L17- Lymphatic system

Question 1

What is in the lymphatic system?

Answer 1

• Lymph
• Lymphatic vessels
• Lymphoid tissues and organs

Question 2

What is lymph?

Answer 2

Clear white cloudy substance made up of:

• WBC, lymphocyte that attack bacteria in blood
• fluid from the GI tract + intestines called chyle which contains proteins and fats and chylomicrons

Question 3

How much lymph is produced and recycled each day?

Answer 3

3-4 litres

Question 4

Order of lymph flow

Answer 4

1. Lymph capillaries (smallest lymph vessels)
2. Lymphatic collecting vessels
3. Lymph node
4. Lymph trunk
5. Lymph duct
6. Heart

Question 5

Structure of lymph vessels?

Answer 5

• lined by endothelial cells (simple squamous epithelium)
• have a thin layer of smooth muscles and adventitia that bind the lymph vessels to the surrounding tissue.
• smooth muscles allows lymph vessels to slowly pump lymph fluid through the body without a central pump or heart.
• valves, which are semilunar structures (capillaries only have minivalves) –> prevent backflow of fluid
• blind ended

Question 6

What aids the flow of lymph fluid?

Answer 6

• lymph vessels lie adjacent to cardiovascular vessels: pulsation of these propel lymph
• muscle contraction aids lymph movement in deep lymphatics
• larger vessels (ducts + trunks) contain smooth muscle cells in their walls

Question 7

Compare a lymphatic capillary to a vein

Answer 7

• low pressure system
• valves present
• usually no cells in a lymphatic capillary

Question 8

What is lymph transport?

Answer 8

the transport of lymph fluid from the interstitial space inside the tissues of the body, through the lymph nodes, and into lymph ducts that return the fluid to venous circulation

Question 9

How does lymph enter capillaries and other vessels

Answer 9

• Lymphatic capillaries are the site of lymph fluid collection from the tissues.
• The fluid accumulates in the interstitial space inside tissues after leaking out through the cardiovascular capillaries.
• The fluid enters the lymphatic capillaries by leaking through the minivalves located in the junctions of the endothelium
• In addition to interstitial fluid, pathogens, proteins, and tumor cells may also leak into the lymph capillaries and be transported through lymph.
• The lymph capillaries feed into larger lymph vessels.
• Semilunar valves work together with smooth muscle contractions and skeletal muscle pressure to slowly push the lymph fluid forward while the valves prevent backflow. - The collecting vessels typically transport lymph fluid either into lymph nodes or lymph trunks.

Question 10

Structure of lymphatic capillaries?

Answer 10

• tiny thin-walled vessels, closed at one end and located in the spaces between cells throughout the body,
• Anchoring filaments attach to the minivalves to anchor the capillary to connective tissue, and also pull the capillary open to increase lymph collection when the tissue is swollen.
• closed end/ blind end: lymph is pushed forward into larger vessels as the pressure inside the capillary increases as lymph accumulates from fluid collection.

Question 11

Where are lymphatic capillaries not found?

Answer 11

CNS

Question 12

What causes interstitial fluid to move into lymphatic capillaries?

Answer 12

• When pressure is greater in the interstitial fluid than in lymph, the minivalve cells separate slightly and interstitial fluid enters the lymphatic capillary. When pressure is greater inside the lymphatic capillary, the cells of the minivalves adhere more closely, and lymph cannot flow back into interstitial fluid.

Question 13

a) Outline the structure of the lymph ducts and drunks?
b) Outline the direction of flow of lymph through these structures?
c) What are the two lymph ducts and what do they carry and where do they carry it from and to?

Answer 13

a) - They are larger vessels with larger fibrocartilaginous valves
- have skeletal muscle and organ movement for flow

b) - The lymph trunks drain into the lymph ducts, which in turn return lymph to the blood by emptying into the respective subclavian veins.
- There are two lymph ducts in the body: the right lymph duct and the thoracic duct.

c)

1. The thoracic lymph duct:
   - takes lymph from the lower and left halves of the body. - - Because the thoracic lymph duct drains the intestinal lymph trunks, it carries a mixture of lymph and emulsified fatty acids called chyle back to the bloodstream.
   - The thoracic duct drains into to the left subclavian vein
2. The right lymphatic duct:
   - receives lymph from the right and upper halves of the body
   - the right duct drains into the right subclavian vein,

• the two subclavian veins then merge into the vena cava,

Question 14

What is the cisterna chyli?

Answer 14

• dilated sac at the lower end of the thoracic duct in into which lymph from the intestinal trunk and two lumbar lymphatic trunks flow.
• It receives fatty chyle from the intestines and thus acts as a conduit for the lipid products of digestion.

Question 15

Where are the most lymph nodes found in the body?

Answer 15

• Neck (cervical)
• Groin (inguinal)
• Armpit (axillae)

Question 16

Structure of lymph nodes?

Answer 16

• Shaped like a kidney
• covered by a capsule of dense connective tissue, and have capsular extensions, of connective tissue, called the trabeculae, which provide support for blood vessels entering into the node
• lymph enters via afferent vessels (via the convex surface)
• lymph leaves via a single efferent vessel (leaves via concave hilium)
• multiple follicles: nodules that contain immune cells (macrophages, dendritic, B and T cells)
• Main connective tissue fibre: reticulin

Question 17

What is the primary function of lymph nodes and how is this carried out?

Answer 17

• serves as filter as lymph perlocates, it traps antigen, processes antigen and macrophage presents processed antigens to t cells
• They contain follicular dendritic cells in germinal centres which antigen-antibody complexes adhere to and then they cause proliferation of B cells
• They contain Antigen presenting cells
• repository of macrophage, B cells an T cells that work together to produce an inflammatory response followed by an immune response

Question 18

What are the germinal centres?

Answer 18

they can form in the lymph node follicles and they are a site where B cells become activated and proliferation during immune response

Question 19

What is lymphadenopathy and how is is caused?

Answer 19

• Swelling of the lymph nodes
• as they fight infection the germinal centres fill with increasing numbers of lymphocytes
• can also be caused by cancers that metastasise to lymph nodes via afferent vessels
• lymphoma often presents (malignancy of the lymphoid tissue itself)

Question 20

What is the difference between Hodgkins and non-hodgkins lymphoma?

Answer 20

Hodgkins is curable

Question 21

What are the lymphatic organs and where are they located?

Answer 21

• Thymus: in the mediastinum
• spleen: left side of the abdomen (posterior to stomach)
• Tonsils: in the oropharynx and nasopharynx
• appendix: lower right quadrant of the abdomen
• payer’s patches: under the mucosal membrane of the small intestine

Question 22

The thymus:

a) Location
b) Structure
c) Function

Answer 22

a) superior mediastinum

b) Similar to lymph node but no hilium
- capsule and septa made of reticulin fibres mainly

c) Thymic cell education: maturation of bone marrow derived stem cells into immunocompetent T cells

Question 23

What is the largest lymphatic organ?

Answer 23

The spleen

Question 24

The spleen:

a) Location
b) Structure
c) Function

Answer 24

a) inferior to diaphragm, posterior to stomach
b) Similar to lymph node but seperated into white and red pulp
c) Filters blood and has functions in the immune and haemopoietic systems

Question 25

Outline the two functions of the spleen and in which part of the spleen they occur?

Answer 25

1. Immune functions: in the white pulp
   - Antigen presentation by APCS
   - activation and proliferation of B and T lymphocytes, production of antibodies
   - removal of antigen from blood (macrophages do this)
2. Haemopoietic functions: red pulp
   - removal and destruction of old damaged and abnormal erythrocytes and platelets
   - retrieval of iron from erythrocyte haemoglobin
   - erythrocyte storage

Question 26

a) What is a splenectomy and what can be the consequences of this?
b) What is Splenomegaly ?
c) Why is a ruptured spleen such a worry?

Answer 26

a) Removal of spleen
- the liver and bone marrow take over removal of RBC BUT there is a risk of infection by encapsualted bacteria and malaria as the spleen normally removes this
b) Enlarged spleen in response to a localised or systemic infection
c) Because it has such a rich blood supply you risk internal bleeding

Question 27

The tonsils:

a) Location
b) Structure
c) Function

Answer 27

a) Oropharynx and nasopharynx
b) Nodules reside inferior to surface invaginations (crypts)
c) - Prevents pathogen ingress through oral and nasal routes
- prevents pathogen ingress through aural route (adenoids)
- crypts increase SA

Question 28

What leads to swollen tonsils?

Answer 28

B and T cell proliferation as the surface epitehlia have microfold (M cells that present antigens to underlying immune cells)

Question 29

The vermiform appendix:

a) Location
b) Structure
c) Function

Answer 29

a) Inferior to and attached to caecum (ascending colon)
b) - nodules reside inferior to surface invaginations (crypts)
- many m-fold cells in epithelial surface
c)
- Prevents pathogen ingress through GI routes
- Prevents pathogen ingress arriving from ileum
- crypts increase SA

Question 30

The Payer’s patches:

a) Location
b) Structure
c) Function

Answer 30

a) Inferior ot and attached to the side of ileum
b) - nodules reside inferior to surface domes
- many m-fold cells in epithelial surface
c) Prevents pathogen ingress through digestion

Question 31

Functions of the lymphatic system?

Answer 31

1. Defence against invading pathogens and diseases
2. Fluid balance: interstitial fluid returned to circulation
3. Transport of fats and fat-soluble vitamins
4. Storage of and destruction of aged erythrocytes: spleen

Question 32

What are sentinel lymph nodes and what are their functions?

Answer 32

• the first set of lymph nodes that swell (recieve lymph from primary tumour)
• The sentinel nodes are the first few lymph nodes into which a tumor drains

Question 33

What is a sentinel needle biopsy?

Answer 33

• surgical procedure used to determine whether cancer has spread beyond a primary tumor into your lymphatic system.
• It’s used most commonly in evaluating breast cancer and melanoma.
• involves injecting a tracer material that helps the surgeon locate the sentinel nodes during surgery. The sentinel nodes are removed and analyzed in a laboratory.

Question 34

a) What is lymphodema?

b) Outline the differences between primary and secondary

Answer 34

a) localized swelling of the body caused by an abnormal accumulation of lymph.
b)

1. Primary: rare, inherited condition caused by problems with the development of lymph vessels in your body.

Types:

• Milroy’s disease: congenital, onset within 2 years, mutated FLT4 gene, small or missing endothelial cells in vessel wall
• Meige’s disease (lymphedema praecox).: onset 2-35 years
• Late-onset lymphedema (lymphedema tarda): This occurs rarely and usually begins after age 35.

2. Secondary lymphodeama causes:
   Any condition or procedure that damages your lymph nodes or lymph vessels can cause lymphedema. Causes include:

• Surgery.
• Radiation treatment for cancer. Radiation can cause scarring and inflammation of your lymph nodes or lymph vessels.
• Cancer. If cancer cells block lymphatic vessels, lymphedema may result.
• Infection. An infection of the lymph nodes or parasites can restrict the flow of lymph fluid. e.g. cellulitis, filariasis (parastic worm)