Chapter 20 The Lymphatic System

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Chapter 20The 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.
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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

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Lymph Flow

• More fluid moves out of the blood capillaries by
  filtration than returns by reabsorption -
  Starlings 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

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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

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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
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Lymph Flow Follows Venous Circulation

• Lymph vessels have the same organization and
  routing as the vascular tree

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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 stagnates
  somewhat in the node
• This allows lymphocytes and macrophages time to
  carry out their protective functions

Only lymph nodes filter lymph!
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Cancer Metastasizes To Lymph Nodes
Cancer cells from the tumor are first trapped in
a lymph node
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Lymphatic Organs - Spleen

• largest lymphoid organ in the body
• fibrous capsule with arteries, veins, and
  efferent lymph vessels
• located between stomach and diaphragm

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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

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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)

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Unencapsulated Lymphatic Tissue

• Diffuse lymphatic tissue
• Small scattered patchs
• In nearly every organ
• Lymphoid follicles (nodules)
• More organized, more cellular clusters

small bronchus
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Mucosa-Associated Lymphatic Tissue (MALT)
found in the lamina propria of mucous membranes
of the GI tract, respiratory tract, urinary
tract, and reproductive tract
Peyers patches in the intestines
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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

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Lymphadenopathy
Enlarged lymph nodes due to increased drainage
from inflammatory lesions or infections. Associat
ed with malignant and nonmalignant diseases.
Lymphocyte leukemia with severe lymphadenopathy
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Hodgkins Diseaseone of thesignificant
malignant lymphomas
Cervical lymph nodes
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Burkitts 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.
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End Chapter 20