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Anatomy and Physiology - The Lymphatic System

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    Study Guide Anatomy and Physiology – The Lymphatic System 1. Lymphatic Vessels Lymphatic vessels are a network of tubes that collect extra fluid from tissues and return it back to the bloodstream. These vessels are found throughout most of the body and usually run: • alongside arteries (especially in the viscera) • alongside veins (especially in the subcutaneous tissue) Where Lymphatic Vessels Are NOT Found Lymphatic vessels are absent from: • central nervous system (CNS) • bone marrow • teeth • avascular tissues (tissues without blood vessels) Lymph Capillaries (Smallest Lymphatic Vessels) The smallest lymphatic vessels are called: • lymph capillaries They begin as: • dead - end vessels (meaning they start in tissues and don’t form a loop like blood capillaries) They look similar to blood capillaries, but they are much more porous , which makes them better at absorbing fluid from the tissues.

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    Study Guide Why Lymph Capillaries Are More Porous (2 Key Features) Lymph capillaries allow fluids to enter easily because of two important structures: 1. Valve - like Openings Between Endothelial Cells The endothelial cells in lymph capillaries: loosely overlap (instead of being tightly joined like blood capillaries) So when fluid pressure outside increases: the overlapping cells separate fluid enters the lymph capillary When pressure inside becomes higher than outside: the openings close fluid stays inside the lymph capillary This works like a one - way entry door for tissue fluid. 2. Anchoring Filaments Lymph capillaries also have: anchoring filaments These attach the endothelial cells to nearby collagen. When interstitial fluid pressure increases, these filaments: • prevent the capillary walls from collapsing • keep the openings between endothelial cells open So lymph can keep flowing into the vessel. Lacteals (Special Lymph Capillaries) Lacteals are specialized lymph capillaries found in the:

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    Study Guide villi (fingerlike projections inside the small intestine) Their major job is: absorbing lipids (fats) from the intestinal tract The lymph inside lacteals is called: chyle Chyle looks creamy white instead of clear because it contains a lot of fats. Lymphatic Collecting Vessels As lymph capillaries join together, they form: lymphatic - collecting vessels These vessels have some features similar to veins: 1. Valves They contain valves that: prevent backward flow of lymph (just like valves in veins prevent backflow of blood) 2. Three Tunics (Like Veins) Their walls contain the same three tunics found in veins, but: • the layers are thinner • the layers are poorly defined Lymphatic Trunks Collecting vessels eventually unite to form larger vessels called: • lymphatic trunks There are nine major trunks , and they drain lymph from the regions they are named after. These include:

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    Study Guide Paired trunks (left and right) • lumbar trunks • jugular trunks • subclavian trunks • bronchomediastinal trunks One single trunk • intestinal trunk Lymphatic Ducts (Largest Lymphatic Vessels) Lymphatic ducts are the largest lymphatic vessels . There are: two lymphatic ducts They drain lymph into veins in the neck — specifically into: the right and left subclavian veins at their junctions with the: internal jugular veins At these junctions, there are valves that: prevent blood from entering the lymphatic vessels The Thoracic Duct The thoracic duct is the larger duct. It collects lymph from: • the left side of the body and also from parts of the right side below the thorax • Finally, it drains into: the left subclavian vein

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    Study Guide Where does the thoracic duct begin? It begins at an enlarged structure called: cisterna chyli The cisterna chyli forms after the joining of: • the intestinal trunk • the right lumbar trunk • the left lumbar trunk The Right Lymphatic Duct (Right Thoracic Duct) The right lymphatic duct (also called the right thoracic duct in your text) drains a much smaller region. It collects lymph from: the upper right side of the body , including: • right arm • right regions of thorax • right side of neck • right side of head It drains into: the right subclavian vein

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    Study Guide Figure 1. Lymphatic trunks and ducts. Figure 1 shows the major lymphatic trunks and ducts, especially: • thoracic duct • right lymphatic duct where lymph enters the venous system near the subclavian veins 2. Quiz: Lymphatic Vessels 1. Question All the lymph that is collected returns to venous circulation by entering into the __________. Answer Choices • villi • lacteals • right and left subclavian veins

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    Study Guide Correct Answer right and left subclavian veins Why This Is Correct Lymph is returned to the bloodstream through the right lymphatic duct and thoracic duct , which empty into the right and left subclavian veins . This is how lymph fluid re - enters venous circulation . 3. Lymphoid Cells Lymphatic (lymphoid) tissue is a special type of connective tissue . Its main job is to support the body’s immune system by containing important immune cells. Lymphoid tissue is made up of several key types of cells. 1. Lymphocytes Lymphocytes are a type of white blood cell (leukocyte) . Their main role is to create an immune response that attacks: • specific nonself cells • foreign substances called antigens There are two major classes of lymphocytes: A. T Cells (T Lymphocytes) T cells originate in the bone marrow but they mature in the thymus gland T cells protect the body by attacking:

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    Study Guide • self cells invaded by pathogens • abnormal self cells (such as cancer cells) • nonself cells (like those from an organ transplant) So T cells are especially important for destroying “bad” body cells. B. B Cells (B Lymphocytes) B cells originate and mature in the bone marrow When B cells encounter an antigen (such as a toxin, virus, or bacterium), they form: • plasma cells • memory cells Plasma Cells Plasma cells release: antibodies These antibodies bind to the antigen and: inactivate it Memory Cells Memory cells continue to circulate in: lymph and blood They help the immune system respond faster in the future because they have the ability to produce additional antibodies during later encounters with the same antigen. 2. Macrophages Macrophages are large immune cells formed from: enlarged monocytes (white blood cells) Their job is to: • engulf (phagocytose) microbes • remove cellular debris They act like the “clean - up crew” of the immune system.

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    Study Guide 3. Reticular Cells and Reticular Fibers Reticular cells and their reticular fibers provide a supportive framework in lymphoid tissue. These fibers are made of: • collagen • glycoproteins Together, they form a network where: lymphocytes and other immune cells can live and work properly 4. Quiz: Lymphoid Cells 1. Question Which cells produce antibodies in response to a foreign antigen? Answer Choices • T cells • B cells • lymphocytes Correct Answer B cells Why This Is Correct B cells can become plasma cells , which produce antibodies to fight specific antigens. 2. Question Which cells originate and mature in the bone marrow?

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