Chapter 20
The Lymphatic System
Use the video clip: CH 20 - Lymph Node Anatomy
for a review of lymph node structure
G.R. Pitts, J.R. Schiller, and James F. Thompson, Ph.D.
The Lymphatic System
• Basic organization
– Lymph fluid in lymph vessels
– Structures: organs with lymphatic tissue, red
bone marrow, liver and spleen
• Functions
– return interstitial fluid and proteins to the blood
– transport dietary fats to adipose tissue
– protect against cancer & infection
• resistance - fight off disease
– nonspecific resistance - general protection against disease
– immunity - specific protection
• susceptibility - lack of resistance
• More fluid moves out of the blood
capillaries by filtration than returns
by reabsorption - Starling’s Law
• ≈ 3Ll day of lymph is generated
• Proteins escaped from the blood or
secreted by tissues are transferred
back to the blood by the lymphatics
• Lymph flow is facilitated by muscle
pumps, the respiratory pump, valves,
and smooth muscle (in the walls of
the trunks & thoracic duct)
• Smaller vessels drain into larger
vessels
Lymph Flow
Lymphatic Capillaries
• “Blind ended,” covered vessels between cells, larger than
capillaries
• Not found in avascular tissues (CNS, cartilage) nor in the
splenic pulp, and bone marrow
Lymphatic Capillaries
• Structure/Function regulates fluid flow
– Anchoring filaments - from lymphatic endothelium attach to
surrounding tissues
– Endothelial cells overlap
• high hydrostatic fluid pressure separates cells, fluid into caps
• hydrostatic fluid pressure in cap prevents fluid movement out
minivalve
Lymph Flow
Follows
Venous
Circulation
• Lymph vessels have
the same
organization and
routing as the
vascular tree
Lymphatic Flow (cont.)
• Lymphatic vessels
have no separate
pump (heart)
• All lymph returns
to the vena cava
and to the right
side of the heart
Lymphatic Flow (cont.)
• Lymph ducts
– Right lymphatic duct
• about ½ inch long
• drains lymph from
upper right side of
body (arm & head)
– Thoracic (left) duct
• main collecting duct of
the lymphatic system
• 38-45 cm long
• drains 75% of body
• begins as a dilation
known as the cisterna
chyli located anterior
to lumbar disk #2
Lymphatic Flow (cont.)
• Lymph returns to the
venous drainage
through right and left
lymphatic ducts at the
junction of the internal
jugular and subclavian
veins
Summary of Lymphatic Vessels
• Lymph Flow from smallest to largest:
• Capillaries  vessels  trunks  ducts
• Lymph vessels anastomose and supply and
drain lymph nodes along their course
Two Main Types Of Lymphocytes
• B lymphocytes = B cells
– attack microbes, especially bacteria
– develop into plasma cells to produce antibodies (Ab)
• bind to antigen to form antibody-antigen (Ag-Ab) complexes
• complexes prevents Ag from interacting with other body cells or
molecules
• memory B cells – dormant until future exposure to Ag
• T lymphocytes = T cells
– regulate many immune responses
– attack viruses, fungi, transplants, cancer, some bacteria
• 4 types of T cells
– cytotoxic (killer) T cells - destroy foreign invaders
– helper T cells - assist B cells and cytotoxic T cells
– suppressor T cells – help bring immune response to an end
– memory T cells - dormant until future exposure to Ag
Lymphocyte Development
• primary lymphatic organs - site of
lymphocyte (B cell and T cell) production
– bone marrow - produces B cells, immature T
cells
– T cells migrate to the thymus gland to
mature or die if determined to be improper
• secondary lymphatic organs
– sites of activated immune responses
– lymphatic nodules (lymph follicles)
– lymph nodes, spleen, tonsils
Other Lymphoid Tissue Cells
• Macrophages & Dendritic cells
–Phagocytize foreign substances and cells
–Transport them to lymphatic tissues
–Process foreign things into individual antigens
–Present Ags to T & B lymphocyte to help
activate them
• Reticular cells
–Similar to fibroblasts
–Produce reticular fibers (stroma) that provide
the framing structure for other cells in
lymphoid organs
Lymphatic Tissue - General
• Stroma of reticular
connective tissue (except
thymus)
• Parenchyma of
macrophages, B and T
lymphocytes, occasional
other leukocytes
• May or may not have a
connective tissue capsule
Lymphatic Organs – Thymus Gland
• Thymus Gland
– Two lobes between the sternum
and the heart
– Thymocytes produce hormones
– Atrophies with age (starting ~20)
• Structure/Function
– Outer cortex – immature T cells
• screened for functional capacity
• stimulated to proliferation
• stimulated to maturation
– Inner medulla
• defective T cells degenerate
• mature T cells move into blood
Lymphatic Organs – Lymph Nodes
• Anatomy
– oval, bean shaped small
structures scattered
throughout body along
lymph vessels
– may be deep or superficial
– concentrated along the
respiratory tree and GI
tract, in the mammary
glands, axillae, and groin
– filter lymph fluid to trap
foreign organisms, cell
debris, and tumor cells
Circulation in the Lymph Nodes
• Lymph enters via a number of
afferent lymphatic vessels
• It then enters a large
subcapsular sinus and travels
into a number of smaller
sinuses
• It meanders through these
sinuses and exits the node at
the hilus via efferent vessels
• The node acts as a “settling
tank,” because there are fewer
efferent vessels, lymph
Only lymph nodes filter lymph!
stagnates somewhat in the
node
• This allows lymphocytes and
macrophages time to carry out
their protective functions
Cancer Metastasizes To Lymph Nodes
Cancer cells from the tumor are first trapped in a lymph node
Lymphatic Organs - Spleen
• largest lymphoid organ in
the body
• fibrous capsule with
arteries, veins, and efferent
lymph vessels
• located between stomach
and diaphragm
Spleen Functions: White Pulp
•
•
•
•
a site of immune surveillance and response
macrophages phagocytize bacteria, worn-out RBC's, platelets
hemoglobin is recycled and components transferred to liver
macrophage antigen-presentation and lymphocyte activation
and proliferation
• some B cells mature into plasma cells
Spleen Functions: Red Pulp
• Site of fetal erythrocyte
production (normally ceases
after birth)
• Stores ~ 1 L of blood which
can be released during an
emergency (hemorrhage)
Unencapsulated Lymphatic Tissue
• Diffuse lymphatic tissue
– Small scattered patchs
– In nearly every organ
• Lymphoid follicles (nodules)
– More organized, more cellular
clusters
small
bronchus
Mucosa-Associated Lymphatic
Tissue (MALT)
found in the lamina propria of mucous membranes of the GI tract,
respiratory tract, urinary tract, and reproductive tract
Peyer’s patches
in the intestines
Lymphatic Organs - Tonsils
• lymphoid tissue
beneath the mucosae
• tonsilar crypts trap
micro-organisms
• immune cells destroy
the micro-organisms
• palantine tonsils –
largest and most
frequently infected
Lymphadenopathy
Enlarged lymph nodes
due to increased
drainage from
inflammatory lesions or
infections.
Associated with
malignant and
nonmalignant diseases.
Lymphocyte leukemia with
severe lymphadenopathy
Hodgkin’s Disease:
one of the
significant malignant lymphomas
Cervical
lymph nodes
Burkitt’s Lymphoma
Commonly found in central
Africa and New Guinea.
Associated with Epstein-Barr
virus which causes infectious
mononucleiosis in North
America and Europe.
Rarer American type has
extensive marrow
replacement.
Cancerous cell is a B
lymphocyte.
End Chapter 20