Power Point Lecture Slides prepared by Janice Meeking

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

Lymphatic System: Functions • Returns interstitial fluid and leaked plasma proteins back to the blood • Carry absorbed fat from intestine to the blood (through lacteals) • Once interstitial fluid enters lymphatics, it is called lymph • Together with lymphoid organs and tissues, provide the structural basis of the immune system Copyright © 2010 Pearson Education, Inc.

Lymphatic Vessels • One-way system, lymph flows toward the heart • Lymph vessels (lymphatics) include: • Lymphatic capillaries • Lymphatic collecting vessels • Lymphatic trunks and ducts Copyright © 2010 Pearson Education, Inc.

Venous system Heart Arterial system Lymphatic system: Lymph duct Lymph trunk Lymph node Lymphatic collecting vessels, with valves Tissue fluid Blood capillaries Lymphatic capillary Tissue cell Blood capillaries Lymphatic capillaries (a) Structural relationship between a capillary bed of the blood vascular system and lymphatic capillaries. Copyright © 2010 Pearson Education, Inc.

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 Copyright © 2010 Pearson Education, Inc.

Lymphatic Capillaries Filaments anchored to connective tissue Endothelial cell Flaplike minivalve Fibroblast in loose connective tissue (b) Lymphatic capillaries are blind-ended tubes in which adjacent endothelial cells overlap each other, forming flaplike minivalves. Copyright © 2010 Pearson Education, Inc.

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 Copyright © 2010 Pearson Education, Inc.

Lymphatic Collecting Vessels • Similar to veins, except • Have thinner walls, with more internal valves • Anastomose more frequently • Superficial collecting vessels • in the skin, travel with superficial veins • Deep collecting vessels travel with arteries • Nutrients are supplied from branching vasa vasorum Copyright © 2010 Pearson Education, Inc.

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 Copyright © 2010 Pearson Education, Inc.

Cisterna Chyli • Located anterior to L 1, L 2 • Collects lymph from lower limbs and from the intestinal trunk that drains the digestive organs • In the intestines, specialized lymphatic capillaries called lacteals that transport absorbed fat from the small intestine to the blood stream • Fatty lymph is called chyle Copyright © 2010 Pearson Education, Inc.

Regional lymph nodes: Cervical nodes Internal jugular vein Entrance of right lymphatic duct into vein Entrance of thoracic duct into vein Axillary nodes Thoracic duct Cisterna chyli Lymphatic collecting vessels Aorta Inguinal nodes Drained by the right lymphatic duct Drained by the thoracic duct (a) General distribution of lymphatic collecting vessels and regional lymph nodes. Copyright © 2010 Pearson Education, Inc. Figure 20. 2 a

Right jugular trunk Right lymphatic duct Right subclavian trunk Right subclavian vein Right bronchomediastinal trunk Brachiocephalic veins Superior vena cava Azygos vein Internal jugular veins Esophagus Trachea Left subclavian trunk Left jugular trunk Left subclavian vein Entrance of thoracic duct into vein Left bronchomediastinal trunk Ribs Thoracic duct Hemiazygos vein Cisterna chyli Right lumbar trunk Left lumbar trunk Inferior vena cava Intestinal trunk (b) Major lymphatic trunks and ducts in relation to veins and surrounding structures. Anterior view of thoracic and abdominal wall. Copyright © 2010 Pearson Education, Inc. Figure 20. 2 b

Lymph Transport • Lymph is propelled by • Pulsations of nearby arteries • Contractions of smooth muscle in the walls of the lymphatics • Skeletal muscle contraction • Breathing • Lymph movement is very slow and it depends on movement of adjacent tissues Copyright © 2010 Pearson Education, Inc.

Lymphoid Cells Copyright © 2010 Pearson Education, Inc.

Lymphoid Cells • Lymphocytes arise in red bone marrow and mature into 1 of

Lymphocytes • T cells and B cells protect against antigens • Antigens are anything that the body perceives as foreign • These antigens will provoke an immune response • Bacteria and their toxins; viruses • Mismatched RBCs or cancer cells Copyright © 2010 Pearson Education, Inc.

Lymphocytes • T cells • Manage the immune response • Attack and destroy foreign cells • B cells • Produce plasma cells, which secrete antibodies • Antibodies bind to antigens and mark cells for destruction Copyright © 2010 Pearson Education, Inc.

Other Lymphoid Cells • Macrophages phagocytize foreign substances and help activate T cells • Dendritic cells capture antigens and deliver them to lymph nodes • Reticular cells produce stroma that supports other cells in lymphoid organs (structural cells) Copyright © 2010 Pearson Education, Inc.

Macrophage Reticular cells on reticular fibers Lymphocytes Medullary sinus Reticular fiber Copyright © 2010

Types of Lymphoid Tissue • Diffuse lymphoid tissue • Lymphoid follicles (or nodes) Copyright

Diffuse Lymphoid Tissue • Loose arrangement of lymphoid cells and some reticular fibers • Found in virtually every body organ • Larger collections appear in mucous membrane areas, like the GI and respiratory tract Copyright © 2010 Pearson Education, Inc.

Lymph Nodes • Principal lymphoid organs of the body • Embedded in connective tissue, in clusters along lymphatic vessels • Near the body surface in inguinal, axillary, and cervical regions of the body • These are clinically important, as they are palpable on PE • Firm, somewhat rubbery non-fixed mass the size of a pea or larger Copyright © 2010 Pearson Education, Inc.

Regional lymph nodes: Cervical nodes Internal jugular vein Entrance of right lymphatic duct into vein Entrance of thoracic duct into vein Axillary nodes Thoracic duct Cisterna chyli Lymphatic collecting vessels Aorta Inguinal nodes Drained by the right lymphatic duct Drained by the thoracic duct (a) General distribution of lymphatic collecting vessels and regional lymph nodes. Copyright © 2010 Pearson Education, Inc. Figure 20. 2 a

Lymph Nodes • Functions 1. Filter lymph—macrophages destroy microorganisms and debris 2. Immune system—lymphocytes are activated and mount an attack against antigens Copyright © 2010 Pearson Education, Inc.

Structure of a Lymph Node • Surrounded by a dense, fibrous capsule, from which connective tissue strands called trabeculae extend inward dividing the node into compartments (follicles) • 2 histologically distinct regions • Cortex • Superficial and deep • Medulla Copyright © 2010 Pearson Education, Inc.

Structure of a Lymph Node • Cortex • Superficial • Made up of follicles with germinal centers where B cells divide and proliferate • Deep • houses T cells • T cells circulate continuously between the blood, lymph nodes, and lymph, performing their surveillance role Copyright © 2010 Pearson Education, Inc.

Structure of a Lymph Node • Medullary cords are thin inward extensions from the cortical lymphoid tissue and contain both types of lymphocytes • Lymph sinuses • Large lymph capillaries where macrophages reside and phagocytize foreign matter in the lymph as it flows by in the sinuses Copyright © 2010 Pearson Education, Inc.

Circulation in the Lymph Node • Lymph enters through many afferent vessels on convex side large subcapsular sinus smaller sinuses that cut through the cortex medullary sinuses exits node at hilum (indented region on concave side) with few efferent vessels Copyright © 2010 Pearson Education, Inc.

Circulation in the Lymph Node • Less efferent vessels, so the flow of lymph stagnates somewhat, allowing time for lymphocytes and macrophages to work • Lymph passes through several nodes before it is cleansed Copyright © 2010 Pearson Education, Inc.

Afferent lymphatic vessels Cortex • Lymphoid follicle • Germinal center • Subcapsular sinus Efferent lymphatic vessels Hilum Medulla: • Medullary cord • Medullary sinus Trabeculae Capsule (a) Longitudinal view of the internal structure of a lymph node and associated lymphatics Copyright © 2010 Pearson Education, Inc. Figure 20. 4 a

Follicles Trabecula Subcapsular sinus Capsule Medullary cords Medullary sinuses (b) Photomicrograph of part of

Spleen • Largest lymphoid organ, size of a fist • Located in the left side of the abdominal cavity, just beneath the diaphragm, lateral to the stomach • Blood supply • Splenic artery and vein that enter and exit the hilum (concave anterior surface) Copyright © 2010 Pearson Education, Inc.

Copyright © 2010 Pearson Education, Inc.

Diaphragm Spleen Adrenal gland Left kidney Splenic artery Pancreas (c) Photograph of the spleen in its normal position in the abdominal cavity, anterior view. Copyright © 2010 Pearson Education, Inc. Figure 20. 6 c

Spleen Function • Functions • Site of lymphocyte proliferation and immune surveillance and response

Spleen • Stores breakdown products of RBCs (e. g. , iron) for later reuse • Releases other breakdown products to the blood for processing in the liver • Stores blood platelets and monocytes to be released when needed • Contains lymphocytes, macrophages, and huge numbers of erythrocytes Copyright © 2010 Pearson Education, Inc.

Histological Structure of the Spleen • Has a fibrous capsule and trabeculae • Two

Histological Structure of Spleen • White Pulp • Where immune function takes place • Composed mostly of lymphocytes suspended on reticular fibers • White pulp forms clusters around central arteries (small branches of the splenic artery) and form what appear to be islands in a sea of red pulp Copyright © 2010 Pearson Education, Inc.

Histological Structure of the Spleen • Red Pulp • Where worn out RBCs and bloodborne pathogens are destroyed • Contains lots of RBCs and macrophages that engulf the RBCs • Consists of splenic tissue that is not white pulp (the rest of the spleen) • Splenic sinuses (venous sinuses) • Splenic cords (reticular CT that separates splenic sinuses) Copyright © 2010 Pearson Education, Inc.

Thymus Copyright © 2010 Pearson Education, Inc.

Thymus • Size with age • In infants, it is found in the inferior neck and extends into the mediastinum, where it partially overlies the heart • Increases in size and is most active during childhood • Stops growing during adolescence and then gradually atrophies Copyright © 2010 Pearson Education, Inc.

Thymus • T lymphocyte precursors mature into T lymphocytes • Even though the gland atrophies, it continues to produce immunocompetent cells as we age, though at a declining rate Copyright © 2010 Pearson Education, Inc.

MALT Copyright © 2010 Pearson Education, Inc.

MALT • Mucosa-associated lymphoid tissue (MALT) • Lymphoid tissues present in all mucous membranes of the body • Function: filter and remove potential pathogens • Largest groupings are tonsils, Peyer’s patches in small intestine, and appendix • Also present in the mucosa of the respiratory tract (bronchi), genitourinary (GU) organs and the rest of the GI tract Copyright © 2010 Pearson Education, Inc.

Tonsils Copyright © 2010 Pearson Education, Inc.

Tonsils • Simplest lymphoid organs • Form a ring of lymphatic tissue around the pharynx • Palatine tonsils • Located on either side at the posterior end of the oral cavity. Largest of the three types • Lingual tonsils • Located at the base of the tongue. Look lumpy. • Pharyngeal tonsil • Posterior wall of the nasopharynx • Aka adenoids Copyright © 2010 Pearson Education, Inc.

Tonsils • Function • Gather and remove pathogens entering the pharynx in food or

Pharyngeal tonsil Palatine tonsil Lingual tonsil Tonsillar crypt Germinal centers in lymphoid follicles Copyright

Peyer’s Patches Copyright © 2010 Pearson Education, Inc.

Peyer’s Patches • Peyer’s patches • Clusters of lymphoid follicles • In the wall of the distal portion of the small intestine • Small intestine does most of the filtration and absorption of food, so it is important to have lymphoid tissue present to help filter out the pathogens/undesirable materials unwanted in the bloodstream • Destroy bacteria, preventing them from breaching the intestinal wall • Generate “memory” lymphocytes for long term immunity Copyright © 2010 Pearson Education, Inc.

Lymphoid nodules (follicles) of Peyer’s patch Smooth muscle in the intestinal wall Copyright ©

Appendix Copyright © 2010 Pearson Education, Inc.

Appendix • Tubular offshoot of the first part of the large intestine • Contains high concentration of lymphoid follicles • Destroy bacteria, preventing them from breaching the intestinal wall • Generate “memory” lymphocytes for long term immunity Copyright © 2010 Pearson Education, Inc.

REVIEW Copyright © 2010 Pearson Education, Inc.

Lymphatic vessels: a. collect excess fluid from interstitial spaces. b. drain blood from lymph nodes. c. are part of the venous system. d. are built like arteries. Copyright © 2010 Pearson Education, Inc.

Lymphatic capillaries owe their permeability to the presence of: a. an open end that siphons fluid from the interstitial fluid. b. minivalves in their walls. c. tight junctions between adjacent cells. d. proteins in the lymph fluid. Copyright © 2010 Pearson Education, Inc.

Why would removal of lymph vessels from the right axillary region cause edema in the right arm? a. Excess blood plasma builds up in regions where there are no lymph vessels. b. Surgery always results in tissue swelling. c. Blood is inefficiently circulated in areas where surgery has occurred. d. Both b and c are true. Copyright © 2010 Pearson Education, Inc.

Which of the following represents a logical sequence of structures that contribute to the return of fluid into the blood via the lymphatic system? a. Blood capillaries, arteries, lymphatic vessels, subclavian vein b. Arteries, lymphatic vessels, blood capillaries, subclavian vein c. Arteries, blood capillaries, lymphatic vessels, subclavian vein d. Subclavian vein, arteries, blood capillaries, lymphatic vessels Copyright © 2010 Pearson Education, Inc.

Which of the following contribute(s) to the flow of lymph through lymphatic vessels? a. The pumping of the heart b. The milking action of skeletal muscle contraction c. Pressure changes in the thorax that result from breathing d. Both b and c Copyright © 2010 Pearson Education, Inc.

Which of the following would the body perceive as an antigen? a. Bacteria b.

An advantage to having reticular connective tissue present in lymph nodes would be that: a. the loose organization of reticular connective tissue provides niches for macrophages and lymphocytes. b. lymph filters through the nodes and is exposed to lymphocytes and macrophages. c. lymphocytes cycle to various areas of the body and back to lymph nodes. d. all of the above take place. Copyright © 2010 Pearson Education, Inc.

The highest density of lymph nodes can be found ____. a. in the arms and legs b. in the brain c. at the locations where lymphatic collecting vessels converge d. in the intestines Copyright © 2010 Pearson Education, Inc.

Lymph tends to stall inside lymph nodes. This is due to: a. small-diameter spaces within the medulla. b. the large volume of lymph entering the node. c. fewer efferent lymphatic vessels than afferent lymphatic vessels. d. fewer afferent lymphatic vessels than efferent lymphatic vessels. Copyright © 2010 Pearson Education, Inc.

_____ can enter lymph capillaries. a. Bacteria b. Large proteins c. Interstitial fluid d.

The ______ is the largest lymphoid organ. a. lymph node b. Spleen c. Thymus

Red pulp of the spleen is most concerned with _______, while white pulp is most concerned with _____. a. immunity; new red blood cell formation b. filtering lymph; T lymphocyte formation c. blood filtering; immunity d. urine formation; blood filtering Copyright © 2010 Pearson Education, Inc.

Which of the following lymphoid tissues removes defective red blood cells from the blood?

The thymus is important for: a. T lymphocyte maturation. b. removal of foreign antigens. c. B lymphocyte maturation. d. secretion of hormones that promote B lymphocyte immunocompetence. Copyright © 2010 Pearson Education, Inc.

Tonsils promote memory of pathogens by: a. secreting antibodies into the blood. b. trapping food particles to support bacterial growth. c. trapping pathogens to develop immune cells with memory. d. producing B lymphocytes. Copyright © 2010 Pearson Education, Inc.