S6) Lymphatic System

Question 1

How does the lymphatic system work in relation to the venous system?

Answer 1

The lymphatic system collects 3 litres per day of interstitial fluid and returns it to the venous system

Question 2

State the names of the fluid and vessels of the lymphatic system

Answer 2

• Fluid – lymph
• Vessels – lymphatics

Question 3

Identify the cells of the lymphatic system

Answer 3

• Lymphocytes: B cells, T cells and NK cells
• Supporting cells: follicular dendritic cells and macrophages

Question 4

Identify the tissues of the lymphatic system

Answer 4

Mucosal associated lymphatic tissue (MALT):

• Gut-associated lymphatic tissue (GALT)
• Bronchus-associated lymphatic tissue (BALT)

Question 5

Identify the organs of the lymphatic system

Answer 5

• Lymph nodes
• Thymus
• Spleen

Question 6

Identify the lymphatic nodules of the lymphatic system

Answer 6

• Tonsils
• Peyer’s patches
• Vermiform appendix

Question 7

What 3 factors help to propel lymph along?

Answer 7

• Skeletal muscle movement
• Pressure changes in the thorax during breathing
• Pulsations of adjacent arteries

Question 8

Describe the arrangement of lymphatic vessels in the body

Answer 8

• Lymphatics tend to lie adjacent to arteries and veins
• Lymphatics are arranged into superficial and deep (deep to the deep fascia)

Question 9

In which region of the body are there no lymphatics?

Answer 9

The Central Nervous System

Question 10

What are the functions of lymph nodes?

Answer 10

• Serve as filters for lymph: traps antigen, processes antigen and presents processed antigen to T cells
• Contains macrophages, B cells and T cells which work to produce an inflammatory response (macrophages) then an immune response (B & T cells)

Question 11

Approximately how many lymph nodes are there in the human body?

Answer 11

700

Question 12

Describe the structure of each lymph node

Answer 12

• Afferent lymphatics that enter via the convex surface
• Efferent lymphatics that leave via the hilum
• Feeding artery that leaves via the hilum
• Draining vein that leaves via the hilum

Question 13

How do lymphocytes enter lymph nodes?

Answer 13

• Enter via the feeding artery
• Leave via the efferent lymphatics

Question 14

Account for possible causes of lymphadenopathy

Answer 14

• Infection as germinal centres in lymph nodes fill with lymphocytes
• Lymphoma as cancer metastasises to afferent lymphatics

Question 15

Lymph nodes contain professional antigen presenting cells (APCs).

What is the role of such cells?

Answer 15

APCs are specially equipped with immunostimulatory receptors to acquire and present antigens which allows for enhanced activation of T cells

Question 16

What is the structure, function and location of follicular dendritic cells?

Answer 16

• Structure: contain antigen-antibody complexes adhere to its dendritic processes
• Function: cause proliferation of B cells, in particular, memory B cells
• Location: found in germinal centres

Question 17

Outline the inflammatory response

Answer 17

• Initial reaction of the body to an antigen
• Mediated by neutrophils and/or macrophages
• Degradation of the antigen may lead to presentation of a portion of the antigen to elicit a specific immune response

Question 18

Outline the humoral response

Answer 18

- Humoral immunity is B lymphocyte mediated

• It involves B lymphocytes which transform into plasma cells that synthesise and secrete a specific antibody

Question 19

What is cell-mediated immunity?

Answer 19

Cell-mediated immunity is when T cells need antigen presenting cells (macrophages, B lymphocytes) to recognise antigens

Question 20

What is the importance of cell-mediated immunity?

Answer 20

Important in defence against:

• Viral, fungal and mycobacterial infections
• Tumour cells
• Transplant rejection

Question 21

Outline the structure, function and location of the thymus gland

Answer 21

• Structure: fully formed and functional at birth, involutes after puberty and ends up being mostly fat
• Function: maturation of bone marrow derived stem cells into immunocompetent T cells (thymic cell education)
• Location: found in superior mediastinum

Question 22

The spleen is the largest lymphatic organ and has a very rich blood supply.

Outline its immune functions

Answer 22

• Antigen presentation
• Activation and proliferation of B and T lymphocytes
• Production of antibodies
• Removal of macromolecular antigen from blood

Question 23

The spleen is the largest lymphatic organ and has a very rich blood supply.

Outline its haemopoietic functions

Answer 23

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

Question 24

Discuss the implications of a splenectomy

Answer 24

• Splenectomy increases the risk of infection by encapsulated bacteria e.g. the meningococcus, malaria
• Splenectomy increases the risk of DVT and pulmonary embolism

Question 25

Which organs/structures perform the spleen's functions after a splenectomy?

Answer 25

Liver and bone marrow take over the removal & destruction of old RBCs

Question 26

Distinguish between the lymph node and spleen response to infection

Answer 26

- Lymph nodes enlarge in response to **local infection** - Spleen enlarges in response to **systemic infection** *e.g. glandular fever, malaria, septicaemia*

Question 27

What is phagocytosis?

Answer 27

**Phagocytosis** is a specific form of endocytosis by which cells internalise solid matter, including microbial pathogens

Question 28

Identify the professional phagocytes of the immune system

Answer 28

- Macrophages - Neutrophils - Immature dendritic cells

Question 29

Outline the 5 steps in the process of phagocytosis

Answer 29

⇒ Binding of **opsonins** and/or PAMPs to cell surface receptors on the phagocyte ⇒ Receptor clustering which triggers **phagocytosis** ⇒ Cell membrane then extends around the target, forming a **phagosome** ⇒ Phagosome fuses with lysosomes & acidifies to form a **phagolysosome** ⇒ Contents are degraded by **hydrolytic enzymes**

Question 30

What is opsonisation?

Answer 30

**Opsonisation** is the molecular mechanism whereby molecules, microbes, or apoptotic cells are chemically modified to have stronger interactions with cell surface receptors on phagocytes and NK cells

Question 31

What effect does opsonisation have?

Answer 31

- With the antigen coated in opsonins, **binding to immune cells is greatly enhanced** - Opsonisation also **mediates phagocytosis** via signal cascades from cell surface receptors

Question 32

What is complement?

Answer 32

**Complement** consists of a group of serum proteins that activates inflammation, destroys cells and participates in opsonisation

Question 33

Complement proteins respond in a sequential manner called the complement cascade. Describe the Classical pathway in the complement cascade

Answer 33

**Classical pathway** – C1 is activated when it binds to an antigen-antibody complex

Question 34

Complement proteins respond in a sequential manner called the complement cascade. Describe the Alternative pathway in the complement cascade

Answer 34

**Alternative pathway** – C3b is activated when it reacts with antigens such as bacterial cell wall

Question 35

What are the results of both of the different complement cascades ?

Answer 35

Question 36

What is oedema?

Answer 36

**Oedema** is an accumulation of an excessive amount of watery fluid in cells, tissues or serous cavities

Question 37

What is lymphoedema?

Answer 37

**Lymphoedema** is swelling (especially in subcutaneous tissues) due to obstruction of lymphatic vessels or lymph nodes and the accumulation of large amounts of lymph in the affected region

Question 38

Describe the appearance of lymphoedema

Answer 38

**Lymphoedema** is non-pitting oedema due to the build-up of lymph and protein in the interstitial space

Question 39

How does oedema change with position?

Answer 39

- If someone is standing up, oedema often appears first at the **ankles** (gravity) - If someone is lying down/sitting in bed, the oedema is expected to appear in the **sacral region**