The Lymphatic System

Question 1

What is lymph and where does it come from

Answer 1

Lymph is interstitial fluid (surrounding cells and tissues) when it is in the lymphatic system. It contains WBCs.

Question 2

What is a mature leukocyte

Answer 2

A mature leukocyte is a white blood cell which is capable of recognising infection and acting on it. The majority of leukocytes become mature in the bone marrow, but T-lymphocytes require maturation (training) in the thymus.

Question 3

List the components of the immune system

Answer 3

Lymphatic tissues and white blood cells.

Question 4

Describe the role of the thymus in T-lymphocyte maturation.

Answer 4

The thymus is responsible for training T-lymphocytes to detect and act on infection as it presents itself around the body.

Question 5

How does the thymus change in size & importance before, during and after puberty?

Answer 5

The thymus is almost as large as the heart in a child (2-3yrs) as they are encountering many new infections (every 6wks). As a result, the thymus is very active. Sex hormones released during puberty stimulate the shrinking of the thymus, as less training of T-lymphocytes is required (they have encountered almost all infections they ever will). Post-puberty, the thymus continues to shrink with age and becomes less essential in the immune system for the same reasons as above.

Question 6

List the levels of lymph vessels

Answer 6

1. Lymph capillaries.
2. Lymph vessels/ Lymphatics.
3. Lymph ducts.

Question 7

What is a lymph node and where are they found?

Answer 7

Lymph nodes are lymph glands, and are located around the body at “weak” spots, i.e. places that need extra protection e.g. tonsils and adenoids where entrances to the body can be found.

Question 8

List the central lymphoid tissues

Answer 8

1. Tonsils.
2. Adenoids.
3. Peyer’s patches.
4. Appendix.
5. Spleen.

Question 9

Describe the role of Peyer’s patches

Answer 9

Peyer’s patches are lymph nodes/ glands found throughout the lining of the small intestine, and function to identify and deal with infections that the stomach may have not filtered out. Material moving down the gut is frequently sampled at Peyer’s patches in order to continuously make sure no infections are missed.

Question 10

What does interstitial fluid have to do with the immune system?

Answer 10

Interstitial fluid bathes around cells and tissues in the body. When interstitial fluid enters the lymphatic system, it becomes ‘lymph’, a fluid which travels through the lymphatic vessels in order to move white blood cells around the body to fight infection.

Question 11

List the functions of the lymphatic vessels

Answer 11

1. To drain lipids from the digestive system to enter them into the bloodstream.
2. To collect & transport interstitial fluid, and return it to the bloodstream (to maintain fluid balance).
3. To protect the body against disease.

Question 12

Compare and contrast blood and lymph capillaries

Answer 12

Functionally, lymph and blood capillaries are quite similar. However, while blood capillaries have their endothelium lined next to one another (with small gaps in between to allow for blood to move in/ out of the vessel), lymphatic capillaries have an overlapping of endothelium which functions to only let fluid IN to the system, and to carry fluid in only one direction.

Question 13

Compare and contrast lymphatics and blood vessels

Answer 13

Similarly to capillaries, functionally lymphatics and blood vessels are very similar. Lymphatics however have larger lumens, thinner vessel walls and more valves in comparison to blood vessels.

Question 14

How does lymph enter a lymph node? What way does it travel around the node?

Answer 14

Lymph enters a node through the afferent vessel, and travels slowly so that it is correctly filtered (any infection is identified).

Question 15

Why do the thymus and spleen have a blue colour when observed under a microscope?

Answer 15

The thymus and spleen are packed full of lymphocytes, which, when stained to view under a microscope, turn blue in colour.

Question 16

What happens to lymphocytes in the thymus as we age?

Answer 16

Lymphocytes reduce in number during puberty (onset of sex hormones), and are instead replaced with adipose tissue, making for a fatty thymus. The number of lymphocytes in the thymus further reduces with age.

Question 17

Where do leukocytes carry out their work?

Answer 17

In tissues, outside of the bloodstream.

Question 18

Why do leukocytes travel outside of the bloodstream to carry out their function?

Answer 18

Leukocytes do not expect to find infection in the bloodstream, and as a result are not patrolling for infection in the blood.

Question 19

At what stage of infection are lymphocytes used?

Answer 19

Lymphocytes are used in the later stages of infection- they do not have an immediate response process.

Question 20

What leukocyte accumulates during infection?

Answer 20

Lymphocytes.

Question 21

How does chronic inflammation occur?

Answer 21

Chronic inflammation occurs in response to prolonged injury or infection.

Question 22

How do neutrophils eradicate infection?

Answer 22

Neutrophils eradicate infection by engulfing the harmful cell and breaking it down using its lysosomes.

Question 23

Are neutrophils granular or agranular?

Answer 23

Granular, they contain lysosomes which aid in breaking down potentially harmful cells.

Question 24

What change takes place in neutrophil cell count during infection?

Answer 24

Neutrophil cell count increases during periods of infection, in order to diminish its effects.

Question 25

How do hydrolytic enzymes work?

Answer 25

Hydrolytic enzymes fill a harmful cell with fluid, and cause it to burst open (process of lysis). Through this, the harmful cell is destroyed.

Question 26

How does myleoperoxidase work?

Answer 26

Myleoperoxidase is an enzyme that is very toxic. When released in small quantities from a neutrophil, it efficiently destroys harmful cells/ infection. Lab tests are carried out when infection is suspected, and a raised level of myleoperoxidase can indicate that infection is indeed present

Question 27

What are pseudoplatelets?

Answer 27

Pseudoplatelets are fragments neutrophils. Note- they are nothing like platelets/ thrombocytes.

Question 28

How can you identify an old neutrophil?

Answer 28

An old neutrophil can be identified under a microscope by observing the number of lobes that the neutrophil has- older ones have more loved

Question 29

Why do we have a low eosinophil count?

Answer 29

Eosinophils function to remove parasites from our body. There is a low eosinophil cell count in humans due to the rarity of parasitic infection.

Question 30

What is histamine in terms of inflammation?

Answer 30

Histamine is an inflammation mediatory.

Question 31

Why do basophils release heparin?

Answer 31

Heparin acts as a vasodilator when it is released by basophils during periods of infection/ inflammation. The purpose of this is to open up blood vessels so more leukocytes/ helper cells can access the damaged tissue.

Question 32

What is vascular permeability?

Answer 32

Vascular permeability- leaky blood vessels.

Question 33

What do monocytes become when they migrate out of the bloodstream?

Answer 33

Macrophages.

Question 34

Why are some macrophages fixed?

Answer 34

Some macrophages are fixed in certain areas of the body, those which would encounter infection on a daily basis, e.g. the lungs (alveolar macrophages- dust cells), the spleen, kidney and liver.

Question 35

What leukocytes can be found in a high quantity in interstitial fluid?

Answer 35

Lymphocytes.

Question 36

What is a lymphocytes function in the interstitial fluid around cells?

Answer 36

To patrol the fluid, ensuring that no infection is not detected.

Question 37

When are natural killer cells used?

Answer 37

Natural killer cells are used as part of the early immune response.

Question 38

Where do B lymphocytes and NK cells develop?

Answer 38

In the bone marrow.

Question 39

Where to T-lymphocytes develop?

Answer 39

In the thymus.

Question 40

Name the three lymphocyte types.

Answer 40

1. B-lymphocytes.
2. T-lymphocytes.
3. Natural killer cells.

Question 41

What type of leukocyte can form antibodies?

Answer 41

B-lymphocytes are the only lymphocyte which can form antibodies as part of their immune defence.

Question 42

How do T-cells kill infection?

Answer 42

By physically and chemically contacting & damaging the cells.

Question 43

How do cytotoxic T-cells kill infection?

Answer 43

By using lysis.

Question 44

What is the importance of the quick response to viruses that NK cells have?

Answer 44

It prevents other cells from being aware that a virus is present- nips the viral infection in the bud.

Question 45

Would it be better or worse to have more NK cells in our immune system?

Answer 45

It would be much better- NK cells are seen to efficiently eliminate infection and to destroy cancerous cells. They are even used in some cancer treatments.