Transcript Chapter 20 - Lymphatic System BIOL 2304 Fall 2008 Chapter 20 functions of lymphatic system: prevents edema by removing extra fluid and proteins from.

Chapter 20 - Lymphatic System
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functions of lymphatic system:
prevents edema by removing extra fluid and
proteins from the tissues and returning them
to the blood
immune surveillance
cells located in the lymph nodes monitor
lymph for pathogens and cancer cells and
initiate immune responses if any are
detected
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the lymphatic system consists of:
various sizes of lymphatic vessels that pick
up and transport fluid
lymph, the fluid that is being transported
lymphoid tissues and organs that are
located along the lymphatic vessels and that
help provide immunity to disease
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A. lymphatic vessels (p. 596)
1. lymph capillaries
• smallest lymph vessels
• found in loose c.t. near vascular capillaries
(except in the CNS
or bone marrow)
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• the capillary wall is made of a single layer of
endothelial cells that overlap and are very loosely
connected
• the capillaries are blind-ended (unlike vascular
capillaries that have two ends: in and out)
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• fluid enters lymph capillaries when tissue fluid
pressure is high
• the overlapping cells let the fluid go in but not back
out
• pathogens and cancer cells hanging around in the
tissues also enter lymph capillaries and are
transported to the blood (as they pass through lymph
nodes they “alert” the immune system to their
presence)
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2. lymphatic collecting vessels
 each one “collects” lymph from many lymphatic
capillaries
 found beside veins and arteries
 walls similar to veins but thinner
 have many valves that prevent backflow
3. lymph trunks
 each collects lymph from several collecting vessels
 each drains a large area of the body (example:
jugular trunks drain neck and head)
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4. lymph ducts = largest lymphatic vessels
see diagram in textbook on page 597 and 599
a. right lymphatic duct drains right arm, head and neck
 enters the junction of the right internal jugular and
subclavian veins
b. thoracic duct drains rest of body
 enters the junction of the left internal jugular and
subclavian veins
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meet “lymph guy” (p. 597)
he shows you the
parts of the body
drained by the
lymphatic ducts
• green-right duct
• tan-thoracic duct
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B. lymphoid organs (lymph nodes, spleen, MALT)
lymphoid tissue functions:
activation of lymphocytes
immunocompetent B and T lymphocytes spread to lymphoid
tissue and wait until the foreign antigen they can recognize
activates them and starts an immune response
generation of memory cells
once a B or T cell is activated, it clones (makes millions of
identical copies); some of the clones fight the infection and
most die off, but some stick around and wait in case the
same foreign antigen gets into the body again—these are
called memory cells
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lymphoid tissue is a special type of c.t. containing:
reticular cells (fibroblasts) and reticular fibers
that form the framework of the organ
T and B lymphocytes that are
immunocompetent
macrophages
all lymphoid tissue contains lymphatic follicles
(also called lymphatic nodules)
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a lymphatic follicle (nodule)
 is a cluster of lymphocytes derived from a single
activated B cell
 has a lighter-staining germinal center, the zone
where mitosis is occurring
 the cloned B cells
differentiate into plasma
cells and leave the
nodule to make
antibodies
(p. 598)
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1. lymph node or gland (p. 597)
a. location
clusters are found in some areas of the body
and all along lymphatic collecting vessels
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b. structure (p. 598)
1 to 25 mm in diameter
surrounded by fibrous capsule which extends
inwards as trabeculae
hilus = indentation on one side
outer cortex contains follicles or nodules
inner medulla contains medullary cords (B
and T cells)
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afferent lymphatic vessels enter on convex
side
inside the node, lymph flows through lymph
sinuses (large lymphatic capillaries) and
leaves through:
efferent lymphatic vessels exit at hilus
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c. functions of a lymph node
monitor lymph
destroy infectious microorganisms and cancer
cells
store memory cells
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2. spleen (p. 605, 607)
 located posterior and lateral to the stomach
 outer fibrous capsule
 splenic artery branches into central arteries
that enter the spleen at the hilus
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 white pulp = lymphoid tissue that surrounds arteries,
destroys blood-borne antigens
 red pulp surrounds white pulp and contains venous
sinuses and splenic cords (reticular tissue rich in
macrophages that remove old blood cells)
 other function: to store platelets
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3. MALT - mucosa associated lymphoid tissue
 aggregated lymph nodules found in mucosa of the
respiratory, digestive, urinary and reproductive tracts
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a. tonsils (p. 608, 616)
 consist of lymphatic tissue in the mucosa of the
pharynx
 surface covered by epithelium that invaginates to
form crypts that trap bacteria
 generate memory
lymphocytes
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pharyngeal tonsil is in the
nasopharynx on the back wall
tubal tonsils surround openings
of auditory tubes in nasopharynx
palatine tonsils are on the lateral
sides of the opening from the
mouth into the pharynx
lingual tonsils are on the posterior
surface of the tongue
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b. GALT (gut) (p. 609)
 Peyer's patches in ileum
 vermiform appendix
c. BALT (bronchioles)
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C. thymus (p. 606)
does not contain lymphoid tissue or B cells
1. location
 posterior to sternum
 superior to heart
2. structure
 2 lobes, each divided into smaller lobules
 cortex generates antigen specific T lymphocytes
 medulla involved in immune tolerance (destroys T
cells that would attack normal body cells)
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 epithelial reticular cells secrete thymic hormones
(thymosin and thymopoietin) that cause T cells to
become immunocompetent
 most active during childhood
 begins to atrophy in adolescence
 replaced by fibrous and fatty tissue
 protected by a thymus-blood barrier that keeps
antigens out
cortex
medulla
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3. function
 programs lymphocytes to become immunocompetent
T cells
 has no direct immune function
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