Chapter 20 Lymphatic system, Lymphoid organs & tissues

How do the lymphatic capillaries differ from blood capillaries?

Although similar to blood capillaries, lymphatic capillaries differ structurally in the following ways: (1) The endothelial cells forming the walls of lymphatic capillaries are not tightly joined. Their edges loosely overlap one another, forming flaplike minivalves. (2) Bundles of fine filaments anchor the endothelial cells to surrounding structures so that any increase in interstitial fluid volume separates the cell flaps, exposing gaps in the wall rather than causing the lymphatic capillary to collapse.

What is the consequence of obstruction of the lymphatics?

Obstruction of the lymphatics results in edema distal in the body to the obstruction.

Name the tonsils and state their body locations.

Palatine tonsils-on either side at the posterior end of the oral cavity. lingual tonsil- lies at the base of the tongue. pharyngeal tonsil- in the posterior wall of the nasopharynx. tiny tubal tonsils- surround the openings of the auditory tubes into the pharynx.

A nurse palpated enlarged lymph nodes. Describe signs and symptoms that help to distinguish cancerous lymph nodes from infected lymph nodes.

Tender nodes are usually due to inflammation, whereas hard, fixed, nontender nodes are suggestive of malignancy.

Where are the lymph node aggregations most dense?

near the body surface in the inguinal, axillary, and cervical regions of the body.

Lymphedema may occur as a complication after a radical mastectomy, in which lymph nodes have been removed. Explain why it might occur.

Anything that prevents the normal return of lymph to the blood, such as blockage of the lymphatics by tumors or removal of lymphatics during surgery, results in severe localized edema (lymphedema).

Describe the structural and functional relationship between a capillary bed of the blood vascular system and lymphatic capillaries.

Blind-ended lymphatic capillaries weave between the tissue cells and blood capillaries in the loose connective tissues of the body. Although similar to blood capillaries, lymphatic capillaries are even more permeable due to minivalves that act as one-way swinging doors. Leaked fluid from blood capillaries is taken up by the lymphatic capillaries as well as proteins in the interstitial space that are unable to enter blood capillaries.

What is the special role of the thymus gland

By secreting hormones, the thymus gland causes T lymphocytes to become immunocompetent (able to defend against specific pathogens in the immune response).

Describe why the prognosis of cancer is best when there is no detectable spread from the region of the primary tumor to the lymph nodes.

Cancer cells that break free from the primary tumor can metastasize via the lymph system. Even if a lymph node is 99% effective in trapping malignant cells, given the ability of a tumor to continuously shed cells into lymphatic capillaries, still means that 100 out of every 10,000 cells get through. So the presence of any trapped cells in a lymph node is a warning that a few others may have escaped entrapment.

How does the lymphatic system both help and hinder the spread of cancer through the body?

Lymph nodes help rid the body of cancer cells by immune mechanisms. Lymph vessels may also be used to spread cancer cells throughout the body if immunity is not effective against the cancer cells because a cancer cell that escapes lymphatic filtration will reach the bloodstream and be carried anywhere in the body.

Characterize lymph transport in terms of rate, volume, and ability to change.

Lymph transport is sporadic and much slower than that occurring in veins. About 3 liters of lymph enters the bloodstream in a 24-hour period. An increase in physical activity will cause lymph flow to increase, balancing the greater rate of fluid outflow from the vascular system.

Describe the mechanisms by which lymphatic fluid is moved through the lymphatics.

Lymphatic fluid is moved through the lymphatics by: the milking action of active skeletal muscles pressure changes within the thorax during breathing valves to prevent back flow and pulsation of adjacent arteries.

Define the term MALT. What is its function?

MALT is an acronym for Mucosa-Associated Lymphoid Tissues. It includes Peyer's patches, the appendix, the tonsils in the digestive tract, lymphoid follicles in the walls of the bronchi, and genitourinary tract. Collectively, MALT protects passages open to the exterior from foreign matter invading the walls.

How does the structure of a lymph node allow lymphocytes and macrophages to perform their protective function?

Macrophages and lymphocytes are located in lymph nodes. Macrophages ingest microorganisms and cellular debris. Lymphocytes monitor the lymphatic stream for the presence of antigens and mount an immune response. Because there are fewer efferent vessels draining the node than afferent vessels that feed it, the flow of lymph through the node stagnates somewhat, allowing time for the lymphocytes and macrophages to work.

A man involved in a traffic accident is rushed to the emergency room of a hospital with severe internal bleeding. Examination reveals a ruptured spleen. What is the treatment of choice and what is the likely long-term outcome (prognosis)?

Supportive care or splenic repair is the treatment of choice, depending on severity. Splenectomy is not as necessary as once believed, and is now performed less frequently. If the spleen does need to be removed, the prognosis is very good, as the functions of the spleen are largely taken over by the liver and bone marrow.

While passing through a village on safari you notice a man with one enormous leg and one normal-sized leg. What could have caused the increased size of the swollen leg?

The man has Filariasis commonly known as elephantiasis, which is caused by parasitic worms that get in the lymph system and reproduce to proportions that block the vessels. The swelling is due to edema.

List the functions of the spleen.

The spleen's main functions are: - to remove aged or defective blood cells and platelets from the blood - to store or release some of the breakdown products of RBCs to the blood for processing by the liver Other functions include: - acting as a blood filter and reservoir - serving as a site for erythrocyte production in developing embryos - storing blood platelets - providing a site for lymphocyte proliferation, immune surveillance, and response.

As the human immunodeficiency virus (HIV) progresses, some individuals develop persistent generalized lymphadenopathy (any disease of the lymph nodes). Explain why this may occur.

This may occur because lymph nodes are overwhelmed by a large number of virus particles trapped in the nodes, which stimulate an ineffective immune reaction but cannot be quickly eliminated due to the weakened immune state. The weak immune reaction persists, causing swelling of the nodes.

A woman had a mastectomy that included the removal of axillary lymph nodes on her left side. What does she risk regarding her left arm and why?

Total removal of the axillary lymph nodes results in severe localized edema because the lymphatic vessels are also lost. This results in chronic edema along the arm, although some lymphatic drainage is eventually reestablished by regrowth of the vessels.

A mother takes her son to the doctor and describes the following symptoms that she has observed. The child is running a fever, has flu-like symptoms, and his lymph glands are very swollen and sore to the touch. Of what significance are the swollen and sore lymph glands?

When tissues are inflamed, such as due to a bacterial infection, lymphatic capillaries develop openings that permit the uptake of the pathogens. The inflammation and pain indicate lymph nodes infected by microorganisms.

How are lymphatic capillaries affected by tissue inflammation?

When tissues become inflamed, lymphatic capillaries develop openings that permit uptake of larger particles such as cell debris, pathogens (disease-causing microorganisms such as bacteria and viruses), and cancer cells. In the lymph nodes, cells of the immune system "examine" the lymph and cleanse it of debris.