Ch. 20 Lymphatic System

lymph nodes are

the principle secondary lymphoid organ of the body

lymph nodes are embedded where?

deeply into connective tissue in clusters along lymphatic vessels

2 main functions of lymph nodes

1. cleansing the lymph
2. immune system activation

macrophages remove and destroy...

microorganisms and debris that enter lymph

macrophages prevent...

unwanted substances from being delivered back into the bloodstream

the lymph node is a location where...

lymphocytes become activated and prepare attack against antigen

lymph nodes are surrounded by

an external fibrous capsule and has trabeculae that divides the node into compartments

2 histologically distinct regions of lymph nodes

cortex and medulla

cortex

a superficial area which contains follicles with germinal centers that are heavy with dividing B cells

the deep cortex houses

T cells in transit (circulating between blood lymph nodes and lymph fluid)

medulla has...

medullary cords that extend inward from the cortex and have B cells, T cells, and plasma cells

lymphatic sinuses

large lymphatic capillaries that are spanned by crisscrossing reticular fibers

primary lymphoid organs

red bone marrow on thymus; where T and B cells mature

secondary lymphoid organs

area where mature lymphocytes first encounter their antigen and become activated

lymph enters the lymph node through

afferent lymphatic vessels

lymph exits the lymph node at

the hilum through efferent lymphatic vessels

the spleen is a

very blood rich organ; largest lymphoid organ

the spleen is the site of...

lymphocyte proliferation and immune surveillance and response

the spleen cleanses...

blood of aged blood cells and platelets; macrophages remove debris

the spleen stores...

broken down products of red blood cells; platelets and monocytes for release into blood

2 histologically important components of the spleen

white pulp and red pulp

white pulp

where immune system functions; contains lymphocytes on reticular fibers

red pulp

where old blood cells and bloodborne pathogens are destroyed; rich in red blood cells and macrophages

Mucosa-associated lymphoid tissue (MALT)

lymphoid tissues found in mucous membranes throughout the body

MALT helps protect from

pathogens trying to enter the body

tonsils

Simplest lymphoid organs; form a ring of lymphatic tissue around the pharynx

palatine tonsils

at posterior end of oral cavity; largest of tonsils, most often infected

lingual tonsils

lumpy collections of follicles at the base of the tongue

pharyngeal tonsils

adenoids, located on posterior wall of nasopharynx

tubal tonsils

surround the openings of auditory tubes in the pharynx

Peyer's patches

clusters of lymphoid follicles in wall of distal portion of small intestine

Peyer's patches help destroy

bacteria, which prevents them from breaching the intestinal wall

Appendix

offshoot of first part of large intestine; contains lymphoid follicles

thymus

bilobed; found in the inferior region of the neck; extends into the mediastinum and partially overlies the heart

the thymus functions as

lymphoid organ where T cells mature

The thymus is most active during ________.

childhood

thymus: cortex

has rapidly dividing lymphocytes; scattered macrophages

thymus: medulla

has fewer lymphocytes and thymic corpuscles

blood thymus barrier

keeps immature T lymphocytes isolated from any antigens to prevent premature activation

regulatory T cells

helps prevent T cells from attacking our body