Chapter 24
*Lecture Outline
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Chapter 24 Outline
• Functions of the Lymphatic
System
• Lymph and Lymph Vessels
• Lymphatic Cells
• Lymphatic Structures
• Aging and the Lymphatic System
• Development of the Lymphatic
System
Functions
1. Return interstitial fluid back to the
bloodstream
2. Transport lipids and lipid-soluble vitamins
into the bloodstream
3. Production and maturation of
lymphocytes
4. Generate an immune response against
antigens in the interstitial fluid
Figure 24.1
Components of the
Lymphatic System
1.
2.
3.
4.
5.
6.
7.
8.
Lymph
Lymphatic capillaries
Lymphatic vessels
Lymphatic trunks
Lymphatic ducts
Lymphatic cells
Lymphatic nodules
Lymphatic organs
Lymph
Lymph is comprised of:
• Interstitial fluid
• Solutes
• Foreign materials
Lymphatic Capillaries
• Lymphatic capillaries are closed-ended
tubes that are found interspersed among
most blood capillary beds.
• They resemble blood capillaries but they
have overlapping endothelial cells that act
as one-way valves allowing interstitial fluid
a one-way entrance into lymphatic
capillaries.
Lymphatic Capillaries
Figure 24.2
Lymphatic Capillaries
• The gastrointestinal tract contains
specialized lymph capillaries
called lacteals that collect not
only interstitial fluid, but also lipids
and lipid-soluble vitamins.
• The lymph collected from the
gastrointestinal system has a
milky color due to the lipid
absorption and is called chyle.
Lymphatic Vessels
• Lymphatic capillaries merge to form
lymphatic vessels.
• They resemble venules, in that they have
components of all three vascular tunics
and possess valves similar to veins.
• Afferent lymphatic vessels bring
lymph to a lymph node.
• Efferent lymphatic vessels transport
filtered lymph away from the lymph node.
Lymphatic Vessels and Valves
Figure 24.3
Lymphatic Trunks
Left and right lymphatic trunks form from merging
lymphatic vessels. Each trunk drains lymph from a
specific region of the body, as follows:
1. Jugular trunks—head and neck
2. Subclavian trunks—upper limbs, breasts and
superficial thoracic wall
3. Bronchiomediastinal trunks—deep thoracic
structures
4. Intestinal trunks—most abdominal structures
5. Lumbar trunks—lower limbs, abdominopelvic
wall and pelvic organs
Lymphatic Trunks
Figure 24.4
Lymphatic Ducts
• Lymphatic ducts are formed from the fusion of
lymphatic trunks.
• The right lymphatic duct is located deep to the
right clavicle and returns lymph at the junction of
the right subclavian and internal jugular veins.
• The right lymphatic duct returns lymph from the
right side of the head and neck, right upper limb
and the right side of the thorax.
Lymphatic Ducts
• The thoracic duct is the largest lymphatic
vessel.
• It begins just inferior to the diaphragm as a
rounded saclike structure called the cisterna
chyli.
• The thoracic duct collects lymph from most of
the body (excluding the right lymphatic duct
drainage).
• The thoracic duct passes through the aortic
opening of the diaphragm and returns lymph into
the junction between the left subclavian and
internal jugular veins.
Lymphatic Ducts
Figure 24.4
Thoracic Duct
Figure 24.4
Lymphatic Cells
There are several types of lymphatic cells
that are located in the lymphatic and
circulatory systems:
• Macrophages=Monocytes (leukocytes)
• Nurse cells=Epithelial at Thymus
• Dendritic cells=Epithelial at L. Nodules
• Lymphocytes=Most abundant
Types of Lymphocytes
•
The body contains three types of
lymphocytes:
1. T-lymphocytes (T-cells)
2. B-lymphocytes (B-cells)
3. Natural killer (NK cells)
•
All three cell types migrate through the
lymphatic system and search for the
presence of antigens.
T-Lymphocytes
•
•
•
Make up about 70–85% of body
lymphocytes
They express a plasma membrane
coreceptor (CD) that can recognize a
particular antigen
There are several types of T-lymphocytes;
two main groups are:
– helper T-lymphocytes
– cytotoxic T-lymphocytes
Helper T-Lymphocytes
•
•
•
Primarily contain the CD4 coreceptor and
are referred to as CD4+ cells or T4 cells
Many types of T4 cells, each one
responds to a different antigen
T4 cells initiate and oversee the immune
response in two ways:
–
–
present the antigen to other lymphocytes
secrete cytokines, which are hormones
that activate other lymphatic cells
Cytotoxic T-Lymphocytes
• Also called CD8+ cells or T8 cells, they
contain the CD8 coreceptor
• Come in direct contact with infected or
foreign cells and kill them
• Act only after activated by a helper Tlymphocyte that presents an antigen to it
Immune Response of T-Lymphocytes
Figure 24.5
B-Lymphocytes
• Make up about 15–30% of body
lymphocytes
• Contain antigen receptors to only one
antigen and produce immunoglobulins or
antibodies to that single antigen
• B-lymphocytes become activated when
presented with an antigen from a helper
T-lymphocyte
B-Lymphocytes
• Most of the activated B-lymphocytes become
plasma cells that produce and secrete large
amounts of antibodies.
• Plasma cells may be either short-lived (less than
a week) or long-lived (months or years).
• The long-lived B-lymphocytes are called
memory B-lymphocytes and confer years or
lifetime immunity to certain antigens.
B-Lymphocytes and Their Role
in the Immune Response
Figure 24.6
NK (Natural Killer) Cells
• Also called large granular lymphocytes
• Relatively small percentage of all
lymphocytes
• Tend to express the CD16 receptors
• Unlike T-cells and B-cells that respond to
one antigen, NK cells can kill a wide
variety of infected cells and some
cancerous cells
Types of Lymphocytes
Lymphopoiesis
• Lymphopoiesis is the process of
lymphocyte development.
• The final result of lymphopoiesis is that the
lymphocyte becomes immunocompetent,
meaning the cell can participate in the
immune response.
• All lymphocytes originate in the red bone
marrow but their maturation sites differ.
Lymphopoiesis
Figure 24.7
Lymphatic Nodules
• Oval clusters of lymphatic cells with some
extracellular matrix but not surrounded by a
connective tissue capsule
• Center of nodule is called the germinal center;
contains proliferating B-lymphocytes and
macrophages
• T-lymphocytes located outside the germinal
center
• Lymphatic nodules filter and attack antigens
MALT(Mucosa-Associated
Lymphatic Tissue)
• Lymphatic nodules located in the mucosa
of the gastrointestinal, respiratory, genital,
and urinary tracts
• These nodules monitor and respond to
antigens that may enter these tracts
• MALT is very prominent in the ileum;
these nodules are called Peyer patches
MALT in Small Intestine
Figure 24.8
Tonsils
• Located mainly in the pharynx
• Large clusters of lymphatic cells and
extracellular matrix that do not have a
completed surrounding capsule
• Outer edges are invaginated to form
crypts, which allow for trapping of antigens
to be presented to the lymphocytes
Tonsils
Figure 24.8
Tonsils
There are three types of tonsils:
1. Pharyngeal tonsils (adenoids)—located
in the posterosuperior wall of the
nasopharynx
2. Palatine tonsils—located in the
posterolateral wall of the oral cavity
3. Lingual tonsils—located along the
posterior one-third of the tongue
Lymphatic Organs
•
•
Consists of lymphatic cells and
extracellular matrix and is completely
surrounded by a connective tissue
capsule
The main lymphatic organs are:
–
–
–
thymus
lymph nodes
spleen
Thymus
• Bilobed organ located superficial to the heart
• Consists of two fused thymic lobes, which are
divided into lobules
• Each lobule has an outer cortex and an inner
medulla
• Continues to grow until puberty and then begins
to regress in size and function and, in adults, it
becomes replaced mostly by adipose connective
tissue
Thymus
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Trabecula
Thyroid gland
Right
lung
Left lung
Thymus
Capsule
Cortex
Lobule
Medulla
Heart
Diaphragm
LM 20x
(b) Child’s thymus
(a) Child’s thorax, anterior view
Lymphocytes
Thymic
corpuscle
Epithelial cells
LM 320x
(c) Thymic corpuscle
b,c: © The McGraw-Hill Companies, Inc./Photo by Dr. Alvin Telser
Figure 24.9
Function of Thymus
• Site of T-lymphocyte differentiation and
maturation
• Cortex contains immature T-lymphocytes
• Medulla contains mature T-lymphocytes
• In adulthood, T-lymphocytes can only be
produced by cell division and not by the
maturation of new cells in the thymus
Lymph Nodes
• Small, round or oval structures located
along the pathway of lymph vessels
• Typically found in clusters ranging from
1–25 mm in diameter
• The primary function of a lymph node is to
filter antigens from the lymph and initiate
an immune response
Lymph Nodes
• Most apparent lymph node clusters occur
as:
–
–
–
axillary lymph nodes
inguinal lymph nodes
cervical lymph nodes
Major Lymph Node Aggregations
Figure 24.1
Structure of Lymph Nodes
• Surrounded by a tough connective tissue
capsule
• Internal extensions of the capsule,
trabeculae, project into the node
• Lymphatic cells surround the trabeculae
and lymphatic sinuses provide a pathway
for lymph flow
Structure of Lymph Nodes
• Lymph node is divided into outer cortex and
inner medulla
• Cortex consists of nodules and sinuses called
cortical sinuses
• The medulla contains medullary cords and
medullary sinuses
• Afferent vessels deliver lymph to the node
• Lymph exits nodes via efferent vessels at an
indentation of the node called the hilum
Structure of Lymph Node
Figure 24.10
Spleen
There are several functions of the spleen:
1. Initiates an immune response when antigens
are found in blood (white pulp function)
2. Serves as a reservoir for erythrocytes and
platelets (red pulp function)
3. Phagocytizes old, defective erythrocytes and
platelets (red pulp function)
4. Phagocytizes bacteria and other foreign
materials
Spleen
• Largest lymphatic organ in body just
lateral to left kidney
• A splenic artery/vein enter/leave the
spleen via a hilum or indentation on its
medial surface
• Spleen surrounded by a dense irregular
connective tissue capsule, which sends
extensions called trabeculae into the
organ
Structure of Spleen
Figure 24.11
Spleen
• Trabecular vessels (branches of splenic
arteries and veins) extend within the
trabeculae.
• Cells around the trabeculae are
subdivided into white pulp and red pulp.
• Red pulp surrounds each cluster of white
pulp.
Red and White Pulp of Spleen
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Central artery
White pulp
Red pulp
Splenic
sinusoids
Trabecula
Splenic cords
Capsule
(b) Red and white pulp of spleen
Trabeculae
Red pulp
Central artery
White pulp
Capsule
LM 40x
Figure 24.11
(c) Histology of spleen
c: © The McGraw-Hill Companies, Inc./Photo by Dr. Alvin Telser
Red and White Pulp of Spleen
• The white pulp is associated with the arterial supply and
consists of T- and B-lymphocytes and macrophages.
• In the center of each cluster is a central artery.
• The red pulp is associated with the venous supply.
• Red pulp consists of splenic cords and splenic
sinusoids that contain erythrocytes, platelets,
macrophages, and some plasma cells.
• Blood cells can easily enter and leave the blood stream
in the spleen because of the discontinuous basal lamina
of the capillaries in the splenic sinusoids.
Lymphatic Structures
and Organs
Development of the Lymphatic System
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Jugular lymph sacs
Retroperitoneal lymph sac
Cisterna chyli
Posterior lymph sacs
(a) Week 6: Primary lymph sacs form
Developing
right lymphatic duct
Jugular lymph sac
Jugular
lymph sac
Superior vena cava
Superior vena cava
Developing
thoracic duct
Developing thoracic duct
Cisterna chyli
Figure 24.12
Posterior
lymph sac
(b) Week 9: Lymph vessels connect
to the lymph sacs
Cisterna chyli
Posterior
lymph sac
(c) Fetal period: Right lymphatic and thoracic ducts
form; lymph sacs will form lymph nodes
Development of the Thymus
Figure 24.13