Histology Final-Lymphoid Tissues

Front 1

Three Types of Lymphoid Tissues?

Back 1

Primary, Secondary, and Tertiary Lymphoid Organs

Front 2

Describe the Primary Lymphoid Organs.

Back 2

-responsible for the production of lymphoid cells
-bone marrow
-Thymus

Front 3

Describe the Secondary Lymphoid Organs.

Back 3

-where lymphocytes are maintained and provide sites for lymphocyte interaction with antigens and each other
-include the spleen, lymph nodes, MALT, GALT, and BALT
-specialized to trap antigens and provide signals for recirculating lymphocytes in the initiation of the adaptive immune response

Front 4

Describe MALT.

Back 4

-Mucosal Associated Lymphoid Tissue
-the less well organized lymphoid tissues underlying various internal epithelial mucous membranes

Front 5

GALT?

Back 5

Gut Associated Lymphoid Tissues

Front 6

BALT?

Back 6

Bronchial (Respiratory) Associated Lymphoid Tissues

Front 7

Describe the Tertiary Lymphoid Organs.

Back 7

-smaller, less well organized clusters of lymphoid elements such as those associated with the skin
-those associated with the skin are cutaneous associated lymphoid tissue

Front 8

Describe the Thymus

Back 8

-lobules of the thymus gland have a cortical region and a medullary region
-cells are more abundant in the cortex and more loosely packed in the medulla as they get eliminated during differentiation
-progenitor cells committed to the lymphocyte lineage migrate to the thymus as early as the 8th week of fetal life
-the thymus gland is most active early in life and undergoes involution following puberty
-its weight in the infant is 70g while in the elderly its 3g

Front 9

Describe T Cells and the Thymus.

Back 9

-all T Cells mature in the Thymus
-epithelially derived cells, the Nurse or Reticular Cells, have cytoplasmic extensions that may surround as many as 50 maturing T Cells
-progenitor cells committed to the lymphocyte lineage migrate to the thymus as early as the 8th week of fetal life
-initial selection of T Cells occurs in the thymus whereby T Cells expressing T Cell Receptors with affinity for self-antigens are eliminated by programmed cell death; 95-99% of T Cells produced initially are eliminated this way

Front 10

Describe Thymic Nurse Cells

Back 10

-TNCs, aka Reticular Cells
-epithelially derived cells that have cytoplasmic extensions that may surround as many as 50 maturing T Cells

Front 11

Describe Lymph Nodes

Back 11

-a system of in-line fibers within the lymphatic vessel system
-lymphatic fluid arrives at the nodes at the subscapular sinus and then moves through the nodal tissue
-have a cortical region containing primary and secondary follicles and a medullary region containing cords and sinuses
-this arrangement ensures the encounter of lymph-borne pathogens with lymphocytes
-lymph nodes filter lymph which drains tissues

Front 12

Describe the Cortical Region of Lymph Nodes

Back 12

-contain primary and secondary follicles
-dendritic cells are abundant in between follicles

Front 13

Describe the Medullary Region of Lymph Nodes

Back 13

-contain medullary cords and sinuses
-interior of the lymph node
-contains linear clusters of cells: the medullary cords rich in fully differentiated B Cells, the plasma cells, and macrophages
-in between these cords of cells are medullary sinuses

Front 14

Describe Primary Follicles

Back 14

composed of resting B Cells

Front 15

Describe Secondary Follicles

Back 15

-germinal centers
-composed of both proliferating and non-proliferating B Cells, Helper T Cells, and macrophages, i.e. various luekocytes

Front 16

Describe the Spleen

Back 16

-large lymphoid organ in the abdominal cavity
-filters blood; approximately 1/2 the total volume of blood in the body passes through the spleen in 24 hours
-responds to systemic infections

Front 17

Describe Splenic Tissue

Back 17

-consists of red pulp which contains sinusoidal vessels and is rich in erythrocytes
-also consists of white pulp where various classes of WBC including T and B Lymphocytes are clustered around a central artery

Front 18

Describe Red Pulp of Splenic Tissue

Back 18

contains sinusoidal vessels and is rich in erythrocytes

Front 19

Describe White Pulp of Splenic Tissue

Back 19

where various classes of WBC including T and B Lymphocytes are clustered around a central artery

Front 20

Describe the effect of removal of the Spleen

Back 20

-depends on the age at which it is removed
-there are more significant effects if it is removed in childhood when the individual has less exposure to various diseases and when the other organs (i.e. liver) are less well developed and less able to take over spleen functions