The Lymphatic System

Consists of two semi-independent parts:

A network of lymphatic vessels that transport fluid that has escaped from the vascular system back into the bloodstream
Lymphoid tissues and organs throughout the body that house phagocytic cells and lymphocytes, which are essential in immunity and resistance to disease.

Lymphatic Vessels

The lymphatic vessels, or lymphatics, are an elaborate system of drainage vessels that collect excess protein-containing interstitial fluid and return it to the bloodstream.

How it works:

Varying hydrostatic and colloid osmotic pressures in the capillary beds force blood out of the arterial ends of the capillaries (in order for gas exchange to occur) and back into the venous ends so that blood is reabsorbed to continue its return journey to the heart. The fluid that remains behind in the tissue spaces in the capillary beds during this exchange becomes part of the interstitial fluid and can be up to 3 liters per day. This leaked fluid has to be returned to the circulating blood stream in order to maintain a sufficient blood volume for the cardiovascular system to operate properly.

Lymphatic vessels are one-way, flowing only toward the heart. This one way system starts with lymph capillaries, found everywhere blood capillaries are, with the exception of bones, teeth, bone marrow and the entire central nervous system. These vessels are so permeable (meaning they easily allow fluid to flow through) due to two unique features:

The endothelial cells that make up the walls of lymphatic capillaries loosely overlap one another, forming flaplike minivalves.
Fine collagen filaments anchor these endothelial cells to surrounding structures, so that when interstitial volume increases, the cell flaps open rather than close to cause capillary collapse.

Proteins in the interstitial space are unable to enter blood capillaries but easily enter lymphatic capillaries. When inflammation is present, the lymphatic capillaries develop wider openings to allow for the uptake of larger particles, including cell debris, pathogens and cancer cells.

Lacteals are even more specialized lymphatic capillaries in the villi of the intestinal mucosa. These lymphatic capillaries drain a milky white fluid that gets its color from the digested fats in the intestine. This fat containing fluid is called chyle.

Path of lymph: lymphatic capillaries to collecting vessels to trunks to lymph ducts

Lymphatic collecting vessels are structurally similar to veins but are thinner-walled, have more internal valves, and anastomose more (meaning cross-connect).

The major lymph trunks are named for the area of the body where they collect lymph: lumbar, bronchomediastinal, subclavian, jugular, and intestinal.

There are two large ducts in the thoracic (chest) region that receive lymph. The right lymphatic duct drains lymph from the right upper arm, and right side of the head and chest.

The thoracic duct is much larger and receives lymph from the rest of the body. The thoracic duct begins as the cysterna chyli, collecting lymph from the two large lumbar trunks draining the lower limbs and the intestinal trunk that drains the digestive organs.

When lymphatic vessels are inflamed, the associated blood vessels become congested with blood. This causes the pathway of the lymphatic vessels to become visible through the skin as red, tender areas. This condition is called lymphangitis (inflammation of the lymph vessel).

Lymphedema or lymphatic edema is localized swelling caused by a compromised lymphatic system.

Edema = swelling

Caused by removal of lymph nodes, blockage of lymphatic pathways,

The lymphatic system does NOT have an organ that acts as a pump. Fluid flows in a low pressure system using the milking action of the skeletal muscles, pressure changes within the thorax during breathing, and valves to prevent backflow.

3L of lymph enters the bloodstream every 24 hours, and the movement of this volume is very sporadic. Movement of adjacent tissue helps propel lymph, as does physical activity. For this reason, it is a good idea to immobilize a badly infected body part to prevent flow of inflammatory material from the infected part.

Lymphangitis-inflamation of the lymphatic vessels.

Lymphoid Cells, Tissues, and Organs

Lymphocytes are the main warrior of the immune system and come from red bone marrow. They mature into one of two major immunocompetent cells: T or B cells, both of which protect the body against antigens (anything perceived as foreign by the body: bacteria, viruses, or cancer cells). Activated T cells manage immune response and some directly attack and destroy foreign cells. B cells produce plasma cells, cells that secrete antibodies into blood or bodily fluid.

Lymphoid macrophages and dendritic cells in lymphoid tissue phagocytize foreign substances and help to activate T cells. Reticular cells produce a reticular fiber stroma or network that supports the other cell types in the lymphoid network.

Lymphoid (lymphatic) tissue houses and provides a production site for lymphocytes and provides a surveillance point for the lymphocytes and macrophages. It is comprised of loose reticular connective tissue and there are various types throughout the body.

Diffuse lymphatic tissue is found in virtually every organ but in greater concentration in the lamina propria of mucous membranes and within lymphoid organs
Lymphatic follicles (nodules)

Lymphoid organs

Nodes indicate and filter infectious materials.

Become swollen with infection.

Are often secondary locations for tumours -> once cancer cells start to migrate, it will allow you to have info on remission. (if it spreads to lymph nodes, remission is more likely).

Spleen.

It filters blood and is very blood rich. Lymphocyte proliferation occurs here (lymphocytes form). It also deals with old/dead blood cells. Erythrocytes can be produced here in developing babies and extramedullary hematopoiesis.

If you injure the spleen, it is an issue which can cause internal bleeding and is an emergency. It mainly occurs during contact sports. It can also occur in severe infection. When it ruptures, it spills blood into the peritoneal cavity. If it ruptures, it must be removed. First, they will tie off the splenic artery

It can be removed, but this removal causes some issues. The liver and bone marrow must take over the duties of the spleen in the case of removal. This causes the patient to be immunocomprimised.

The spleen can regenerate in children younger than 12.

Thymus.

It is mainly important in the early years of life, as it secrets hormones and causes T-Cells to mature. Thymosine and thymopoeitin are the hormones that are released which cause the T cells to be immunocompetent. It has no influence on B Cells.

It increases in size during childhood, stops growing in adolescence and atrophies (shrivels up) with age. By age 60, it has basically disappeared and been taken over by fatty and connective tissue.

The only lymph organ that does not actively fight disease/infection.

The stroma of the thymus has star shaped epithelials rather than

Tonsils.

Tonsilectomies can be dangerous due to the blood vessels near them, so recently tonsilectomies have been less utilized.

A +1 tonsil is slightly enlarged and +6 the tonsils on both sides of the throat are touching (kissing tonsils).

+6 causing breathing issues.

Tonsils can help with immune memory against inhaled pathogens.

Non-bacterial tonsillitis is ok as it leads to immune memory, but more than 6 strep infections in a 12 month period is not ok.

Question:	Answer:
What does the white pulp do? What is its structure?	1) It serves a function similar to that of lymph nodes. 2) It is circular in nature, and composed mainly of lymphocytes.
What does the red pulp do? What is its structure?	1) It repairs and phagocytizes erythrocytes. 2) It surrounds the white pulp and mainly contains red blood cells and macrophages.
What does the spleen do?	It phagocytizes and repairs erythrocytes, produces erythrocytes and leukocytes until the fifth month gestation, promotes phagocytosis and the destruction of bacteria, is the site of immune response against bloodborne illness, and in autoimmune anemias, it is the site of excessive destruction.
Describe the sites of hematopoiesis and how they change throughout the years.	In the eary pregnancy, it occurs in the yolk sac and the moves to the liver and spleen, in childhood it occurs in the distal long bones and in adults it occurs the axial skeleton.
What would a typical case of splenic trauma look like?	It would most likely result from a blunt upper abdominal injury and is associated with fractured ribs of the left chest. They can either cause continuous hemorrhage or subcapsular hematomas that could burst at any time. Symptoms include generalized LUQ (left upper quadrant) pain.
How should the ruptured spleen be treated?	Via splenic preservation operations, partial splenectomy, capsular repair, and some non-operative treatments.
What is delayed rupture of the spleen? What is the interval between injury and hemorrhage?	1) When the spleen bleeds inside its capsule and when the capsule fills up it bursts. 2) It is usually within two weeks.
What is splenosis? Is it usually an issue?	1) Auto-transplantation of splenic tissue after splenic trauma to somewhere else in the peritoneal cavity. 2) It usually causes no issue, but there is renewed interest in it due to post-splenectomy sepsis.
What infections may cause splenomegaly?	Typhoid fever, endocarditis, septicemia, abscess, ebola virus, CMV, malaria, and toxoplasmosis.
What hematologic processes cause splenomegaly?	Hemolytic anemia and extramedullary hematopoiesis.
What neoplasms may cause splenomegaly?	Leukemia, lymphoma, histiocytosis, metastatic tumors, hemangioma, hamartoma.
What is hypersplenism?	A variety of ill effects that result from increased splenic function. It may be improved by a splenectomy. Symptoms include anemia, leukopenia, and thrombocytopenia.
What influences the probability of splenic involvement in Hodkin’s lymphoma?	The probability of splenic involvement increases with splenic size (absense of splenomegaly does not exclude splenic involvement).
What would Hodkin’s lymphoma look like in the spleen?	A greyish-white nodule ranging from several millimeters to several centimeters will be apparent upon gross examination of the spleen in Hodkin’s lymphoma.
Is the liver usually involved in Hodkin’s lymphoma if the spleen is not?	No. This occurs only very rarely.
What is Felty’s syndrome?	A syndrome consisting of rheumatoid arthritis, granulocytopenia, and splenomegaly. Severe, persistent, and recurrent infections are charecteristic. A splenectomy usually fixes it.
What is gaucher’s disease?	A disorder of lipid metabolism that may result in massive splenomegaly and hypersplenism. It is commonly found in the Jewish population.
What are splenic cysts caused by?	Compression of adjacent viscera.
What are the two types of splenic cysts? Define them.	1) Parasitic cysts-caused mainly by echinococcal disease. 2) Non-parasitic cysts-not caused by parasites, either true/primary which have an epithelial lining or pseudocysts which don’t.
When should splenectomies be performed for cysts?	In the case that the cyst is large or has an uncertain diagnosis.
How does infectious mononucleosis impact the spleen?	The spleen is enlarged and palpable in over 50% of patients, and splenic rupture may occur.
What are Howell-Jolly bodies?	Nuclear remnents of erythrocytes.
Is a splenectomy ever performed for a hematologic disease? What would the desired result of this be?	1) Yes. 2) Thrombocytosis.
How does a splenectomy increase the risk of sepsis? How does it typically occur?	1) It increases the risk by 60 times. 2) It typically occurs in a previously healthy individual after a mild upper respiratory infection associated with fever. Then sepsis occurs.
What is hyposplenism?	A syndrome including diminished splenic function, with a peripheral blood smear that shows that they are asplenic. It is dangerous due to the risk of sepsis. It can occur in the presence of an abnormal sized or enlarged spleen.
What is asplenia?	Lack of a spleen, can be congenital or acquired.

Lymph Nodes

Question:	Answer:
What do lymph nodes do?	They filter out micro-organisms and foreign substances from the lymphatic fluid.

Thymus

Question:	Answer:
Where is the thymus located?	Directly posterior to the sternum and between the lungs.
How does the size of the thymus change with age?	It increases in size until puberty, and then atrophies with age.
Describe the structure of the thymus.	There are two lobes, each surrounded by a capsule, which are divided into lobules which are separated by interlobular septa.
What does the cortex of the thymus contain?	A large number of immature T cells (thymocytes).
What does the medulla of the thymus contain?	A large number of concentric bodies known as hassal’s corpuscles.
What does the thymus secrete?	Thymosin, from which thymulin, thymosisn alpha 1, and thymopoietin are derived.
What does thymosin do?	It stimulates the development and maturation of t lymphocytes.
What is pure red cell aplasia?	Reduction of red blood cells produced by bone marrow.
What is hypogammaglobulinemia?	Not enough gamma globulins (immunoglobulins) in the blood.

Question:	Answer:
What does the white pulp do? What is its structure?	1) It serves a function similar to that of lymph nodes. 2) It is circular in nature, and composed mainly of lymphocytes.
What does the red pulp do? What is its structure?	1) It repairs and phagocytizes erythrocytes. 2) It surrounds the white pulp and mainly contains red blood cells and macrophages.
What does the spleen do?	It phagocytizes and repairs erythrocytes, produces erythrocytes and leukocytes until the fifth month gestation, promotes phagocytosis and the destruction of bacteria, is the site of immune response against bloodborne illness, and in autoimmune anemias, it is the site of excessive destruction.
Describe the sites of hematopoiesis and how they change throughout the years.	In the eary pregnancy, it occurs in the yolk sac and the moves to the liver and spleen, in childhood it occurs in the distal long bones and in adults it occurs the axial skeleton.
What would a typical case of splenic trauma look like?	It would most likely result from a blunt upper abdominal injury and is associated with fractured ribs of the left chest. They can either cause continuous hemorrhage or subcapsular hematomas that could burst at any time. Symptoms include generalized LUQ (left upper quadrant) pain.
How should the ruptured spleen be treated?	Via splenic preservation operations, partial splenectomy, capsular repair, and some non-operative treatments.
What is delayed rupture of the spleen? What is the interval between injury and hemorrhage?	1) When the spleen bleeds inside its capsule and when the capsule fills up it bursts. 2) It is usually within two weeks.
What is splenosis? Is it usually an issue?	1) Auto-transplantation of splenic tissue after splenic trauma to somewhere else in the peritoneal cavity. 2) It usually causes no issue, but there is renewed interest in it due to post-splenectomy sepsis.
What infections may cause splenomegaly?	Typhoid fever, endocarditis, septicemia, abscess, ebola virus, CMV, malaria, and toxoplasmosis.
What hematologic processes cause splenomegaly?	Hemolytic anemia and extramedullary hematopoiesis.
What neoplasms may cause splenomegaly?	Leukemia, lymphoma, histiocytosis, metastatic tumors, hemangioma, hamartoma.
What is hypersplenism?	A variety of ill effects that result from increased splenic function. It may be improved by a splenectomy. Symptoms include anemia, leukopenia, and thrombocytopenia.
What influences the probability of splenic involvement in Hodkin’s lymphoma?	The probability of splenic involvement increases with splenic size (absense of splenomegaly does not exclude splenic involvement).
What would Hodkin’s lymphoma look like in the spleen?	A greyish-white nodule ranging from several millimeters to several centimeters will be apparent upon gross examination of the spleen in Hodkin’s lymphoma.
Is the liver usually involved in Hodkin’s lymphoma if the spleen is not?	No. This occurs only very rarely.
What is Felty’s syndrome?	A syndrome consisting of rheumatoid arthritis, granulocytopenia, and splenomegaly. Severe, persistent, and recurrent infections are charecteristic. A splenectomy usually fixes it.
What is gaucher’s disease?	A disorder of lipid metabolism that may result in massive splenomegaly and hypersplenism. It is commonly found in the Jewish population.
What are splenic cysts caused by?	Compression of adjacent viscera.
What are the two types of splenic cysts? Define them.	1) Parasitic cysts-caused mainly by echinococcal disease. 2) Non-parasitic cysts-not caused by parasites, either true/primary which have an epithelial lining or pseudocysts which don’t.
When should splenectomies be performed for cysts?	In the case that the cyst is large or has an uncertain diagnosis.
How does infectious mononucleosis impact the spleen?	The spleen is enlarged and palpable in over 50% of patients, and splenic rupture may occur.
What are Howell-Jolly bodies?	Nuclear remnents of erythrocytes.
Is a splenectomy ever performed for a hematologic disease? What would the desired result of this be?	1) Yes. 2) Thrombocytosis.
How does a splenectomy increase the risk of sepsis? How does it typically occur?	1) It increases the risk by 60 times. 2) It typically occurs in a previously healthy individual after a mild upper respiratory infection associated with fever. Then sepsis occurs.
What is hyposplenism?	A syndrome including diminished splenic function, with a peripheral blood smear that shows that they are asplenic. It is dangerous due to the risk of sepsis. It can occur in the presence of an abnormal sized or enlarged spleen.
What is asplenia?	Lack of a spleen, can be congenital or acquired.

Lymph Nodes

Question:	Answer:
What do lymph nodes do?	They filter out micro-organisms and foreign substances from the lymphatic fluid.

Thymus

Question:	Answer:
Where is the thymus located?	Directly posterior to the sternum and between the lungs.
How does the size of the thymus change with age?	It increases in size until puberty, and then atrophies with age.
Describe the structure of the thymus.	There are two lobes, each surrounded by a capsule, which are divided into lobules which are separated by interlobular septa.
What does the cortex of the thymus contain?	A large number of immature T cells (thymocytes).
What does the medulla of the thymus contain?	A large number of concentric bodies known as hassal’s corpuscles.
What does the thymus secrete?	Thymosin, from which thymulin, thymosisn alpha 1, and thymopoietin are derived.
What does thymosin do?	It stimulates the development and maturation of t lymphocytes.
What is pure red cell aplasia?	Reduction of red blood cells produced by bone marrow.
What is hypogammaglobulinemia?	Not enough gamma globulins (immunoglobulins) in the blood.