As blood circulates some fluid leaks into the surrounding tissue a network of vessels, nodes and organs collect the fluid and returns it back to the circulatory system. This network is called the lymphatic system.
The lymphatic system is made of cells and biochemical that travel in lymphatic vessels, organs and glands that produce them.
1. L vessels carry away excess fluid from interstitial spaces in the tissues and return it to the bloodstream.
2. It also plays an important role in nutrient absorption specific lymphatic capillaries called “lacteals” located in the lining of the intestine transport lipid soluble vitamins. – A, D, E and K.
a. Lacteals also absorb fats and transport them to veins
3. Carries out immune responses it initiates specific responses against particular microbes and abnormal cells.
Parts of the lymphatic system
1. Lymphatic Capillaries- closed end microscopic tubes; they extend into interstitial spaces forming a network similar to those of blood capillaries.
2. Lymph – it the clear pale yellow fluid inside the L capillaries.
a. If it contains lipids – white
The capillaries merge to form larger
3. Lymphatic vessels- similar to veins but thinner- they also have valves that help to prevent backflow of Lymph.
4. Lymph nodes- they are specialized organs that act as filters trapping bacteria and other microorganisms that cause diseases.
a. They are located along the lymph vessels
b. Bean shaped- usually occur in groups
c. They are covered by a capsule of dense connective tissue that extends into the node
d. Foreign substances are trapped by their reticular fibers within sinuses. Then macrophages destroy some of the foreign substances by phagocytosis while lymphocytes destroy other substances by immune response – The filtered lymph then leaves the other
e. After leaving the nodes the vessels merge together to form
5. Lymphatic trunk- Drains lymph and are named for the area they serve
a. Lumbar- lower limbs, organs of pelvis, kidney, adrenal glands and abdominal wall.
b. Intestinal- stomach intestine, pancreas, spleen and parts of the liver.
c. Brochomediastinal- thoracic wall, lungs and heart
d. Subclavian- upper limbs
e. Jugular- head and neck
The Lymphatic trunks joins the
6. Lymphaic collecting Ducts
a. Thoracic Duct- It is the larger of the 2 and longer.
i. It receives lymph from lower limbs, abdominal regions, left upper limb, left side of thoray, head and neck. ii. The Thoracic Duct empties into Left subclavian vein.
b. Right Lymphatic Duct- receives lymph from right side of head and neck, right upper limb and right thorax.
i. It empties into Right subclavian vein. ii. After leaving the collecting ducts, lymph enters the venous system and becomes part of the plasma just before the blood returns to the right atrium.
7. Thymus- soft bi lobed structure enclosed in a connective tissue capsule located anterior to the aorta and posterior to the sternum found in the mediastinum cavity. It is large during infancy and childhood and shrinks with age – in old people it is replaced with adipose and connective tissue- divided into 2 sections called “lobules”.
a. Lobules contain lymphocytes. They are inactive; some will mature into T Cells.
b. T lymphocytes, which leave the thymus, provide immunity against diseases.
c. Epithelial cells in the thymus secrete hormones called “Thymosins” which stimulates the maturation of T cells after they leave the thymus.
8. Spleen- Largest organ in ‘Lymph’ system found in the upper left portion of the abdominal cavity inferior to diaphragm posterior and lateral to stomach. Has lobules, the spaces, the sinuses of the spleen contain blood instead of lymph.
a. It has 2 tissues
i. White pulp – contains many lymphocytes and macrophages. ii. Red pulp- contains red blood cells, plus lymphocytes, plasma cells macrophages and granulocytes.
1. Blood cap. Within Red pulp are quite permeable. Red blood cells can squeeze