Chapter 28: The human lymphatic system

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)

Lymphatic System

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

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

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

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

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