Lymphoid Structures Flashcards
What is a Lymph node?
A 2° lymphoid organ that has many afferents, 1 or more efferents. Encapsulated w/ trabeculae
What are the functions of a lymph node?
Nonspecific filtration by macrophages, storage & activation of B & T cells, Ab production
What is a Follicle?
Site of B-cell localization & proliferation in the outer cortex of a LN
What are 1° follicles?
Dense & dormant
What are 2° follicles?
Pale central germincal centers (GC) & are active
What does the LN medulla consist of?
Medullary cords (closely packed lymphocytes & plasma cells) & medullary sinuses
What do the Medullary sinuses communicate w/?
Efferent lymphatics & contain reticular cells & macrophages
What does the Paracortex of LN do?
Houses T cells
Where is the Paracortex?
Region of cortex b/w follicles & medulla
What does the Paracortex contain?
High endothelial venules through which T & B cells enter from blood
What happens in an extreme cellular immune response?
Paracortex becomes greatly enlarged
When is the paracortex NOT well dev?
Pts w/ DiGeorge synd
What is the LN drainage for the upper limb & lateral breast?
Axillary
What is the LN drainage for the Stomach?
Celiac
What is the LN drainage for the duodenum & jejunum?
Superior mesenteric
What is the LN drainage for the sigmoid colon?
Colic→ inferior mesenteric
What is the LN drainage for the rectum (lower portion) & anal canal (above the pectinate line)?
Internal iliac
What is the LN drainage for the anal canal (below pectinate line)?
Superficial inguinal
What the the LN drainage for the testes?
Superficial & deep plexus→ para-arotic
What is the LN drainage for the scrotum?
Superficial inguinal
What is the LN drainage for the thigh (superficial)?
Superficial inguinal
What is the LN drainage for the lateral side of the dorsum of foot?
Popliteal
What does the Right lymphatic duct drain?
Righ arm, right chest & right half of the head
What does the Thoracic duct drain?
Everything else
What are the sinusoids of the spleen?
Long, vascular channels in red pupl w/ fenestrated “barrel hoop” basement membrane (BM)
Macrophages found nearby
Where are T cells found in the spleen?
Periarterial lymphatic sheath (PALS) w/in the white pulp of the spleen
Where are the B cells found in the spleen?
Found in follicles w/in the white pulp of the spleen
What do macrophages do in the spleen?
Remove encapsulated bacteria
What causes splenic dysfucntion?
Dec IgM→ dec complement activation→ Dec C3b opsonization→ Inc suspectibility to encapsulated organisms
What are the encapsulated organisms splenic dysfunction pts are susceptible to?
- Streptococcus pneumoniae
- Haemophilus influenzae type B
- Neisseria meningitidis
- Salmonella
- Klebsiella pneumoniae
- Group B Streptococci
What are the signs of Postsplenectomy?
- Howell-Jolly bodies (nuclear remnants)
- Target cells
- Thrombocytosis
What is the Thymus?
Encapsulated site of T-cell differentiation & maturation
Where does the Thymus develop from?
Epithelium of 3rd brachial pouches
What is in the cortex of the Thymus?
Dense w/ immature T cells
What is in the medulla of the Thymus?
Pale w/ mature T cells & epithelial reticular cells containing Hassall’s corpuscles
What is Positive selection?
MHC restriction occurs in the cortex
What is Negative selection?
Nonreactive to self occurs in the medulla
