UNIT 8: LEARNING AIM B
Unit 8: Physiology of Human Body Systems
Learning Aim B: Understand the impact of disorders on the physiology of the lymphatic
system and the associated corrective treatments
Introduction:
In this assignment, I will be discussing the lymphatic system which will include the structure of the lymphatic
system, function of the lymphatic system and the function of each part of the lymphatic system. I will also be
detailing a disorder associated with the lymphatic system which is Lymphoedema and I will be detailing the
causes, symptoms of lymphoedema, risk factors, effects of lymphoedema, limitations of lymphoedema and
treatments of lymphoedema. I will also be comparing the treatments of lymphoedema so that I can conclude
which treatment is worthwhile.
Structure of Lymphatic System:
The lymphatic system is made up of:
- Vessels to transport lymph fluid.
- Lymphatic organs such as the lymph nodes, spleen and thymus. All these lymphatic organs have
lymphatic tissue that is enclosed in a capsule.
- Lymphatic nodules that are not enclosed by a capsule. Lymphatic nodules are oval-shaped and contain
lymphatic tissue. Large lymphocytes can be found in the centre of lymphatic nodules and smaller
lymphocytes can be found around the periphery. The smaller lymphocytes are found in areas of the
gastrointestinal (GI) tract, like the tonsils, Peyer’s patches in the ileum wall, and the appendix wall.
- Bone marrow that produces lymphocytes.
- Lymphatic tissue in the mucous membranes, airways, urinary and reproductive tracts, walls of the GI
tract and small amounts in all organs.
1
,Function of Lymphatic System:
Formation and Transport of Lymphocytes and Lymph:
● Lymph:
Lymph is the fluid that moves through the lymphatic system and contains substances such as salts,
glucose, water, white blood cells, fats and proteins. The composition of lymph varies depending on
where in the body it is formed. The role of lymph is to return excess interstitial fluid and proteins to the
bloodstream. Lymph may also pick up pathogens on the way and transport them to the lymph nodes
where the pathogens are identified and destroyed. Lymph is transported to one of two large ducts that
include the right lymphatic duct and the thoracic duct. The right lymphatic duct drains lymph from the
right side of the head, thorax and the right upper arm. The thoracic duct receives lymph from the rest of
the body. The lymph fluid from the two ducts then drains into the blood vessels in the neck region.
Most of the arterial blood that enters the arterial capillaries flows into the venous capillaries. Some of the
blood plasma forms interstitial fluid when it escapes and waste products, bacteria, toxins and tumours
are picked up. A process called lymphogenesis takes place when the interstitial fluid enters the lymphatic
capillaries and turns into lymph. Lymph is transported via the lymph vessels and the flow of lymph is
controlled by muscle contractions. There are semi-lunar valves which prevent the backflow of lymph.
● Lymphocytes:
Macrophages are derived from monocytes and are a type of white blood cell. Macrophages are
specialised to detect pathogenic material in the body and engulf and destroy the material before it
causes harm to the body. They are found in the lymph nodes of the lymphatic system and are
responsible for ingesting bacteria, cancer cells and other foreign particles through a process known as
phagocytosis. Macrophages are examples of antigen-presenting cells (APC) which are able to present
pieces of pathogens for recognition to other immune cells. They are also able to release cytokines, which
are chemicals that cause the initiation of an inflammatory response by activating other immune cells.
Macrophages can travel and circulate within almost all tissue and carry out their role in finding
pathogenic material and destroying it. Likewise, macrophages are also able to destroy dead cells as well
as pathogenic material that can cause harm to the body. Macrophages are heterogenic meaning that
they are different in different areas of the body in terms of:
- The pathogens they can recognise
- The levels of inflammatory cytokines they are able to produce
- Morphology
Dendritic cells are also derived from monocytes and are responsible for initiating immune responses.
Dendritic cells are also antigen-presenting cells. They are part of the body’s innate immune system. They
are specialised in capturing and processing antigens, then converting the proteins from the antigens to
peptides and presenting the peptides on membrane-mounted major histocompatibility complex (MHC)
molecules. They are presented to these molecules so that T cells can recognise them. Dendritic cells can
be found in the lymph nodes and are responsible for trapping, processing and presenting pieces of
pathogens to T cells which results in a further production of B-cells and T-cells which leads to an immune
response against the recognised pathogen.
2
, In the bone marrow, B-lymphocytes and T-lymphocytes are produced and originate from stem cells in
the bone marrow. Both B-cells and T-cells are part of the adaptive immune system which is specific.
Whilst they mature, the B-cells stay in the bone marrow. However, the T-cells mature in the thymus
therefore they travel to the thymus. Antibody production is a role of B-cells and it is a part of the humoral
immune response. Killing infected cells and activating other immune cells is the role of the T-cells and is
a part of the cell-mediated immune response. The areas where naive B-cells mature include the spleen,
bone marrow and lymph nodes. The antibody-like receptors on their membranes are slightly different in
every B-cell and they are able to recognise and attach to the antigen of a certain pathogen. The receptors
of the B-cells are unique. To make sure that their receptors don’t bind to self-antigens, B-cells undergo a
selection process and if their receptors do bind to self-antigens then they are destroyed through
apoptosis. Once a B-cell has matured, if it comes across and recognises a pathogenic antigen, it divides
into two types of cells:
- Plasma cells that secrete antibodies that recognise the same pathogen
- Memory B-cells that remain dormant in circulation. However, they divide quickly if they
re-encounter the pathogen which provides a long-lasting immunity.
When the T-cells migrate to the thymus gland, they are able to mature and become activated. On the
membranes of T-cells, there are specific receptors. The T-cells undergo a similar selection process to the
B-cells where the T-cell receptors have to be able to recognise and attach to an antigen-presenting cell
that presents a pathogenic antigen. However, the receptors of the T-cells must not attach to the
non-infected sel-cells and must not destroy them. When a pathogen’s antigen is presented by an APC and
is encountered by T-cells, the T-cells become activated and divide into:
- T- memory cells that remain dormant in circulation but can divide quickly when re-encountering
the same pathogen.
- T-helper cells that activate B-cells which results in cytokines to be released to stimulate
phagocytic cells.
- Cytotoxic T-cells that kill cells infected by a recognised pathogen.
- T- regulatory cells that regulate and suppress other immune cells.
Removal of Interstitial Fluid from Tissues:
The tissue fluid found between the cells within tissues is known as interstitial fluid. Interstitial fluid comes from
blood plasma from the blood capillaries at the arterial end of a capillary bed that has been forced out. For the
exchange of materials to take place, the cells are bathed in the tissue fluid so that oxygen and nutrients diffuse
into the cells from the tissue fluid. Also, carbon dioxide, urea and other wastes, as well as some proteins, diffuse
into the tissue fluid from the cells.
It is possible that excess tissue fluid leaks out of the blood capillaries at the tissue and this is why the excess
leaked fluid is passed into the lymph capillaries. There are larger holes in the walls of the lymph capillaries than
the blood capillaries therefore large protein molecules in the tissue fluid can pass into the lymph capillaries. The
protein molecules are then carried away from the tissues in the lymphatic system and this is because if they were
not carried away then they would cause the removal of tissue fluid to be prevented as a result of exerting
osmotic effects. This would eventually lead to oedema (swelling).
3
