lymphatic and immune system
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PRESENTED BY:
DR MARIAM ASIF
IMMUNE SYSTEM
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LYMPHATIC AND IMMUNE SYSTEM
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The Lymphatic and Immune Systems
• Main structures of the lymphatic system– Lymphatic vessels
• Main components of the immune system– Lymphocytes– Lymphoid tissue– Lymphoid organs
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The Lymphatic System
• Lymphatic vessels collect tissue fluid from loose connective tissue – Carry fluid to great veins
in the neck– Fluid flows only toward
the heart
Figure 20.1
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Functions of Lymphatic Vessels
• Collect excess tissue fluid and blood proteins
• Return tissue fluid and blood proteins to bloodstream
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Orders of Lymphatic Vessels
• Lymph capillaries - smallest lymph vessels– first to receive lymph
• Lymphatic collecting vessels– collect from lymph capillaries
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Orders of Lymphatic Vessels
• Lymph nodes– scattered along collecting vessels
• Lymph trunks– collect lymph from collecting vessels
• Lymph ducts– empty into veins of the neck
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Lymphatic Capillaries
• Located near blood capillaries
• Receive tissue fluid from CT
- increased volume of tissue fluid - minivalve flaps open and allow fluid to enter
• Highly permeability allows entrance of– tissue fluid– bacteria, viruses, and cancer cells
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Lymphatic Capillaries
• Lacteals
– specialized lymphatic capillaries
- located in the villi of the small intestines
- receive digested fats
- fatty lymph – chyle
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Lymphatic Capillaries
Figure 20.2a, b
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Lymphatic Collecting Vessels
• Accompany blood vessels
• Composed of the same three tunics as BVs
• Contain more valves than veins do – helps direct the flow of blood
• Lymph propelled by– bulging of skeletal muscles– pulsing of nearby arteries– tunica media of the lymph vessels
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Lymph Nodes
• Cleanse the lymph of pathogens
• Human body contains around 500
• Lymph nodes are organized in clusters
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Lymph Nodes
Figure 20.3
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Microscopic Anatomy of a Lymph Node
• Fibrous capsule – surrounds lymph nodes
• Trabeculae – connective tissue strands
• Lymph vessels– Afferent lymphatic vessels– Efferent lymphatic vessels
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Figure 20.4a
Lymph Node Microscopic
Anatomy
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Lymph Trunks• Lymphatic collecting vessels converge
Five major lymph trunks:
• Lumbar trunks - receives lymph from lower limbs
• Intestinal trunk - receives chyle, digestive organs
• Bronchomediastinal trunks - collects lymph from thoracic viscera
• Subclavian trunks - receive lymph from upper limbs and thoracic wall
• Jugular trunks - drain lymph from head & neck
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Lymph Nodes, Trunks, and Ducts
Figure 20.3
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The Lymphatic
Trunks
Figure 20.6a
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Lymph Ducts
• Cisterna chyli– located at the union of lumbar and intestinal trunks
• Thoracic duct– Ascends along vertebral bodies– Empties into venous circulation – Junction of left internal jugular and left subclavian veins– Drains three quarters of the body
• Right lymphatic duct – empties into right internal jugular and subclavian veins
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The Immune System
• Recognizes specific foreign molecules
• Destroys pathogens effectively
• Key cells – lymphocytes
• Also includes lymphoid tissue and lymphoid organs
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Lymphocytes
• Infectious organisms attacked by inflammatory response– macrophages, then lymphocytes
• Cytotoxic T lymphocytes – Attack foreign cells directly– Binds to antigen-bearing cells– Perforates cell membrane– Signals cell to undergo apoptosis
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Lymphocytes
• B lymphocytes- become plasma cells
- secrete antibodies, mark cells for destruction by macrophages
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Figure 20.7
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Lymphocyte Activation
• Lymphocytes originate in bone marrow
• T lymphocytes travel to the thymus gland
• B lymphocytes stay in bone marrow
• Able to recognize a unique antigen
• Gain immunocompetence– travels through blood stream– meets and binds to a specific antigen
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Lymphocyte Activation
• Activating T or B cells produce– Effector lymphocytes
• Short-lived, attack immediately
– Memory lymphocytes• Wait until body encounters their antigen again
– Basis of acquired immunity– Guard against subsequent infections
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Figure 20.8
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Lymphoid Tissue
• Most important tissue of the immune system
Two general locations:
• Mucous membranes of digestive, urinary, respiratory, and reproductive tracts- Mucosa-associated lymphoid tissue (MALT)
• Lymphoid organs (except thymus)
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Lymphoid Organs
• Primary lymphoid organs– Bone marrow– Thymus
• Secondary lymphoid organs– Lymph nodes, spleen, tonsils– Aggregated lymphoid nodules– Appendix
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Figure 20.10
Lymphoid Organs
• Designed to gather, destroy infectious microorganisms
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Thymus
• Immature lymphocytes develop into T lymphocytes - secretes thymic hormones - most active in childhood
• Functional tissue atrophies with age- composed of cortex and medulla- medulla contains Hassall’s corpuscles (thymic corpuseles)
• Differs from other lymphoid organs- functions strictly in lymphocyte maturation- arises from epithelial tissue
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Thymus
Figure 20.11
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Lymph Nodes
Functional pathway
• Lymph percolates through lymph sinuses
• Most antigenic challenges occur in lymph nodes
• Antigens destroyed – activate B and T lymphocytes
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Spleen
• Largest lymphoid organ
• Two main blood-cleansing functions– Removal of blood-borne antigens– Removal and destruction of old or defective blood cells
• Site of hematopoiesis in the fetus
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Spleen
• Destruction of antigens
• Site of B cell maturation into plasma cells
• Phagocytosis of bacteria and worn-out RBCs, WBCs and platelets
• Storage of platelets
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• White pulp – thick sleeves of lymphoid tissue
• Red pulp - surrounds white pulp- composed of venous sinuses
- splenic cords
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Spleen
Figure 20.12
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Tonsils
• Simplest lymphoid organs
• Four groups of tonsils– palatine, lingual, pharyngeal, and tubal tonsils
• Arranged in a ring to gather and remove pathogens
• Underlying lamina propria consists of MALT
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Palatine Tonsil
Figure 20.13
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Aggregated Lymphoid Nodules and Appendix
• MALT – abundant in walls of intestines
• Fight invading bacteria
• Generate a wide variety of memory lymphocytes- aggregated lymphoid nodules (Peyer’s patches)
- located in the distal part of the small intestine
• Appendix – tubular offshoot of the cecum
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Aggregated Lymphoid Nodule
Figure 20.14
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Disorders of the Lymphatic and Immune Systems
• Chylothorax - leakage of fatty lymph into the thorax
• Lymphangitis - inflammation of a lymph vessel
• Mononucleosis - caused by Epstein-Barr virus- attacks B lymphocytes
• Hodgkin’s disease - malignancy of lymph nodes• Non-Hodgkin’s lymphoma - uncontrolled
multiplication- metastasis of undifferentiated lymphocytes
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The Lymphatic and Immune Systems Throughout Life
• Lymphatic vessels and lymph nodes– develop from lymphatic sacs
• Thymus originates as an outgrowth of endoderm
• Spleen, lymph nodes, and MALT – arise from mesodermal mesenchyme