Transcript Ch 20 Lymph Lecture

PowerPoint® Lecture Slides
prepared by
Janice Meeking,
Mount Royal College
CHAPTER
20
The Lymphatic
System and
Lymphoid
Organs and
Tissues
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Lymphatic System
•
Consists of three parts
1. A network of lymphatic vessels (lymphatics)
2. Lymph (fluid inside vessels)
3. Lymph nodes (cleanse the lymph)
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Lymphatic System: Functions
• Returns interstitial fluid and leaked plasma
proteins back to the blood
• Carry absorbed fat from intestine to the blood
(through lacteals)
• Once interstitial fluid enters lymphatics, it is
called lymph
• Together with lymphoid organs and tissues,
provide the structural basis of the immune
system
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Lymphatic Vessels
• One-way system, lymph flows toward the
heart
• Lymph vessels (lymphatics) include:
• Lymphatic capillaries
• Lymphatic collecting vessels
• Lymphatic trunks and ducts
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Venous system
Heart
Arterial system
Lymphatic
system:
Lymph duct
Lymph trunk
Lymph node
Lymphatic
collecting vessels,
with valves
Tissue
fluid
Blood
capillaries
Lymphatic
capillary
Tissue cell
Blood
capillaries
Lymphatic
capillaries
(a) Structural relationship between a
capillary bed of the blood vascular
system and lymphatic capillaries.
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Lymphatic Capillaries
• Similar to blood capillaries, except
• Very permeable (take up cell debris,
pathogens, and cancer cells)
• Endothelial cells overlap to form one-way
minivalves, and are anchored by collagen
filaments, preventing collapse of capillaries
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Lymphatic Capillaries
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.
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Lymphatic Capillaries
• Absent from bones, teeth, bone marrow and
the CNS
• Lacteals: specialized lymph capillaries present
in intestinal mucosa
• Absorb digested fat and deliver fatty lymph
(chyle) to the blood
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Lymphatic Collecting Vessels
• Similar to veins, except
• Have thinner walls, with more internal valves
• Anastomose more frequently
• Superficial collecting vessels
• in the skin, travel with superficial veins
• Deep collecting vessels travel with arteries
• Nutrients are supplied from branching vasa
vasorum
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Lymphatic Ducts
• Lymph is delivered into one of two large ducts
• Right lymphatic duct drains the right upper arm
and the right side of the head and thorax
• Thoracic duct arises from the cisterna chyli
and drains the rest of the body
• Each empties lymph into venous circulation at
the junction of the internal jugular and
subclavian veins on its own side of the body
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Cisterna Chyli
• Located anterior to L1, L2
• Collects lymph from lower limbs and from the
intestinal trunk that drains the digestive organs
• In the intestines, specialized lymphatic
capillaries called lacteals that transport
absorbed fat from the small intestine to the
blood stream
• Fatty lymph is called chyle
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Regional
lymph nodes:
Cervical nodes
Internal jugular vein
Entrance of right
lymphatic duct into vein
Entrance of thoracic
duct into vein
Axillary nodes
Thoracic duct
Cisterna chyli
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.
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Figure 20.2a
Right jugular trunk
Right lymphatic duct
Right subclavian trunk
Right subclavian vein
Right bronchomediastinal trunk
Brachiocephalic veins
Superior vena cava
Azygos vein
Internal jugular veins
Esophagus
Trachea
Left subclavian trunk
Left jugular trunk
Left subclavian vein
Entrance of thoracic
duct into vein
Left bronchomediastinal
trunk
Ribs
Thoracic duct
Hemiazygos vein
Cisterna chyli
Right lumbar trunk
Left lumbar trunk
Inferior vena cava
Intestinal trunk
(b) Major lymphatic trunks and ducts in relation to veins and
surrounding structures. Anterior view of thoracic and abdominal wall.
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Figure 20.2b
Lymph Transport
• Lymph is propelled by
• Pulsations of nearby arteries
• Contractions of smooth muscle in the walls of
the lymphatics
• Skeletal muscle contraction
• Breathing
• Lymph movement is very slow and it depends
on movement of adjacent tissues
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Lymphoid Cells
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Lymphoid Cells
• Lymphocytes arise in red bone marrow and
mature into 1 of 2 main varieties
• T cells (T lymphocytes)
• B cells (B lymphocytes)
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Lymphocytes
• T cells and B cells protect against antigens
• Antigens are anything that the body perceives
as foreign
• These antigens will provoke an immune
response
• Bacteria and their toxins; viruses
• Mismatched RBCs or cancer cells
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Lymphocytes
• T cells
• Manage the immune response
• Attack and destroy foreign cells
• B cells
• Produce plasma cells, which secrete
antibodies
• Antibodies bind to antigens and mark cells for
destruction
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Other Lymphoid Cells
• Macrophages phagocytize foreign substances
and help activate T cells
• Dendritic cells capture antigens and deliver
them to lymph nodes
• Reticular cells produce stroma that supports
other cells in lymphoid organs (structural
cells)
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Macrophage
Reticular cells on
reticular fibers
Lymphocytes
Medullary sinus
Reticular fiber
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Figure 20.3
Types of Lymphoid Tissue
• Diffuse lymphoid tissue
• Lymphoid follicles (or nodes)
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Diffuse Lymphoid Tissue
• Loose arrangement of lymphoid cells and
some reticular fibers
• Found in virtually every body organ
• Larger collections appear in mucous
membrane areas, like the GI and respiratory
tract
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Lymph Nodes
• Principal lymphoid organs of the body
• Embedded in connective tissue, in clusters
along lymphatic vessels
• Near the body surface in inguinal, axillary, and
cervical regions of the body
• These are clinically important, as they are
palpable on PE
• Firm, somewhat rubbery non-fixed mass the
size of a pea or larger
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Regional
lymph nodes:
Cervical nodes
Internal jugular vein
Entrance of right
lymphatic duct into vein
Entrance of thoracic
duct into vein
Axillary nodes
Thoracic duct
Cisterna chyli
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.
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Figure 20.2a
Lymph Nodes
•
Functions
1. Filter lymph—macrophages destroy
microorganisms and debris
2. Immune system—lymphocytes are activated
and mount an attack against antigens
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Structure of a Lymph Node
• Surrounded by a dense, fibrous capsule, from
which connective tissue strands called
trabeculae extend inward dividing the node
into compartments (follicles)
• 2 histologically distinct regions
• Cortex
• Superficial and deep
• Medulla
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Structure of a Lymph Node
• Cortex
• Superficial
• Made up of follicles with germinal centers
where B cells divide and proliferate
• Deep
• houses T cells
• T cells circulate continuously between the
blood, lymph nodes, and lymph, performing
their surveillance role
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Structure of a Lymph Node
• Medulla
• Medullary cords are thin inward extensions
from the cortical lymphoid tissue and contain
both types of lymphocytes
• Lymph sinuses
• Large lymph capillaries where macrophages
reside and phagocytize foreign matter in the
lymph as it flows by in the sinuses
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Circulation in the Lymph Node
• Lymph enters through many afferent vessels
on convex side  large subcapsular sinus 
smaller sinuses that cut through the cortex 
medullary sinuses  exits node at hilum
(indented region on concave side) with few
efferent vessels
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Circulation in the Lymph Node
• Less efferent vessels, so the flow of lymph
stagnates somewhat, allowing time for
lymphocytes and macrophages to work
• Lymph passes through several nodes before it
is cleansed
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Afferent lymphatic
vessels
Cortex
• Lymphoid follicle
• Germinal center
• Subcapsular sinus
Efferent lymphatic
vessels
Hilum
Medulla:
• Medullary cord
• Medullary sinus
Trabeculae
Capsule
(a) Longitudinal view of the internal structure of a lymph
node and associated lymphatics
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Figure 20.4a
Follicles
Trabecula
Subcapsular sinus
Capsule
Medullary cords
Medullary sinuses
(b) Photomicrograph of part of a lymph node (72x)
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Figure 20.4b
Spleen
• Largest lymphoid organ, size of a fist
• Located in the left side of the abdominal
cavity, just beneath the diaphragm, lateral to
the stomach
• Blood supply
• Splenic artery and vein that enter and exit the
hilum (concave anterior surface)
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Diaphragm
Spleen
Adrenal
gland
Left
kidney
Splenic
artery
Pancreas
(c) Photograph of the spleen in its normal position
in the abdominal cavity, anterior view.
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Figure 20.6c
Spleen Function
• Functions
• Site of lymphocyte proliferation and immune
surveillance and response
• Cleanses the blood of aged cells and platelets
and debris
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Spleen
• Stores breakdown products of RBCs (e.g.,
iron) for later reuse
• Releases other breakdown products to the
blood for processing in the liver
• Stores blood platelets and monocytes to be
released when needed
• Contains lymphocytes, macrophages, and
huge numbers of erythrocytes
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Histological Structure of the Spleen
• Has a fibrous capsule and trabeculae
• Two distinct areas
• White pulp
• Red pulp
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Histological Structure of Spleen
• White Pulp
• Where immune function takes place
• Composed mostly of lymphocytes
suspended on reticular fibers
• White pulp forms clusters around central
arteries (small branches of the splenic
artery) and form what appear to be islands
in a sea of red pulp
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Histological Structure of the Spleen
• Red Pulp
• Where worn out RBCs and bloodborne
pathogens are destroyed
• Contains lots of RBCs and macrophages that
engulf the RBCs
• Consists of splenic tissue that is not white pulp
(the rest of the spleen)
• Splenic sinuses (venous sinuses)
• Splenic cords (reticular CT that separates
splenic sinuses)
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Thymus
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Thymus
• Size with age
• In infants, it is found in the inferior neck and
extends into the mediastinum, where it partially
overlies the heart
• Increases in size and is most active during
childhood
• Stops growing during adolescence and then
gradually atrophies
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Thymus
• T lymphocyte precursors mature into T
lymphocytes
• Even though the gland atrophies, it continues
to produce immunocompetent cells as we
age, though at a declining rate
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MALT
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MALT
• Mucosa-associated lymphoid tissue (MALT)
• Lymphoid tissues present in all mucous
membranes of the body
• Function: filter and remove potential
pathogens
• Largest groupings are tonsils, Peyer’s patches
in small intestine, and appendix
• Also present in the mucosa of the respiratory
tract (bronchi), genitourinary (GU) organs and
the rest of the GI tract
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Tonsils
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Tonsils
• Simplest lymphoid organs
• Form a ring of lymphatic tissue around the pharynx
• Palatine tonsils
• Located on either side at the posterior end of the
oral cavity. Largest of the three types
• Lingual tonsils
• Located at the base of the tongue. Look lumpy.
• Pharyngeal tonsil
• Posterior wall of the nasopharynx
• Aka adenoids
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Tonsils
• Function
• Gather and remove pathogens entering the
pharynx in food or inhaled air
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Pharyngeal tonsil
Palatine tonsil
Lingual tonsil
Tonsil
Tonsillar crypt
Germinal centers
in lymphoid follicles
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Figure 20.8
Peyer’s Patches
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Peyer’s Patches
• Peyer’s patches
• Clusters of lymphoid follicles
• In the wall of the distal portion of the small intestine
• Small intestine does most of the filtration and
absorption of food, so it is important to have
lymphoid tissue present to help filter out the
pathogens/undesirable materials unwanted in the
bloodstream
• Destroy bacteria, preventing them from breaching the
intestinal wall
• Generate “memory” lymphocytes for long term
immunity
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Lymphoid nodules
(follicles) of
Peyer’s patch
Smooth muscle in
the intestinal wall
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Figure 20.9
Appendix
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Appendix
• Appendix
• Tubular offshoot of the first part of the large intestine
• Contains high concentration of lymphoid follicles
• Destroy bacteria, preventing them from breaching the
intestinal wall
• Generate “memory” lymphocytes for long term
immunity
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REVIEW
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Lymphatic vessels:
a. collect excess fluid from interstitial spaces.
b. drain blood from lymph nodes.
c. are part of the venous system.
d. are built like arteries.
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Lymphatic capillaries owe their permeability
to the presence of:
a. an open end that siphons fluid from the
interstitial fluid.
b. minivalves in their walls.
c. tight junctions between adjacent cells.
d. proteins in the lymph fluid.
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Why would removal of lymph vessels from
the right axillary region cause edema in the
right arm?
a. Excess blood plasma builds up in regions
where there are no lymph vessels.
b. Surgery always results in tissue swelling.
c. Blood is inefficiently circulated in areas
where surgery has occurred.
d. Both b and c are true.
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Which of the following represents a logical sequence
of structures that contribute to the return of fluid into
the blood via the lymphatic system?
a. Blood capillaries, arteries, lymphatic
vessels, subclavian vein
b. Arteries, lymphatic vessels, blood
capillaries, subclavian vein
c. Arteries, blood capillaries, lymphatic
vessels, subclavian vein
d. Subclavian vein, arteries, blood capillaries,
lymphatic vessels
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Which of the following contribute(s) to the
flow of lymph through lymphatic vessels?
a. The pumping of the heart
b. The milking action of skeletal muscle
contraction
c. Pressure changes in the thorax that result
from breathing
d. Both b and c
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Which of the following would the body
perceive as an antigen?
a. Bacteria
b. Virus
c. Mismatched red blood cell
d. All of the above
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An advantage to having reticular connective
tissue present in lymph nodes would be
that:
a. the loose organization of reticular connective
tissue provides niches for macrophages and
lymphocytes.
b. lymph filters through the nodes and is
exposed to lymphocytes and macrophages.
c. lymphocytes cycle to various areas of the
body and back to lymph nodes.
d. all of the above take place.
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The highest density of lymph nodes can be
found ________.
a. in the arms and legs
b. in the brain
c. at the locations where lymphatic collecting
vessels converge
d. in the intestines
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Lymph tends to stall inside lymph nodes.
This is due to:
a. small-diameter spaces within the medulla.
b. the large volume of lymph entering the node.
c. fewer efferent lymphatic vessels than
afferent lymphatic vessels.
d. fewer afferent lymphatic vessels than
efferent lymphatic vessels.
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_________ can enter lymph capillaries.
a. Bacteria
b. Large proteins
c. Interstitial fluid
d. All of the above
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The ______ is the largest lymphoid organ.
a. lymph node
b. Spleen
c. Thymus
d. tonsil
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Red pulp of the spleen is most concerned
with _______, while white pulp is most
concerned with _________.
a. immunity; new red blood cell formation
b. filtering lymph; T lymphocyte formation
c. blood filtering; immunity
d. urine formation; blood filtering
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Which of the following lymphoid tissues
removes defective red blood cells from the
blood?
a. Lymph node
b. Thymus
c. Spleen
d. Peyer’s patches
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The thymus is important for:
a. T lymphocyte maturation.
b. removal of foreign antigens.
c. B lymphocyte maturation.
d. secretion of hormones that promote B
lymphocyte immunocompetence.
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Tonsils promote memory of pathogens by:
a. secreting antibodies into the blood.
b. trapping food particles to support bacterial
growth.
c. trapping pathogens to develop immune cells
with memory.
d. producing B lymphocytes.
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