THE LYMPHATIC SYSTEM
THE lymphatic system communicates with the blood circulatory system and is closely associated with it. As described on page 141 the tissue fluid is derived from the blood plasma. A certain amount of this fluid and waste products from the cells is returned to the venous capillaries, but within the
tissue spaces there start fine capillary vessels known as lymphatic capillaries which also help to drain the waste products from the cells and tissues.
As the pressure in the tissue spaces rises the fluid which they contain passes into the minute lymphatic capillaries, in the same way as into the venous capillaries.
The fluid within the lymphatic capillaries and vessels is known as lymph.
The composition of lymph is very like that of the blood plasma but in different concentrations. Lymph also contains materials which may be damaging to the body. For example, if infection is present and phagocytosis has occurred the neutrophils and monocytes with their ingested micro-organisms are drained away in the lymphatic capillaries and vessels.
The lymphatic system consists of:—
Lymphatic capillaries. Lymphatic vessels. Lymphatic nodes. The thoracic duct. The right lymphatic duct. 184
Structure of lymphatic capillaries.
The lymphatic capillaries are composed of very fine connective tissue and a single layer of endothelial cells.
Structure of lymphatic vessels.
VALVE
An outer coat consisting of fibrous tissue which acts as a protective covering. A middle coat of muscular and elastic tissue. An inner lining composed of a single layer of endothelial cells. Lymphatic vessels contain many valves and have a knotted or beaded appearance. The valves prevent the back-flow of the lymph. The lymphatic capillaries commence in the tissue spaces of the body as minute blind end tubes. These minute capillaries join with one another to form the lymphatic vessels until eventually two main lymphatic ducts are formed
LYMPHATIC NODES
All the lymphatic vessels open into lymphatic nodes. These nodes are situated in strategic positions throughout the body. The lymph from the lymphatic vessels drains through at least one lymphatic node. These nodes vary in size from a pin's head to an almond. Structure of a lymphatic node. Lymphatic nodes have a surrounding capsule of fibrous tissue which dips down into the node substance forming partitions known as trabeculae. The main substance of the node consists of reticular and lymphatic tissue containing many lymphocytes. The area of the node where the blood vessels enter and the lymphatic vessels leave is concave and is known as the hilum of the node. The lymphatic vessels entering the node are known as afferent vessels and those leaving are known as efferent vessels.
THE MORE IMPORTANT LYMPHATIC NODES
There is a vast number of lymphatic nodes situated in strategic positions throughout the body. They are arranged usually in deep and superficial groups. Those through which lymph must pass from the head and neck are:— The deep and superficial cervical nodes. The lymph from the upper limbs must pass through nodes situated in the elbow region and eventually all lymph is drained through:— The deep and superficial axillary nodes. Lymph from the thoracic cavity is drained through many nodes, the more important nodes are:— The tracheobronchial nodes. The intercostal nodes. Lymph from the pelvic and abdominal cavities is drained through many lymphatic nodes which are named in association with the organs involved. Most of the lymph is finally drained through nodes which are situated either in front of, or on either side of the aorta. These nodes are known as:— The pre-aortic nodes. The lateral aortic nodes. The lymph from the lower limbs is drained through deep and superficial nodes behind the knee and in the groin. These nodes are:— The popliteal nodes. The deep and superficial inguinal nodes. Diagram showing position of lymphatic nodes of the leg In the abdominal cavity the lymphatic capillaries draining the small intestine are known as lacteals. The lacteals are responsible for absorbing about sixty per cent of the digested fat (in the form of fatty acids and glycerol) from the small intestine. The lymph containing this high concentration of fatty acids and glycerol is known as chyle.
FUNCTIONS OF THE LYMPHATIC NODES
Formation and position of the thoracic duct The lymphatic nodes are responsible for filtering all the lymph in the body. They are also responsible for liquifying and destroying any damaging material within the lymph, thus purifying it, for example, if infection is present the lymphatic nodes are responsible for destroying the phagocytes and any micro-organisms which they may contain. The nodes also destroy any body cells which may have been damaged due to the process of inflammation. Due to the presence of reticular and lymphatic tissue lymphocytes are manufactured in the lymphatic nodes. The nodes are also responsible for the production of some of the antibodies and antitoxins which prevent infection.
THE CISTERNA CHYLI
The cisternachyli is a sac-like dilatation on the lymphatic pathway which has drained the lower limbs, pelvic and abdominal cavities. It is about 5 cm. (2 inches) in length and is situated in front of the bodies of the first and second lumbar vertebrae to the right of the abdominal aorta. All the lymph from the legs, pelvic and abdominal cavities must pass into this sac.
THE THORACIC DUCT
The thoracic duct is a continuation of the cisterna chyli. It is the largest lymphatic vessel in the body and contains several valves. It is approximately 40 cm. (16 inches) in length. It extends from the lower border of the body of the twelfth thoracic vertebra to the root of the neck and opens into the left subclavian vein. The thoracic duct conveys to the blood all purified lymph from the lower limbs, pelvic cavity, abdominal cavity, left side of the chest, left side of the head, neck and left arm. It is also responsible for conveying the chyle from the small intestine and passing it into the blood stream. The structure of the thoracic duct is the same as that of the lymphatic vessels.
VALVE
An outer coat consisting of fibrous tissue which acts as a protective covering. A middle coat of muscular and elastic tissue. An inner lining composed of a single layer of endothelial cells. Lymphatic vessels contain many valves and have a knotted or beaded appearance. The valves prevent the back-flow of the lymph. The lymphatic capillaries commence in the tissue spaces of the body as minute blind end tubes. These minute capillaries join with one another to form the lymphatic vessels until eventually two main lymphatic ducts are formed
LYMPHATIC NODES
All the lymphatic vessels open into lymphatic nodes. These nodes are situated in strategic positions throughout the body. The lymph from the lymphatic vessels drains through at least one lymphatic node. These nodes vary in size from a pin's head to an almond. Structure of a lymphatic node. Lymphatic nodes have a surrounding capsule of fibrous tissue which dips down into the node substance forming partitions known as trabeculae. The main substance of the node consists of reticular and lymphatic tissue containing many lymphocytes. The area of the node where the blood vessels enter and the lymphatic vessels leave is concave and is known as the hilum of the node. The lymphatic vessels entering the node are known as afferent vessels and those leaving are known as efferent vessels.
THE MORE IMPORTANT LYMPHATIC NODES
There is a vast number of lymphatic nodes situated in strategic positions throughout the body. They are arranged usually in deep and superficial groups. Those through which lymph must pass from the head and neck are:— The deep and superficial cervical nodes. The lymph from the upper limbs must pass through nodes situated in the elbow region and eventually all lymph is drained through:— The deep and superficial axillary nodes. Lymph from the thoracic cavity is drained through many nodes, the more important nodes are:— The tracheobronchial nodes. The intercostal nodes. Lymph from the pelvic and abdominal cavities is drained through many lymphatic nodes which are named in association with the organs involved. Most of the lymph is finally drained through nodes which are situated either in front of, or on either side of the aorta. These nodes are known as:— The pre-aortic nodes. The lateral aortic nodes. The lymph from the lower limbs is drained through deep and superficial nodes behind the knee and in the groin. These nodes are:— The popliteal nodes. The deep and superficial inguinal nodes. Diagram showing position of lymphatic nodes of the leg In the abdominal cavity the lymphatic capillaries draining the small intestine are known as lacteals. The lacteals are responsible for absorbing about sixty per cent of the digested fat (in the form of fatty acids and glycerol) from the small intestine. The lymph containing this high concentration of fatty acids and glycerol is known as chyle.
FUNCTIONS OF THE LYMPHATIC NODES
Formation and position of the thoracic duct The lymphatic nodes are responsible for filtering all the lymph in the body. They are also responsible for liquifying and destroying any damaging material within the lymph, thus purifying it, for example, if infection is present the lymphatic nodes are responsible for destroying the phagocytes and any micro-organisms which they may contain. The nodes also destroy any body cells which may have been damaged due to the process of inflammation. Due to the presence of reticular and lymphatic tissue lymphocytes are manufactured in the lymphatic nodes. The nodes are also responsible for the production of some of the antibodies and antitoxins which prevent infection.
THE CISTERNA CHYLI
The cisternachyli is a sac-like dilatation on the lymphatic pathway which has drained the lower limbs, pelvic and abdominal cavities. It is about 5 cm. (2 inches) in length and is situated in front of the bodies of the first and second lumbar vertebrae to the right of the abdominal aorta. All the lymph from the legs, pelvic and abdominal cavities must pass into this sac.
THE THORACIC DUCT
The thoracic duct is a continuation of the cisterna chyli. It is the largest lymphatic vessel in the body and contains several valves. It is approximately 40 cm. (16 inches) in length. It extends from the lower border of the body of the twelfth thoracic vertebra to the root of the neck and opens into the left subclavian vein. The thoracic duct conveys to the blood all purified lymph from the lower limbs, pelvic cavity, abdominal cavity, left side of the chest, left side of the head, neck and left arm. It is also responsible for conveying the chyle from the small intestine and passing it into the blood stream. The structure of the thoracic duct is the same as that of the lymphatic vessels.