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Questions and Answers
Which mechanism contributes to lymph flow in lymphatic vessels?
Which mechanism contributes to lymph flow in lymphatic vessels?
What is a potential cause of lymphedema?
What is a potential cause of lymphedema?
What type of lymphocyte is responsible for producing antibodies?
What type of lymphocyte is responsible for producing antibodies?
Which of the following statements about lymphatic flow is true?
Which of the following statements about lymphatic flow is true?
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How do macrophages assist in the immune response?
How do macrophages assist in the immune response?
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Which of the following cells form the structural framework of lymphoid tissues?
Which of the following cells form the structural framework of lymphoid tissues?
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What role do dendritic cells play in lymphoid tissues?
What role do dendritic cells play in lymphoid tissues?
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What physical activity effect impacts lymph flow?
What physical activity effect impacts lymph flow?
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Where are lymphatic capillaries absent from?
Where are lymphatic capillaries absent from?
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What role does the glymphatic system play?
What role does the glymphatic system play?
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What is a unique feature of lymphatic capillaries compared to blood capillaries?
What is a unique feature of lymphatic capillaries compared to blood capillaries?
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What happens to the minivalve flaps of lymphatic capillaries when pressure rises inside them?
What happens to the minivalve flaps of lymphatic capillaries when pressure rises inside them?
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What causes lymphangitis?
What causes lymphangitis?
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Which of these conditions may be associated with glymphatic system malfunction?
Which of these conditions may be associated with glymphatic system malfunction?
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What is the role of the vasa vasorum in the lymphatic system?
What is the role of the vasa vasorum in the lymphatic system?
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How do inflamed lymphatics appear during lymphangitis?
How do inflamed lymphatics appear during lymphangitis?
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What are lymph nodes primarily responsible for?
What are lymph nodes primarily responsible for?
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Where are large clusters of lymph nodes typically located?
Where are large clusters of lymph nodes typically located?
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Which cells are primarily responsible for presenting antigens to T cells in lymph nodes?
Which cells are primarily responsible for presenting antigens to T cells in lymph nodes?
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What is the primary function of macrophages in lymph nodes?
What is the primary function of macrophages in lymph nodes?
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Which of the following describes the cortex of a lymph node?
Which of the following describes the cortex of a lymph node?
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What is a unique characteristic of the medulla in a lymph node?
What is a unique characteristic of the medulla in a lymph node?
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Lymph sinuses in a lymph node are primarily composed of which structures?
Lymph sinuses in a lymph node are primarily composed of which structures?
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What assists in the transport of lymph to the bloodstream?
What assists in the transport of lymph to the bloodstream?
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What is the primary function of tonsils?
What is the primary function of tonsils?
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Which type of tonsil is located in the posterior wall of the nasopharynx?
Which type of tonsil is located in the posterior wall of the nasopharynx?
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What feature distinguishes Peyer’s patches from other lymphoid tissues?
What feature distinguishes Peyer’s patches from other lymphoid tissues?
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Which lymphoid structure aids in preventing bacteria from breaching the intestinal wall?
Which lymphoid structure aids in preventing bacteria from breaching the intestinal wall?
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What type of immune response do tonsils help to generate?
What type of immune response do tonsils help to generate?
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Which tonsils are the largest and most frequently infected?
Which tonsils are the largest and most frequently infected?
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What is the role of lymphocytes in tonsils?
What is the role of lymphocytes in tonsils?
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What are tubal tonsils responsible for?
What are tubal tonsils responsible for?
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What is the primary function of MALT?
What is the primary function of MALT?
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Which feature is unique to the thymus in comparison to MALT?
Which feature is unique to the thymus in comparison to MALT?
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Which lymphoid organ is the site for T cell maturation?
Which lymphoid organ is the site for T cell maturation?
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What type of connective tissue is found in the stroma of MALT?
What type of connective tissue is found in the stroma of MALT?
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Which component is absent in the thymus?
Which component is absent in the thymus?
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What is a characteristic feature of MALT?
What is a characteristic feature of MALT?
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Which statement about the thymus is incorrect?
Which statement about the thymus is incorrect?
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Which component is associated with MALT?
Which component is associated with MALT?
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Where is the thymus located?
Where is the thymus located?
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The thymus is most active during adulthood.
The thymus is most active during adulthood.
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The cortex of the thymus contains rapidly dividing lymphocytes and scattered ______.
The cortex of the thymus contains rapidly dividing lymphocytes and scattered ______.
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Which of the following is a function of the thymus?
Which of the following is a function of the thymus?
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What type of cells does the stroma of the thymus consist of?
What type of cells does the stroma of the thymus consist of?
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How does the thymus differ from secondary lymphoid organs?
How does the thymus differ from secondary lymphoid organs?
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Match the lymphoid organs with their major functions:
Match the lymphoid organs with their major functions:
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What is the primary function of the lymphatic system?
What is the primary function of the lymphatic system?
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The major lymphatic structures include lymphatic vessels, lymph, and lymph _____.
The major lymphatic structures include lymphatic vessels, lymph, and lymph _____.
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Which of the following is NOT a function of lymph nodes?
Which of the following is NOT a function of lymph nodes?
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Lymphatic vessels have high pressure compared to the blood vessels.
Lymphatic vessels have high pressure compared to the blood vessels.
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What type of cells do T lymphocytes directly attack?
What type of cells do T lymphocytes directly attack?
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What are the primary lymphoid organs?
What are the primary lymphoid organs?
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The spleen performs functions such as storing iron and recycling breakdown products of red blood cells, as well as destroying ______.
The spleen performs functions such as storing iron and recycling breakdown products of red blood cells, as well as destroying ______.
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What is lymphedema?
What is lymphedema?
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Where do B cells mature?
Where do B cells mature?
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The spleen has a fibrous capsule.
The spleen has a fibrous capsule.
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What are Peyer's patches?
What are Peyer's patches?
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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.
- Cortex (outer part):
- 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.
