LYMPHATICORGANSANDTISSUES

INTRODUCTION a. right lymphatic duct

Parts: Functions: - drains lymph from the right upper arm and the right side of the
1. lymphatic vessels 1. returns fluids that have leaked from the head and thorax
2. lymph nodes blood vascular system back to the b. thoracic duct
3. other lymphoid organs and tissues blood - receives lymph from the rest of the body; as it runs superiorly,
2. protects the body by removing foreign it receives lymphatic drainage from the left side of the thorax,
lymph - the interstitial fluid that enters the material from the lymph stream left upper limb, and the head region
lymphatics; clear, pale-yellow except chyle 3. provides a site for immune surveillance
Each duct empties its lymph at the junction of the internal jugular vein and
LYMPHATICVESSELS subclavian vein.
- aka lymphatics Lymph Transport
Functions The lymphatic system lacks an organ that acts as a pump.
return excess tissue fluid to the bloodstream The flow of lymph is slow (~3 L per day); it is maintained by skeletal muscle
return leaked proteins to the blood contraction, pressure changes in the thorax, and contractions of the lymphatic
carry absorbed fat from the intestine to the blood (through lacteals). vessels. Backflow is prevented by valves.
Distribution and Structure of Lymphatic Vessels
form a one-way system in which lymph flows only toward the heart LYMPHOIDCELLS
begins in microscopic blind-ended lymphatic capillaries lymphocytes
- between the cells and blood capillaries in the loose connective tissues - arise in red bone marrow
- remarkably permeable - mature into either:
the edges of adjacent cells overlap each other loosely, forming easily 1. T cells (T lymphocytes) - manage the immune response; some directly
opened, flaplike minivalves attack and destroy infected cells
collagen filaments anchor the endothelial cells to surrounding 2. B cells (B lymphocytes) - produce plasma cells that secrete antibodies
structures into the blood (or other body fluids)
- lacteals: highly specialized lymphatic capillaries present in the villi of the lymphoid macrophages - phagocytize foreign substances and helps activate T
intestinal mucosa cells
- chyle: milky white fatty lymph draining from the digestive viscera spiny-looking dendritic cells - capture antigens and bring them back to the lymph
from the lymphatic capillaries, lymph flows through successively larger and nodes
thicker-walled channels reticular cells - fibroblast-like cells that produce the reticular fiber stroma

1. collecting vessels LYMPHOIDTISSUE
- have the same three tunics as veins but are thinner-walled, have houses and provides a proliferation site for lymphocytes
more internal valves, and interconnects more furnishes an ideal surveillance vantage point for lymphocytes and macrophages
2. trunks largely composed of reticular connective tissue
- formed by the union of the largest collecting vessels dominates all the lymphoid organs except the thymus
- drain fairly large areas of the body where the lymphocytes reside temporarily (then leave to patrol the body again)
- major trunks: Lymphoid tissue comes in various "packages."
a. lumbar - lower limbs, wall and viscera of pelvis, kidneys, adrenal 1. diffuse lymphatic tissue - consists of a few scattered reticular tissue elements
glands, and abdominal wall 2. Lymphoid follicles (nodules) - solid, spherical bodies consisting of tightly
b. bronchomediastinal - thoracic wall, lung, and heart packed reticular elements and cells; often display germinal centers (areas
c. subclavian - upper limbs where B cells are proliferating)
d. jugular - head and neck
e. intestinal - stomach, intestines, pancreas, spleen, & part of the REDBONEMARROW
liver houses the hemopoietic stem cells which give rise to B cells and pre-T cells
3. ducts pre-T cells then migrate to the thymus gland where they mature
- lymph is eventually delivered to one of two large ducts in the thoracic
LYMPHNODES
region
PILAPIL,K. Marieb,E.&Hoehn,K.(2007).HumanAnatomy&Physiology(7thed.).NewYork:Pearson,774-782

LYMPHATICORGANSANDTISSUES
principal lymphoid organs - causes T lymphocytes to become immunocompetent by secreting
discrete encapsulated structures containing both diffusely arranged and dense thymopoietin and the thymosins
reticular tissue - continues to increase in size during the first year; after puberty, it starts to
Functions atrophy gradually; by old age it has been replaced almost entirely by fibrous
lymph filters and fatty tissue
help activate the immune system - Most thymic cells are lymphocytes.
Structures - cortex: densely packed rapidly dividing lymphocytes and a few
capsule - surrounds each node macrophages
trabeculae - divide the node into compartments - medulla: fewer lymphocytes plus thymic (Hassall's) corpuscles; site of T cell
stroma - physically supports the lymphocytes destruction
cortex: contains densely packed follicles and mostly lymphocytes - lacks B cells no follicles
medulla: defined by medullary cords; contains macrophages, lymphocytes and - functions strictly in T lymphocyte maturation - the only one that does not
plasma cells directly fight antigens
lymph sinuses - large lymph capillaries spanned by crisscrossing reticular fibers - blood-thymus barrier keeps bloodborne antigens from leaking into the
Circulation in the Lymph Nodes cortical regions to prevent premature activation of the immature
1. lymph nodes convex side (via afferent lymphatic vessels) lymphocytes
2. subcapsular sinus - large, baglike sinus - the stroma of the thymus consists of epithelial cells (rather than reticular
3. smaller sinuses that cut through the cortex and enter the medulla fibers) - secrete the hormones thymopoietin and the thymosins
4. hilum (via efferent lymphatic vessels) - the indented region on the concave side 3. Tonsils
There are fewer efferent vessels than afferent vessels, so the flow of lymph - form a ring of lymphatic tissue around the entrance to the pharynx (throat),
through the node stagnates somewhat, allowing time for the cells to carry out their where they appear as swellings of the mucosa
functions. - gather and remove many of the pathogens entering the pharynx in food or in

inhaled air
OTHERLYMPHOIDORGANS - their lymphoid tissue contains follicles with obvious germinal centers
1. Spleen surrounded by diffusely scattered lymphocytes
- soft, blood-rich; about the size of a fist; largest lymphoid organ - not fully encapsulated
- located in the left side of the abdominal cavity just beneath the diaphragm; - the epithelium overlying them invaginates deep into their interior, forming
curls around the anterior aspect of the stomach blind-ended tonsillar crypts which trap bacteria and particulate matter
Functions: a. palatine tonsils - located on either side at the posterior end of the oral cavity;
a. a site for lymphocyte proliferation and immune surveillance and response largest of the tonsils; the ones most often infected
b. blood-cleansing functions: extracts aged and defective blood cells and b. lingual tonsil - a lumpy collection of lymphoid follicles at the base of the
platelets; macrophages remove debris and foreign matter tongue
c. stores some of the breakdown products of red blood cells for later reuse and c. pharyngeal tonsil (adenoids if enlarged) - in the posterior wall of the
releases others to the blood for processing by the liver nasopharynx
d. a site of erythrocyte production in the fetus (ceases after birth) d. tubal tonsils - surround the openings of the auditory tubes into the pharynx
e. stores blood platelets 4. PeyersPatches
- white pulp: mostly lymphocytes; involved with immune functions - large isolated clusters of lymphoid follicles
- red pulp: the venous sinuses and the splenic cords (exceptionally rich in - located in the wall of the distal portion of the small intestine
macrophage); disposal of worn-out red blood cells and bloodborne - Peyer's patches (and the appendix) is in an ideal position to destroy bacteria
pathogens and to generate many "memory" lymphocytes for long-term immunity.
2. Thymus
- bilobed; functions primarily during the early years of life Mucosa-associatedLymphaticTissue(MALT)
- found in the inferior neck and extends into the superior thorax, where it protects passages that are open to the exterior from the never-ending onslaughts of foreign
partially overlies the heart deep to the sternum matter entering them
parts: Peyer's patches, the appendix, the tonsils, and lymphoid follicles in the walls of the
bronchi and in the mucosa of genitourinary organs
PILAPIL,K. Marieb,E.&Hoehn,K.(2007).HumanAnatomy&Physiology(7thed.).NewYork:Pearson,774-782

LYMPHATICORGANSANDTISSUES

PILAPIL,K. Marieb,E.&Hoehn,K.(2007).HumanAnatomy&Physiology(7thed.).NewYork:Pearson,774-782