White pulp
Central artery
Splenic artery
Splenic vein
(b) Diagram of spleen histology
Splenic
artery
Splenic
vein Hilum
(a) Diagram of the
spleen, anterior view
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Thymus
• Involution
– Stops growing during adolescence and then gradually
atrophies
• Replaced by adipose and connective tissue
• Hormones
– Thymopoetin and thymosin
• Assist in lymphocyte differentiation
Tonsils
• Simplest lymphoid organs– 3 pairs
• Palatine tonsils
– Posterior end oral cavity
– “Sore throat”
• Lingual tonsils
– Grouped at the base of
the tongue
• Pharyngeal tonsils
– Adenoids
– Posterior wall of the
nasopharynx
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