Download Ch 12 Lymphatic Structures and Functions

Pages 398-403
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Two parts:
1. Lymphatic vessels
2. Lymphoid tissues and organs
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Functions:
◦ Transports escaped fluids back to the blood
◦ Body defense and resistance to disease
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Lymph—excess tissue fluid and plasma proteins
carried by lymphatic vessels
◦ Also includes cell debris, bacteria, viruses
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Lymphatic vessels
◦ pick up lymph and return it to the blood
 Lymph capillaries (smallest) absorb leaked fluid
 Contain minivalves to ensure one-way flow to heart
 Stay closed when vessel pressure > interstitial fluid
 Remain open when vessel pressure < interstitial fluid
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If fluids are not picked up, edema occurs (fluid
accumulates in tissues and the area swells)
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Venous
system
Arterial
system
Heart
Lymph duct
Lymph trunk
Lymph node
Lymphatic
system
Lymphatic
collecting
vessels,
with valves
Lymph
capillary
Tissue fluid
(becomes
lymph)
Blood
capillaries
Loose connective
tissue around
capillaries
Tissue fluid
Tissue cell
Lymphatic
capillary
Blood
capillaries
(a)
Arteriole
Venule
Fibroblast in loose
connective tissue
Endothelial
cell
(b)
Flaplike
minivalve
Filaments
anchored to
connective
tissue
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Lymph is collected through a system of
vessels that gets progressively larger
Two large ducts return fluid to circulatory
veins near the heart
◦ Right lymphatic duct
 drains the lymph from the right arm and the right side
of the head and thorax
◦ Thoracic duct
 drains lymph from rest of body
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Regional
lymph nodes:
Entrance of right
lymphatic duct into right
subclavian vein
Cervical
nodes
Axillary
nodes
Internal jugular vein
Thoracic duct
entry into left
subclavian vein
Thoracic duct
Aorta
Spleen
Inguinal
nodes
Cisterna chyli (receives
lymph drainage from
digestive organs)
Lymphatics
KEY:
Drained by the right lymphatic duct
Drained by the thoracic duct
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similar to veins of the cardiovascular system
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◦
◦
◦
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(have the same tunics: intima, media, externa)
Thin endothelial walls
Valves in larger vessels
Low-pressure, pumpless system
Lymph transported is aided by:
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◦
◦
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Milking action of skeletal muscles
Pulsations of nearby arteries
Pressure changes in thorax during breathing
Smooth muscle in walls of vessels
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About 500 nodes in the body
◦ Large clusters in specific regions:
 inguinal, axillary, cervical
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Structure:
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filter harmful materials before it is returned to the
blood
◦
◦
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◦
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Surrounded by a dense connective tissue capsule
Compartmentalized: sinuses lined with endothelial cells
Outer cortex contains lymphocytes (B cells & T cells)
Inner medulla contains phagocytic macrophages
Bacteria
Viruses
Cancer cells
Cell debris
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Afferent
lymphatic
vessels
Germinal
center in
follicle
Capsule
Subcapsular
sinus
Trabecula
Afferent
lymphatic
vessels
Cortex
Follicle
Efferent
lymphatic
vessels
Hilum
Medullary sinus
Medullary cord
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Several other organs contribute to lymphatic
function:
◦
◦
◦
◦
Spleen
Thymus
Tonsils
Peyer’s patches
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Tonsils (in
pharyngeal region)
Thymus (in thorax;
most active during
youth)
Spleen (curves
around left side of
stomach)
Peyer’s patches
(in intestine)
Appendix
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left side of the abdomen, beneath diaphragm,
around the stomach
Functions:
◦ Filters pathogenic debris from blood
◦ Destroys worn-out red blood cells
 Iron is reused for hemoglobin mfr.
 Remainder is secreted in bile
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Acts as a platelet reservoir
Site of hematopoesis in the fetus
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Located low in the throat, just under the
sternum
Function:
◦ (at peak levels only during childhood)
◦ Produces hormones (such as thymosin)
 hormones cause T lymphocytes to gain
immunocompetency
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masses of lymphoid tissue around the
pharynx
◦ Palatine tonsils are most often infected
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Trap and remove bacteria/foreign materials
Tonsillitis -caused by congestion with
bacteria
The ability of the tonsils to trap bacteria
generates a wide variety of memory
lymphocytes that protect throughout life
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Found in the wall of the small intestine and
appendix
Resemble tonsils in structure
Capture and destroy bacteria in the intestine
◦ Prevent bacteria from getting into blood here
◦ Generate memory lymphocytes for long-term
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Includes:
◦ Peyer’s patches
◦ Tonsils
◦ Other small accumulations of lymphoid tissue
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Acts as a sentinel to protect respiratory and
digestive tracts
© 2015 Pearson Education, Inc.