Lymphoid Structures

Question 1

Lymph node

Answer 1

A 2° lymphoid organ that has many afferents, 1 or more efferents. Encapsulated, with trabecular.
Functions are nonspecific filtration by macrophages, storage of B and T cells, and immune response activation.

Question 2

Lymph node - Follicle

Answer 2

Site of B-cell localization and proliferation. In outer cortex. 1° follicles are dense and dormant. 2° follicles have pale central germinal centers and are active.

Question 3

Lymph node - Medulla

Answer 3

Consists of medullary cords (closely packed lymphocytes and plasma cells) and medullary sinuses. Medullary
sinuses communicate with efferent lymphatics and contain reticular cells and macrophages.

Question 4

Lymph node - Paracortex

Answer 4

Houses T cells. Region of cortex between follicles and medulla. Contains high endothelial venules through which T and B cells enter from blood.
Not well developed in patients with DiGeorge syndrome.

Question 5

Lymph drainage

Answer 5

Right lymphatic duct—drains right side of body above diaphragm.
Thoracic duct—drains everything else into junction of left subclavian and internal jugular veins.

LYMPH NODE CLUSTER – AREA OF BODY DRAINED
Cervical – Head and neck
Hilar – Lungs
Mediastinal – Trachea and esophagus
Axillary – Upper limb, breast, skin above umbilicus
Celiac – Liver, stomach, spleen, pancreas, upper duodenum
Superior mesenteric – Lower duodenum, jejunum, ileum, colon to splenic flexure
Inferior mesenteric – Colon from splenic flexure to upper rectum
Internal iliac – Lower rectum to anal canal (above pectinate
line), bladder, vagina (middle third), prostate
Para-aortic – Testes, ovaries, kidneys, uterus
Superficial inguinal – Anal canal (below pectinate line), skin below umbilicus (except popliteal territory)
Popliteal – Dorsolateral foot, posterior calf

Question 6

Sinusoids of spleen

Answer 6

Long, vascular channels in red pulp with fenestrated “barrel hoop” basement membrane. Macrophages found nearby.
T cells are found in the periarterial lymphatic sheath within the white pulp of the spleen.
B cells are found in follicles within the white pulp of the spleen. The marginal zone, in between the red pulp and white pulp, contains APCs and specialized B cells, and is where APCs present blood-borne antigens.
Macrophages in the spleen remove encapsulated bacteria.

Question 7

Splenic dysfunction

Answer 7

(e.g., postsplenectomy, sickle cell disease):
decr IgM –> decr complement activation–> decr C3b opsonization->incr susceptibility to encapsulated organisms

(SHiNE SKiS):

• Streptococcus pneumoniae
• Haemophilus influenzae type B
• Neisseria meningitidis
• Escherichia coli
• Salmonella spp.
• Klebsiella pneumoniae
• Group B Streptococci

Postsplenectomy:
-Howell-Jolly bodies (nuclear remnants)
-Target cells
Thrombocytosis

Question 8

Thymus

Answer 8

Site of T-cell differentiation and maturation.
Encapsulated.
From epithelium of 3rd pharyngeal pouches.
Lymphocytes of mesenchymal origin.
Cortex is dense with immature T cells; medulla is pale with mature T cells and Hassall corpuscles containing epithelial reticular cells.
T cells = Thymus
B cells = Bone marrow