Lymphatic System Overview

The Lymphatic System

• Consists of two semi-independent parts: lymphatic vessels and lymphoid tissues and organs

Lymphatic Vessels

• Transport escaped fluids from the cardiovascular system back to the blood
• Form an elaborate drainage system that picks up excess interstitial fluid (lymph) and returns it to the blood
• Form a one-way system, with lymph flowing only toward the heart

Lymph Capillaries

• Weave between tissue cells and blood capillaries, absorbing leaked fluid
• Walls overlap to form flap-like minivalves that open when fluid pressure is higher in the interstitial space, allowing fluid to enter the lymphatic capillary

Lymphatic Collecting Vessels

• Collect lymph from lymphatic capillaries
• Carry lymph to and away from lymph nodes
• Return fluid to the venous system through two large ducts in the thoracic region: right lymphatic duct and thoracic duct

Characteristics of Lymphatic Vessels

• Thin-walled
• Larger vessels have valves
• Low-pressure, pumpless system
• Lymph is transported by the same mechanisms as the milking action of skeletal muscles, pressure changes in the thorax during breathing, and smooth muscle in the walls of lymphatics

Lymph Nodes

• Cells in lymph nodes help protect the body by removing foreign material, producing lymphocytes that function in the immune response
• Filter lymph before it is returned to the blood
• Other materials that are filtered include viruses, cancer cells, and cell debris

Defense Cells within Lymph Nodes

• Macrophages engulf and destroy bacteria, viruses, and other foreign substances in the lymph
• Lymphocytes respond to foreign substances in the lymphatic stream

Structure of a Lymph Node

• Most lymph nodes are kidney-shaped, less than 1 cm long, and buried in connective tissue
• Each surrounded by a fibrous capsule called trabeculae and divided into a number of compartments
• Cortex (outer part) contains follicles and germinal centers
• Medulla (inner part) contains phagocytic macrophages

Flow of Lymph through Nodes

• Lymph enters the convex side of a lymph node through afferent lymphatic vessels
• Lymph flows through a number of sinuses (spaces) inside the node
• Lymph exits via efferent lymphatic vessels

Other Lymphoid Organs

• Spleen: filters and cleanses blood, destroys worn-out red blood cells, stores platelets, and acts as a blood reservoir
• Thymus: functions at peak level only during youth
• Tonsils: trap and remove bacteria or other foreign pathogens entering the throat
• Peyer's patches: capture and remove bacteria or other foreign pathogens from the small intestine
• Appendix: contributes to lymphatic function

This quiz covers the basics of the lymphatic system, including its components, functions, and roles in body defense and resistance.