Lecture 32: Lymphoid Organs and Tissues

Question 1

Lymphoid organs

Answer 1

Primary: Bone Marrow, Thymus
Secondary: Lymph nodes, spleen, MALT (mucosa associated lymphoid tissue)

Question 2

Bone Marrow gives rise to

Answer 2

T cell precursors and mature B cells.

Question 3

Where do T cell precursors mature?

Answer 3

In the thymus

Question 4

Two types of T cells

Answer 4

Helper T cells –> activate cytotoxic t cells
Cytotoxic T cells, kill tumor cells, virus-infected cells, etc by contact
Cell-mediated immunity

Question 5

Function of B cells

Answer 5

transform into plasma cells. Kill by secretion of antibodies, humoral immunity.

Question 6

Thymus is active/formed when

Answer 6

Well-formed before birth, active until puberty at which point it turns into fatty mass. Made of two lobes

Question 7

Thymus anatomy

Answer 7

Two lobes.
Each lobe has lobules.
Each lobule ahs cortex ad medulla.
What are Capsule and CT septa?

Question 8

Lymphatics of thymus

Answer 8

No afferent lymphatics, but has draining efferent lymphatics which drain the capsule and CT septa.

Question 9

Layers of lobule of thymus?

Answer 9

Outer cortex –> inner cortex –> medulla

Question 10

Functions of thymus

Answer 10

Provides an environment where T cell precursors proliferate, mature and acquire their immunocompetence.
Supplies mature T cells to secondary lymphoid organs.
Secretes hormone-like substances which stimulate T cell proliferation and maturation.

Question 11

how do maturing T-cells die?

Answer 11

Through apoptosis when they are incpable of reacting with any antigens in the thymus, this process is called negative selection. 95% of cells die this way. 5% of cells do recognize an antigen and are fully matured.

Question 12

How does apoptosis of T-cells happen?

Answer 12

through phagocytosis of macrophages. This eliminates self-reactive T-cells. If you have self-reactive T cells can cause systemic lupus erythematosus (SLE).

Question 13

epithelial reticular cells purpose

Answer 13

Present antigens to maturing T cells in the thymus, “instruct” maturing T-cells.

Question 14

What do epithelial reticular cells secrete

Answer 14

hormone-like polypeptide substances. Regulate T-cell proliferation and maturation.

Question 15

Hassall’s corpuscle

Answer 15

Found in medulla in thymus. Appear as concentric layers of epithelial reticular cells that appear eosinophilic, keratinized and degenerative. Very obvious, looks like pink rose.

Question 16

Thymic involution

Answer 16

Degeneration of thymus , lymphoid tissue which is separated by adipose tissue, turns very fatty.

Question 17

MALT (mucosa associated lymphoid tissue) are found where?

Answer 17

Diffuse lymphoid cells in mucosa
Lymphoid follicles in GI, respiratory and genitourinary tracts
Peyers patches of the ileum
tonsils

Question 18

Intraepithelial lymphocytes

Answer 18

Reside in the intercellular space of enterocytes in the small intestine. Are cytotoxic T-cells. Fall under MALT.

Question 19

How do plasma cells work in the gut.?

Answer 19

The plasma cells in the lamina propria. Secrete IgA into lumen of gut, this prevents attachment of bacteria/toxins to enterocytes. HOW?

Question 20

Primary vs. Secondary lymphoid follicle

Answer 20

Primary follicle –> ovoid structures containing aggregates of lymphocytes
Secondary follicles –> follicles containing a central pale area –> germinal center (site of B cell activation)

Question 21

Peyer’s patches of the ileum contents

Answer 21

Large aggregates of secondary follicles (site of B cell activation). T cells between follicles, B cells localized to within germinal centers within follicles.

Question 22

M cells

Answer 22

Found in epithelium overlying patches,