Chapter 21 Lecture Outline See separate PowerPoint slides for all figures and tables pre-inserted into PowerPoint without notes.

21.1 Lymph and Lymph Vessels Describe lymph and its contents. Discuss the location and anatomic structure of lymphatic capillaries. Explain how fluid enters lymphatic capillaries. Explain the mechanisms that move lymph through lymphatic vessels, trunks, and ducts. Name the five types of lymphatic trunks and the regions of the body from which they drain lymph. Describe the regions that are drained by the right lymphatic duct and by the thoracic duct. 21.1 Lymph and Lymph Vessels Learning Objectives:

21.1 Lymph and Lymph Vessels Lymphatic system functions Transport and house lymphocytes and other immune cells Return excess fluid in body tissues to blood to maintain blood volume Lymphatic system components Lymph vessels, lymphatic issues and organs Lymph is the fluid transported within lymph vessels

Lymphatic System Figure 21.1

21.1a Lymph and Lymphatic Capillaries Characteristics of lymph Some fluid leaves blood capillaries and is not reabsorbed by them Such fluid moves into lymphatic capillaries where it is called lymph Components of lymph Water, dissolved solutes, and small amount of protein Sometimes cell debris, pathogens, or cancer cells

21.1a Lymph and Lymphatic Capillaries Small, closed-ended vessels that absorb interstitial fluid Interspersed around most blood capillaries Absent in avascular tissues, red marrow, spleen, and CNS Slightly larger than blood capillaries; no basement membrane Walls are made of overlapping endothelial cells Have flaps between cells through which fluid enters but can’t exit Anchoring filaments hold endothelial cells to nearby structures Lacteals: lymphatic capillaries in GI tract Absorb lipid-soluble substances from GI tract

Lymphatic Capillaries Figure 21.2

21.1a Lymph and Lymphatic Capillaries Movement of lymph into lymphatic capillaries Hydrostatic pressure of interstitial fluid pushes it into capillary Anchoring filaments linking endothelial cells to surrounding structures prevent vessel collapse Pressure of lymph inside vessel forces intercellular openings (“flaps”) of capillary wall to close with lymph inside Lymph moves through vessels of larger and larger size Lymphatic capillaries, lymphatic vessels, lymphatic trunks, and lymphatic ducts Ultimately, fluid is returned to blood circulation

Clinical View: Metastasis Wandering cancerous cells establishing secondary tumors Develop in other locations in the body (metastasis) E.g., breast cancer may metastasize to the lung Cancerous cells break free from primary tumor Transported in the lymph

21.1b Lymphatic Vessels, Trunks, and Ducts Lymphatic vessels are fed by lymphatic capillaries Located adjacent to arteries and veins Have all three vessel tunics (intima, media, externa) Have valves to prevent pooling and backflow of lymph Lymphatic system lacks a pump; moves lymph using Skeletal muscles and respiratory pumps (as seen in veins) Pulsatile movement of blood in nearby arteries Rhythmic contraction of smooth muscle in larger lymph vessel walls Some vessels connect to lymph nodes for lymph filtration

21.1b Lymphatic Vessels, Trunks, and Ducts Lymphatic trunks are fed by lymphatic vessels Jugular trunks drain lymph from head and neck Subclavian trunks drain upper limbs, breasts, and superficial thoracic wall Bronchomediastinal trunks drain deep thoracic structures Intestinal trunks drain most abdominal structures Lumbar trunks drain lower limbs, abdominopelvic wall, and pelvic organs

21.1b Lymphatic Vessels, Trunks, and Ducts Lymphatic ducts are fed by lymphatic trunks Largest lymphatic vessels Bring lymph to venous blood circulation There are two: right lymphatic duct and thoracic duct Right lymphatic duct is near right clavicle Drains upper right quadrant of body Right side of head and neck, right upper limb, and right side of thorax Delivers lymph to junction of right subclavian and right internal jugular veins

21.1b Lymphatic Vessels, Trunks, and Ducts Lymphatic ducts (continued) Thoracic duct is largest lymphatic vessel Runs from diaphragm to junction of left subclavian and left jugular veins Saclike cisterna chyli at its base Receives lipid-rich chyle from GI tract Drains lymph from left side of head and neck, left upper limb, left side of thorax, abdomen, and both lower limbs Figure 21.3b

Lymphatic Trunks and Ducts Figure 21.3a

Clinical View: Lymphedema Accumulation of interstitial fluid due to interference with lymphatic drainage Causes swelling and pain in affected area May interfere with wound healing and contribute to infection Most caused by blockage of lymph vessels E.g., trauma or infection of lymph vessels or tumors E.g., radiation therapy scarring or surgical removal of lymph nodes Controlled with compression garments, exercise, massage Extreme cases known as elephantiasis Caused by infection with parasitic worms

What did you learn? How does fluid enter lymphatic capillaries, and what prevents its escape from them? What is the order of flow through different lymphatic vessels? Which lymphatic duct receives lymph from the right leg?

21.2 Overview of Lymphatic Tissue and Organs Name the two categories of lymphatic tissue and organs, and identify components of the body that belong to each category. Learning Objective:

21.2 Overview of Lymphatic Tissue and Organs Primary lymphatic structures Involved in formation and maturation of lymphocytes Red bone marrow and thymus Secondary lymphatic structures Do not form lymphocytes, but house them and other immune cells Sites of immune response initiation Include lymph nodes, spleen, tonsils, and lymphatic nodules Include MALT (mucosa-associated lymphatic tissue)

What did you learn? What does the acronym MALT stand for? What is an example of a primary lymphatic structure?

21.3 Overview of Lymphatic Tissue and Organs Describe the location and general function of red bone marrow. Identify the two major types of lymphocytes. Describe the structure and general function of the thymus. Learning Objectives:

21.3a Red Bone Marrow Red bone marrow Located between trabeculae of spongy bone In flat bones of skull, ribs, and sternum, vertebrae, ossa coxae, heads of humerus and femur Site of hemopoiesis: production of blood’s formed elements Formed elements include T-lymphocytes and B-lymphocytes T-lymphocytes migrate to thymus to complete maturation Figure 21.4

21.3b Thymus Thymus involved in T-lymphocyte maturation Located in mediastinum Larger in children than adults Grows until puberty, then regresses; gradually replaced by adipose tissue Consists of two thymic lobes, each surrounded by connective tissue capsule Trabeculae of capsules subdivide lobes into lobules Each lobule has outer cortex and inner medulla regions Both regions are lymphoepithelial (contain lymphatic cells and epithelial tissue) Cortex contains immature T-lymphocytes Medulla contains mature T-lymphocytes

Thymus Figure 21.5a

Thymus Figure 21.5b-c

What did you learn? Where does hemopoiesis occur? What is the function of the thymus?

21.4 Secondary Lymphatic Structures Describe the structure of lymph nodes. Explain the function of lymph nodes. Describe the spleen and its location. Distinguish between white pulp and red pulp. List the functions of the spleen. Identify the main groups of tonsils and their location and function. Describe the composition of individual lymphatic nodules. Compare the locations of MALT and Peyer patches. Learning Objectives:

21.4 Secondary Lymphatic Structures House lymphocytes and other immune cells within a reticular connective tissue matrix Organized into lymphatic organs and aggregates of lymphatic nodules Organs have a complete capsule of dense irregular connective tissue Spleen and lymph nodes Other lymphatic structures have an incomplete capsule or lack one Tonsils, MALT, diffuse lymphatic nodules

21.4a Lymph Nodes Lymph nodes filter lymph, remove unwanted substances Small, oval, encapsulated structures Located along deep and superficial pathways of lymph vessels Occur in clusters receiving lymph from body regions Cervical lymph nodes receive lymph from head, neck Axillary lymph nodes receive lymph from breast, axilla, and upper limb Inguinal lymph nodes in groin receive lymph from lower limb and pelvis

21.4a Lymph Nodes Lymph node components Afferent lymphatic vessels bring lymph to node An efferent vessel drains a lymph node Located at hilum (involuted portion of node) Dense connective tissue capsule encloses node Trabeculae of capsule subdivide node into compartments Outer cortex, inner medulla Figure 21.6a

21.4a Lymph Nodes Node’s cortex contains lymphatic nodules Reticular fibers support a germinal center Houses proliferating B-lymphocytes and some macrophages Surrounding mantle zone contains T-lymphocytes, macrophages, and dendritic cells Cortical sinuses are tiny open channels lined by macrophages Figure 21.6b (part)

21.4a Lymph Nodes Node’s medulla contains medullary cords Connective tissue fibers that support B-lymphocytes, T-lymphocytes, and macrophages Medullary sinuses are tiny open channels lined with macrophages Figure 21.6b (part) 21.6c

21.4a Lymph Nodes Lymph flow through nodes Lymph enters through several afferent vessels Creates pressure to push it through node to the single exit vessel Lymph is monitored for presence of foreign material Macrophages remove foreign debris from lymph Lymphocytes may initiate immune response Lymphocytes proliferate especially in germinal centers Can cause enlarged nodes that can be palpated in neck and axilla Lymph exits node through efferent vessel May enter nearby lymph node within the cluster of nodes

Clinical View: Lymphoma Malignant neoplasm from lymphatic structures Nontender, enlarged lymph node Possible night sweats, fever, and weight loss Hodgkin lymphoma Affects young adults and people over 60 If caught early, cured by excision, radiation, and chemotherapy Non-Hodgkin lymphoma More common Some kinds aggressive, others slow growing

21.4b Spleen The spleen is the largest lymphatic organ Located in left upper abdominal quadrant Lateral to left kidney and posterolateral to stomach Posterolateral aspect is convex and rounded Anteromedial border is concave Hilum: indentation where blood vessels and nerves enter Splenic artery supplies blood; splenic vein drains it Surrounded by connective tissue capsule Trabeculae from capsule extend into spleen dividing red and white pulp

21.4b Spleen Tissues of the spleen White pulp Red pulp Clusters of T- and B-lymphocytes and macrophages around central artery Red pulp Contains erythrocytes, platelets, macrophages, and B-lymphocytes Splenic cords: cells and reticular connective tissue in red pulp Splenic sinusoids: very permeable capillaries Storage site for erythrocytes and platelets

Spleen Figure 21.7 Figure 21.7

21.4b Spleen Monitoring blood as it flows through the spleen The spleen filters and monitors blood (not lymph) White pulp monitors it for foreign materials and bacteria Macrophages in sinusoids of red pulp remove particles Phagocytize bacteria, debris, defective erythrocytes and platelets Path of flow: splenic artery, central artery, sinusoids, venules, splenic vein Summary of functions: eat foreign particles, clear defective erythrocytes and platelets, store erythrocytes and platelets In first 5 months of fetal life, spleen makes blood cells This function can be reactivated under certain conditions E.g., some hematologic disorders

Clinical View: Splenectomy Surgical removal of the spleen May be performed due to Ruptured spleen from abdominal injury (most common) Infection, cyst, or tumor Lymphoma or other cancer Blood disorders (e.g., sickle cell anemia) May be more prone to life-threatening infection

21.4c Tonsils Tonsils Secondary lymphatic structures Immune surveillance of inhaled and ingested substances Tonsillar crypts Invaginations that trap material Contain lymphatic nodules Some with germinal centers Figure 21.8b, c

21.4c Tonsils Tonsils (continued) Pharyngeal tonsil Palatine tonsils In nasopharynx Called adenoids when enlarged Palatine tonsils In posterolateral oral cavity Lingual tonsils Along posterior one-third of tongue Figure 21.8a

Clinical View: Tonsillitis and Tonsillectomy Acute tonsillitis: inflammation and infection of tonsils Palatine tonsils most commonly affected Redden and enlarge May partially obstruct pharynx Fever, chills, sore throat, and difficulty swallowing May be infected by viruses or bacteria Persistent recurrent infections, chronic tonsillitis May require tonsillectomy, surgical removal of tonsils

21.4d Lymphatic Nodules and MALT Clusters of lymphatic cells with some extracellular matrix Not completely surrounded by connective tissue capsule Scattered nodules termed diffuse lymphatic tissue Found in every body organ Help defend against infection In some areas, group together to form larger structures E.g., MALT

21.4d Lymphatic Nodules and MALT Mucosa-associated lymphatic tissue Located in gastrointestinal, respiratory, genital, and urinary tracts Found in lamina propria of the mucosa Help defend against foreign substances Prominent in small intestines, especially ileum Peyer patches: large collections of lymphatic nodules that form bulges in ileum wall

Relationship of the Lymphatic System to the Cardiovascular System Figure 21.9a

Relationship of the Lymphatic System to the Immune System Figure 21.9b

What did you learn? What is the typical ratio of afferent and efferent vessels at a lymph node? Which side of the body is the spleen on? Which direction does its hilum face? What functions does the red pulp of the spleen serve? What are Peyer patches?