Lymphoid

Question 0

Thymus

Answer 0

Thymus does not have B cells!! (except isolated in vessels)
Cortex - developing T with supportive cells
- ERC = epithelial reticular cells - form barrier with desmosomes - must recognize self (positive selection)
Medulla - Hassall’s corpuscles (not significant, old ERCs)
- must not react against self cells (negative selection)
- lower density

Involutes with age - can look like nodules, but really is still connected and has cortex and medulla

Question 1

Primary vs secondary

Answer 1

Maturity during dev’t vs where they reside now

Bone marrow, thymus vs nodes, spleen, MALT (unencapsulated)

Question 2

Maturity of T lymphocytes

Answer 2

In thymus
Must be able to recognize self MHC1 (multihistocompatibility complex = universal) = first test (cortex)
Must not have any response to self = second test (medulla)

Released T lymphocytes can then form colonies, educate progeny

Question 3

Lymph nodes

Answer 3

Follicles dense peripherally - B cells and some antigen presenting
- activated if B cells in core are cytoplasmic, active -> plasma “clearing/germinal center”
Cortex surrounds follicles, paracortex/deep/parafollicular - T cells - surveillance and reproducing
- High endothelial venules - pumps T-lymphocytes into paracortex - looks cuboidal
Medulla - cords and lymphoid sinuses in between follicles -> efferent lymph vessel
Vascular system
Surrounded by capsule and subcapsular sinus (receives trunks)

Question 4

Antigen presenting cells

Answer 4

MEC2 on it’s surface -
Scattered throughout body - ex Langerhans, Kuffper, macrophage
-> migrate through lymph system

Question 5

Spleen

Answer 5

Should be 8 cm, below 8th rib
Capsule, reticular fibers (soft), trabeculae (larger vessels)
White pulp = lymphocytes - B cells -> balls (germinal centers), periarteriolar lymphatic sheets around arterioles = T cells
- filters blood, blood-borne pathogens (vs lymph)
Red pulp = large venous sinusoids, large cytoplasmic endothelial cells
- filters RBCs - based on flexibility of membranes (stiff = old)

Question 6

Blood flow through spleen

Answer 6

Open circulation!
Trabecular artery -> central artery (with PALS) -> marginal zone -> open into parenchyma!
-> RBCs return to venous sinus - discontinuous basement membrane, Stave cells with openings that filter for RBC flexibility

Question 7

MALT

Answer 7

Unencapsulated
Within lamina propria of GI
Many little blue cells = lymphoid!
	- any germinal center = activated B cells
Many make IgA for secretion
GALT = gut-associated - "Peyer's patch" - nodule within GI (usu ilium)
 - M cells - antigen presenting cells
Also includes tonsils

Question 8

Tonsils

Answer 8

Usually lots of germinal centers/”nodules”
Epithelium is determined by surface (strat squam, respiratory)
Pharyngeal/adenoids - back of pharynx, resp epithelium (ciliated columnar), no crypts
Palatine - lateral, strat squam, long + branched crypts
Lingual - base of tongue, strat squam, long unbranched crypts