Chapter 22 The Lymphatic System

1
Chapter 22 The Lymphatic System

• BIO 211 Lab
• Instructor Dr. Gollwitzer

2

• Today in class we will discuss
• Functions of the lymphatic system
• Identify the major components of the lymphoid
  system
• Describe the structure and distribution of
  lymphatic vessels
• Trace lymph flow from peripheral tissues to the
  heart

3
Functions of the Lymphatic System

• Produces, maintains, and distributes lymphocytes
  (primary cells of the lymphatic system)
• Returns fluids and solutes from the peripheral
  tissues to circulation and maintains volume
• Distributes nutrients, waste products and
  hormones from tissues of origin to general
  circulation
• e.g., lipids absorbed by GI tract cannot enter
  capillaries enter lymphatics (lacteals) to
  return to circulation

4
Figure 22-1
5
Components/Organization

• Lymphocytes primary cells
• Lymphoid tissues CT dominated by lymphocytes
• Lymphoid nodule densely packed lymphocytes in
  areolar tissue no fibrous capsule
• Lymphoid organs connected to lymphatic vessels
  and have a capsule
• Nodes filter and purify lymph and provide early
  warning system
• Thymus produces mature T cells
• Spleen filters and purifies blood
• Network of lymphatic vessels (lymphatics)
  distribution system that begins in peripheral
  tissues and ends at veins
• Lymph fluid connective tissue similar to
  plasma, but with no plasma proteins

6
Lymphocytes

• 20-30 of circulating WBCs
• Most of lymphocytes are not circulating in blood
  found in tissues and organs
• Respond to presence of
• Invading pathogens (bacteria, viruses)
• Abnormal body cells (virus-infected cells or
  cancer cells)
• Foreign proteins (toxins released from bacteria)
• Attempt to eliminate these threats or make them
  harmless by a combination of physical and
  chemical attacks

7
Types of WBCs
Figure 1910
8
Lymphocytes

• Produced by lymphopoiesis in
• Red bone marrow (initial site)
• Lymphoid tissues (e.g., tonsils)
• Lymphoid organs (e.g., thymus)
• Derived from hemocytoblasts, lymphoid stem cells
• Stored in lymphoid tissues and organs and red
  bone marrow

9
Lymphopoiesis
Figure 22-6
10
3 Main Types of Lymphocytes

• T cells
• Thymus-dependent
• B cells
• Bone-marrow derived
• NK cells
• Natural killer cells

11
Types of Lymphocytes

• T cells 80 of circulating lymphocytes
• Cytotoxic T cells
• Attack foreign cells or cells infected by viruses
• Often involves direct contact
• Primary cells involved in CMI (cell-mediated
  immunity)
• Helper T cells
• Stimulate responses of T and B cells
• B cells must be activated by helper T cells
  before they can produce antibodies
• Suppressor T cells
• Inhibit T and B cell activites
• Modify the immune response

12
Types of Lymphocytes

• B cells 15 of circulating lymphocytes
• Differentiate into plasma cells ? antibodies
• Antibody target antigen ? destruction of target
  compound or organism
• Anti-body-mediated immunity or humoral (liquid)
  immunity
• Natural killer (NK) cells - 5 of circulating
  lymphocytes
• Police of peripheral tissues immunological
  surveillance
• Directly attack
• Foreign cells
• Cells infected with viruses
• Cancer cells

13
Lymphoid Tissues

• CT dominated by lymphocytes
• Form lymphoid/lymphatic nodules
• Densely packed lymphocytes in areolar tissue
• No capsule
• Have germinal center where lymphocytes are
  dividing
• Found in CT deep to epithelia lining respiratory,
  digestive, and urinary tracts

14
Lymphoid Tissues

• Include
• Tonsils 5 large nodules in wall of pharynx
• 1 pharyngeal tonsil (adenoids) in posterior
  superior wall of nasopharynx
• 2 palatine tonsils at posterior margin of oral
  cavity, along boundary with pharynx
• 2 lingual tonsils under tongue
• Vermiform appendix
• Blind pouch that contains fused lymphoid nodules
• Originates near junction between small and large
  intestines
• MALT (mucosa-associated lymphoid tissues)
• Collection of lymphoid tissues linked with
  digestive system e.g., Peyers Patches clusters
  of lymphoid nodules deep to lining of intestines

15
Figure 22-7b
16
Figure 22-7a
17
Lymphoid Organs

• Tissue capsule
• Distinguishing characteristic
• Fibrous CT capsule separates organs from
  surrounding tissues
• Include
• Lymph nodes
• Thymus
• Spleen

18
Lymph Nodes

• Filter/purify lymph
• Small (ca 1 in. max), kidney bean-shaped organs
• Anatomy
• Capsule - tough, fibrous CT that separates organ
  from surrounding tissues
• Trabeculae - bundles of collagen fibers that
  extend from the capsule and form partitions/walls
• Hilus - shallow indentation where vessels and
  nerves enter/leave

19
Lymph Nodes

• Anatomy (continued)
• Cortex - outer (B cells) and deep (T cells)
• Germinal centers central zones in the cortex of
  a lymphoid nodule that contain dividing
  lymphocytes
• Medulla - core contains B cells and plasma cells
  organized into medullary cords
• Sinuses - open passageways with incomplete walls
• Other cells dendritic dells parenchymal
  cells that bind antigens involved in initiation
  of immune response
• Lymph node vessels
• Afferent vessels - carry lymph to node from
  peripheral tissues
• Efferent vessel - carries lymph away from node
  toward venous circulation at hilus

20
Cortical sinus
Fig. 22-8, part 2, 9th edition
21
Figure. 22-7, part 1, 7th edition
22
Lymph Flow through Lymph Node

• Occurs through network of sinuses
• From afferent lymphatics, enters subcapsular
  sinus that contains a meshwork of
• Branching reticular fibers
• Macrophages
• Dendritic cells antigen-presenting cells
  involved in initiation of immune response

23
Lymph Flow through Lymph Node

• To cortex
• Outer cortex contains B cells with germinal
  centers (like lymphoid nodules)
• Deep cortex dominated by T cells lymphocytes
  leave blood stream and enter lymph nodes here
• To medulla/medullary sinus
• Core of lymph node
• Contains B cells and plasma cells organized into
  medullary cords
• Exits via efferent lymphatic at hilus

24
Lymph Nodes

• Aggregations of lymph nodes (lymph glands a
  misnomer)
• Located where peripheral lymphatics connect with
  trunk
• Axillary
• Inguinal
• Cervical
• Swollen glands
• Indicate inflammation or infection in peripheral
  tissues
• Painful enlargement due to increase in number of
  lymphocytes and phagocytes in response to minor,
  localized infection
• Nonpainful, chronic or excessive enlargement
  lymphadenopathy
• May occur in response to bacterial or viral
  infections, endocrine disorders, cancer

25
Functions of Lymph Nodes

• Filter and purify lymph before entering venous
  circulation
• Fixed macrophages in walls of sinuses engulf
  debris and pathogens
• Remove 99 of antigens
• Some processed by macrophages and presented to
  nearby lymphocytes
• Others bind to dendritic cells where they can
  stimulate lymphocyte activity antigen
  presentation first step in immune response
• Provide an early warning system
• Infection or abnormality in peripheral tissue ?
  abnormal antigens into interstitial fluid ? lymph
  ? lymph nodes ? stimulate macrophages and
  lymphocytes

26
Thymus

• Produces mature T cells
• Location in mediastinum, posterior to sternum
• Appearance is pink with a grainy consistency
• Changes over lifespan
• Largest size (relative to body weight) in first 2
  years of life
• Maximum size just before puberty
• After puberty, begins to involute (get smaller)
• Continues to decrease in size and becomes
  fibrous may be cause of decreased immunity in
  older population

27
Figure 22-9 The Thymus
Thyroid gland
Trachea
Rightlobe
Leftlobe
THYMUS
Right lobe
Leftlobe
Septa
Leftlung
Rightlung
Heart
Lobule
Diaphragm
Anatomicallandmarks onthe thymus.
The appearance and position of the thymus
inrelation to other organs in the chest.
Septa
Cortex
Medulla
Lymphocytes
Lobule
Thymiccorpuscle
Reticularcells
Lobule
The thymus gland
LM ? 50
A thymic corpuscle
LM ? 550
Fibrous septa divide the tissue of the thymus
into lobulesresembling interconnected lymphoid
nodules.
Higher magnification reveals the
unusualstructure of thymic corpuscles. The
smallcells are lymphocytes in various stages
ofdevelopment.
28
Thymus

• Anatomy
• Has a capsule
• 2 connected lobes
• Septae (plural)
• Fibrous partitions divide lobes into lobules
• Lobules
• Cortex - densely packed cells, including
• Dividing lymphocytes, arranged in clusters
  surrounded by
• Reticular epithelial cells
• Maintain blood-thymus barrier
• Secrete thymic hormones (thymosins) that
  stimulate stem cell divisions and T cell
  differentiation into mature T cells
• Mature T cells then migrate to medulla
• Medulla - no barrier so cells can now enter blood

29
Spleen

• Filters/purifies blood
• Largest collection of lymphoid tissue
• Functions
• Removes abnormal blood cells and other blood
  components by phagocytosis
• Stores iron from recycled RBCs
• Initiates immune responses by B cells and T cells
  in response to antigens in circulating blood

30
Spleen

• Anatomy
• Soft consistency reflects shape of organs that
  surround it (stomach, left kidney, diaphragm)
• Fibrous capsule
• Hilus (groove, blood lymphatic vessels
  enter/exit)
• Red pulp - large sinusoids containing many RBCs
  plus macrophages and lymphocytes
• White pulp - dense lymphocytes ? white
  appearance resembles lymphoid nodules can
  respond to any antigen in blood

31
Spleen

• Impact to left side in automobile accidents,
  contact sportsspleen can tear easily ? internal
  bleeding and circulatory shock
• Due to fragility, difficult to repair surgically
• Usually remove entire organ (splenectomy)
• Person survives without difficulty but at risk
  for bacterial infections

32
Figure 22-10, 7th edition
33
Lymphatic Vessels

• From peripheral tissues to venous system
• Lymphatic capillaries
• Terminal lymphatics misnomer because mark
  beginning of lymphatic vessels
• Branches in peripheral tissues
• Different from regular capillaries
• Originate as blind pockets
• Larger in diameter
• Thinner walls
• In cross-section- have flattened/irregular
  outline
• Lined by endothelium, with incomplete/absent
  basement membrane

34
Lymphatic Vessels

• Lymphatic capillaries (continued)
• Endothelial cells not tightly bound, but overlap
• Acts as 1-way valve, propels lymph in one
  direction
• Permits entry of large solutes, e.g., proteins,
  bacteria, viruses, cell debris, but prevents
  their return to intercellular spaces
• Present in almost every tissue and organ (except
  cornea, bone marrow, CNS)
• Lacteals
• Special lymphatic capillaries in small intestine
• Transport lipids from digestive tract

35
Figure 22-2
36
Lymphatic Vessels

• Small lymphatic vessels
• Lead toward trunk (via larger lymphatics)
• Similar to veins
• Same vessel walls
• Minimal pressures
• Have valves
• Prevent backflow
• Often in close association with blood vessels
• Differ in relative size (smaller), general
  appearance (e.g. color), and branching pattern

37
Figure 22-3a, b
38
Lymphatic Vessels

• Larger lymphatic vessels (2 kinds)
• Superficial lymphatics
• Found underlying membranes throughout body
  (e.g., skin mucus, serous)
• Deep lymphatics
• Largest vessels
• Accompany deeper arteries and veins

39
Lymphatic Vessels

• Larger lymphatics converge to form large
  lymphatic trunks (RL)
• Jugular trunks
• Drain head, neck
• Subclavian trunks
• Drain upper limbs
• Bronchomediastinal trunks
• Drain thoracic tissues/organs
• Lumbar trunks
• Drain back, lower limbs
• Intestinal trunk
• Drain abdominopelvic area

40
Figure 22-4b The Relationship between the
Lymphatic Ducts and the Venous System
Brachiocephalic veins
Left internal jugular vein
Left jugular trunk
Right internal jugular vein
Thoracic duct
Right jugular trunk
Left subclavian trunk
Right lymphatic duct
Left bronchomediastinaltrunk
Right subclavian trunk
Right subclavian vein
Left subclavianvein
Right bronchomediastinal trunk
Superiorvena cava (cut)
First rib(cut)
Azygos vein
Highestintercostalvein
Rib (cut)
Thoracicduct
Thoraciclymph nodes
Hemiazygosvein
Parietalpleura (cut)
Diaphragm
Cisterna chyli
Inferior vena cava (cut)
Intestinal trunk
Left lumbar trunk
Right lumbar trunk
The thoracic duct empties into the left
subclavian vein. The rightlymphatic duct drains
into the right subclavian vein.
41
Lymphatic Vessels

• Lymphatic trunks empty into two large collecting
  vessels
• Thoracic duct
• Collects lymph from tissues
• From L side of upper body (above diaphragm)
• Inferior to the diaphragm
• R lymphatic duct
• Collects lymph from tissues
• From R side of upper body (above diaphragm)

42
Figure 22-4a, 7th edition
43
Lymphatic Vessels

• Thoracic duct
• Base expanded chamber cisterna chyli
• Receives lymph from
• Inferior abdomen, pelvis, and lower limbs
• via R and L lumbar trunks and intestinal trunks
• Collects lymph from L bronchomediastinal trunk, L
  subclavian trunk, and L jugular trunk
• Empties into L subclavian vein
• Right lymphatic duct
• Formed by merging of R jugular, R subclavian, and
  R bronchomediastinal trunks
• Empties into R subclavian vein

44
(No Transcript)
45
Lymph

• Fluid in lymphatic vessels
• Formed from blood plasma forced out of capillary
  by hydrostatic pressure into interstitial spaces
  (? interstitial fluid)
• Interstitial fluid accumulates and increases
  pressure
• Lymphatics pick up excess so edema doesnt occur
• As lymph returns to CVS, cells of immune system
  (e.g. lymphocytes, macrophages in lymphoid
  tissues/organs) monitor its composition and
  respond to signs of injury or infection
• Cells
• 99 lymphocytes (T and B cells)
• Remaining 1 are primarily phagocytes
  microphages (eosinophils, neutrophils) and
  macrophages (monocytes)

46
Lymphedema

• Blockage of lymph drainage from a limb (e.g.,
  following removal of lymph nodes)
• Causes severe swelling
• Interferes with immune system function