Lymphatic System

Functions of the Lymphatic System

1. Return interstitial fluid to bloodstream

2. Transport lipids and lipid-soluble vitamins in the bloodstream

3. Production and maturation of lymphocytes

4. Generates an immune response against antigens in interstitial fluid

Lymphatic System

Lymph

Lymph is fluid in lymphatic vessels

Comprised of:

• Interstitial fluid

• Solutes

• Foreign materials

Lymphatic Capillaries

• Closed-ended tubes; among blood capillary beds

• GI tract contains specialized lymph capillaries called lacteals – collect lipids and lipid-soluble vitamins

Lymphatic Vessels• Lymphatic capillaries merge

to form lymphatic vessels– Resemble venules

• Possess valves similar to veins

• Afferent lymphatic vessels into lymph node

• Efferent lymphatic vessels away from lymph node

• Lymphatic vessels merge lymphatic trunks

Lymphatic Trunks

Lymphatic Ducts• Lymphatic trunks

Lymphatic ducts• Right lymphatic duct -

– Returns lymph from right side of head/neck, upper limb and thorax

• Thoracic duct - largest lymphatic vessel– collects lymph from rest of

body

Lymphatic Cells

• Macrophages– Monocytes that have migrated– Phagocytize foreign substances

• Nurse cells– Secrete hormones in thymus

• Dendritic cells– In lymph nodules– Antigen-presenting cells

• Lymphocytes

Types of Lymphocytes

• Three types of lymphocytes:1. T-lymphocytes (T-cells)

2. B-lymphocytes (B-cells)

3. NK cells

T-Lymphocytes

• 70-85% of lymphocytes• Can recognize a particular antigen• Main types:

Helper T-lymphocytes Cytotoxic T-lymphocytes Memory T-lymphocytes

Helper T-Lymphocytes

• Also called CD4 or T4 cells• Many types, each responds to a different

antigen• T4 cells initiate and oversee the immune

response1. Present antigen to other lymphocytes2. Secrete cytokines - hormones that activate other

lymphatic cells

• HIV infects these cells– Shuts down immune response

Cytotoxic T-Lymphocytes

• Also called CD8 or T8 cells

• Come in direct contact w/infected or foreign cells and kill them

• Must be activated by helper T-cell that presents an antigen to it

Immune Response of T-Lymphocytes

Memory T-Lymphocytes

• Arise from T cells that have encountered antigen

• Mount faster response than initial exposure

B-Lymphocytes

• 15-30% of body lymphocytes

• Produce immunoglobins (Ig), or antibodies, to a single antigen

• Become activated when presented with antigen from helper T- cell– Undergo division to two cell types:

• Most become plasma cells – produce antibodies– Live less than a week

• Some become memory B cells– Live weeks to years– Confer lifetime immunity

B-Lymphocytes and Their Role in the Immune Response

NK (Natural Killer) Cells

• Small percentage of all lymphocytes

• Can kill a wide variety of infected cells and some cancerous cells

Lymphatic Organs

• Tonsils – trap antigens

• Thymus – T cell maturation

• Lymph nodes – filter antigens from lymph

• Spleen

Spleen1. Initiates immune response

when antigens found in blood

2. Reservoir for erythrocytes and platelets

3. Phagocytizes old, defective erythrocytes and platelets

4. Phagocytizes bacteria and other foreign materials