a-short-review-of-histology

Lymph Nodes - Structure:

Lymph nodes are accumulations of lymphocytes, macrophages and support cells which are located along the pathway of lymphatic capillaries
Lymph nodes are small structures, about the size of a pea, although they may be enlarged when mounting an immune response
Lymph nodes have a thin but dense connective tissue capsule from which septae arise
These pass through the node towards the hilus and provide support for the lymph node
Between the septae, reticular connective tissue cells and fibres provide a framework to support the lymphocytes and other leucocytes which function in lymph nodes
The lymph node is divided into an outer cortex and an inner medulla
In the cortex, there are numerous lymphatic nodules composed largely of lymphocytes
Lymph, delivered via afferent lymphatic capillaries into lymphatic sinuses in the lymph node, passes through the cortex and medulla
It leaves at the hilus, in the (single) efferent lymphatic capillary
As the lymph passes through the sinuses, macrophages and lymphocytes monitor the fluid for the presence of particulate material and foreign antigens
In the medulla the sinuses pass between medullary cords
The medullary cords contain plasma cells, which produce antibodies
The antibodies are secreted into the lymph fluid in the sinuses
These antibodies will be delivered into the blood from where they are distributed around the body

Lymph Nodes - (cortex):

In this image of the outer cortex of a lymph node the connective tissue capsule is labelled C
Deep to the capsule is a sinus (space X) into which lymphatic fluid is delivered from the lymphatic capillaries
The lymph in this sinus and in other sinuses that pass through the lymph node (arrow) is monitored by macrophages and other lymphoid cells for any foreign antigens that may be present, eg associated with a bacterial infection of the organ that the lymph node receives lymph from
When foreign antigen is detected an immune response is mounted
This includes a clonal expansion of immune cells in the lymph node which causes an increase in the overall size of the lymph node, hence 'swollen glands' when you get an infection
NB Lymph nodes are sometimes referred to as lymph glands (particularly in old texts)

Lymph Nodes - (medulla):

Whereas the cortex of a lymph node is largely concerned with the detection of foreign antigens and the initiation of an appropriate immune response, the medulla collects the lymph and passes it to a single efferent lymphatic capillary which carries the lymphatic fluid out of the lymph node
It also houses plasma cells which are the cells which produce and secrete antibody
This is secreted into the lymphatic fluid leaving the lymph node which will ultimately be delivered into the venous blood circulation
The antibody will be distributed in the blood around the body and to the source of infection

MS - medullary sinuses (containing lymph)

MC - medullary cords, containing plasma cells