1. Chapter 28: The human lymphatic system

2. The Lymphatic System
Involves a one-way system of vessels that returns excess tissue fluid to the bloodstream
Tissue fluid is the extremely thin layer of fluid (plasma) that surrounds all cells and comes from diffusion of plasma through capillary walls
Diffusion occurs through the capillary wall due to blood pressure
Lymph vessels, like capillaries, are present throughout all tissues and collect this excess tissue fluid which is then called lymph
After entering the lymph vessel it travels back to the blood through the subclavian veins (3L/d)

3. Lymphatic System

4. Flow of Lymph
Lymph flows along the lymph vessels by rhythmic contraction of the muscular walls of the lymph vessels and by contraction of the skeletal muscles
Lymph vessels (like veins) have valves to prevent backflow of lymph
The lymphatic drainage system is absent from the teeth, bone, bone marrow, and the central nervous tissue

5. Lymph Nodes
Lymph nodes are small bean-shaped structures that have dense masses of lymphocytes and monocytes
They are widely distributed throughout the body along the lymphatic pathways where they filter the lymph before it is returned to the blood
Lymph nodes are not present in the central nervous system
There are three superficial regions on each side of the body where lymph nodes tend to cluster:
Groin
Armpit
Neck

6. The Lymphatic System
There are two general roles of the lymphatic system:
Circulatory role
Defence role

7. The Lymphatic System Circulatory role:
Returns the proteins lost from capillaries
Returns fluid lost from capillaries – maintains blood pressure and volume
Removes excess tissue fluid – prevents swelling (oedema)
Collection of lipids from the small intestine and transfer to the blood via the subclavian veins

8. The Lymphatic System Defence role:
Bacteria, viruses, cancer cells, cell debris and toxins are removed from the lymph by lymph nodes
Lymph nodes continually monitor lymph for infections and cancer
Lymphocytes and monocytes multiply in lymph nodes during an infection