HAP Chapter 20: The Lymphatic System and Lymphoid Organs PDF

Marieb Human Anatomy & Physiology Twelfth Edition Chapter 20 The Lymphatic System and Lymphoid Organs and Tissues PowerPoint® Lecture Slides...

Marieb Human Anatomy & Physiology Twelfth Edition Chapter 20 The Lymphatic System and Lymphoid Organs and Tissues PowerPoint® Lecture Slides prepared by Justin A. Moore, American River College Copyright © 2025 Pearson Education, Inc. All Rights Reserved Video: Why This Matters (Career Connection) Understanding the structure and function of the lymph nodes allows you to evaluate a patient for signs of infection Copyright © 2025 Pearson Education, Inc. All Rights Reserved The Lymphatic System and Lymphoid Organs and Tissues Lymphatic system returns fluids leaked from blood vessels back to blood; consists of: – Lymphatic vessels - Network of drainage vessels – Lymph- Fluid in lymphatic vessels. – Lymph nodes - Structures that cleanse lymph as it passes through Lymphoid organs and tissues provide structural basis of immune system – Role in body’s defense mechanisms and resistance to disease – Structures include spleen, thymus, tonsils, lymph nodes, other lymphoid tissues Lymph Fluid Copyright © 2025 Pearson Education, Inc. All Rights Reserved  20.1 The Lymphatic System Includes Lymphatic Vessels , Lymph, and Lymph Nodes Hydrostatic and colloid osmotic pressures in blood capillaries force fluid out at one end of the capillary and reabsorb it at the other end – The difference (up to 3 L daily) becomes part of the interstitial fluid Lymphatic vessels, or lymphatics, collect the excess protein- containing interstitial fluid and return it to the blood – Also transport pathogens to lymph nodes and absorbed fats from intestine to blood Copyright © 2025 Pearson Education, Inc. All Rights Reserved Distribution and Structure of Lymphatic Vessels Lymphatic capillaries – Blind-ended vessels that weave between tissue cells and blood capillaries ▪ Absent from bones and teeth ▪ In brain, astrocytes form channels that connect to lymphatics in meninges; together form glymphatic system – Helps drain E C F (interstitial and cerebrospinal fluids) and their wastes – Malfunction may play role in degenerative diseases (e.g., Alzheimer’s) – Like blood capillaries, but much more permeable due to two unique endothelial cell modifications: ▪ Overlap loosely to form one-way minivalves ▪ When pressure rises inside lymphatic capillaries, minivalve flaps forced shut; prevents lymph from leaking back out as pressure moves it along Copyright © 2025 Pearson Education, Inc. All Rights Reserved Distribution and Special Features of Lymphatic Capillaries (1 of 2) Figure 20.1a Distribution and special features of lymphatic capillaries. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Distribution and Special Features of Lymphatic Capillaries (2 of 2) Figure 20.1b Distribution and special features of lymphatic capillaries. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Major Lymphatic Trunks and Ducts Figure 20.2 Major lymphatic trunks and ducts. Copyright © 2025 Pearson Education, Inc. All Rights Reserved The Lymphatic System Figure 20.3 The lymphatic system. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Clinical—Homeostatic Imbalance 20.1 Like larger blood vessels, larger lymphatics receive blood supply from a vasa vasorum (small blood vessels providing oxygen and nutrients to the walls of larger arteries and veins) – Become congested with blood during severe inflammation, called lymphangitis – Inflamed lymphatics appear as red streaks that are tender to the touch Copyright © 2025 Pearson Education, Inc. All Rights Reserved Lymph Transport Lymphatic vessels are low-pressure conduits; rely on same structures and mechanisms that promote unidirectional blood flow through low- pressure veins – Mechanisms (with help of one-way valves) that promote flow through lymphatics: ▪ Milking action of skeletal muscles ▪ Pressure changes in thorax during breathing ▪ Pulse pressure waves from adjacent arteries ▪ Rhythmic contractions of smooth muscle in walls of (all but smallest) lymphatics Physical activity increases flow of lymph – Immobilize badly infected body part to restrict outflow of inflammatory materials Copyright © 2025 Pearson Education, Inc. All Rights Reserved Clinical—Homeostatic Imbalance 20.2 Lymphedema: insufficient return of lymph to blood resulting in severe localized edema – May be caused by tumors blocking lymphatics or removal of lymphatics during cancer surgery – May improve if some lymphatic pathways remain and enlarge Copyright © 2025 Pearson Education, Inc. All Rights Reserved 20.2 Lymphoid Cells and Tissues Are Found in Lymphoid Organs and in Connective Tissue of Other Organs Copyright © 2025 Pearson Education, Inc. All Rights Reserved Lymphoid Cells (1 of 2) Consist of immune system cells found in lymphoid tissues together with supporting cells that form “scaffolding” of those tissues Immune system cells in lymphoid tissues: ▪ T lymphocytes (T cells) – Activated T cells manage immune response; some directly attack and destroy infected cells ▪ B lymphocytes (B cells) – Activated B cells produce plasma cells, which secrete antibodies that mark antigens for destruction by phagocytosis or other means – Macrophages phagocytize foreign substances and activate T cells – Dendritic cells capture and deliver antigens to lymph nodes to activate T cells Copyright © 2025 Pearson Education, Inc. All Rights Reserved Lymphoid Cells (2 of 2) Supporting cells – Reticular cells: fibroblast-like cells that produce reticular fiber stroma (network that supports other cell types) in lymphoid organs and tissues Copyright © 2025 Pearson Education, Inc. All Rights Reserved  Lymphoid Tissue (1 of 2) Lymphoid tissue is: – An important component of the immune system: ▪ Houses and provides activation and proliferation sites for lymphocytes ▪ Ideal surveillance location for lymphocytes and macrophages – Largely composed of (loose) reticular connective tissue ▪ Dominates all the lymphoid organs except thymus ▪ Macrophages reside on reticular fibers ▪ Spaces between fibers provide place for lymphocytes to “live” when they return from patrolling body Copyright © 2025 Pearson Education, Inc. All Rights Reserved Lymphoid Tissue (2 of 2) Lymphoid tissue comes in various “packages”: – Diffuse lymphoid tissue: loose arrangement of lymphoid cells and reticular fibers ▪ Found in virtually every body organ ▪ Larger collections in lamina propria of mucous membranes – Lymphoid follicles (lymphoid nodules): solid, spherical bodies consisting of tightly packed lymphoid cells and reticular fibers ▪ Often have lighter-staining germinal centers of proliferating B cells ▪ May form part of larger lymphoid organs, like lymph nodes ▪ Isolated aggregations of lymphoid follicles found in: – Intestinal wall (of ileum), called Peyer’s patches – The appendix Copyright © 2025 Pearson Education, Inc. All Rights Reserved  Lymphoid Organs (1 of 4) Lymphoid organs are grouped into two functional categories: – Primary lymphoid organs: where T and B cells mature ▪ B cells mature in red bone marrow ▪ T cells mature in thymus – Secondary lymphoid organs: where mature lymphocytes first encounter their antigens and become activated; include: ▪ Lymph nodes and spleen ▪ Collections of mucosa-associated lymphoid tissue (MALT) that form: – Tonsils, Peyer’s patches in small intestine, and appendix ▪ Diffuse lymphoid tissues Copyright © 2025 Pearson Education, Inc. All Rights Reserved Lymphoid Organs (2 of 4) Figure 20.5 Lymphoid organs. Copyright © 2025 Pearson Education, Inc. All Rights Reserved 20.3 Lymph Nodes Cleanse Lymph and House Lymphocytes Clustered along lymphatics, lymph nodes are the most important secondary lymphoid organs – Hundreds throughout body, mostly imbedded in connective tissue – Large clusters near body surface in inguinal, axillary, and cervical regions (where collecting lymphatic vessels converge to form trunks) Two basic protective functions: – Cleansing the lymph: act as lymph “filters” as lymph is transported back to blood ▪ Macrophages remove and destroy microorganisms and other substances that enter lymph (that we don’t want entering blood) – Immune system activation: strategically located in sites where lymphocytes encounter antigens and are activated to mount attack against them ▪ Many antigens brought to lymph nodes from their point of entry by dendritic cells, which present them to (and activate) T cells Copyright © 2025 Pearson Education, Inc. All Rights Reserved The Lymphatic System (2 of 2) Figure 20.3 The lymphatic system. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Structure of a Lymph Node Shape and size vary, but most are bean shaped and small (length < 2.5 cm or 1 in) – Surrounded by external fibrous capsule; fibers extend inward as trabeculae to divide node into compartments Two histologically distinct regions: – Cortex (outer part): ▪ Superficial part contains densely packed follicles, many with germinal centers filled with dividing B cells ▪ Deep part houses T cells in transit (circulate among blood, nodes, and lymph) ▪ Abundant dendritic cells throughout – Medulla (inner part): consists of medullary cords, thin inward extensions of cortical tissue ▪ Contains B cells, T cells, and plasma cells Lymph sinuses: large lymphatic capillaries spanned by crisscrossing reticular fibers; found throughout node – Macrophages reside on reticular fibers; phagocytize foreign matter in lymph Copyright © 2025 Pearson Education, Inc. All Rights Reserved Lymph Node (1 of 2) Figure 20.6 Lymph node. Copyright © 2025 Pearson Education, Inc. All Rights Reserved  Circulation in the Lymph Nodes Lymph enters via afferent lymphatic vessels – Then travels through large subcapsular sinus followed by smaller sinuses of cortex and medulla Lymph passes through medullary sinuses before exiting node at the hilum (indented region on concave side) via efferent lymphatic vessels Fewer efferent vessels draining node than afferent vessels feeding it, so flow of lymph very slow, providing time for lymphocytes and macrophages to function – Lymph travels through several nodes before completely cleansed Copyright © 2025 Pearson Education, Inc. All Rights Reserved Lymph Node (2 of 2) Figure 20.6a Lymph node. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Clinical—Homeostatic Imbalance 20.3 Buboes: infected lymph nodes (often pus-filled); bubonic plague named for them – Overwhelmed by bacteria they are trying to destroy – Results in inflamed, swollen, and tender nodes—a condition often referred to (erroneously) as swollen “glands”—but correctly called lymphadenopathy Lymph nodes can become secondary cancer sites if metastasizing cells become trapped – Cancer-infiltrated lymph nodes are swollen but usually not painful, which helps distinguish cancerous nodes from infected Copyright © 2025 Pearson Education, Inc. All Rights Reserved 20.4 The Spleen Removes Bloodborne Pathogens and Aged Red Blood Cells (1 of 2) Spleen is soft, blood-rich organ about size of fist – Largest lymphoid organ; located in left side of abdominal cavity, under diaphragm – Served by splenic artery and vein, which enter and exit at the hilum – Provides site for lymphocyte proliferation and immune surveillance and response – Cleanses blood of aged and defective blood cells and platelets (via macrophages) Spleen also performs three additional, and related, functions: – Stores iron and recycles breakdown products of red blood cells for later reuse – Stores blood platelets and monocytes for release into the blood when needed – May be a site of fetal erythrocyte production Copyright © 2025 Pearson Education, Inc. All Rights Reserved Lymphoid Organs (3 of 4) Figure 20.5 Lymphoid organs. Copyright © 2025 Pearson Education, Inc. All Rights Reserved The Spleen (1 of 4) Figure 20.7a The spleen. Copyright © 2025 Pearson Education, Inc. All Rights Reserved The Spleen (2 of 4) Figure 20.7c The spleen. Copyright © 2025 Pearson Education, Inc. All Rights Reserved 20.4 The Spleen Removes Bloodborne Pathogens and Aged Red Blood Cells (2 of 2) Like lymph nodes, spleen is surrounded by fibrous capsule and has trabeculae Histologically, spleen consists of two components: – White pulp: where immune function occurs ▪ Mostly lymphocytes on reticular fibers, forming “cuffs” around central arteries; appear as islands of white in sea of red – Red pulp: where old blood cells and bloodborne pathogens are destroyed ▪ Lots of RBCs and macrophages that engulf them ▪ Composed of splenic cords (reticular tissue) that separate blood-filled splenic sinusoids (venous sinuses) Copyright © 2025 Pearson Education, Inc. All Rights Reserved The Spleen (3 of 4) Figure 20.7b The spleen. Copyright © 2025 Pearson Education, Inc. All Rights Reserved The Spleen (4 of 4) Figure 20.7d The spleen. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Clinical—Homeostatic Imbalance 20.4 Spleen has a thin capsule, so direct blow or severe infection may cause it to rupture, spilling blood into peritoneal cavity Splenectomy: surgical removal of spleen – Was standard treatment, thought necessary to prevent life- threatening hemorrhage and shock, but surgeons have discovered spleen can often repair itself if left alone ▪ Frequency of emergency splenectomies has decreased dramatically Liver and bone marrow take over most of spleen’s functions if removed – In children younger than 12, spleen will regenerate if a small part remains Copyright © 2025 Pearson Education, Inc. All Rights Reserved 20.5 MALT Guards the Body’s Entryways Against Pathogens Mucosa-associated lymphoid tissue (MALT) – Lymphoid tissues in mucous membranes throughout body ▪ Lining the respiratory, genitourinary, and digestive tracts ▪ Protects us from pathogens trying to enter body – Largest collections include: ▪ Tonsils ▪ Peyer’s patches ▪ Appendix Copyright © 2025 Pearson Education, Inc. All Rights Reserved  Tonsils Form ring of lymphoid tissue around entrance to pharynx (seen as swellings of mucosa) – Gather and remove pathogens in food or inhaled air Named according to location – Paired palatine tonsils: on either side at posterior end of oral cavity ▪ Largest and most often infected – Lingual tonsil: lumpy collection of lymphoid follicles at base of tongue – Pharyngeal tonsil (adenoid if enlarged): in posterior wall of nasopharynx – Pair of tubal tonsils: surround openings of auditory tubes into pharynx Contain follicles with obvious germinal centers and diffusely scattered lymphocytes – Trap debris and bacteria (which cross epithelium to enter lymphoid tissue) ▪ Immune cells activated and build “memory” against these pathogens Copyright © 2025 Pearson Education, Inc. All Rights Reserved Histology of the Palatine Tonsil Figure 20.8 Histology of the palatine tonsil. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Peyer’s Patches Peyer’s patches (aggregated lymphoid nodules): large clusters of lymphoid follicles in wall of distal portion of small intestine – Structurally like tonsils – Ideally located to: ▪ Prevent bacteria from breaching intestinal wall ▪ Generate “memory” lymphocytes for long-term immunity Copyright © 2025 Pearson Education, Inc. All Rights Reserved Peyer’s Patch (Aggregated Lymphoid Nodules) Figure 20.9 Peyer’s patch (aggregated lymphoid nodules). Copyright © 2025 Pearson Education, Inc. All Rights Reserved  Appendix Appendix: tubular offshoot of first part of large intestine that contains large number of lymphoid follicles Like Peyer’s patches, ideally located to: – Prevent bacteria from breaching intestinal wall – Generate “memory” lymphocytes for long-term immunity Copyright © 2025 Pearson Education, Inc. All Rights Reserved 20.6 T Lymphocytes Mature in the Thymus (1 of 2) Thymus: bilobed lymphoid organ found in inferior neck; extends into mediastinum and partially overlies heart Thymus is site of T lymphocyte development – Most active and largest during childhood – After puberty, gradually atrophies – In older adults, replaced almost entirely by fibrous and fatty tissue ▪ Becomes difficult to distinguish from surrounding connective tissue ▪ Still produces immunocompetent cells, though more slowly Copyright © 2025 Pearson Education, Inc. All Rights Reserved 20.6 T Lymphocytes Mature in the Thymus (2 of 2) Thymus divided into thymic lobules that contain an outer cortex and inner medulla – Cortex contains rapidly dividing lymphocytes (the bulk of thymic cells) and scattered macrophages – Medulla contains fewer lymphocytes and structures called thymic corpuscles ▪ Involved in the development of regulatory T cells (important for preventing autoimmune responses) – Thymus (primary lymphoid organ) differs from secondary lymphoid organs in three important ways: ▪ Has no follicles because it lacks B cells ▪ Does not directly fight antigens, functions strictly in T lymphocyte maturation – Blood thymus barrier keeps immature T lymphocytes isolated from antigens to prevent premature activation ▪ Stroma consists of epithelial cells (not reticular fibers), which provide environment in which T lymphocytes mature Copyright © 2025 Pearson Education, Inc. All Rights Reserved The Thymus Figure 20.10 The thymus. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Table 20.1 Summary of Lymphoid Organs and Tissues* (1 of 2) Cortex and Lymphoid Special Blank Major Functions Capsule Medulla Follicles Stroma Features Lymph nodes Cleanse lymph Yes Yes Yes (in cortex) Reticular Both afferent Site for connective and efferent lymphocyte tissue lymphatic An illustration shows a lymph node. activation and vessels proliferation Spleen Cleanses blood Yes No Yes (in white Reticular Red and white and removes pulp) connective pulp aged or tissue An illustration shows the spleen. defective red blood cells Site for lymphocyte activation and proliferation Stores platelets, monocytes, and iron Copyright © 2025 Pearson Education, Inc. All Rights Reserved Table 20.1 Summary of Lymphoid Organs and Tissues* (2 of 2) Cortex and Lymphoid Special Major Functions Capsule Medulla Follicles Stroma Features Prevent No No Yes Reticular Diffuse M A L T super dagger symbol. MALT † pathogens from connective lymphoid penetrating tissue tissue in An illustration shows mucosa-associated lymphoid tissues, or M A L T, in the intestines. mucous addition to membrane follicles Site for lymphocyte activation and proliferation Thymus Site of T cell Yes Yes No Epithelial Thymic An illustration shows the thymus. maturation tissue corpuscles *Red bone marrow, a primary lymphoid organ, is not included. † MALT = mucosa-associated lymphoid tissues. Copyright © 2025 Pearson Education, Inc. All Rights Reserved The Big Picture: Lymph is “leaked” fluid recovered from tissues - this fluid is transported back to the heart to maintain blood volume - this fluid may contain cellular debris, pathogens (in the case of injury or infection) The immune system scans this fluid and cleans it up - non-specific mechanisms (macrophages) - specific mechanisms (B-cell/plasma cell antibodies) The cardiovascular system receives this fluid Copyright © 2025 Pearson Education, Inc. All Rights Reserved Review Animation https://mediaplayer.pearsoncmg.com/assets/secs-ipweb-immune-system-rev Copyright © 2025 Pearson Education, Inc. All Rights Reserved