A&P 20: The Lymphatic System & Lymphoid Organs/Tissues Flashcards
Lymphatic system
system that returns fluids that have leaked from the blood vascular system back to the blood; 3 parts - lymphatic vessels, lymph, lymph nodes
Lymphoid organs & tissues
provide the structural basis of the immune system
Lymphatic vessels (lymphatics)
elaborate networks of drainage vessels that collect the excess protein-containing interstitial fluid and return it to the bloodstream
Lymph
once interstitial fluid enters the lymphatic vessels, it is called this, which means “clear water”
Lymphatic capillaries
the transport of lymph begins in these microscopic blind-ended vessels
Lacteals
special set of lymphatic capillaries; transports absorbed fat from the small intestine to the bloodstream; named because of the milky white lymph that drains through them
Chyle
the fatty lymph (“juice”) that drains from the fingerlike villi of the intestinal mucosa
Collecting lymphatic vessels
have the same 3 tunics as veins, but these have thinner walls and more internal valves, and they anastomose more
Lymphatic trunks
the largest collecting vessels unite to form these, which drain fairly large areas of the body
Major trunks
named for the regions from which they drain lymph - paired lumbar, bronchomediastinal, subclavian, and jugular trunks; single intestinal trunk
Right lymphatic duct
1 of 2 large ducts in the thoracic region; drains lymph from the right upper limb and the right side of the head and thorax
Thoracic duct
larger of the 2 ducts in the thoracic region; receives lymph from the rest of the body
Cisterna chyli
the thoracic duct arises anterior to the 1st 2 lumbar vertebrae as this enlarged sac, which collects lymph from the 2 large lumbar trunks that drain the lower limbs and from the intestinal trunk that drains the digestive organs
Lymphocytes
the main warriors of the immune system; arise in red bone marrow (along with other formed elements)
T cells (T lymphocytes)
when activated, these cells manage the immune response; some of them directly attack and destroy infected cells
B cells (B lymphocytes)
cells that protect the body by producing plasma cells
Plasma cells
daughter cells that secrete antibodies into the blood or other body fluids
Antigens
anything that provokes an immune response, such as bacteria and their toxins, viruses, mismatched RBC’s, or cancer cells
Macrophages
play a crucial role in body protection and the immune response by phagocytizing foreign substances and by helping to activate T cells
Dendritic cells
spiny-looking cells that capture antigens and bring them back to the lymph nodes
Reticular cells
fibroblast-like cells that produce the reticular fiber stroma
Stroma
network that supports the other cell types in lymphoid organs and tissues
Lymphoid tissue
important component of the immune system, mainly because it (1) houses and provides a proliferation site for lymphocytes and (2) furnishes an ideal surveillance vantage point for lymphocytes and macrophages
Reticular connective tissue
lymphoid tissue is largely composed of this loose connective tissue (dominates all lymphoid organs except the thymus)
Diffuse lymphoid tissue
loose arrangement of lymphoid cells and some reticular fibers - found in virtually every body organ; larger collections appear in the lamina propria of mucous membranes such as those lining the digestive tract
Lymphoid follicles (lymphoid nodules)
solid, spherical bodies consisting of tightly packed lymphoid cells and reticular fibers
Germinal centers
follicles often have these lighter-staining areas where proliferating B cells predominate
Lymph nodes
principal lymphoid organs in the body; cluster along the lymphatic vessels of the body
Capsule
each lymph node is surrounded by this dense fibrous structure from which connective tissue strands (trabeculae) extend inward to divide the node into a number of compartments
Trabeculae
connective tissue strands that extend inward to divide a lymph node into a number of compartments
Cortex
outer part of a lymph node
Medulla
inner part of a lymph node
Medullary cords
thin, inward extensions from the cortical lymphoid tissue; contain both types of lymphocytes
Lymph sinuses
large lymph capillaries spread throughout a lymph node and spanned by crisscrossing reticular fibers
Afferent lymphatic vessels
lymph enters the convex side of a lymph node through these
Subcapsular sinus
from the afferent lymphatic vessels, lymph travels through this large, baglike sinus into a number of smaller sinuses that cut through the cortex and enter the medulla
Medullary sinuses
smaller sinuses in the lymph nodes
Hilum
lymph exits the node at this indented region on the concave side
Efferent lymphatic vessels
lymph exits the node through these structures
Lymphoid organs
aggregates of lymphoid tissue in the body; includes nodes, spleen, thymus, tonsils, Peyer’s Patches (aggregated lymphoid nodules) of the small intestine, bits of lymphoid tissue scattered in connective tissues
Spleen
soft, blood-rich organ about the size of a fist; largest lymphoid organ; located in the left side of the abdominal cavity just beneath the diaphragm; curls around the anterior aspect of the stomach; site for lymphocyte proliferation and immune surveillance and response; also has blood-cleansing functions
White pulp
part of the spleen where immune functions take place; composed mostly of lymphocytes suspended on reticular fibers; forms cuffs around central arteries (appears to be islands in a sea of red pulp)
Red pulp
where worn-out red blood cells and bloodborne pathogens are destroyed; contains huge numbers of erythrocytes and the macrophages that engulf them; essentially = all splenic tissue that is not white pulp
Splenic cords
regions of reticular connective tissue that makes up red pulp in the spleen
Splenic sinusoids
blood-filled venous sinuses
Thymus
bilobed organ with important functions, primarily during the early years of life; found in the inferior neck and extends into the superior thorax, where it partially overlies the heart deep to the sternum
Thymic corpuscles
bizarre structures of the lighter-staining medullary areas of the thymus; consist of concentric whorls of keratinized epithelial cells - once thought to be sites of T cell destruction; recent evidence suggests they are involved in the development of regulatory T cells (class of T lymphocytes that are important for preventing autoimmune responses)
Mucosa-associated lymphoid tissues (MALT)
set of distributed lymphoid tissues strategically located in mucous membranes throughout the body; helps protect us from the never-ending onslaught of pathogens that seek to enter our bodies; largest of these include the tonsils, Peyer’s Patches, and the appendix; also occurs in the mucosa of the respiratory tract and genitourinary organs as well as the rest of the digestive tract
Tonsils
form a ring of lymphoid tissue around the entrance to the pharynx (throat) where they appear as swellings of the mucosa; named according to location; gather and remove many of the pathogens entering the pharynx in food or in inhaled air
Palatine tonsils
paired; located on either side at the posterior end of the oral cavity; largest, most often infected
Lingual tonsil
collective term for a lumpy collection of lymphoid follicles at the base of the tongue
Pharyngeal tonsil
referred to as the adenoids if enlarged; in the posterior wall of the nasopharynx
Tubal tonsils
tiny; surround the openings of the auditory tubes into the pharynx
Tonsillar crypts
epithelium overlying the tonsils invaginates deep into their interior to form these blind-ended areas that trap bacteria and particulate matter
Peyer’s Patches
AKA aggregated lymphoid nodules; large clusters of lymphoid follicles, structurally similar to tonsils; located in the wall of the distal portion of the small intestine
Appendix
tubular offshoot of the 1st part of the large intestine; contains a high concentration of lymphoid follicles; in an ideal position to destroy bacteria before these pathogens can breach the intestinal wall and to generate many “memory” lymphocytes for long-term immunity
Lymph sacs
by the 5th week of embryonic development, the beginnings of the lymphatic vessels and the main cluster of lymph nodes are apparent; these arise as ___ ___ that bud from developing veins
