9. Lymphatic (immune) system. Lymph vessels – microscopic, ultramicroscopic and functional
characteristics of the wall. Lymph.
The lymphatic system is a crucial component of both the circulatory and immune systems. It serves multiple functions:
• Returns interstitial fluid (lymph) to the bloodstream.
• Absorbs lipids from the intestine (via lacteals).
• Plays a key role in immune surveillance and the transport of antigen-presenting cells, lymphocytes, and antibodies.
Its major components include: Lymph capillaries and vessels, Lymph nodes, Lymphoid organs (thymus, spleen, tonsils, MALT), Lymph
(fluid)
The LYMPHOID SYSTEM, an integral part of the immune and circulatory systems, comprises a network of organs, tissues, and vessels
that produce, store, and transport lymph—a clear fluid containing white blood cells (especially lymphocytes) that helps rid the body of
toxins, waste, and other unwanted materials. Its primary functions include maintaining fluid balance, defending the body against
infections, and facilitating the absorption of dietary fats and fat-soluble vitamins from the digestive system.
Constituting Blood Supply: The lymphoid system is closely associated with the blood supply. Blood plasma filters out of capillaries to
become interstitial fluid, which is then collected by lymphatic vessels. This fluid, now called lymph, passes through lymph nodes where
it is filtered and immune responses are initiated. Ultimately, lymph rejoins the bloodstream via the lymphatic ducts. Thus, the blood
supply and lymphatic system work in concert to maintain fluid homeostasis and immune surveillance.
Lymphoid system includes lymph, lymph nodes, lymphoid tissue and lymphatic vessels through which the lymph travels in a one-way
open system (lymph flows only toward the heart). Lymphoid tissue is found in many organs (spleen, thymus, bone marrow), lymph
nodes, lymphoid follicles and tonsils.
Functions:
• production of lymphocytes T in thymus and lymphocytes B in bone marrow and their maturation in bone marrow;
• removal of interstitial fluid from tissues;
• absorption and transport of fatty acids and fats out of the circulatory system;
• transport of immune cells to and from the lymph nodes into the blood like the antigen-presenting cells (APCs), such as dendritic
cells to trigger immune response (indeed, Lymph nodes swell during infection).
Lymph Vessels: Microscopic Characteristics
Lymphatic vessels resemble veins but are thinner-walled and more irregular in shape. They are categorized as:
• Lymphatic capillaries
• Precollecting vessels
• Collecting lymphatic vessels
• Lymphatic trunks and ducts
1. Lymphatic Capillaries: Blind-ended vessels found in most tissues except CNS, bone marrow, and avascular tissues. Wall composed
of:
• Single layer of endothelial cells, with no basement membrane or only a discontinuous one.
• Overlapping junctions between endothelial cells form valve-like openings, allowing one-way entry of fluid, proteins, and immune
cells.
Anchoring filaments connect endothelial cells to surrounding tissue, keeping the lumen open when interstitial pressure rises. In
particular:
Lymph capillaries are the smallest vessels in the lymphatic system, beginning as blind-ended tubes located in the interstitial spaces of
tissues. They possess a distinctive microstructure adapted to their role in fluid absorption:
1. Endothelial Cells: The walls of lymph capillaries are composed of a single layer of overlapping endothelial cells, which function as one-
way valves. These cells are not tightly joined, allowing interstitial fluid to enter the capillaries while preventing its backflow.
2. Basement Membrane: Unlike blood capillaries, lymph capillaries have an incomplete or absent basement membrane, enhancing their
permeability to large molecules and particles.
3. Anchoring Filaments: These fine filaments attach endothelial cells to surrounding connective tissue, preventing the collapse of
capillaries and ensuring they remain open during increased tissue pressure.
2. Collecting Lymphatic Vessels: Have larger diameters and thinner walls than veins. Structured with:
• Endothelium: Continuous, with a thin basement membrane.
• Tunica media: Thin layer of smooth muscle cells, often arranged circularly or spirally.
• Tunica adventitia: Composed of collagen and elastic fibers, with surrounding connective tissue.
Bicuspid valves (semilunar) are frequent and closely spaced, ensuring unidirectional lymph flow. Located in parallel with veins.
Ultramicroscopic (Electron Microscopic) Characteristics
1. Endothelial Cells: Flat and elongated with few organelles. Form overlapping flaps, not tight junctions. Possess numerous pinocytotic
vesicles. Rest on a discontinuous or absent basal lamina, facilitating permeability.
2. Absence of Pericytes: Unlike blood capillaries, lymphatic capillaries lack pericytes, making them more permeable.
3. Smooth Muscle Cells: Found in the media of larger lymphatic vessels. Appear less organized than in veins. Contribute to lymph
propulsion via rhythmic contraction (lymphangion activity).
4. Valves: Made of double folds of endothelial lining with a connective tissue core (rich in collagen and elastic fibers). Project into the
lumen and prevent backflow.
Functional Characteristics of the Lymph Vessel Wall
High permeability: Especially in capillaries, to absorb interstitial fluid, proteins, pathogens, and immune cells.
One-way flow: Maintained by valves and external compression (muscle movement, arterial pulsation).
Low-pressure system: Requires extrinsic forces to move lymph, as there is no central pump.
Immune function: Transports antigens, dendritic cells, lymphocytes, and cytokines to lymph nodes for immune response.
Drainage: Returns lymph to the venous system via the thoracic duct (left) and right lymphatic duct, which drain into the subclavian
veins.
,Lymph: Composition and Function
Lymph is a clear to slightly yellow fluid similar to plasma but with lower protein concentration. It contains:
• Water and electrolytes
• Proteins (especially albumin, globulins)
• Immune cells: T and B lymphocytes, macrophages, dendritic cells
• Lipids: Especially chylomicrons in intestinal lymph (chyle)
• Cell debris, pathogens, and antigens (in inflamed tissues)
Functions
• Maintains fluid balance by returning interstitial fluid to the bloodstream.
• Transports dietary fats from the small intestine to the bloodstream (via lacteals).
• Immune surveillance: Filters lymph through lymph nodes where immune responses are initiated.
• Removes waste and foreign materials from tissues.
Clinical Correlations
Lymphedema: Swelling due to impaired lymph drainage (e.g., post-mastectomy or parasitic infection).
Chylothorax: Accumulation of lymph (chyle) in the pleural space due to thoracic duct damage.
Lymphangitis: Inflammation of lymph vessels, often visible as red streaks on the skin.
Metastasis: Tumor cells often spread via lymphatics before entering the bloodstream.
MOVEMENTS OF THE LYMPH: The lymph is moved through the body in its own vessels making a one-way journey from the
interstitial spaces to the subclavian veins at the base of the neck. Since the lymphatic system does not have a heart to pump it, its
upward movement depends on the motions of the muscle and joint. The movement of lymph through the lymphatic system is a
coordinated process driven by several mechanisms:
1. Lymphatic Pump: The contraction of smooth muscles in the walls of lymphatic vessels propels lymph forward. Valves within the
vessels prevent backflow, ensuring unidirectional movement towards the thoracic and right lymphatic ducts.
2. Skeletal Muscle Contraction: The contraction and relaxation of skeletal muscles during physical activity compress lymphatic
vessels, aiding in the movement of lymph. This mechanism is particularly effective in the limbs.
3. Respiratory Movements: Changes in thoracic pressure during respiration create a pumping effect. During inhalation, decreased
thoracic pressure facilitates the flow of lymph into the thoracic duct, while exhalation helps move lymph from peripheral vessels
towards the thoracic cavity.
4. Arterial Pulsation: The pulsations of nearby arteries exert pressure on adjacent lymphatic vessels, promoting lymph movement.
5. Gravity: In areas above the heart, gravity aids in the movement of lymph.
, 10. Lymphatic (immune) system. Lymph organs. Classification. General microscopic, ultramicroscopic and functional
characteristics of the organs.
The lymphatic system is a crucial component of both the circulatory and immune systems. It serves multiple functions:
• Returns interstitial fluid (lymph) to the bloodstream.
• Absorbs lipids from the intestine (via lacteals).
• Plays a key role in immune surveillance and the transport of antigen-presenting cells, lymphocytes, and antibodies.
Its major components include: Lymph capillaries and vessels, Lymph nodes, Lymphoid organs (thymus, spleen, tonsils, MALT), Lymph
(fluid)
The LYMPHOID SYSTEM, an integral part of the immune and circulatory systems, comprises a network of organs, tissues, and vessels
that produce, store, and transport lymph—a clear fluid containing white blood cells (especially lymphocytes) that helps rid the body of
toxins, waste, and other unwanted materials. Its primary functions include maintaining fluid balance, defending the body against infections,
and facilitating the absorption of dietary fats and fat-soluble vitamins from the digestive system.
Constituting Blood Supply: The lymphoid system is closely associated with the blood supply. Blood plasma filters out of capillaries to become
interstitial fluid, which is then collected by lymphatic vessels. This fluid, now called lymph, passes through lymph nodes where it is filtered
and immune responses are initiated. Ultimately, lymph rejoins the bloodstream via the lymphatic ducts. Thus, the blood supply and
lymphatic system work in concert to maintain fluid homeostasis and immune surveillance.
Lymphoid system includes lymph, lymph nodes, lymphoid tissue and lymphatic vessels through which the lymph travels in a one-way open
system (lymph flows only toward the heart). Lymphoid tissue is found in many organs (spleen, thymus, bone marrow), lymph nodes,
lymphoid follicles and tonsils. Functions:
• production of lymphocytes T in thymus and lymphocytes B in bone marrow and their maturation in bone marrow;
• removal of interstitial fluid from tissues;
• absorption and transport of fatty acids and fats out of the circulatory system;
• transport of immune cells to and from the lymph nodes into the blood like the antigen-presenting cells (APCs), such as dendritic cells
to trigger immune response (indeed, Lymph nodes swell during infection).
Main structures involved:
1. Lymph vessels: lymph capillaries, principal lymph vessels and main lymph vessels (ductus thoracicus and ductus lymphaticus dexter);
2. Central organs: bone marrow and thymus;
3. Peripheral organs: lymph nodes, spleen and the mucosa associated lymphoid tissue (MALT);
Primary Lymphoid Organs: Responsible for the production and maturation of lymphocytes. Lymphocytes become immunocompetent in
these organs (able to recognize specific antigens). Include: Bone marrow (B-cell maturation and origin of all lymphocytes) and Thymus (T-
cell maturation).
Secondary Lymphoid Organs: Sites where mature lymphocytes encounter antigens, become activated, and initiate immune responses.
Include: Lymph nodes, Spleen, Mucosa-associated lymphoid tissue (MALT): tonsils, Peyer’s patches, appendix, etc.
Microscopic and Ultramicroscopic Features of Lymphoid Organs
1. Bone Marrow (Primary Organ)
Microscopic Features: Highly vascularized soft tissue within bone cavities. Composed of:
• Hematopoietic cells, adipocytes, and sinusoidal capillaries.
• Reticular fibers (type III collagen) forming a supporting meshwork.
Ultramicroscopic Features:
• Hematopoietic stem cells with large nuclei and prominent nucleoli.
• Reticular stromal cells and macrophages interact with developing lymphocytes.
Function: Site of lymphocyte origin; B lymphocyte maturation (acquires surface immunoglobulins); Provides a niche for plasma cells during
active immunity.
2. Thymus (Primary Organ)
Microscopic Features: Encapsulated bilobed organ in the superior mediastinum. Divided into lobules with:
• Cortex: densely packed with immature T lymphocytes (thymocytes).
• Medulla: lighter staining, contains mature T cells and Hassall’s corpuscles.
Stroma formed by epithelial reticular cells, not fibroblasts.
Ultramicroscopic Features:
• Thymic epithelial cells (TECs) form a scaffold and secrete thymic hormones (e.g., thymosin).
• Blood-thymus barrier in the cortex prevents premature antigen exposure.
Function: Maturation of T lymphocytes (positive and negative selection); Induces self-tolerance to prevent autoimmunity.
3. Lymph Nodes (Secondary Organ)
Microscopic Features: Small, encapsulated, bean-shaped structures along lymphatic vessels. Structure:
• Cortex: contains lymphoid follicles, with germinal centers (active B-cell proliferation).
• Paracortex: rich in T cells and high endothelial venules (HEVs).
• Medulla: cords of lymphocytes, plasma cells, and macrophages.
Surrounded by connective tissue capsule with trabeculae.
Ultramicroscopic Features:
• Endothelial cells of HEVs allow selective entry of lymphocytes.
• Follicular dendritic cells present antigen to B cells.
• Macrophages and reticular fibers in sinuses filter lymph.
Function: Filters lymph for pathogens and debris; Initiates adaptive immune responses; B and T cell activation, clonal expansion, and
antibody production.
characteristics of the wall. Lymph.
The lymphatic system is a crucial component of both the circulatory and immune systems. It serves multiple functions:
• Returns interstitial fluid (lymph) to the bloodstream.
• Absorbs lipids from the intestine (via lacteals).
• Plays a key role in immune surveillance and the transport of antigen-presenting cells, lymphocytes, and antibodies.
Its major components include: Lymph capillaries and vessels, Lymph nodes, Lymphoid organs (thymus, spleen, tonsils, MALT), Lymph
(fluid)
The LYMPHOID SYSTEM, an integral part of the immune and circulatory systems, comprises a network of organs, tissues, and vessels
that produce, store, and transport lymph—a clear fluid containing white blood cells (especially lymphocytes) that helps rid the body of
toxins, waste, and other unwanted materials. Its primary functions include maintaining fluid balance, defending the body against
infections, and facilitating the absorption of dietary fats and fat-soluble vitamins from the digestive system.
Constituting Blood Supply: The lymphoid system is closely associated with the blood supply. Blood plasma filters out of capillaries to
become interstitial fluid, which is then collected by lymphatic vessels. This fluid, now called lymph, passes through lymph nodes where
it is filtered and immune responses are initiated. Ultimately, lymph rejoins the bloodstream via the lymphatic ducts. Thus, the blood
supply and lymphatic system work in concert to maintain fluid homeostasis and immune surveillance.
Lymphoid system includes lymph, lymph nodes, lymphoid tissue and lymphatic vessels through which the lymph travels in a one-way
open system (lymph flows only toward the heart). Lymphoid tissue is found in many organs (spleen, thymus, bone marrow), lymph
nodes, lymphoid follicles and tonsils.
Functions:
• production of lymphocytes T in thymus and lymphocytes B in bone marrow and their maturation in bone marrow;
• removal of interstitial fluid from tissues;
• absorption and transport of fatty acids and fats out of the circulatory system;
• transport of immune cells to and from the lymph nodes into the blood like the antigen-presenting cells (APCs), such as dendritic
cells to trigger immune response (indeed, Lymph nodes swell during infection).
Lymph Vessels: Microscopic Characteristics
Lymphatic vessels resemble veins but are thinner-walled and more irregular in shape. They are categorized as:
• Lymphatic capillaries
• Precollecting vessels
• Collecting lymphatic vessels
• Lymphatic trunks and ducts
1. Lymphatic Capillaries: Blind-ended vessels found in most tissues except CNS, bone marrow, and avascular tissues. Wall composed
of:
• Single layer of endothelial cells, with no basement membrane or only a discontinuous one.
• Overlapping junctions between endothelial cells form valve-like openings, allowing one-way entry of fluid, proteins, and immune
cells.
Anchoring filaments connect endothelial cells to surrounding tissue, keeping the lumen open when interstitial pressure rises. In
particular:
Lymph capillaries are the smallest vessels in the lymphatic system, beginning as blind-ended tubes located in the interstitial spaces of
tissues. They possess a distinctive microstructure adapted to their role in fluid absorption:
1. Endothelial Cells: The walls of lymph capillaries are composed of a single layer of overlapping endothelial cells, which function as one-
way valves. These cells are not tightly joined, allowing interstitial fluid to enter the capillaries while preventing its backflow.
2. Basement Membrane: Unlike blood capillaries, lymph capillaries have an incomplete or absent basement membrane, enhancing their
permeability to large molecules and particles.
3. Anchoring Filaments: These fine filaments attach endothelial cells to surrounding connective tissue, preventing the collapse of
capillaries and ensuring they remain open during increased tissue pressure.
2. Collecting Lymphatic Vessels: Have larger diameters and thinner walls than veins. Structured with:
• Endothelium: Continuous, with a thin basement membrane.
• Tunica media: Thin layer of smooth muscle cells, often arranged circularly or spirally.
• Tunica adventitia: Composed of collagen and elastic fibers, with surrounding connective tissue.
Bicuspid valves (semilunar) are frequent and closely spaced, ensuring unidirectional lymph flow. Located in parallel with veins.
Ultramicroscopic (Electron Microscopic) Characteristics
1. Endothelial Cells: Flat and elongated with few organelles. Form overlapping flaps, not tight junctions. Possess numerous pinocytotic
vesicles. Rest on a discontinuous or absent basal lamina, facilitating permeability.
2. Absence of Pericytes: Unlike blood capillaries, lymphatic capillaries lack pericytes, making them more permeable.
3. Smooth Muscle Cells: Found in the media of larger lymphatic vessels. Appear less organized than in veins. Contribute to lymph
propulsion via rhythmic contraction (lymphangion activity).
4. Valves: Made of double folds of endothelial lining with a connective tissue core (rich in collagen and elastic fibers). Project into the
lumen and prevent backflow.
Functional Characteristics of the Lymph Vessel Wall
High permeability: Especially in capillaries, to absorb interstitial fluid, proteins, pathogens, and immune cells.
One-way flow: Maintained by valves and external compression (muscle movement, arterial pulsation).
Low-pressure system: Requires extrinsic forces to move lymph, as there is no central pump.
Immune function: Transports antigens, dendritic cells, lymphocytes, and cytokines to lymph nodes for immune response.
Drainage: Returns lymph to the venous system via the thoracic duct (left) and right lymphatic duct, which drain into the subclavian
veins.
,Lymph: Composition and Function
Lymph is a clear to slightly yellow fluid similar to plasma but with lower protein concentration. It contains:
• Water and electrolytes
• Proteins (especially albumin, globulins)
• Immune cells: T and B lymphocytes, macrophages, dendritic cells
• Lipids: Especially chylomicrons in intestinal lymph (chyle)
• Cell debris, pathogens, and antigens (in inflamed tissues)
Functions
• Maintains fluid balance by returning interstitial fluid to the bloodstream.
• Transports dietary fats from the small intestine to the bloodstream (via lacteals).
• Immune surveillance: Filters lymph through lymph nodes where immune responses are initiated.
• Removes waste and foreign materials from tissues.
Clinical Correlations
Lymphedema: Swelling due to impaired lymph drainage (e.g., post-mastectomy or parasitic infection).
Chylothorax: Accumulation of lymph (chyle) in the pleural space due to thoracic duct damage.
Lymphangitis: Inflammation of lymph vessels, often visible as red streaks on the skin.
Metastasis: Tumor cells often spread via lymphatics before entering the bloodstream.
MOVEMENTS OF THE LYMPH: The lymph is moved through the body in its own vessels making a one-way journey from the
interstitial spaces to the subclavian veins at the base of the neck. Since the lymphatic system does not have a heart to pump it, its
upward movement depends on the motions of the muscle and joint. The movement of lymph through the lymphatic system is a
coordinated process driven by several mechanisms:
1. Lymphatic Pump: The contraction of smooth muscles in the walls of lymphatic vessels propels lymph forward. Valves within the
vessels prevent backflow, ensuring unidirectional movement towards the thoracic and right lymphatic ducts.
2. Skeletal Muscle Contraction: The contraction and relaxation of skeletal muscles during physical activity compress lymphatic
vessels, aiding in the movement of lymph. This mechanism is particularly effective in the limbs.
3. Respiratory Movements: Changes in thoracic pressure during respiration create a pumping effect. During inhalation, decreased
thoracic pressure facilitates the flow of lymph into the thoracic duct, while exhalation helps move lymph from peripheral vessels
towards the thoracic cavity.
4. Arterial Pulsation: The pulsations of nearby arteries exert pressure on adjacent lymphatic vessels, promoting lymph movement.
5. Gravity: In areas above the heart, gravity aids in the movement of lymph.
, 10. Lymphatic (immune) system. Lymph organs. Classification. General microscopic, ultramicroscopic and functional
characteristics of the organs.
The lymphatic system is a crucial component of both the circulatory and immune systems. It serves multiple functions:
• Returns interstitial fluid (lymph) to the bloodstream.
• Absorbs lipids from the intestine (via lacteals).
• Plays a key role in immune surveillance and the transport of antigen-presenting cells, lymphocytes, and antibodies.
Its major components include: Lymph capillaries and vessels, Lymph nodes, Lymphoid organs (thymus, spleen, tonsils, MALT), Lymph
(fluid)
The LYMPHOID SYSTEM, an integral part of the immune and circulatory systems, comprises a network of organs, tissues, and vessels
that produce, store, and transport lymph—a clear fluid containing white blood cells (especially lymphocytes) that helps rid the body of
toxins, waste, and other unwanted materials. Its primary functions include maintaining fluid balance, defending the body against infections,
and facilitating the absorption of dietary fats and fat-soluble vitamins from the digestive system.
Constituting Blood Supply: The lymphoid system is closely associated with the blood supply. Blood plasma filters out of capillaries to become
interstitial fluid, which is then collected by lymphatic vessels. This fluid, now called lymph, passes through lymph nodes where it is filtered
and immune responses are initiated. Ultimately, lymph rejoins the bloodstream via the lymphatic ducts. Thus, the blood supply and
lymphatic system work in concert to maintain fluid homeostasis and immune surveillance.
Lymphoid system includes lymph, lymph nodes, lymphoid tissue and lymphatic vessels through which the lymph travels in a one-way open
system (lymph flows only toward the heart). Lymphoid tissue is found in many organs (spleen, thymus, bone marrow), lymph nodes,
lymphoid follicles and tonsils. Functions:
• production of lymphocytes T in thymus and lymphocytes B in bone marrow and their maturation in bone marrow;
• removal of interstitial fluid from tissues;
• absorption and transport of fatty acids and fats out of the circulatory system;
• transport of immune cells to and from the lymph nodes into the blood like the antigen-presenting cells (APCs), such as dendritic cells
to trigger immune response (indeed, Lymph nodes swell during infection).
Main structures involved:
1. Lymph vessels: lymph capillaries, principal lymph vessels and main lymph vessels (ductus thoracicus and ductus lymphaticus dexter);
2. Central organs: bone marrow and thymus;
3. Peripheral organs: lymph nodes, spleen and the mucosa associated lymphoid tissue (MALT);
Primary Lymphoid Organs: Responsible for the production and maturation of lymphocytes. Lymphocytes become immunocompetent in
these organs (able to recognize specific antigens). Include: Bone marrow (B-cell maturation and origin of all lymphocytes) and Thymus (T-
cell maturation).
Secondary Lymphoid Organs: Sites where mature lymphocytes encounter antigens, become activated, and initiate immune responses.
Include: Lymph nodes, Spleen, Mucosa-associated lymphoid tissue (MALT): tonsils, Peyer’s patches, appendix, etc.
Microscopic and Ultramicroscopic Features of Lymphoid Organs
1. Bone Marrow (Primary Organ)
Microscopic Features: Highly vascularized soft tissue within bone cavities. Composed of:
• Hematopoietic cells, adipocytes, and sinusoidal capillaries.
• Reticular fibers (type III collagen) forming a supporting meshwork.
Ultramicroscopic Features:
• Hematopoietic stem cells with large nuclei and prominent nucleoli.
• Reticular stromal cells and macrophages interact with developing lymphocytes.
Function: Site of lymphocyte origin; B lymphocyte maturation (acquires surface immunoglobulins); Provides a niche for plasma cells during
active immunity.
2. Thymus (Primary Organ)
Microscopic Features: Encapsulated bilobed organ in the superior mediastinum. Divided into lobules with:
• Cortex: densely packed with immature T lymphocytes (thymocytes).
• Medulla: lighter staining, contains mature T cells and Hassall’s corpuscles.
Stroma formed by epithelial reticular cells, not fibroblasts.
Ultramicroscopic Features:
• Thymic epithelial cells (TECs) form a scaffold and secrete thymic hormones (e.g., thymosin).
• Blood-thymus barrier in the cortex prevents premature antigen exposure.
Function: Maturation of T lymphocytes (positive and negative selection); Induces self-tolerance to prevent autoimmunity.
3. Lymph Nodes (Secondary Organ)
Microscopic Features: Small, encapsulated, bean-shaped structures along lymphatic vessels. Structure:
• Cortex: contains lymphoid follicles, with germinal centers (active B-cell proliferation).
• Paracortex: rich in T cells and high endothelial venules (HEVs).
• Medulla: cords of lymphocytes, plasma cells, and macrophages.
Surrounded by connective tissue capsule with trabeculae.
Ultramicroscopic Features:
• Endothelial cells of HEVs allow selective entry of lymphocytes.
• Follicular dendritic cells present antigen to B cells.
• Macrophages and reticular fibers in sinuses filter lymph.
Function: Filters lymph for pathogens and debris; Initiates adaptive immune responses; B and T cell activation, clonal expansion, and
antibody production.
