This PPT covers the concepts of Lymphatic system and Immunity. This includes functions of Lymphatic system, components of Lymphatic system, Lymphatic organs and tissues, formation and flow of lymph and composition of Lymph

1. THE LYMPHATIC SYSTEM AND IMMUNITY
PREPARED BY: JEGAN. S. NADAR

2. LYMPHATIC SYSTEM
Lymphatic system consist of
 A fluid called-Lymph,
 Vessels called-Lymphatic vessels,
 Structures and organs containing lymphatic tissue, red bone marrow
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3. FUNCTIONS OF LYMPHATIC SYSTEM
Functions of the lymphatic system
 Drain excess interstitial fluid
 Transport dietary lipid
 Carry our immune responses
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4. COMPONENTS OF THE LYMPHATIC SYSTEM
 Lymph
 Lymphatic Vessels
 Lymphatic Capillaries
 Lymphatic Vessels
 Lymphatic Trunks
 Lymphatic Ducts
Lymphatic Organs
 Thymus
 Lymph Nodes
 Spleen
 Tonsils
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5. LYMPH
 What is lymph ?
Tissue fluid (interstitial fluid) that
enters the lymphatic vessels
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6. LYMPHATIC
VESSELS
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7. LYMPH VESSELS
 Lymphatic capillaries –
 Lymphatic collecting vessels
 Lymphatic trunks –
 Lymphatic ducts –
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10. LYMPHATIC CAPILLARY
 Lymphatic capillaries, are located in the spaces between cells and are
closed at one end
 Just as blood capillaries converge to form venules and then veins,
lymphatic capillaries unite to form larger lymphatic vessels
 Lymphatic capillaries have greater permeability than blood capillaries
 Lymphatic capillaries are slightly larger in diameter than blood capillaries
 It is made up of Single layer of overlapping endothelial cells
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11.  It has unique one-way structure that permits interstitial fluid to flow into them
but not out
 When pressure is greater in the interstitial fluid than in lymph, the cells
separate slightly, like the opening of a one-way swinging door, and
interstitial fluid enters the lymphatic capillary.
 When pressure is greater inside the lymphatic capillary, the cells adhere
more closely, and lymph cannot escape back into interstitial fluid
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12.  The small intestine contains special types of lymphatic capillaries called
lacteals.
 Lacteals pick up not only interstitial fluid, but also dietary lipids and lipid-
soluble vitamins.
 The lymph of this area has a milky color due to the lipid and is also called
chyle.
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14. LYMPHATIC COLLECTING VESSEL
 Lymphatic capillaries unite to form larger lymphatic vessels, which resemble
small veins in structure
 Three layered wall but thinner than vein
 More numerous valves than in vein
 At intervals along the lymphatic vessels, lymph flows through lymph nodes,
encapsulated bean-shaped organs consisting of masses of B cells and T
cells

15. LYMPHATIC TRUNKS
 Lymphatic vessels exit lymph nodes and they unite to form lymph trunks
 The principal trunks are the lumbar, intestinal, bronchomediastinal,
subclavian, and jugular trunks
 The lumbar trunks drain lymph from the lower limbs, the wall and viscera of
the pelvis, the kidneys, the adrenal glands, and the abdominal wall.
 The intestinal trunk drains lymph from the stomach, intestines, pancreas,
spleen, apart of the liver.

16.  The bronchomediastinal trunks drain lymph from the thoracic wall,
lung, and heart.
 The subclavian trunks drain the upper limbs.
 The jugular trunks drain the head and neck.
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18. LYMPHATIC DUCTS
 Lymph passes from lymph trunks into two main channels, the thoracic duct
(left lymphatic duct) and the right lymphatic duct, and then drains into
venous blood.
THORACIC (LEFT LYMPHATIC) DUCT
 The thoracic (left lymphatic) duct is about 38–45 cm long
 Begins as a dilation called the cisterna chyli, anterior to the second lumbar
vertebra
 The thoracic duct is the main duct for the return of lymph to blood.
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20.  The cisterna chyli receives lymph from the right and left lumbar trunks and
from the intestinal trunk
 In the neck, the thoracic duct also receives lymph from the left jugular, left
subclavian, and left bronchomediastinal trunks
 Therefore, the thoracic duct receives lymph from the left side of the head,
neck, and chest, the left upper limb, and the entire body inferior to the ribs
 The thoracic duct in turn drains lymph into venous blood at the junction of
the left jugular vein and left subclavian veins.
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23. THE RIGHT LYMPHATIC DUCT
 The right lymphatic duct is about 1.2 cm long
 It receives lymph from the right jugular, right subclavian, and right
bronchomediastinal trunks.
 Thus, the right lymphatic duct receives lymph from the upper right side of
the body.
 From the right lymphatic duct, lymph drains into venous blood at the
junction of the right jugular and right subclavian veins
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24. LYMPHATIC ORGANS
AND
TISSUES
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25. LYMPHATIC ORGANS AND TISSUES
 The lymphatic organs and tissues are classified into two groups based
on their functions.
 Primary lymphatic organs and tissues
 Secondary lymphatic organs and tissues
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26.  The Primary lymphatic organs are the sites where stem cells divide
and become immunocompetent
 The primary lymphatic organs are the red bone marrow and the
thymus.
 The secondary lymphatic organs and tissues are the sites where most
immune responses occur.
 They include lymph nodes, the spleen, and lymphatic nodules
(follicles).
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27. THYMUS
 The thymus is a bilobed organ
 Located in the mediastinum
 Reddish appearance
 Outer layer of connective tissue
holds the two lobes closely together
 But inner a connective tissue
capsule separates the two.
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28.  Extensions of the capsule is called trabeculae
 Trabeculae penetrate inward and divide each lobe into lobules
 Each thymic lobule consists of a dark colored outer cortex and a light
colored central medulla
 The cortex is composed of large numbers of
 T cells
 Dendritic cells,
 Epithelial cells,
 Macrophages
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31.  Immature T cells (pre-t cells) migrate from red bone marrow to
the cortex of the thymus, where they proliferate and begin to mature.
 Dendritic cells are derived from monocytes and assist in maturation
 The epithelial cells help to “educate” the pre-t cells in a process known as
positive selection
 Only about 2% of developing T cells survive in the cortex.
 The remaining cells die via apoptosis (programmed cell death).
 Thymic macrophages help clear out the debris of dead and dying cells.
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32.  The surviving T cells enter the medulla
 The medulla consists of more mature T cells, epithelial cells, dendritic cells,
and macrophages
 Some of the epithelial cells become arranged into concentric layers of flat
cells that degenerate and become filled with keratohyalin granules and
keratin.
 These clusters are called thymic (Hassall’s) corpuscles
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33.  Cells that leave the
thymus via the blood
migrate to lymph
nodes, the spleen,
and other lymphatic
tissues
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34. LYMPH NODES
 Located along lymphatic vessels are about 600 bean-shaped lymph nodes
 Lymph nodes are 1–25 mm (0.04–1 in.) long
 Like thymus lymph nodes are covered by capsule
 Extensions of the capsule is called trabeculae
 Trabeculae penetrate inward and divide each node into lobules
 Internal to the capsule is a supporting network of reticular fibers and
fibroblasts.
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35. Afferent
lymphatic
vessel
Trabecula
Trabecular sinus
Medulla
Capsule
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37.  The capsule, trabeculae, reticular fibers, and fibroblast constitute the
stroma (supporting framework of connective tissue) of a lymph node
 The parenchyma (functioning part) of a lymph node is divide into a
superficial cortex and a deep medulla
 The cortex consists of an outer cortex and an inner cortex.
 Within the outer cortex are egg-shaped aggregates of B cells called
lymphatic nodules
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39.  There are two types of lymphatic nodules
 Primary lymphatic nodule- consisting chiefly of B cells
 Secondary lymphatic nodules- sites of plasma B cell and memory B cell
formation
 The center of a secondary lymphatic nodule contains a region of light
staining cells called a germinal center.
 In the germinal center are B cells, follicular dendritic cells (a special type of
dendritic cell), and macrophages.
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41.  When follicular dendritic cells “present” an Antigen, B cells proliferate and
develop into antibody-producing plasma cells or develop into memory B
cells
 B cells that do not develop properly undergo apoptosis (programmed cell
death)
 Macrophages clear out the debris of dead and dying cells.
 The inner cortex does not contain lymphatic nodules.
 It consists mainly of T cells and dendritic cells that enter a lymph node from
other tissues.
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44.  The dendritic cells present antigens to T cells, causing their proliferation.
 The newly formed T cells then migrate from the lymph node to areas of the
body where there is antigenic activity
 The medulla of a lymph node contains B cells, antibody producing plasma
cells that have migrated out of the cortex into the medulla, and
macrophages
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45. FLOW OF LYMP IN LYMPH NODE
 Lymph flows through a node in one direction only
 It enters lymph node through several afferent lymphatic vessels
 Within the node, lymph enters sinuses, a series of irregular channels
 Efferent lymphatic vessels leave the node at the hilum
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46. (a) Partially sectioned lymph node
Valve
Afferent lymphatic
vessel
Afferent
lymphatic
vessels
Subcapsular sinus
Trabecula
Trabecular sinus
Medullary sinus
Efferent lymphatic vessels
Valve
Hilum
Capsule
Cells in germinal center of outer
cortex
B cells
Follicular dendritic cells
Macrophages
Cells around germinal
center of outer cortex
B cells
Cells of inner cortex
T cells
Dendritic cells
Cells of medulla
B cells
Plasma cells
Macrophages
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47. SPLEEN
 Spleen is the largest single mass of lymphatic tissue in the body measuring
about 12 cm (5 in.) In length
 It is located in the left hypochondriac region
 The superior surface of the spleen is smooth and convex
 Neighboring organs make indentations in the visceral surface of the
spleen—
 The gastric impression (stomach),
 The renal impression (left kidney), and
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49.  Like lymph nodes, the spleen has a hilum.
 Through hilum pass the splenic artery, splenic vein, and efferent
lymphatic vessels.
 A capsule of dense connective tissue surrounds the spleen
 Extension of capsule is Trabeculae,
 Trabeculae extend inward from the capsule.
 The capsule plus trabeculae, reticular fibers, and fibroblasts constitute the
stroma of the spleen
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50.  The parenchyma of the spleen consists of two different kinds of
tissue called white pulp and red pulp
 The White pulp is lymphatic tissue, consisting mostly of lymphocytes
and macrophages arranged around branches of the splenic
artery called central arteries.
 The red pulp consists of blood filled venous sinuses and cords of splenic
tissue called splenic (Billroth’s) cords.
 Splenic cords consist of red blood cells, macrophages, lymphocytes,
plasma cells, and granulocytes.
 Veins are closely associated with the red pulp.
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52.  Blood flowing into the spleen through the splenic artery enters
the central arteries of the white pulp.
 Within the white pulp, B cells and T cells carry out immune functions
 Spleen macrophages destroy blood-borne pathogens by phagocytosis.
 Within the red pulp, the spleen performs three functions related to blood
cells:
 Removal of ruptured, worn out, or defective blood cells and platelets by
macrophages
 Storage of platelets, up to one-third of the body’s supply
 Production of blood cells (hemopoiesis) during fetal life.
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53. LYMPHATIC NODULES
 Lymphatic nodules (follicles) are egg-shaped masses of lymphatic tissue
that are not surrounded by a capsule
 They are scattered throughout the lamina propria of mucous membranes
lining the
 Gastrointestinal tract
 Urinary tract
 Reproductive tract
 Respiratory airways
 lymphatic nodules in these areas are also referred to as mucosa-
associated lymphatic tissue (MALT)
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54. Formation and Flow of Lymph
 Most components of blood plasma, such as nutrients, gases, and
hormones, filter freely through the capillary walls to form interstitial fluid.
 More fluid filters out of blood capillaries than returns to them by
reabsorption
 The excess fluid filtered from blood—about 3 liters per day—drains into
lymphatic vessels and becomes lymph
 Because most plasma proteins are too large to leave blood vessels,
interstitial fluid contains only a small amount of protein
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55.  Thus, an important function of lymphatic vessels is to return the
lost plasma proteins and plasma to the bloodstream
Blood
Interstitial spaces
Lymphatic capillaries Lymphatic vessels
Lymphatic trunks
Lymphatic ducts
Junction of the
internal jugular and
Subclavian veins
FLOW
OF
LYMPH
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56.  Like veins, lymphatic vessels contain valves
 The same two “pumps” that aid the return of venous blood to the heart
maintain the flow of lymph.
1. Skeletal muscle pump
2. Respiratory pump.
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57. SKELETAL MUSCLE PUMP
 The “milking action” of skeletal
muscle contractions compresses
lymphatic vessels (as well as veins)
and forces lymph toward the
junction of the internal jugular and
subclavian veins
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58. RESPIRATORY PUMP
 Lymph flow is also maintained by pressure changes that occur during
inhalation (breathing in)
 Lymph flows from the abdominal region, where the pressure is higher,
toward the thoracic region, where it is lower.
 When the pressures reverse during exhalation (breathing out), the valves in
lymphatic vessels prevent backflow of lymph.
 In addition, when a lymphatic vessel distends, the smooth muscle in its wall
contracts, which helps move lymph from one segment of the vessel to the
next.
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59. COMPOSITION OF LYMPH
 It consist of
Water
Proteins-albumin, globulin, fibrinogens
Carbohydrates
Fats
Chloride, calcium, Phosphorous
Enzymes
Antibodies
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60. Thank You