Immune System

Question 1

What are the four parts of the lymphatic system?

Answer 1

Lymphatic vessels, fluid, nodes and lymphoid organs and tissues.

Question 2

What are the main lymphoid organs?

Answer 2

The spleen, thymus, tonsils and lymph nodes.
Last week, we talked about how fluid leaks out of the vessels at the capillary beds, as much as 3 liters of fluid per day.

Question 3

What does the lymphatic system have to do with this fluid?

Answer 3

The lymphatic vessels collect this fluid and return it back to the

Question 4

Explain how these 3 liters of fluid leaks out of the capillary beds.

Answer 4

Blood moves through the capillary beds, fluids diffuse or move by bulk flow from the capillary to the interstitial space due to hydrostatic pressure. Then, fluid moves back into the blood at the venule side due to colloidal osmotic pressure. Some fluid is left behind, it isn’t a perfect system.

Question 5

What are lymphatic capillaries and where are they found? Are they two directional or one directional? What direction/s do they run?

Answer 5

Lymphatic capillaries are one cell thick, just like capillaries that carry blood. However, they are more permeable than a capillary carrying blood. The endothelial cells aren’t tightly joined, the edges of adjacent cells overlap loosely, forming a flap-like mini-valve. So, when there is a lot of interstitial fluid, it causes the valve to open and fluid moves into the lymphatic capillaries.

Question 6

What type of tissue forms the lymphatic capillaries?

Answer 6

Epithelial tissue forms the endothelium. There are collagen fibers holding the capillary to the connective tissue surrounding the vessel.

Question 7

Explain why they are so permeable. What causes the mini-valves to open?

Answer 7

When pressure outside is greater than inside, fluid moves into the mini-valves - this means that it moves right between cells, it doesn’t have to diffuse through the cells. When pressure inside is higher than the pressure outside (the inside is full of fluid), the mini-valves are forced to close, so no fluid escapes.

Question 8

When pressure is greater inside the capillary, what happens to the mini-flaps?

Answer 8

See above.

Question 9

What kinds of molecules can move into lymphatic capillaries, but can’t move into blood capillaries? Why?

Answer 9

Proteins. This is because they are too big to diffuse into the capillaries of blood, but they can move through the flap-like mini-valves of the lymphatic system.

Question 10

Describe the structure of a lymphatic collecting vessel.

Answer 10

A lymphatic collecting vessel has all three tunics (same as veins), but with thinner walls and more valves.

Question 11

What are the main lymphatic trunks of the body. Identify them on a figure

Answer 11

There are 2 lumbar, 2 bronchomediastinal, 2 subclavian, 2 jugular, and 1 intestinal.

Question 12

What are the two main lymphatic ducts of the body? What do they drain into? What areas of the body do they drain fluid from?

Answer 12

They are the right lymphatic duct and the thoracic duct, which is much bigger. The right lymphatic duct drains the right upper limb, right side of the head, and thorax. The thoracic duct drains the rest of the body. They both drain into the venous return at the junction of the subclavian and the internal jugular (on both sides of the body).

Question 13

Because there is no pump in the lymphatic system, what are the factors that power the movement of lymph through the system?

Answer 13

The milking action of skeletal muscle, pressure changes in the thorax and during breathing, valves to prevent backflow, and smooth muscle in the vessels contracting to move the lymph along.

Question 14

What are the three types of cells in the lymph system and what are their functions?

Answer 14

The three types of cells are reticular cells, macrophages and lymphocytes. Reticular cells produce the reticular tissue that is the network of reticular fibers that support the growth of the macrophages and lymphocytes. Macrophages phagocytose foreign things and activate T cell (one type of lymphocyte). There are two types of lymphocytes: T cells and B cells. T cells attack and destroy infected cells. Cells can be infected if they have a virus, cancer, and so forth. B cells produce antibodies. Antibodies mark certain cells for destruction

Question 15

What is the main type of connective tissue in the lymph system? What cells are associated with this tissue?

Answer 15

Reticular connective tissue. Fibrocytes form this tissue, but the majority of cells found in reticular CT are macrophages and lymphocytes that are growing and maturing

Question 16

Diffuse lymphoid tissue is comprised of lymphoid cells and some reticular fibers.

Answer 16

The fibers are loosely arranged. This type of tissue occurs all over the body, in almost every organ.
Lymphoid follicles are solid, round bodies. They have tightly packed lymphoid cells and reticular fibers. The follicles have a germinal center, where B cells are dividing to form plasma cells, which will give rise to antibodies. In some cases these follicles form part of a lymph node or other lymph tissue, but they can also exist on their own (Peyers patches, tonsils, in the appendix).

Question 17

Describe how lymph fluid circulates through a lymph node.

Answer 17

An afferent lymphatic vessel brings lymph to the lymph node. The subscapular sinus, right underneath the capsule is the first place fluid circulates. It then enters other sinuses that guide the fluid through the cortex and into the medulla. It travels through the medullary sinuses, exits through the hilum, through an efferent vessel. There are more afferent vessels as compared to efferent, so the fluid slows down as it goes through the lymph node, giving more time for the macrophages and lymphocytes to cleanse it.

Question 18

Describe the structure of a lymph node.

Answer 18

They are bean shaped, covered in a capsule, they have C.T. strands indenting inwards, separating the tissue into compartments. There are two regions, the cortex is on the outside and the medulla on the inside. The cortex has follicles with germinal centers with dividing B cells. The deeper part of the cortex has T cells, which circulate between the blood, lymph, lymph nodes and reticular C.T. looking for antigens to activate them. The medulla has both types of lymphocytes (B and T cells).

Question 19

What are the two main lymphatic ducts of the body? What do they drain into? What areas of the body do they drain fluid from?

Answer 19

They are the right lymphatic duct and the thoracic duct, which is much bigger. The right lymphatic duct drains the right upper limb, right side of the head, and thorax. The thoracic duct drains the rest of the body. They both drain into the venous return at the junction of the subclavian and the internal jugular (on both sides of the body)

Question 20

Because there is no pump in the lymphatic system, what are the factors that power the movement of lymph through the system?

Answer 20

The milking action of skeletal muscle, pressure changes in the thorax and during breathing, valves to prevent backflow, and smooth muscle in the vessels contracting to move the lymph along.

Question 21

What are the main lymphatic trunks of the body. Identify them on a figure.

Answer 21

There are 2 lumbar, 2 bronchomediastinal, 2 subclavian, 2 jugular, and 1 intestinal.

Question 22

What are the three types of cells in the lymph system and what are their functions?

Answer 22

The three types of cells are reticular cells, macrophages and lymphocytes. Reticular cells produce the reticular tissue that is the network of reticular fibers that support the growth of the macrophages and lymphocytes. Macrophages phagocytose foreign things and activate T cell (one type of lymphocyte). There are two types of lymphocytes: T cells and B cells. T cells attack and destroy infected cells. Cells can be infected if they have a virus, cancer, and so forth. B cells produce antibodies. Antibodies mark certain cells for destruction.

Question 23

What is the main type of connective tissue in the lymph system? What cells are associated with this tissue?

Answer 23

Reticular connective tissue. Fibrocytes form this tissue, but the majority of cells found in reticular CT are macrophages and lymphocytes that are growing and maturing.

Question 24

Compare and contrast diffuse lymphoid tissue and lymphoid follicles.

Answer 24

Diffuse lymphoid tissue is comprised of lymphoid cells and some reticular fibers. The fibers are loosely arranged. This type of tissue occurs all over the body, in almost every organ. Lymphoid follicles are solid, round bodies. They have tightly packed lymphoid cells and reticular fibers. The follicles have a germinal center, where B cells are dividing to form plasma cells, which will give rise to antibodies. In some cases these follicles form part of a lymph node or other lymph tissue, but they can also exist on their own (Peyers patches, tonsils, in the appendix).

Question 25

What are the primary lymphoid organs? Secondary?

Answer 25

The primary lymphoid organs are where B and T cells originate and mature. Red bone marrow are where both T and B cells originate. B cells also mature in the red bone marrow. T cells mature in the thymus. So, the primary lymphoid organs are the red bone marrow and the thymus gland. The secondary organds are where mature lymphocytes hang out and first encounter antigens. These include the spleen, lymph nodes and MALT tissues (Peyer’s patches, appendix, tonsils…).

Question 26

Describe the structure of the spleen.

Answer 26

It is on the left side of the abdominal cavity right underneath the diaphragm. There is a fibrous capsule with CT extending inward, dividing it into regions. The hilum is a slight indentation on the anterior surface. There is white and red pulp. White pulp is lymphocytes on reticular fibers. Red pulp are where worn out red blood cells and pathogens are broken down.

Question 27

What are the functions of the spleen?

Answer 27

The spleen recycles breakdown products of red blood cells, stores lymphocytes and platelets for later use, cleanses the blood of old RBC’s and platelets, houses macrophages which remove foreign bodies, and houses lymphocytes which are dividing and becoming activated here.

Question 28

What is MALT?

Answer 28

Mucosa-associated lymphoid tissue. Found in the mucous membranes throughout the body and guard against foreign things that might enter. Examples are the tonsils, peyer’s patches in the small intestine, the appendix and the mucosa of the respiratory, digestive, reproductive, and urinary tracts.

Question 29

Describe the structure of a tonsil and how this structure allows the tonsil to carry out its function.

Answer 29

Tonsils are found forming a ring around the pharynx (the entrance to the throat). There are lymphoid follicles with a germinal center, where B cells are dividing to create plasma cells that are making antibodies. The epithelium that lies over them indents towards them forming infoldings that trap anything foreign. The bacteria that end up trapped there work their way through the epithelium and come into contact with the lymphoid tissue, where they are destroyed.

Question 30

What is a Peyer’s patch? Where does it exist? What is its function?

Answer 30

A peyer’s patch is a cluster of lymphoid follicles. They are in the wall of the last part of the small intestine. Any bacteria that enter with our food are subjected to this tissue.

Question 31

Why is the appendix an example of MALT?

Answer 31

There is a high concentration of lymphoid follicles in the appendix, which is an offshoot of the small intestine. It is in a perfect place to catch any bacteria entering with our food.

Question 32

Explain the two functions of lymph nodes.

Answer 32

Cleansing the lymph that travels through them on the way back from capillary beds. Macrophages in the lymph nodes remove and destroy bacteria, parasites, viruses and other debris. Second, the immune system can be activated in the lymph node. T cells in the lymph nodes are activated when they come into contact with anything foreign (antigens, bacteria, etc)