ch_20.ppt - 20 The Lymphatic System and Lymphoid Organs and Tissues Lymphatic System \u2022 Consists of three parts 1 A network of lymphatic

20 The Lymphatic System and Lymphoid Organs and Tissues

Lymphatic System • Consists of three parts 1. A network of lymphatic vessels (lymphatics) 2. Lymph 3. Lymph nodes

Lymphatic System: Functions • Returns interstitial fluid and leaked plasma proteins back to the blood – Once interstitial fluid enters lymphatics, it is called lymph • Together with lymphoid organs and tissues, provide the structural basis of the immune system

Lymphatic system: Lymph duct Lymph trunk Lymph node Lymphatic capillary Blood capillaries Lymphatic collecting vessels, with valves Heart Arterial system Venous system Tissue fluid Tissue cell Blood capillaries Lymphatic capillaries (a) Structural relationship between a capillary bed of the blood vascular system and lymphatic capillaries. Filaments anchored to connective tissue Fibroblast in loose connective tissue Endothelial cell Flaplike minivalve (b) Lymphatic capillaries are blind-ended tubes in which adjacent endothelial cells overlap each other, forming flaplike minivalves.

Lymphatic Vessels • One-way system, lymph flows toward the heart • Lymph vessels (lymphatics) include: – Lymphatic capillaries – Lymphatic collecting vessels – Lymphatic trunks and ducts

Lymphatic Capillaries • Similar to blood capillaries, except – Very permeable (take up cell debris, pathogens, and cancer cells) – Endothelial cells overlap to form one-way minivalves, and are anchored by collagen filaments, preventing collapse of capillaries

Lymphatic Capillaries • Absent from bones, teeth, bone marrow and the CNS • Lacteals: specialized lymph capillaries present in intestinal mucosa – Absorb digested fat and deliver fatty lymph (chyle) to the blood

Filaments anchored to connective tissue Fibroblast in loose connective tissue Endothelial cell Flaplike minivalve (b) Lymphatic capillaries are blind-ended tubes in which adjacent endothelial cells overlap each other, forming flaplike minivalves.

Lymphatic Collecting Vessels • Similar to veins, except – Have thinner walls, with more internal valves – Anastomose more frequently • Collecting vessels in the skin travel with superficial veins • Deep vessels travel with arteries • Nutrients are supplied from branching vasa vasorum

Lymphatic Trunks • Formed by the union of the largest collecting ducts – Paired lumbar – Paired bronchomediastinal – Paired subclavian – Paired jugular trunks – A single intestinal trunk

Lymphatic Ducts • Lymph is delivered into one of two large ducts – Right lymphatic duct drains the right upper arm and the right side of the head and thorax – Thoracic duct arises from the cisterna chyli and drains the rest of the body • Each empties lymph into venous circulation at the junction of the internal jugular and subclavian veins on its own side of the body

Cervical nodes Entrance of right lymphatic duct into vein Internal jugular vein Entrance of thoracic duct into vein Thoracic duct Cisterna chyli Lymphatic