2. The Lymphatic System
• Two semi-independent parts
– Lymphatic vessels
– Lymphoid tissues and organs
• Function of lymphatic system
– Transport fluids back to the blood
– Essential role in body defense and disease
resistance
3. Lymphatic Vessels
• Function
– Pick up excess tissue fluid – Lymph – and return it
to the blood stream
• Also known as lymphatics
• One way system flows only to the heart
• Characteristics
– Thin-walled
– Valved
– pumpless
4. Lymph capillaries
• Web between tissue cells and blood capillaries
• Remarkably permeable
• Held by fine collagen fibres
• Act as one way doors
– Flap like mini valves close as high pressure builds
up inside
– Keeps lymph from leaking back
5. Lymphatic collecting vessels
• Collects lymph from lymph capillaries
• Carries lymph to and away from lymph node
• Returns fluid to the heart through two ducts
– Right lymphatic duct
• Drains lymph from right arm and right side of head and
thorax
– Thoracic duct
• Receives lymph from rest of the body
7. Lymph Nodes
• Function
– Remove foreign material from lymph
• Cluster along vessels in three main areas
– Inguinal
– Axillary
– Cervical
• Contain 2 types of cells
– Macrophages
• Engulf and destroy bacteria, viruses and foreign
substances
– Lymphocytes (white blood cells)
• Respond to foreign substances
8. Lymph Nodes (continued)
• Structure
– Kidney shaped, less than 1” long
– “buried” in connective tissue
– Cortex
• Outer part
• Contains follicles (collections of lymphocytes) and T-
cells
– Medulla
• Inner part
• Contains phagocytic macrophages
9. Flow of Lymph through Nodes
• Lymph enters through afferent lymph vessels
• Flows through sinuses
• Exits at indented region - hilus – through
efferent lymphatic vessels
• Slow process
– Allows time for lymphocytes and macrophages to
perform
11. Other Lymphoid Organs
• Spleen
• Thymus
• Tonsils
• Peyer’s patch
• Common features
– Predominance of
reticular connective
tissues and lymphocytes
12. Other Lymphoid Organs
• Spleen
– Filters blood of bacteria, viruses
– Located on left side of abdominal cavity
– Destroys worn out red blood cells
– Acts as blood reservoire
– Produces lymphocytes
• Thymus
– Function peaks at youth
– Found low in throat over heart
– Produces hormones that program lymphocytes
13. Other Lymphoid Organs
• Tonsils
– Small masses of lymphatic tissue around pharynx
– Trap and removes bacteria or pathogens entering
throat
– So efficient can become congested
• tonsillitis
• Peyer’s patches
– Like tonsils but in small intestine
– Captures and destroys bacteria
14. Mucosa-associated Lymphatic
Tissue (MALT)
• Composed of
– Peyer’s patches
– Tonsils
– Other small collections of lymphatic tissue
• Protects respiratory and digestive tracts
