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Lymphatic System
•
Cardiovascular System
•
Capillary system: outflow of fluid slightly
exceeds return
Fluid is returned to the bloodstream via
lymphatic system
LYMPH AND LYMPHATIC VESSELS
Arterial system
Venous system
Large veins
(capacitance
vessels)
Heart
Large
lymphatic
vessels
Lymph
node
Lymphatic
system
Arteriovenous
anastomosis
Small veins
(capacitance
vessels)
Elastic arteries
(conducting
vessels)
Internal jugular vein
Muscular arteries
(distributing
vessels)
Entrance of thoracic
duct into vein
Entrance of right
lymphatic duct into vein
Axillary nodes
Thoracic duct
Cisterna chyli
Postcapillary
venule
Thoroughfare
channel
Regional
lymph nodes:
Cervical nodes
Lymphatic
Sinusoid
capillary
Arterioles
(resistance vessels)
Terminal arteriole
Metarteriole
Precapillary
sphincter
Capillaries
(exchange vessels)
Lymphatic
collecting vessels
Aorta
Inguinal nodes
Drained by the right
lymphatic duct
Drained by the
thoracic duct
(a) General distribution of lymphatic collecting vessels
and regional lymph nodes.
Figure 19.2
Figure 20.2a
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
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
– Lymphoid organs
•
Participate in disease prevention
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Venous system
Arterial system
Heart
Lymphatic
system:
Lymph duct
Lymph trunk
Lymph node
Lymphatic
collecting vessels,
with valves
Blood
capillaries
Lymphatic
capillary
Lymph
• Interstitial fluid which enters lymph capillaries
Tissue
fluid
– Lower concentration of proteins than blood
– Electrolyte differences
Tissue cell
Blood
Lymphatic
capillaries
capillaries
(a) Structural relationship between a
capillary bed of the blood vascular
system and lymphatic capillaries.
• Hydrostatic and colloid osmotic pressure
regulate exchange
Filaments anchored
to connective tissue
Endothelial cell
Flaplike minivalve
Fibroblast in loose
connective tissue
(b) Lymphatic capillaries are blind-ended tubes in which
adjacent endothelial cells overlap each other,
forming flaplike minivalves.
Figure 20.1
Lymphatic Vessels
Lymphatic Capillaries
• One-way system, lymph flows toward the heart
• Lymph vessels (lymphatics) include
– Lymphatic capillaries
– Lymphatic collecting vessels
– Lymphatic trunks and ducts
• 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 minivalves
Filaments anchored
to connective tissue
Endothelial cell
Flaplike minivalve
Fibroblast in loose
connective tissue
(b) Lymphatic capillaries are blind-ended tubes in which
adjacent endothelial cells overlap each other,
forming flaplike minivalves.
Figure 20.1b
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Lymphatics
Lymphatic Ducts
• Collecting vessels
• Capillaries join to form larger vessels =
lymphatics
• Lymph is delivered into one of two large ducts
– Right lymphatic duct
• Drains the right upper arm & the right side of the head &
thorax
– Empty into thoracic duct or right lymphatic duct
– Thoracic duct
• Similar to veins, except
• Arises from the cisterna chyli & drains the rest of the
body
– Have thinner walls
– Anastomose more frequently
– More valves
– Occasionally modified to form nodes
Lymphatics
• Connect with subclavian veins
Lymph Transport
Regional
lymph nodes:
Cervical nodes
Internal jugular vein
• No pump
• Lymph movement similar to venous return
Entrance of right
lymphatic duct into vein
Entrance of thoracic
duct into vein
– Valves
– Skeletal muscle contraction
– Thoracic pump
– Pressure gradients
– Contraction of nearby arteries & smooth muscle
within vessels
– Movement is slow and sporadic
Axillary nodes
Thoracic duct
Cisterna chyli
Aorta
Inguinal nodes
Lymphatic
collecting vessels
Drained by the right
lymphatic duct
Drained by the
thoracic duct
(a) General distribution of lymphatic collecting vessels
and regional lymph nodes.
Figure 20.2a
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
Lymph Nodes
•
Functions
1. Filter lymph
•
Macrophages destroy microorganisms and debris
2. Immune system
– Behind the ear, inferior mandible and lateral neck
• Axillary region
• Abdomen
•
Lymphocytes are activated and mount an attack against
antigens
– Along abdominal aorta and mesenteric arteries
• Inguinal region
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
Capsule
Trabecula
Splenic cords
Venous sinuses
Arterioles and
capillaries
Splenic
artery
Splenic
vein
Hilum
Red pulp
White pulp
Central artery
(a) Diagram of the
spleen, anterior view
Splenic artery
Splenic vein
(b) Diagram of spleen histology
Figure 20.6a,b
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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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