15) Lymph node

What is the lymph node?

Filters lymph
→ permits detection & destruction of foreign substances

• contains B cell/Tcell

• afferent/efferent lymphatic vessels

• small bean shape

(LO1)

Describe the histological architecture of the lymph node.

1) Stroma = structural tissue (overall architecture)
- capsule of dense irregular CT
- trabeculae penetrates into lymph node
- reticular fiber mesh (via fibroblastic reticular tissue)

2) Parenchyma = functional tissue (function)
- cortex, paracortex, medulla

(LO2) Describe the different layers of the lymph node & population of cells found in each layer

central region = germinal centre

Describe the process of ONE-WAY FLOW of lymph through the lymph node

1) IN via Afferent lymphatic vessels
(w/ valves; one way flow)

2) Lymph enters sinus of lymph node
- subscapular sinus
→ trabecular sinus
→ medullary sinus

3) OUT via efferent lymphatic vessels
- secretes:
- AB
- activated T cells

Why are there less efferent lymphatic vessels than afferent lymphatic?

aka why less OUT than IN

-slows flow of filtrate

Describe the significance of the hilum in the lymph node.

Area for exit of efferent lymphatic vessels
- carries AB & activated T cells
- site for blood vessel access to LN

What is the HIGH ENDOTHELIAL VENULE?

found in ALL secondary lymphoid organs (except spleen; aka just LN?..)

- circulating B & T cells gain access to lymph node parenchyma via these specialized vessels

TLDR: circulating T/Bcells can help out in these LN → and then go away when not needed