- The lymphatic system is a vascular system which performs 3 main functions:
o Removal and return of blood plasma that hasn’t been reabsorbed into the capillaries during circulation
o Absorption of fats from the small intestine
o Most importantly, it plays a huge role in immunity
It is the body’s protective system - It is made up of:
o Lymphatic capillaries and vessels o Lymph Nodes situated along the vessels
o Organs such as the thymus, spleen and bone marrow o Circulating immune cells
- All blood and lymphatic vessels are lined by endothelium
o Tears In the vessels expose connective tissue which triggers the clotting cascade.
- 80-90% of interstitial fluid gets reabsorbed back into capillaries with the remainder being taken up into the lymphatic system.
- Note that lymphatic vessels run parallel with the venous system and eventually drains back into it.
o The lymph vessels drain back through the right lymphatic or thoracic ducts which then drain into the subclavian vein.
6.1. Lymphatic Capillaries
- The lymphatic system is purely drainage similar to veins, i.e. there is no arterial part to the lymphatic system
- They begin in vascular tissues as blind-ended lymphatic capillaries o They do not exist in avascular structures
- They are lined by endothelium which overlap each other so form flaps for fluid to enter under hydrostatic pressure. Once the fluid is in the lumen, it cannot go back out.
Page | 45 - Similarly to veins, lymph capillaries have valves to ensure the fluid travels in one direction;
towards and through the lymph nodes on their way back to the venous circulation
6.2. Lymphatic Nodules
- They are small masses of lymphatic tissue that are distributed strategically around the body to protect the underlying tissues, especially those at risk from penetration by microorganisms from the GIT, respiratory and urinary tracts.
o Remember that GIT, respiratory and urinary tracts are regarded as ‘outside the body’
o They mainly occur in the connective tissue beneath mucous membranes.
- They are packed with lymphocytes. Unlike actual nodes, they do not directly connect to the lymph vessels
- Whilst most nodules exist as small and on their own, they are sometimes found in large clusters called Lymph Nodes
o An example of these are our tonsils.
o Our tonsils form a ring around the entry of the oro and nasopharynx, made up of:
Pharyngeal Tonsil
Two Palatine Tonsils
Lingual Tonsil
o This ring is referred to as Waldeyer’s Lymphatic Ring
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6.3. Lymph Nodes
- Lymph nodes are small, bean-shaped masses of lymphatic tissues of varying size.
- They are enclosed in a strong fibro-elastic capsule. This capsule extends down into the node forming trabeculae which partially divide the node into separate compartments.
- You’ll notice that lymph nodes strongly resemble the kidneys
- The fluid is forced through a series of channels called Lymphatic Sinuses within the node in order to get to the outgoing vessel.
o These sinuses are lined by lymphocytes and macrophages to filter the fluid.
- Lymph nodes are scattered and positioned such that by the time the fluid is returned to the venous circulation, it has been cleaned of all impurities.
- Lymph node position is therefore important. This is because if we know the route by which a body part is drained and which nodes lie in the drainage part, we can assess those nodes via palpation for swelling and hardness.
- Lymph node positions around the body are divided into regions. For us, the head and neck nodes are important as we can assess them to determine the spread of infection.
6.3.1. Nodes of the Head and Neck
- The nodes of the head and neck can be divided into superficial and deep nodes. The superficial ones are usually more relevant to us clinically since they are much more easily palpated.
Superficial Groups:
- Pericervical Ring
- Nodes accompanying superficial neck veins Deep Groups:
- Perivisceral Ring - Deep Cervical Chain
Page | 47 6.3.1.1. Pericervical Ring (Superficial)
- Found around the base of the head and neck (peri = outer; cervical = neck region) - Clinically important and is made up of:
o Submental Group (below the front of the chin)
o Submandibular Group (near the Submandibular gland) o Parotid or Pre-Auricular Group (Anterior to the ear) o Mastoid Group (near the mastoid process)
o Occipital Group (around the back of the neck.
Figure 9 The above diagram shows the drainage patterns of each node group. They all eventually drain into one of the Deep Cervical Nodes. The significance of this will be demonstrated later.
- Note that the further anterior the fluid origin is, the more cervical the Deep Cervical Node it’ll drain into.
o The deep cervical nodes sit on the carotid sheath and drains the whole head.
- This pattern is very useful in determining the origin of an infection.
o E.g. Using the diagram above, if there is an infection in the bottom Deep Cervical Node, it must be from the Submental Group of nodes as they are the only ones which drain into this node.
Parotid Nodes
Mastoid Nodes
Occipital Nodes
Submental Nodes Submandibular
Nodes
Deep Cervical Nodes
Page | 48 6.3.1.2. Superficial Neck Nodes (Superficial)
- The nodes which accompany the superficial neck veins are also important since they are easily palpable. They tell us about superficial and systemic infections.
- These lie in two chains which follow the anterior jugular vein and the external jugular vein.
o Nodes following the external jugular vein are easily palpated since they lie superficially to the sternocleidomastoid.
6.3.1.3. Perivisceral Ring (Deep)
- Named due to the fact that it surrounds the viscera of the neck.
- The most anterior group of these nodes are named based on their position as the group ascends the neck. They are:
o Pre-tracheal nodes
In front of trachea o Pre-laryngeal Nodes
In front of larynx o Infrahyoid Nodes
Below hyoid bone
- The posterior group are similarly named and are as follows:
o Retro-Oesophageal Nodes (behind oesophagus) o Retro-Pharyngeal Nodes (behind the pharynx) 6.3.1.4. The Deep Cervical Chain (Deep)
- Difficult to palpate as it mainly sits deep to the sternocleidomastoid.
- It’s upper and lower ends are defined by two major nodes, named for the muscles near which they lie.
o Jugulo-digastric Node (Upper) o Jugulo-omohyoid Node (Lower)
o The other nodes within this chain are not named.
- All of the lymph from the head and neck will eventually drain into the deep cervical chain on both sides.
o However, the connections are at different points, a fact which is important in diagnosis.
- The deep cervical drain drains into the Right Lymphatic Duct on the right side and the Thoracic duct on the left side.
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