Anatomy & Physiology

Anatomy & Physiology Study Guide

©2018 Achieve Page 280 , a fluid that resembles plasma but contains a much lower concentration of suspended proteins; a network of lymphatic vessels ; an array of lymphoid tissues and lymphoid organs scattered throughout the body; and lymphocytes along with smaller numbers of phagocytes and other cells. Most of the body’s lymphocytes are produced and stored within lymphoid tissues (such as the tonsils) and lymphoid organs (such as the spleen and thymus). However, red bone marrow also produces lymphocytes along with other defense cells, such as monocytes and macrophages. 21.2 Lymphatic Vessels The lymphatic network begins with lymphatic capillaries , or terminal lymphatics, which branch through peripheral tissues. The endothelial cells of a lymphatic capillary are not bound tightly together, but they do overlap. The region of overlap acts as a one-way valve, permitting the entry of fluids and solutes, as well as viruses, bacteria, and cell debris, but preventing their return to the intercellular spaces. Nearly all bodily tissues and organs contain Lymphatic capillaries. Two sets of lymph vessels collect lymph from the lymphatic capillaries: superficial lymphatics and deep lymphatics . Superficial and deep lymphatics converge to form even larger vessels called lymphatic trunks . These trunks empty into two large collecting vessels: the thoracic duct and the right of 368 Chapter 21: The Lymphatic System Many organs and systems work together to keep us alive and healthy. In the ongoing struggle to maintain health, the lymphatic system plays a central role. The environment contains an assortment of viruses, bacteria, fungi, and parasites capable of not only surviving but thriving inside the body— and potentially causing great harm. These organisms, called pathogens , are responsible for many diseases in humans. Different pathogens affect the body in specific ways depending on their lifestyle. The lymphatic system includes the cells, tissues, and organs responsible for defending the body against both environmental hazards (e.g., pathogens) and internal threats, such as cancer cells. Lymphocytes , the primary cells of the lymphatic system, are vital to the body’s ability to resist or overcome infection and disease. Lymphocytes respond to the presence of invading pathogens, abnormal body cells, and foreign proteins. They work to eliminate these threats or render them harmless through a combination of physical and chemical attacks. Lymphocytes respond very specifically. If a bacterial pathogen invades the body, lymphocytes organize a defense against that particular type of bacterium. For this reason, lymphocytes are said to provide a specific defense , known as the immune response . Immunity is the ability to resist disease and infection through the activating specific defenses. All the cells and tissues involved in the production of immunity are sometimes considered part of an immune system . 21.1 Anatomy The lymphatic system consists of lymph