The Lymphatic System The Lymphatic System Consists of

The Lymphatic System

The Lymphatic System ► Consists of two semi-independent parts § Lymphatic vessels § Lymphoid tissues and organs ► Lymphatic system functions § Transports escaped fluids back to the blood § Plays essential roles in body defense and resistance to disease

Lymphatic Characteristics ► Lymph—excess tissue fluid carried by lymphatic vessels ► Properties of lymphatic vessels § One way system toward the heart § No pump § Lymph moves toward the heart ►Milking action of skeletal muscle ►Rhythmic contraction of smooth muscle in vessel walls

Relationship of Lymphatic Vessels to Blood Vessels Figure 12. 1

Learning Check ► What are the parts of the Lymphatic System? ► What are the functions of the lymphatic system? ► What are the properties of lymphatic vessels?

Lymphatic Fluid Formation

Lymph fluid ► The Net pressure out at the arterial end of the capillary is 10 mm ► The net pressure in at the venule end of the capillary is 8 mm ► Therefore there is a net difference of -2 mm ► This means more fluid moves out in to the tissues than is taken back in. ► The tissue fluid drains in to the lymphatic vessels to be taken away.

Learning Check ► More fluid move out to the tissues in the venule end of the capillaries – True or False

Lymphatic Vessels ► Lymph capillaries § Walls overlap to form flap-like minivalves § Fluid leaks into lymph capillaries § Capillaries are anchored to connective tissue by filaments § Higher pressure on the inside closes minivalves § Fluid is forced along the vessel

Lymphatic Vessels Figure 12. 2 a

Lymphatic Vessels Figure 12. 2 b

Lymphatic Vessels ► Lymphatic collecting vessels § Collect lymph from lymph capillaries § Carry lymph to and away from lymph nodes § Return fluid to circulatory veins near the heart ►Right lymphatic duct ►Thoracic duct

Learning Check? ► What are the two types of lymphatic vessels? ► What are the functions of the lymphatic capillaries? ► What are the functions of the lymphatic collecting ducts?

Lymphatic Vessels & Nodes Figure 12. 3

Lymph ► Harmful materials that enter lymph vessels § Bacteria § Viruses § Cancer cells § Cell debris

Lymph Nodes ► Filter lymph before it is returned to the blood ► Defense cells within lymph nodes § Macrophages—engulf and destroy foreign substances § Lymphocytes—provide immune response to antigens

Learning Check? ► What is the function of the lymph nodes? ► What are the two types of defense cells in the lymph nodes?

Other Lymphoid Organs ► Several other organs contribute to lymphatic function § Spleen § Thymus § Tonsils § Peyer’s patches

Other Lymphoid Organs Figure 12. 5

Learning Check? ► Name four other lymphoid organs?

Spleen ► Located on the left side of the abdomen ► Filters blood ► Destroys worn out blood cells ► Forms blood cells in the fetus ► Acts as a blood reservoir

Learning Check? ► What are the four functions of the spleen?

Thymus Gland ► Located low in the throat, overlying the heart ► Functions at peak levels only during childhood ► Produces hormones (like thymosin) to program lymphocytes

Learning Check? ► What is the function of the Thymus?

Tonsils ► Small masses of lymphoid tissue around the pharynx ► Trap and remove bacteria and other foreign materials ► Tonsillitis is caused by congestion with bacteria

Learning Check? ► What is the function of the Tonsils?

Peyer’s Patches ► Found in the wall of the small intestine ► Resemble tonsils in structure ► Capture and destroy bacteria in the intestine

Learning Check? ► What is the function of the Peyer’s Patches?

Final Learning Check What are the parts of the Lymphatic System? What are the functions of the lymphatic system? What are the properties of lymphatic vessels? What are the two types of lymphatic vessels? What are the functions of the lymphatic capillaries? What are the functions of the lymphatic collecting ducts? What is the function of the lymph nodes? What are the two types of defense cells in the lymph nodes? ► Name four other lymphoid organs? ► What are the four functions of the spleen? ► What is the function of the Thymus? ► What is the function of the Tonsils? ► What is the function of the Peyer’s Patches? ► ► ► ►