L17: The lymphatic system

Question 1

What is the lymphatic system?

Answer 1

Network of tissue and organs to help rid the body of toxins, waste and other unwanted materials
Maintain the body balance of fluids

Question 2

How is the lymphatic system organised?

Answer 2

Lymph
Lymphatic vessels
Lymphatic tissue and organs

Question 3

What is lymph?

Answer 3

Fluid that resembles plasma→ lower amount of protein
(chyle→ lymph that arises int he GI tract, white, cloudy substance contains fats and dissolved lipids- chylomicrons and fat soluble vitamins)

Question 4

What are the lymph vessels?

Answer 4

Transport lymph throughout the body

Capillaries→ trunks→ ducts→ veins

Question 5

What is the structure of the lymphatic capillaries?

Answer 5

Single endothelial cells in basement membrane
Overlap with one another
Make reticulin- Collagen 3 to anchor cells in place
Overlapping cells allows fluid to flow inwards
→ No pressure ‘valve’ closed
→ High interstitial pressure ‘valve’ open

Question 6

How does the lymph flow?

Answer 6

• Vessels lie adjacent to capillaries, veins and arteries
• Arranged into superficial and deep (deep to fascia)
• Deep lymphatic vessels in the limbs pass through muscles where contraction aids lymph movement
• Larger lymphatic vessels (ducts and trunks) contain smooth muscle cells in their wall
• Contraction of smooth muscle is an important contributor to lymph flow at these sites

Question 7

Compare a lymphatic capillary to a normal vein?

Answer 7

Low pressure system
Valves present
No cells (normally)
Lymphangion→ compression by local veins and arteries propels the lymph

Question 8

Compare lymphatic trunks and ducts to a vein?

Answer 8

Equivalent to larger veins
Large fibrocartilaginous valves
Skeletal muscle and organ movement for ‘flow’

Question 9

Where does the left and right lymphatic system drain?

Answer 9

Right→ upper right quadrant of the body (right arm, righ shoulder, upper right chest, right half of head) into the right subclavian vein/internal jugular vein
Left→ rest of the body into the left subclavian vein/internal jugular vein

Question 10

What is a lymph node?

Answer 10

• 600-700 of them
• Organised collection of lymphatic tissue
• Shaped like a kidney bean
• Each node has multiple afferent lymphatic vessels→ enter via convex surface
• Single efferent lymphatic vessels→ leaves via the concave hilum
• Feeding artery and draining vein that also enter and leave via the hilum
• Multiple follicles ‘nodules’ that contain the immune cells (macrophages, dendritic cells, B and T cells)
• Surrounded by a fibrous capsule

Question 11

How do lymphocytes enter the lymph node?

Answer 11

Most through the feeding artery

Question 12

How do dendritic cells enter?

Answer 12

Enter with pathogens within the lymph

Question 13

What is lymphadenopathy?

Answer 13

Enlarged lymph node
Occur when fighting infection
Germinal centres fill with increasing number of lymphocytes causing the lymph nodes to swell
Can occur in all the nodal region or affect lymphatic organs
OR
Lymphoma - malignancy of lymphoid tissue itself

Question 14

What are the different lymphatic organs in the body? Where are they located?

Answer 14

Thymus → mediastinum
Spleen → left side of abdomen
Tonsils → on the oropharynx and nasopharynx
Appendix → lower right quadrant of abdomen
Payer’s patches → under the mucosal membrane of SI

Question 15

The thymus is one of the lymphatic organs, describe the anatomical location and structure of it?

Answer 15

Location
- Superior mediastinum
- Fully formed at birth, involutes after puberty and by late teens is mostly fat
Structure
- Similar to lymph node (but no hilum)

Question 16

What is the function of the thymus?

Answer 16

Maturation of bone marrow derived stem cells into immunocompetent T cells
Thymic cell education

Question 17

What is the largest lymphatic organ in the body?

Answer 17

The spleen

Question 18

What is the location, structure and function of the spleen?

Answer 18

Inferior to diaphragm, posterior to stomach
Similar structure to lymph node, separated into white pulp and red pulp
Function→
- White pulp→ Immune part
- Red pulp→ Haemopoietic part- removes aged RBC

Question 19

What are the immune functions of the spleen?

Answer 19

Antigen presenting by APCs
Activation and proliferation of B and T lymphocytes, production of antibodies
Removal of macromolecular antigen (e.g. charcoal) from blood

Question 20

What are the haemopoietic functions of the spleen?

Answer 20

Removal and destruction of old, damaged, and abnormal erythrocytes and platelets
Retrieval of iron from erythrocyte haemoglobin
Erythrocyte storage

Question 21

What are some clinical complication with the spleen?

Answer 21

Rich blood supply and is relatively fragile

• Ruptured spleen= death by exsanguination (bleed out)
• Splenectomy if damaged

Splenectomy
→ increased risk of infection by encapsulated bacteria and malaria
→ liver and bone marrow take over removal and destruction of aged RBCs

Splenomegaly
→ Enlarges in response to localised infections (like lymoh nodes)
→ Enlarges in response to systemic infection (glandular fever, malaria, septicaemia)- enlarge to 10 times it size

Question 22

What is the function of the tonsils?

Answer 22

Prevent pathogen ingress through oral and nasal routes
Prevents pathogen ingress through aural route (adenoids)
Crypts increases surface area
Form Walderyer’s ring→ Adenoids, 2 tubal tonsils, 2 palatine tonsils and lingual tonsils
In the oropharynx and nasopharynx

Question 23

What are the clinical complications associated with the tonsils?

Answer 23

Surface epithelia have numerous microfold (M cells)
Present antigens to underlying immune cells
Swelling due to proliferation of B and T cells

Question 24

What is the veriform appendix? (location, structure, function)

Answer 24

• Inferior to and attached to caecum (ascending colon)
• Nodules reside inferior to surface invaginations, many M fold cells in epithelial surface
• Prevents pathogen ingress through GI routes
• Prevent pathogen ingress arriving from ileum
• Crypts increase surface area

Question 25

What are the Payer’s patches?

Answer 25

• Inferior to and attached to side of ileum
• Nodules reside inferior to surface domes
• Many M fold cells in epithelial surface
• Prevents pathogen ingress through digestion

Question 26

What are function of the lymphatic system?

Answer 26

1. Fluid balance→ return of interstitial fluid to the circulation
2. Transport of fats and fat-soluble vitamins→ from digestive system to the venous circualtion
3. Defence against invading pathogens and disease→ remove microorganisms, parasites, foreign and cancer cells
4. Storage of and destruction of aged erythrocytes→ spleen is responsible (liver takes over after splenectomy)

Question 27

Define sentinel lymph node?

Answer 27

First lymph node to receive lymph from primary tumour

Question 28

Define primary lymphoedema?

Answer 28

Usually congenital

Problem with development of lymph vessels in the body

Question 29

Define secondary lymphoedema?

Answer 29

Caused as a result of treatment of another disease/illness or as a result of another illness/disease
Caused by damage to the lymphatic system or problems with movement and drainage of fluid in the lymphatic system

Question 30

What are the different routes for cancer cells to travel?

Answer 30

Through newly produced vasculature
Through interstitial space
Through lymph

Question 31

How can cancer cell be tracked?

Answer 31

Fluorography
Fluorscent marker attached to glucose→ taken up by cancer cell due to high metabolic rate
Photograph pt later to see where cancer cells are and if they have metastasised

Question 32

What are the different causes of primary lymphoedema?

Answer 32

Congenital (Milroy’s disease)→ mutated FLT4 genes (VEGF-r), small or missing endothelial cells in vessel wall
Praecox (Meige’s disease)→ currently unknown cause
Tarda→ currently unknown cause

Question 33

What are the different causes of secondary lymphoedema?

Answer 33

Neoplasia→ infiltration of lymph nodes
Surgery→ accidental removal or damage to lymph nodes
Radiotherapy→ nodal fibrosis
Autoimmune disease→ Rheumatoid arthritis and eczema
Infections→ cellulitis (obstruction of vessels), filarais (parasitic worm that invades and survives in the lymphatic vessels)

Question 34

What is the treatment for lymphodema?

Answer 34

Lympha press system
Compression stocking
From toe upwards→ sends lymph back towards body