16 - Lymphatic System Flashcards
What is the lymph system made up of?
- Lymph
- Lymph vessels (lymphatics)
- Organs
- Lymphocytes
- Follicular dendritic cells and macrophages
What is lymph?
Similar to plasma. Excess fluid collected from the interstitial space.
What are the primary and secondary organs of the lymphatic system, and what are the functions of primary and secondary?
Primary:
- Thymus + Bone marrow
- Generate lymphocytes from immature progenitor cells that arise from stem cells in the bone marrow
Secondary:
- Spleen + Lymph Nodes
- Site of lymphocyte activation and provide environment for antigens to interact with lymphocytes
What is tertiary lymphoid tissue?
Formed during autoimmune diseases, e.g rheumatoid arthiritis. Assume a role when challenged with antigens tha result in inflammation.
Ectopic lymphoid follicles
What is the function of the thymus and what happens to it over a life span?
- Located in superior mediastinum
- Thymic cell education (matures T-cells) and induction of central tolerance
- Increases in size from birth due to post-natal antigen stimulation, atrophy by teenage years, by adult thymic stroma is mostly replaced by adipose tissue
What is the structure of the thymus?
Lobules joined by septa and encapsulated by a capsule.
Capsule and Septa made mainly by reticulun fibres in ECM
ONLY HAS EFFERENT LYMPH VESSELS
What is the structure of the spleen and where is it located?
Left side of abdomen, posterior to stomach, inferior to diaphragm.
ONLY HAS EFFERENT LYMPH VESSELS
What is the function of the spleen?
FILTER BLOOD LIKE LYMPH NODE FILTERS LYMPH
Haemopoietic:
- Remove of old, abnormal, damaged blood cells
- Store erythrocytes
- Retrieve Fe from Hb
- Produce blood cells up to 5 months foetus
Immune:
- Removing big antigens from blood using macrophages
- Antigen presenttion
- Activation and proliferation of lymphocytes
- Produce immune cells
What is a germinal centre?
Sites within secondary lymphatic organs where B-cells proliferate and undergo monoclonal selection
Contain memory cells and IgA produced here
What is splenomegaly?
Where the spleen enlarges in response to localised/systemic infection due to proliferation B-cells.
Can lead to rupturing and exsanguiation
What would you do with a ruptured spleen and why would you try to avoid it?
Splenectomy
- Needed in case it ruptures and causes internal bleeding
- Removal leads to increased risk of infection by encapsulated bacteria and malaria
- Liver can take over haemolysis
What is the structure of a lymph node?
- Several afferent vessels, lymph follicles in cortex, medulla, hilum, single efferent vessel.
- Arteries and veins enter node via hilum
- Reticulin CT
How many lymph nodes are there and where are they mainly located?
- 600-700
- Cervical, Inguinal, Axillae
- Clusters anywhere that lymph is collected from regions likely to sustain pathogen contamination
What are sentinel lymph nodes?
Lymph nodes closest to major organs, that interact with foreign antigens or tumour cells.
First lymph node to interact with metastasising cancer.
What is the function of a lymph node?
Acts as a filter as the lymph goes back to the vascular system. Traps antigens and mediates immune response using macrophages, T-cells and B-cells
What is an enlarged lymph node called and why is it enlarged?
- Lymphadenopathy
- Proliferation of T and B-cells in germinal centres because of infection
- Can also be due to metastatic tumours in nodes
- Can be due to lymphoma
- Painful
What is local and generalised lymphadenopathy?
Local: Few nodes locally are enlarged due to infection
Generalised: Nodes in different areas enlarged. Can be due to cancer or infection
What is MALT?
Mucosae-associated LT
- Beneath epithelia in submucosa are lymphoid follicles
- Nodule contains lymphocytes, plasma cells, macrophages
- Tonsils, Peyers Patches (ileum), Appendix
What do follicular dendritic cells do? APC
- Take pathogen into lymph node to macrophage zone
- Activate T-cells which can then activate B-cells
What are the main differences between T and B cells?
- B cells recognise antigens, T cells do not
- T cells attack invades in cell, B-cells attack outside evaders
What are tonsils?
- Collection of lymphoid tissue near throat and facing into oral cavity.
- Have M-cells and crypts to increase SA
- Function is to prevent ingress of pathogens through ears, nose and throat
What is Waldeyer’s Tonsillar ring?
- 2 Palatine (posterior end of oral cavity)
- 1 Lingual (back of tongue)
- 1 Adenoid (posterior wall of nasopharynx)
- 2 Tubal (opening of auditory tubes into pharynx)
Why are tonsils poorly encapsulated, apart from tubal?
Allow ingress of pathogens and egress of immune cells.
Poor capsulated areas are where M cells are. Capture antigens and present them to underlying immune cells
Where is the vermiform appendix and what is it’s structure?
Where?
Attached to area where SI and LI attach.
What?
Tube that has longitudinal and circular smooth muscle laying over submucosa. Nodules below crypts and M-cells on surface
Why?
Prevent ingress of pathogens,
What are Payer’s patches?
- In SI
- Epithelia above is M cells that are simple cuboidal, not columnar like rest of SI, so no microvilli, glycocalyx etc
- Large number of B-cell follicles. Few T-cells between follicles.
- Prevent ingress of pathogens
How do M cells work in context of Peyer’s patches?
- Trap pathogen by phagocytosis
- Present pathogen to T/B-cells in basement membrane
- Activated lymphocytes can enter lymphatics below and generate immune response
What are the four functions of the lymphatic system?
- Removal of interstitial fluid and replacement
- Absorb and transports fats as chyle from DT
- Storage and destruction of RBC
- Defence against pathogens
How does lymph travel?
- Located close to veins and arteries pulse causes tissue near lymph vessel to contract and so does the vessel
- Deep lymph vessels rely on muscle contraction
- Large ducts and trunks have smooth muscle
- Pressure changes during breathing
What area of the body has no lymphatic drainage?
CNS, to prevent oedema
Where does lymph flow to and from?
Lymphatics lie adjacent to cardiac vessels
Describe structure of a lymph vessel?
- Blind ended
- Intraluminal valves for uni flow (muscle in collecting vessels)
- Overlapping endothelial cells (flaps)
Compare a lymph vessel and vein
- Smaller
- Not as much smooth muscle
- Less/no cells
- Both have fibrocartilagenous valves
- Flaps between endothelial cells
What are the two main collecting vessels and where do things drain into them from?
- Thoracic Duct (Left) : Left sub-clavian. Rest of body.
- Right Lymphatic: Right sub-clavian. Upper right quadrant above cisterna chyli
USEFUL TO KNOW FOR DIAGNOSIS!!
What is the cisterna chyli?
Recieves lymph drainage from digestive organs, chyle!
Links to thoracic duct
What is chyle?
Milky fluid consisting of lymph and emulsified fats from lacteals of small intestine
How is fat absorbed in the small intestine?
Fats asorbed into lymph and move through it in chylomicrons.
Chylomicrons drain to cisterna chyli, then thoracic duct and then to left subclavian vein so miss livers first metabolism
What is the difference between a lymphoma and a leukemia?
Lymphoma - Cancer of lymphatic tissue
Leukaemia - Cancer in lymphatic tissue but originates from bone marrow
What is the difference between Hodgkin and Non-Hodgkin Lymphoma?
Hodgkin:
- Presence of Reed-Stenburg cell
- Associated with past infection and lymphadenopathy
Non-Hodgkin:
- Increased proliferation of B and T cells
- Old age
- Poor prognosis
How can cancer end up in the lymph system?
- Angiogenesis
OR
- Invade into lymph vessels and release exosomes into node to make right environment
- Melanoma cell goes down vessel into node, settles and proliferates
(breast, endometrial, malignant melanoma)
How are sentinel (first nodes to swell) detected?
- Old: frozen section in surgery and masectomy
- New: Inject blue tagged glucose close to node before surgery. Blue will be taken up by cancer cells as fast proliferating. Remove only nodes with die
What is lymphoedema, and what is a primary and secondary cause?
Accumulation of lymph, due to damaged or malformed lymphatic system.
Primary = Genetic predisposition
Secondary = caused by another disease or condition
What are some primary lymphoedema?
- Congenital (Milroy) : onset in 2 years, mutation in FLT4 gene (VEGF-r) so missing endothelial cells for vessels
- Praecox (Meige’s): 2-35 years, unknown, familial
- Tarda: After 35, unknown
Whar are some secondary lymphoedema causes?
- Lymphatic Filariasis
- Cellulitis
- Removal of nodes in cancer treatment
- Accidental damage to lymphatics during surgery
- Radiotherapy
- Flying after cancer treatment
How can lymphoedema be treated?
NO CURE JUST IMPROVE SYMPTOMS
- Manual drainage by massage (not permanent)
- Stockings
- Exercise to get muscles moving
Label all the parts of the lymphatic system.
What is the innate immune system?
- Non-specific first line of defence
- Physical barriers, Phagocytes, NK cells
- Fever, Inflammation
What is the inflammatory response in basic terms?
It is part of the innate response
- Mast cells in CT release histamines which cause vasodilation and increased permeability of capillaries
- Vasodilaiton causes red, permeability causes fluid build up
- Fluid build up allows phagocytes to enter and clotting
What is the humoral immune response?
- One part of adaptive immune system
- Involves B-cells recognising antigens and releasing antibodies
- Produces memory cells and plasma cells
- Antibodies released either neutralise or agglutinate
- Allows immunity
What is the cell mediated response?
- Macrophages present antigens to T-lymphocytes
- T-cells divide and form cytotoxic or helper cells
- Cytotoxic kill (releasing enzymes and perforating so apoptosis) and helper activate other cells by releasing cytokines
- Some memory cells formed
What are the differences between humoral and cell-mediated immune response?
Where is the vermiform appendix and what is it’s function?
Contains lymphatic nodules with germinal centres so must be part of the lymphatics
