Lymphatic System Overview
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Questions and Answers

Which mechanism contributes to lymph flow in lymphatic vessels?

  • Milking action of skeletal muscles (correct)
  • Increased atmospheric pressure
  • Constant lymphatic pressure from muscles
  • Regulated blood pressure from arteries
  • What is a potential cause of lymphedema?

  • Tumors blocking lymphatics (correct)
  • High protein intake
  • Increased lymphocyte activity
  • Excessive exercise
  • What type of lymphocyte is responsible for producing antibodies?

  • T lymphocytes
  • Macrophages
  • Dendritic cells
  • B lymphocytes (correct)
  • Which of the following statements about lymphatic flow is true?

    <p>Lymph flow is aided by one-way valves.</p> Signup and view all the answers

    How do macrophages assist in the immune response?

    <p>By activating T cells</p> Signup and view all the answers

    Which of the following cells form the structural framework of lymphoid tissues?

    <p>Reticular cells</p> Signup and view all the answers

    What role do dendritic cells play in lymphoid tissues?

    <p>Capturing and delivering antigens</p> Signup and view all the answers

    What physical activity effect impacts lymph flow?

    <p>Physical activity increases lymph flow.</p> Signup and view all the answers

    Where are lymphatic capillaries absent from?

    <p>Bones and teeth</p> Signup and view all the answers

    What role does the glymphatic system play?

    <p>Drains interstitial and cerebrospinal fluids</p> Signup and view all the answers

    What is a unique feature of lymphatic capillaries compared to blood capillaries?

    <p>They have overlapping endothelial cells that form minivalves</p> Signup and view all the answers

    What happens to the minivalve flaps of lymphatic capillaries when pressure rises inside them?

    <p>They close to prevent backflow of lymph</p> Signup and view all the answers

    What causes lymphangitis?

    <p>Congestion of blood in larger lymphatics</p> Signup and view all the answers

    Which of these conditions may be associated with glymphatic system malfunction?

    <p>Alzheimer’s disease</p> Signup and view all the answers

    What is the role of the vasa vasorum in the lymphatic system?

    <p>To provide nutrients and oxygen to larger lymphatics</p> Signup and view all the answers

    How do inflamed lymphatics appear during lymphangitis?

    <p>As red streaks that are tender to the touch</p> Signup and view all the answers

    What are lymph nodes primarily responsible for?

    <p>Cleansing lymph and activating the immune system</p> Signup and view all the answers

    Where are large clusters of lymph nodes typically located?

    <p>In the inguinal, axillary, and cervical regions</p> Signup and view all the answers

    Which cells are primarily responsible for presenting antigens to T cells in lymph nodes?

    <p>Dendritic cells</p> Signup and view all the answers

    What is the primary function of macrophages in lymph nodes?

    <p>To remove and destroy microorganisms</p> Signup and view all the answers

    Which of the following describes the cortex of a lymph node?

    <p>Houses densely packed follicles filled with B cells</p> Signup and view all the answers

    What is a unique characteristic of the medulla in a lymph node?

    <p>It contains medullary cords with thin extensions of cortical tissue</p> Signup and view all the answers

    Lymph sinuses in a lymph node are primarily composed of which structures?

    <p>Lymphatic capillaries spanned by reticular fibers</p> Signup and view all the answers

    What assists in the transport of lymph to the bloodstream?

    <p>Collecting lymphatic vessels</p> Signup and view all the answers

    What is the primary function of tonsils?

    <p>Gather and remove pathogens</p> Signup and view all the answers

    Which type of tonsil is located in the posterior wall of the nasopharynx?

    <p>Pharyngeal tonsil</p> Signup and view all the answers

    What feature distinguishes Peyer’s patches from other lymphoid tissues?

    <p>Contain large clusters of lymphoid follicles</p> Signup and view all the answers

    Which lymphoid structure aids in preventing bacteria from breaching the intestinal wall?

    <p>Appendix</p> Signup and view all the answers

    What type of immune response do tonsils help to generate?

    <p>Long-term immunity</p> Signup and view all the answers

    Which tonsils are the largest and most frequently infected?

    <p>Palatine tonsils</p> Signup and view all the answers

    What is the role of lymphocytes in tonsils?

    <p>Activate immunity against pathogens</p> Signup and view all the answers

    What are tubal tonsils responsible for?

    <p>Surrounding openings of auditory tubes</p> Signup and view all the answers

    What is the primary function of MALT?

    <p>Prevention of pathogens from penetrating mucous membranes</p> Signup and view all the answers

    Which feature is unique to the thymus in comparison to MALT?

    <p>Epithelial tissue corpuscles</p> Signup and view all the answers

    Which lymphoid organ is the site for T cell maturation?

    <p>Thymus</p> Signup and view all the answers

    What type of connective tissue is found in the stroma of MALT?

    <p>Reticular connective tissue</p> Signup and view all the answers

    Which component is absent in the thymus?

    <p>Lymphoid follicles</p> Signup and view all the answers

    What is a characteristic feature of MALT?

    <p>Site of lymphocyte activation and proliferation</p> Signup and view all the answers

    Which statement about the thymus is incorrect?

    <p>It is a site for B cell activation.</p> Signup and view all the answers

    Which component is associated with MALT?

    <p>Lymphoid follicles</p> Signup and view all the answers

    Where is the thymus located?

    <p>Inferior neck, extending into the mediastinum and partially overlying the heart.</p> Signup and view all the answers

    The thymus is most active during adulthood.

    <p>False</p> Signup and view all the answers

    The cortex of the thymus contains rapidly dividing lymphocytes and scattered ______.

    <p>macrophages</p> Signup and view all the answers

    Which of the following is a function of the thymus?

    <p>Maturation of T lymphocytes</p> Signup and view all the answers

    What type of cells does the stroma of the thymus consist of?

    <p>Epithelial cells</p> Signup and view all the answers

    How does the thymus differ from secondary lymphoid organs?

    <p>Does not directly fight antigens</p> Signup and view all the answers

    Match the lymphoid organs with their major functions:

    <p>Lymph nodes = Cleanse lymph and activate lymphocytes Spleen = Cleanses blood and removes aged red blood cells Thymus = Site of T cell maturation MALT = Prevents pathogens from penetrating mucous membranes</p> Signup and view all the answers

    What is the primary function of the lymphatic system?

    <p>Returns fluids leaked from blood vessels back to blood.</p> Signup and view all the answers

    The major lymphatic structures include lymphatic vessels, lymph, and lymph _____.

    <p>nodes</p> Signup and view all the answers

    Which of the following is NOT a function of lymph nodes?

    <p>Producing red blood cells</p> Signup and view all the answers

    Lymphatic vessels have high pressure compared to the blood vessels.

    <p>False</p> Signup and view all the answers

    What type of cells do T lymphocytes directly attack?

    <p>Infected cells.</p> Signup and view all the answers

    What are the primary lymphoid organs?

    <p>Thymus</p> Signup and view all the answers

    The spleen performs functions such as storing iron and recycling breakdown products of red blood cells, as well as destroying ______.

    <p>aged red blood cells</p> Signup and view all the answers

    What is lymphedema?

    <p>Insufficient return of lymph to blood leading to severe localized edema.</p> Signup and view all the answers

    Where do B cells mature?

    <p>Red bone marrow</p> Signup and view all the answers

    The spleen has a fibrous capsule.

    <p>True</p> Signup and view all the answers

    What are Peyer's patches?

    <p>Large clusters of lymphoid follicles in the wall of the distal portion of the small intestine.</p> Signup and view all the answers

    Study Notes

    Lymphatic Vessels

    • Lymphatic capillaries are blind-ended vessels that weave between tissue cells and blood capillaries
    • Lymphatic capillaries are absent from bones and teeth
    • In the brain, astrocytes form channels that connect to lymphatics in meninges, together forming the glymphatic system
    • The glymphatic system helps drain ECF (interstitial and cerebrospinal fluids) and their wastes
    • Malfunction of the glymphatic system may contribute to degenerative diseases like Alzheimer’s
    • Lymphatic capillaries are more permeable than blood capillaries
    • Lymphatic capillary permeability is due to overlapping endothelial cells that form one-way minivalves
    • Pressure inside lymphatic capillaries forces minivalve flaps shut, preventing lymph backflow

    Lymphatic Trunks and Ducts

    • Lymphatic trunks are large lymphatic vessels formed by the convergence of collecting lymphatic vessels
    • Lymphatic ducts are the largest lymphatic vessels, formed by the union of lymphatic trunks
    • The two major lymphatic ducts are the right lymphatic duct and the thoracic duct
    • The right lymphatic duct drains lymph from the right upper limb, right side of the head and thorax, and right upper quadrant of the abdomen
    • The thoracic duct drains lymph from the rest of the body

    Lymph Transport

    • Lymphatic vessels are low-pressure conduits
    • Lymphatic vessels rely on mechanisms used to promote unidirectional blood flow through low-pressure veins
    • These mechanisms include the milking action of skeletal muscles, pressure changes in the thorax during breathing, pulse pressure waves from adjacent arteries, and rhythmic contractions of smooth muscle in the walls of lymphatics

    Lymphoid Cells

    • Lymphoid cells are immune system cells found in lymphoid tissues
    • Lymphoid cells include T lymphocytes (T cells), B lymphocytes (B cells), macrophages, dendritic cells, and reticular cells
    • Activated T cells manage immune responses and directly attack and destroy infected cells
    • Activated B cells produce plasma cells which secrete antibodies that mark antigens for destruction

    Lymphoid Tissues

    • Lymphoid tissues contain lymph nodes, tonsils, Peyer’s patches and the appendix
    • Lymphoid tissues are strategically located sites where lymphocytes encounter antigens and are activated

    Lymph Nodes

    • Lymph nodes are the most important secondary lymphoid organs
    • Lymph nodes are clustered along lymphatic vessels, mostly imbedded in connective tissue
    • Large clusters of lymph nodes are found near the body surface in the inguinal, axillary, and cervical regions
    • Lymph nodes cleanse lymph by acting as lymph “filters”
    • Macrophages in lymph nodes remove and destroy microorganisms and other substances that enter lymph
    • Lymph nodes are involved in immune system activation
    • Dendritic cells in lymph nodes present antigens to T cells, activating them to mount an attack

    Structure of a Lymph Node

    • Most lymph nodes are bean-shaped and small
    • Lymph nodes are surrounded by an external fibrous capsule with fibers extending inward to divide the node into compartments
    • The outer part of a lymph node is the cortex, containing densely packed follicles with germinal centers filled with dividing B cells
    • The deep part of the cortex houses T cells in transit
    • The inner part of a lymph node is the medulla, consisting of medullary cords containing B cells, T cells, and plasma cells
    • Lymph sinuses are large lymphatic capillaries throughout the node
    • Macrophages reside on reticular fibers in the lymph sinuses, phagocytizing foreign matter in the lymph

    Tonsils

    • Tonsils are a ring of lymphoid tissue around the entrance to the pharynx
    • Tonsils gather and remove pathogens in food or inhaled air
    • Tonsils are named according to location: Palatine, Lingual, Pharyngeal, and Tubal
    • Tonsils contain follicles with germinal centers and diffusely scattered lymphocytes
    • Tonsils trap debris and bacteria, activating immune cells and building “memory” against these pathogens

    Peyer’s Patches

    • Peyer’s patches are large clusters of lymphoid follicles in the wall of the distal portion of the small intestine
    • Peyer’s patches are structurally similar to tonsils
    • Peyer’s patches prevent bacteria from breaching the intestinal wall and generate “memory” lymphocytes for long-term immunity

    Appendix

    • The appendix is a tubular offshoot of the first part of the large intestine containing a large number of lymphoid follicles
    • The appendix prevents bacteria from breaching the intestinal wall and generates “memory” lymphocytes for long-term immunity

    Clinical Homeostatic Imbalances

    • Lymphangitis occurs when larger lymphatics become congested with blood during severe inflammation
    • Lymphangitis appears as red streaks that are tender to the touch
    • Lymphedema is insufficient return of lymph to the blood, resulting in severe localized edema
    • Lymphedema can be caused by tumors blocking lymphatics or removal of lymphatics during cancer surgery

    The Lymphatic System

    • The lymphatic system returns fluids leaked from blood vessels back to blood.
    • It consists of lymphatic vessels, lymph, and lymph nodes.
    • Lymphoid organs and tissues provide the structural basis of the immune system.
    • Lymphoid organs and tissues play a role in the body’s defense mechanisms and resistance to disease.
    • Structures include the spleen, thymus, tonsils, lymph nodes, and other lymphoid tissues.

    Lymphatic Vessels

    • Lymphatic vessels collect excess protein-containing interstitial fluid and return it to the blood.
    • They also transport pathogens to lymph nodes and absorbed fats from the intestine to the blood.

    Lymphatic Capillaries

    • Lymphatic capillaries are blind-ended vessels that weave between tissue cells and blood capillaries.
    • They are absent from bones and teeth.
    • In the brain, astrocytes form channels that connect to lymphatics in the meninges; together, they form the glymphatic system.
    • They are much more permeable than blood capillaries due to two unique endothelial cell modifications:
      • Overlap loosely to form one-way minivalves.
      • When pressure rises inside lymphatic capillaries, minivalve flaps are forced shut; this action prevents lymph from leaking back out as pressure moves it along.

    Lymphatic Transport

    • Lymphatic vessels are low-pressure conduits; they rely on the same structures and mechanisms that promote unidirectional blood flow through low pressure veins.
    • Mechanisms that promote flow through lymphatics:
      • Milking action of skeletal muscles.
      • Pressure changes in the thorax during breathing.
      • Pulse pressure waves from adjacent arteries.
      • Rhythmic contractions of smooth muscle in the walls of (all but the smallest) lymphatics.

    Lymphoid Cells and Tissues

    • Lymphoid cells consist of immune system cells found in lymphoid tissues together with supporting cells that form the “scaffolding” of those tissues.
    • Immune system cells in lymphoid tissues:
      • T lymphocytes (T cells): activated T cells manage the 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 methods.
      • Macrophages phagocytize foreign substances and activate T cells.
      • Dendritic cells capture and deliver antigens to lymph nodes to activate T cells.

    Lymphoid Tissues

    • Lymphoid tissues are an important component of the immune system.
    • They house and provide activation and proliferation sites for lymphocytes.
    • They are largely composed of (loose) reticular connective tissue.
    • They dominate all the lymphoid organs except the thymus.
    • Macrophages reside on reticular fibers.
    • Spaces between fibers provide a place for lymphocytes to “live" when they return from patrolling the body.

    Lymphoid Organs (Primary Lymphoid Organs)

    • Primary lymphoid organs are where T and B cells mature.
    • B cells mature in red bone marrow.
    • T cells mature in the thymus.

    Lymphoid Organs (Secondary Lymphoid Organs)

    • Secondary lymphoid organs include:
      • Lymph nodes and spleen.
      • Collections of mucosa-associated lymphoid tissue (MALT) that form:
        • Tonsils, Peyer’s patches in the small intestine, and the appendix
        • Diffuse lymphoid tissues

    Lymph Nodes

    • Lymph nodes cleanse lymph and house lymphocytes.
    • They are clustered along lymphatics and are the most important secondary lymphoid organs.
    • Hundreds are found throughout the body, mostly imbedded in connective tissue.
    • Two basic protective functions:
      • Cleansing the Lymph: Act as lymph “filters” as lymph is transported back to blood.
      • Immune system activation: Strategically located in sites where lymphocytes encounter antigens and are activated to mount an attack against them.

    Lymph Node Structure

    • Most lymph nodes are bean-shaped and small (length < 2.5 cm or ~1 in).
    • The shape and size vary, however, with the largest cluster near the body surface in the inguinal, axillary, and cervical regions.
    • They are surrounded by an external fibrous capsule; fibers extend inward as trabeculae to divide the node into compartments.
    • There are 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 the 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 that can be found throughout the node.
      • Macrophages reside on reticular fibers and phagocytize foreign matter found in the lymph.

    Lymphatic System Circulation

    • Lymph enters the node via afferent lymphatic vessels.
    • It travels through a large subcapsular sinus, followed by smaller sinuses of the cortex and medulla.
    • Lymph passes through the medullary sinuses before exiting the node at the hilum (indented region on the concave side) via efferent lymphatic vessels.
    • The flow of lymph is very slow because there are fewer efferent vessels draining the node than afferent vessels feeding it.
    • This slow flow provides sufficient time for lymphocytes and macrophages to function.

    The Spleen

    • The spleen removes bloodborne pathogens and aged red blood cells.
    • It is about the size of a fist and is the largest lymphoid organ.
    • It is located on the left side of the abdominal cavity, under the diaphragm.
    • Three additional 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.

    Spleen Structure

    • Like lymph nodes, the spleen is surrounded by a fibrous capsule and has trabeculae.
    • It consists of two components:
      • White pulp: where immune function occurs (mostly lymphocytes on reticular fibers, forming "cuffs" around the central arteries, it appears as islands of white in a 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]).

    MALT

    • Mucosa-associated lymphoid tissue (MALT) guards the body’s entryways against pathogens.
    • It is found in mucous membranes throughout the body.
    • It protects the body from pathogens trying to enter.
    • Largest collections include the tonsils, Peyer’s patches, and the appendix.

    Tonsils

    • Tonsils form a ring of lymphoid tissue around the entrance to the pharynx.
    • They gather and remove pathogens in food or air we inhale.
    • Types of tonsils:
      • Paired palatine tonsils (on either side at the posterior end of the oral cavity; largest and most often infected).
      • Lingual tonsil (lumpy collection of lymphoid follicles at the base of the tongue).
      • Pharyngeal tonsil (adenoid if enlarged; in the posterior wall of the nasopharynx).
      • Pair of tubal tonsils (surround the openings of the auditory tubes into the pharynx).
    • They contain follicles with obvious germinal centers and diffusely scattered lymphocytes.
    • They trap debris and bacteria that cross epithelium to enter lymphoid tissue; immune cells are activated and build “memory” against these pathogens.

    Peyer's Patches

    • Peyer’s patches (aggregated lymphoid nodules) are large clusters of lymphoid follicles in the wall of the distal portion of the small intestine.
    • They are structurally like tonsils.
    • They prevent bacteria from breaching the intestinal wall and generate “memory” lymphocytes for long-term immunity.

    Appendix

    • The appendix is a tubular offshoot of the first part of the large intestine that contains a large number of lymphoid follicles.
    • It is ideally located to:
      • Prevent bacteria from breaching the intestinal wall.
      • Generate “memory” lymphocytes for long-term immunity.

    The Thymus

    • The thymus is a bilobed lymphoid organ found in the inferior neck; it extends into the mediastinum and partially overlies the heart.
    • It is the site of T lymphocyte development.
    • It is most active and largest during childhood.
    • After puberty, it gradually atrophies; in older adults, it is replaced mostly by fibrous and fatty tissue and becomes difficult to distinguish from the surrounding connective tissue.
    • Even though it atrophies through life, the thymus still produces immunocompetent cells, though more slowly.

    The Thymus Structure

    • The thymus is 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, which are important for preventing autoimmune responses.
    • The thymus (primary lymphoid organ) differs from secondary lymphoid organs in three important ways:
      • It has no follicles because it lacks B cells.
      • It does not directly fight antigens; its function is strictly in T lymphocyte maturation.
      • Its stroma consists of epithelial cells (not reticular fibers), which provide an environment in which T lymphocytes mature.

    Lymphoid Organs and Tissues

    • Lymph Nodes:
      • Cleanse lymph, acting as a filter.
      • Site for lymphocyte activation and proliferation.
      • Possess a capsule, medulla, and cortex containing follicles.
      • Stroma is composed of reticular connective tissue.
      • Features include both afferent and efferent lymphatic vessels.
    • Spleen:
      • Cleanse blood and removes aged or defective red blood cells.
      • Site for lymphocyte activation and proliferation.
      • Stores platelets, monocytes, and iron.
      • Possesses a capsule but no medulla.
      • Features include white and red pulp.
      • White pulp contains lymphoid follicles.
      • Stroma is composed of reticular connective tissue.
    • MALT (Mucosa-Associated Lymphoid Tissues):
      • Prevents pathogens from penetrating mucous membranes.
      • Site for lymphocyte activation and proliferation.
      • Contains lymphoid follicles and diffuse lymphoid tissue.
      • Stroma is composed of reticular connective tissue.
      • No capsule or medulla.
    • Thymus:
      • Site of T cell maturation.
      • Possesses a capsule, medulla, and cortex.
      • Stroma is composed of epithelial tissue and features thymic corpuscles.
      • No lymphoid follicles.
    • Lymph:
      • Leaked fluid recovered from tissues.
      • Transported back to the heart to maintain blood volume.
      • May contain cellular debris or pathogens.
    • Immune System:
      • Scans lymph for debris and pathogens.
      • Employs both non-specific (macrophages) and specific (B-cell/plasma cell antibodies) mechanisms.
      • Returns cleansed fluid to the cardiovascular system.

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    Description

    This quiz covers the structure and function of lymphatic vessels, including lymphatic capillaries and ducts. It explores the role of the glymphatic system in fluid drainage and its connection to neurodegenerative diseases. Test your knowledge of lymphatic vessel characteristics and their significance in the human body.

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