Human Anatomy

1. © 2012 Pearson Education, Inc.
23
The Lymphoid System
PowerPoint®
Lecture Presentations prepared by
Steven Bassett
Southeast Community College
Lincoln, Nebraska

2. © 2012 Pearson Education, Inc.
Introduction
The lymphoid system
 Lymphatic vessels
 Lymph (fluid connective tissue)
 Lymphoid tissues
 Diffuse lymphoid tissues
 Lymph nodule
 Lymphoid organs
 Lymph node
 Thymus: most active during infancy and youth.
 Spleen (the largest organ of the lymphatic system)
Plays central role in body’s defenses against viruses, bacteria, and
other microorganisms
Lymphatic vessels originate in peripheral tissues and deliver lymph to
the venous system.

3. © 2012 Pearson Education, Inc.
An Overview of the Lymphoid System
Lymph consists of:
 Interstitial fluid, which resembles blood
plasma, but with a lower concentration of
proteins
 Lymphocytes, cells responsible for the
immune response
 Macrophages of various types

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Functions of the lymphatic system
Primary functions of the lymphoid system:
 Produce, maintain, and distribute lymphocytes
 Maintain normal blood volume and eliminate
local variations in the chemical composition of
the interstitial fluid
 Provide an alternative route for the transport of
hormones, nutrients, and waste products

5. © 2012 Pearson Education, Inc.
Figure 23.2a Lymphatic Capillaries
A three-dimensional view of the association
of blood capillaries and lymphatic capillaries.
Arrows show the direction of blood,
interstitial fluid, and lymph movement.
Loose
connective
tissue
Endothelial
cells
Lymph
flow
Interstitial
fluid
Venule
Smooth
muscle
Blood
capillaries
Arteriole
Lymphatic
capillary

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Structure of Lymphatic Vessels
 Lymphatic capillaries (or terminal lymphatics) form a complex
network within peripheral tissues.
 Lymphatics contain internal valves that prevent backflow of
lymph.
 Lymphatic vessels (or lymphatics) carry lymph from peripheral
tissues to the venous system.
 The right lymphatic duct receives lymph from the right side of
the thorax.
 The rest of the body’s lymph (most of the lymph) returns to
the venous system through thoracic duct. Thoracic duct joins
the left subclavian vein at the junction of left internal jugular
vein.
 Large lymphatic trunks are located in the posterior thoracic and
abdominal wall.

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Figure 23.2b Lymphatic Capillaries
Sectional view through a cluster of lymphatic capillaries
Incomplete
basal lamina
Lymph
flow
Loose
connective
tissue
Lymphocyte
To larger
lymphatics
Interstitial
fluid
Interstitial fluid
Blood
capillary
Lymphatic
capillary

8. © 2012 Pearson Education, Inc.
Figure 23.3ac Lymphatic Vessels and Valves
The cross-sectional view emphasizes
the structural differences between
blood vessels and lymphatic vessels.
Lymphatic
vessel
Vein
Artery
Toward
venous
system
Lymphatic
valve
Lymphatic
vessel
From lymphatic
capillaries
Artery
Vein
A diagrammatic view of loose connective
tissue showing small blood vessels and
a lymphatic vessel. Arrows indicate the
direction of lymph flow.

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Structure of Lymphatic Vessels
Two sets of lymphatic vessels:
 Superficial lymphatic vessels travel with superficial
veins
 The subcutaneous layer next to the skin
 The loose connective tissues of the mucous membranes
 The loose connective tissues of the serous membranes
 Deep lymphatic vessels are large lymphatic vessels
that accompany the deep arteries and veins.
 Collect lymph from skeletal muscles and other organs of the
neck, limbs, and trunk, as well as visceral organs in the
thoracic and abdominopelvic cavities

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Figure 23.1 Lymphoid System
Tonsil
Cervical
lymph nodes
Right lymphatic duct
Thymus
Thoracic duct
Cisterna chyli
Lumbar
lymph nodes
Lymphatics
of lower
limb
Lymphatics
of upper limb
Axillary lymph nodes
Thoracic (left lymphatic) duct
Lymphatics of mammary gland
Spleen
Mucosa-associated lymphoid
tissue (MALT)
Pelvic
lymph nodes
Inguinal
lymph nodes

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Figure 23.4a Lymphatic Ducts and Lymphatic Drainage
The collecting system of lymph vessels, lymph nodes, and major lymphatic
collecting ducts and their relationship to the brachiocephalic veins
Right lumbar trunk
Inferior vena cava
(cut)
Azygos vein
Rib (cut)
Superior
vena cava (cut)
Right bronchomediastinal
trunk
Right subclavian vein
Right internal jugular vein
Right jugular trunk
Right lymphatic duct
Right subclavian trunk
Brachiocephalic veins
Left internal jugular vein
Left jugular trunk
Thoracic duct
Left subclavian trunk
Left bronchomediastinal
trunk
Left subclavian
vein
First rib
(cut)
Highest
intercostal
vein
Thoracic
duct
Thoracic
lymph nodes
Hemiazygos
vein
Parietal
pleura (cut)
Diaphragm
Cisterna chyli
Intestinal trunk
Left lumbar trunk

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Figure 23.4b Lymphatic Ducts and Lymphatic Drainage
The thoracic duct collects lymph
from tissues inferior to the
diaphragm and from the left side of
the upper body. The right lymphatic
duct drains the right half of the
body superior to the diaphragm.
Drainage
of thoracic
duct
Drainage
of right
lymphatic
duct

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Lymphocytes
Lymphocytes are the primary cells of the
Lymphoid system, and they are responsible for
specific immunity.
They respond to the presence of
 Invading organisms, such as bacteria and viruses
 Abnormal body cells, such as virus-infected cells or
cancer cells
 Foreign proteins, such as the toxins released by some
bacteria

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Lynphocytes
Three different classes of lymphocytes in the blood:
 T cells (thymus dependent)
 Cytotoxic T cells
 Helper T cells
 Suppressor T cells
 Memory T cells
 B cells (bone marrow derived)
 Plasma cells (providing humoral immunity)
 Memory B cells (stay in the body to fight off the second time
infection easier)
 NK cells (natural killer)

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Figure 23.6a Lymphocytes and the Immune Response
BACTERIA
Macrophage
activation
Antigen
presentation
Activation of
cytotoxic T cells
Activation of
helper T cells
Activation of
B cells
Destruction of
bacteria by
cell lysis
Antibody
production by
plasmocytes
Defenses against bacterial pathogens
are usually initiated by active
macrophages.

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Figure 23.7 Derivation and Distribution of Lymphocytes
The second group of stem
cells migrates to the thymus,
where subsequent divisions
produce daughter cells that
mature into T cells.
One group remains in the
bone marrow, producing
daughter cells that mature
into B cells and NK cells
that enter peripheral
tissues.
Mature T cells leave the circulation to take temporary residence in peripheral
tissues. All three types of lymphocytes circulate throughout the body in the
bloodstream.
Cell-mediated
immunity
Antibody-mediated
immunity
Immunological
surveillance
Peripheral Tissues
Red Bone MarrowThymus
Lymphoid stem cells
Mature T cell
Thymic
hormones
Production and
differentiation of
T cells
Migrate to
thymus
Transported by
circulatory system
Lymphoid stem cells
Mature T cell B cells NK cells
Lymphoid stem cells
Pluripotential stem cell
Interleukin-7
As they mature, B cells
and NK cells enter the
bloodstream and migrate
to peripheral tissues.

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Lymphoid Tissues
Any tissue containing an abundance of
lymphocytes
 Diffuse lymphoid tissues—loosely packed
lymphocytes within connective tissue
 Lymphoid nodules—densely packed
lymphocytes within loose connective tissue
 Tonsils
 Pharyngeal tonsils(Adenoid)
 Lingual tonsils (at the base of the tongue)
 Palatine tonsils(at the entrance to oropharynx)
 Aggregated lymphoid nodules (Peyer’s patches)

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Figure 23.8c Histology of Lymphoid Tissues
The location of the tonsils and the histological organization of a single tonsil
Pharyngeal tonsil
Pharyngeal
epithelium
Germinal centers
within nodules
LM × 50
Pharyngeal tonsil
Palatine tonsil
Lingual tonsil
Palate

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Lymphoid Organs
Lymphoid tissues that are separated from
surrounding tissues by a capsule
 Lymph nodes
 Receive the lymph through afferent vessels and the
cleanest lymph will leave the node through efferent
vessels.
 Thymus
 Spleen

20. © 2012 Pearson Education, Inc.
Figure 23.1 Lymphoid System
Tonsil
Cervical
lymph nodes
Right lymphatic duct
Thymus
Thoracic duct
Cisterna chyli
Lumbar
lymph nodes
Lymphatics
of lower
limb
Lymphatics
of upper limb
Axillary lymph nodes
Thoracic (left lymphatic) duct
Lymphatics of mammary gland
Spleen
Mucosa-associated lymphoid
tissue (MALT)
Pelvic
lymph nodes
Inguinal
lymph nodes

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Figure 23.9 Structure of a Lymph Node
Lymph node artery and vein
Hilum
Lymph nodes
Lymph
nodes
Lymph
vessel
Efferent
vessel
Trabeculae
Medulla
Cortex
Subcapsular
space
Deep cortex
(T cells)
Capsule Medullary cord
(B cells and
plasmocytes)
Afferent
vessel
Medullary sinus
Outer cortex (B cells)
Dividing
B cell
Germinal
center
Subcapsular
space
Outer cortex Capsule
Dendritic
cells
Nuclei of
B cells
Capillary

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Figure 23.10 Lymphatic Drainage of the Head and Neck
Periauricular
lymph node
Retroauricular
lymph node
Occipital lymph node
Parotid lymph node
Superficial cervical
lymph node
Deep cervical
lymph node
Sternocleidomastoid
muscle
Orbicularis oculi
muscle
Infraorbital
lymph node
Submandicular
lymph node
Buccal lymph node
Mandibular lymph node
Submental lymph node
Parotid salivary gland

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Figure 23.11a Lymphatic Drainage of the Upper Limb
Superficial lymphatic
vessels and nodes that
drain the upper limb
and chest of a male
Deltopectoral lymph node
Deltoid muscle
Pectoralis major muscle
Cephalic vein
Basilic vein
Axillary
lymph nodes
Supratrochlear
lymph node

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Figure 23.11b Lymphatic Drainage of the Upper Limb
Superficial and deeper lymphatic vessels and
nodes of the upper limb and chest of a female
Subclavian
lymph node
Axillary
lymph nodes
Pectoralis major
muscle (cut)
Axillary
vein
Subscapular
lymph node
Pectoral
lymph node
Mammary
gland
Central
lymph node
Parasternal
lymph node

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Figure 23.12 Lymphatic Drainage of the Lower Limb
Superficial inguinal
lymph nodes
Deep inguinal
lymph nodes
Popliteal lymph
nodes
Great saphenous
vein

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Figure 23.14b Lymphatic Drainage of the Inguinal Region
A superficial and deeper view of the inguinal region of a male
showing the distribution of lymph nodes and lymphatics
Deep Inguinal
and Iliac Lymph Nodes
Superficial
Inguinal Lymph Nodes
Superficial inguinal
lymph nodes
Lymphatic
vessels
Fascia
Anterior superior iliac spine
External iliac artery
External iliac vein
Inguinal
ligament
Femoral
artery
Deep inguinal
lymph nodes
Femoral vein
Great
saphenous vein

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Figure 23.15 Lymph Nodes in the Large Intestine and Associated Mesenteries
Inferior mesenteric
lymph nodes
Inferior mesenteric
artery
Distal portion
of duodenum
Superior mesenteric
artery
Descending colon
Sigmoid colon
Rectum
Appendix
Appendicular
lymph nodes
Transverse mesocolic
lymph nodes
Cecum
Ileum
Ascending colon
Transverse colon
Superior mesenteric
lymph nodes
Ileocolic lymph
nodes

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Figure 23.16a Anatomy and Histological Organization of the Thymus
The location of the thymus on gross dissection;
note the relationship to other organs in the chest
Right lobe
Diaphragm
Trachea
Thyroid gland
Right
lung
Left
lung
Left
lobe
THYMUS
Heart

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Figure 23.16bc Anatomy and Histological Organization of the Thymus
Anatomical landmarks
on the thymus
Histology of the thymus. Note the fibrous septa
that divide the thymic tissue into lobules
resembling interconnected lymphoid nodules.
Left
lobe
Right
lobe
Septa
Lobule
SeptaMedulla Cortex
Lobule
Lobule
The thymus gland LM × 50

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Figure 23.16cd Anatomy and Histological Organization of the Thymus
Histology of the thymus. Note the fibrous septa
that divide the thymic tissue into lobules
resembling interconnected lymphoid nodules.
Histology of the unusual structure of thymic
corpuscles. The small cells in view are
lymphocytes in various stages of development.
A thymic corpuscle LM × 550
Lymphocytes
Thymic
corpuscle
Reticular
cells
SeptaMedulla Cortex
Lobule
Lobule
The thymus gland LM × 50

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Figure 23.17a Anatomy and Histological Organization of the Spleen
The shape of the spleen roughly conforms to the
shapes of adjacent organs. This transverse section
through the trunk shows the typical position of the
spleen within the abdominopelvic cavity (inferior view).
Spleen
Aorta
Rib
Pancreas
Liver
Parietal peritoneum
Visceral peritoneum
Stomach
Diaphragm
Kidneys
Gastrosplenic ligament
Gastric area
Diaphragmatic surface
SPLEEN
Hilum
Renal area

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Figure 23.17b Anatomy and Histological Organization of the Spleen
External appearance of the visceral surface of the
intact spleen showing major anatomical landmarks.
This view should be compared with that of part (a).
SUPERIOR
INFERIOR
Splenic lymphatic
vessel
Splenic artery
Splenic vein
Hilum
Renal
area
Gastric
area

33. © 2012 Pearson Education, Inc.
Aging and the Lymphoid System
With advancing age, the lymphoid system
becomes less effective at combating
disease.
 T cells become less responsive to antigens.
 The number of helper T cells is reduced.
 B cells are less responsive.
 Antibody levels do not rise as quickly after
antigen exposure.
The net result is an increased susceptibility
to viral and bacterial infection, and cancer.