(2) Smooth muscle. The walls of the larger lymphatic vessels include
smooth muscle fibers that aid in lymph flow.
(3) Negative thoracic pressure. Negative intrathoracic pressure is due to
the elastic recoil of the lungs. It exerts a continual aspiratory effect on the lymphatic
system in the same manner as on the venous system.
(4) Skeletal muscle contraction. Contraction of the skeletal muscles has the
same effect on the lymphatic system as it does on the venous system. This works in
the same manner because of the flaccidity of the walls of the lymphatics, and because
of the existence of valves.
(5) Pulsating arteries. The pulsating of arteries close to the lymphatics also
increases lymphatic flow.
(6) Gravity. Gravity either speeds up or slows down the flow of lymph. If
the lymphatic territory is above its opening into a vein, the flow is speeded up by gravity.
If the lymphatic territory is below its opening into a vein, gravity retards the flow of
f. Lymphatic Tissue.
Return of vital substances, especially proteins, to the blood vessels.
Formation of lymphocytes.
Detoxification of foreign molecules and particles.
(d) Antibody production.
(e) Prevention of edema by constant removal of excess fluid from
Structure (figure 26).
(a) Afferent lymphatics. Lymph enters a node by way of the afferent
lymphatics which are situated around the periphery of the node.
(b) Efferent lymphatics. Lymph leaves a lymph node by way of the
efferent lymphatics which lead to veins.
Capsule. The outer covering of a lymph node is referred to as a