Lymphatic System and Body DefensesLymphatic System and Body Defenses

Chapter 12Chapter 12

The Lymphatic SystemThe 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

Lymphatic VesselsLymphatic 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

Lymph capillariesLymph 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

Lymphatic collecting vesselsLymphatic 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

Lymphatic VesselsLymphatic Vessels

Lymph NodesLymph 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

Lymph Nodes (continued)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

Flow of Lymph through NodesFlow 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

Other Lymphoid OrgansOther Lymphoid Organs

• Spleen

• Thymus

• Tonsils

• Peyer’s patch

• Common features– Predominance of

reticular connective tissues and lymphocytes

Other Lymphoid OrgansOther 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

Other Lymphoid OrgansOther 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

Mucosa-associated Lymphatic Tissue (MALT)

Mucosa-associated Lymphatic Tissue (MALT)

• Composed of– Peyer’s patches

– Tonsils

– Other small collections of lymphatic tissue

• Protects respiratory and digestive tracts

Body DefensesBody Defenses

Nonspecific Body DefensesNonspecific Body Defenses

Specific Body Defenses: The Immune System

Specific Body Defenses: The Immune System