The Lymphatic and Immune Systems

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The Lymphatic and Immune Systems

• Chapter 20

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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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Lymph Node Microscopic Anatomy
Figure 20.4a
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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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Lymphoid Organs

• Designed to gather, destroy infectious
  microorganisms

Figure 20.10
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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 Hassalls 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 (Peyers 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
• Hodgkins disease - malignancy of lymph nodes
• Non-Hodgkins 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