The Lymphatic
Biology 2122
Chapter 20
Functions of the Lymphatic System
1. Drain Excess ‘interstitial’ fluid
◦ 2-3 L of fluid lost from the blood stream/day
2. Transport dietary lipids
◦ From GI tract to the blood (lipids and lipid-soluble vitamins)
3. Immune Response
◦ A. Cell-mediated response
 T-cell response (cytotoxic cells destroy antigens)
◦ B. Humoral – response
 Antibody-mediated (B-Cells)
Basic Structure
1. Lymph Fluid
◦ Interstitial fluid ------ lymph
capillaries
2. Lymph Vessels
◦ Capillaries, ducts, etc.
3. Lymph Tissue and Organs
◦ Specialized reticular tissue
◦ Large numbers of lymphocytes
◦ Organs: Thymus gland;
Tonsils; Spleen
Lost lymph fluid - returned to the
heart.
1. Capillaries
◦ Endothelial Cells and mini-valves
 Supported by collagen
 One way pressure from the capillaries
move lymph towards the capillaries
◦ Very permeable
2. Capillaries form vessels
◦ Skin follow veins; viscera follow path of
arteries
◦ Lymph flows into the nodes
◦ No lymph vessels (cartilage, epidermis,
cornea- all avacular); CNS
and red bone marrow
Tissues to the
Heart
Chyle and Lacteals
Lipids absorption take place in the small intestine
Lacteals
◦ Small capillaries in the absorptive cells
◦ Lipids transported from lacteals into the blood
 Specialized lipid absorption
Chyle
◦ In small intestine lymph is white or creamy due to lipid presence
(lymph is normally clear)
Flow and Structure
Capillaries -----
Collecting vessels ----
Nodes --- Trunks ------
Lymph ducts (thoracic
and right lymphatic) ---- Internal jugular and
Subclavian vein ----
Heart
On the way to the heart
1. Trunks – lumbar, intestinal, bronchomediastinal,
subclavian, jugular
◦
◦
◦
◦
◦
A. lumbar
B. intestinal
C. bronchomediastinal
D. subclavian
E. Jugular
2. Thoracic (left lymphatic) duct
◦
Cisterna chyli
◦ Main duct for return of lymph to blood from left side of body
◦ Drains into the L.internal jugular and L.subclavian vein
On the way to the heart
3. Right lymphatic duct
– Receives lymph from
right side of the body
– Drains blood into
venous blood at
junction of R. internal
jugular and R.
subclavian veins
Flow of Lymph against Gravity
Same problems as encountered by venous return
Pumps
◦ 1. Skeletal system pump
◦ 2. Respiratory pump
Organs and
Tissues
Organs and Tissues
1. Primary Organs – stem cell division produces mature
cells – immunocompetent
◦ Red bone marrow
 B – cells; pre-T cells
◦ Thymus
 Pre-T cells migrate to thymus to become immunocompetent
2. Secondary Organs
◦ Site of immune system response
◦ Nodes, spleen, nodules
 Bi-lobed- surrounded by CT
and separated by capsule
 Trabeculae -separates tissue
into lobes
 Lobe
◦ Cortex -(T-cells and Dendritic
cells, Epithelial cells and
Macrophages)
◦ Medulla – mature T-cells,
dendritic cells and macrophoges
◦ Thymic (Hassal’s corpusles)
Thymus
Lymphatic Nodules
Lymph Nodes
◦ B-cells (primary lymphatic nodule)
◦ Plasma and memory B cells in outer
cortex (secondary lymphatic nodule)
B-cell in primary nodule recognizes
antigen and transforms into a
secondary nodule
◦ Germinal center
◦ B-cells, follicular dendritic cells,
macrophages
Antigen presented by APC (B-cell;
dendritic , etc.) B- cells develop into
plasma and memory cells
Inner cortex and medulla
 Covered by Dense CT capsule
Covered by Dense CT capsule
Visceral peritoneum – serous membrane
Stroma
◦ Trabeculae, reticular fibers and fibroblasts
Parenchyma
◦ 1. White pulp – lymphocytes and macrophages around central
arteries (splenic artery branches)
◦ 2. Red pulp – venous sinuses, cords of splenic tissue or splenic cords
(RBCs, macrophages, lymphocytes, plasma cells, granulocytes
Spleen
Nodules
 No capsule
 Found in mucous membranes (near lamina propria) in GI
tract, urinary, reproductive, respiratory airways
◦ “Mucosa-associated lymphatic tissue (MALT)
 Can be small or larger tissue
◦ Tonsils (5)-Pharyngeal area
 Pharyngeal (adenoid- posterior nasopharynx)
 Palatine (2)-posterior region of oral cavity (tonsillectomy)
 Lingual (2)-base of tongue