Lecture 25: Immune/Lymphatic System II

Question 1

Capsule of thymus

Answer 1

Contains blood vessels - efferent lymphatics present but NOT afferent; extends trabeculae into parenchyma

Question 2

Trabeculae of thymus

Answer 2

Delicate connective tissue that divides thymus into incomplete lobules

Question 3

Lobules of thymus

Answer 3

Composed of outer/darker staining cortex and inner/lighter staining medulla

Question 4

Cortex of thymus lobules

Answer 4

epithelial reticular cells that secrete thymosin; T cells in various stages of differentiation; blood vessels surrounded by continuous epithelial barrier that allows thymus to maintain lymphopoiesis while segregated from antigens

Question 5

Medulla of thymus lobules

Answer 5

Specialized to allow entry channel into blood stream of mature lymphocytes, leaky capillary beds; Hassall’s corpuscles: whorls of highly keratinized medullary epithelial cells producing cytokine thymic stromal lymphopoietin

Question 6

What is the source of thymosin?

Answer 6

Epithelial reticular cells in the cortex of the lobules

Question 7

Hassall’s Corpuscles

Answer 7

Whorls of highly keratinized medullary epithelial cells that produce lymphopoietin, which stimulates thymic dendritic cells needed for maturation of single positive T cells

Question 8

Double negative T cells

Answer 8

IMMATURE: lack CD4+ and CD8+ cells, enter cortex from blood vessels, proliferate in subcapsular space

Question 9

Double positive T cells

Answer 9

Move to outer cortex of thymus and are confronted with epithelial cells with cell surface MHC classes I and II; express BOTH CD4 and CD8 coreceptors and TCR receptors

Question 10

Single positive T cells

Answer 10

Move to inner cortex and express either CD4 or CD8 coreceptors and TCR receptors (Mature)

Question 11

Foxn1 gene

Answer 11

Transcription factor that controls differentiation of thymic epithelial cells into either cortical or medullary cells

Question 12

Aire gene

Answer 12

Transcription factor that promotes expression of a portfolio of tissue-specific cell proteins by thymic medullary epithelial cells (which normally do not express these proteins) - these proteins identify and dispose of autoreactive T cells

Question 13

Keratin 5+

Answer 13

Expressed only in MEDULLARY THYMIC epithelial cells

Question 14

Keratin 18+

Answer 14

Expressed only in CORTICAL THYMIC epithelial cells

Question 15

Blood Thymus Barrier

Answer 15

Located in the thymic cortex and prevents antigens in blood from reaching developing T cells; leaky during fetal life allowing for development of immunologic tolerance to self-antigen

Question 16

What are the functions of the spleen?

Answer 16

Filtering blood and screening for foreign material in blood

Question 17

White pulp

Answer 17

Elongated, branched strands associated with arteries, zones of diffuse lymphoid tissue and germinal centers, site of clonal expansion of antigen-stimulated lymphocytes; B cell area contains secondary follicles in which central arteriole is off center; T cells in areas surrounding central artery near center of white pulp

Question 18

Periarterial Lymphatic Sheath (PALS)

Answer 18

Cluster of T cells in areas surrounding central artery near center of white pulp

Question 19

Marginal Zone

Answer 19

sinusoidal interface between red and white pulp with abundance of antigen-presenting cells; lymphocytes first encounter antigens here. activated T-helper cells activate B cells here

Question 20

Red pulp

Answer 20

Surrounds white pulp and makes up 80% of the spleen, filters BLOOD, large number or RBCs; Billroth cords form red pulp parenchyma, contain venous sinusoids which store healthy RBCs

Question 21

Billroth cords

Answer 21

Open circulation system in RED PULP which contains blood cells, plasma cells, antigen presenting cells and contain terminal capillaries which open directly into substance of cords; this allows macrophages to “grab” worn out/defective RBCs