Lymphatic System

Question 1

Function of lymphatic system

Answer 1

The body’s cleansing anddrainage system as well as being a transport route for immune cells and fat.

consists of lymphatic vesselsoperating as a one-waydrainage system(containinglymph) and the lymphoid organs (the roleof which is mainly in hostdefence).

Question 2

Anatomy of lymphatic system

Answer 2

One way drainage system

Tissue fluid absorbed by initial lymphatics- blind ending lymphatic capillaries to become lymph

Lymph flows in small streams and to bigger channels to lymph nodes

Question 3

Where is lymph collected and where does it exit the lymphatic system?

Answer 3

Largest lymph vessels collect it from both peripheral (superficial) and central tissues

Lymph draining channels converge on thoracic duct + lymph exits system here to enter great veins of neck

Question 4

What are lymphoid organs?

Answer 4

Lymphoid organs/tissuesare organized structures within the lymphatic system that support immune responses through lymphocyte production or activationand are important for host defence

Question 5

What are the primary lymphoid orgas=ns?

Answer 5

Thymus and Bone Marrow

They generate lymphocytes from immature progenitor cells. (responsible for production and maturation of lymphocytes)

Question 6

What are the secondary lymphoid organs?

Answer 6

Lymph nodes, spleen, and mucosa-associated lymphoid tissue (MALT)

where lymphocytes are activated

Question 7

What are the tertiary lymphoid organs?

Answer 7

acquired loose lymph node-like immune cell clusters in tissues

Develop in response to inflammation

Question 8

What is the difference in function between the reticuloendothelial system (RES) and the lymphoid organs?

Answer 8

The RES is responsible for phagocytosis and the removal of organic and inorganic material from blood and tissues

The lymphoid organs are responsible for immunity and specifically the production and activation of lymphocytes in order to generate immune responses to microbes

Question 9

What are the 2 types of lymphatic vessel?

Answer 9

1. Initial lymphatic- absorbs fluid and material

2. Collecting lymphatic

Question 10

Passage of lymph down upper limb

Answer 10

Initial lymphatics generates lymph -> travels downstream through arm to lymph glands in axilla

Question 11

What type of vessel are collecting lymphatics?

Answer 11

Contractile - have smooth muscle

Also have valves

Question 12

Lymphatic capillaries vs collecting vessels

Answer 12

Initial lymphatics:
blind ended
no SM
incontinuous basement membrane

Collecting vessels:
SM coverage
luminal valves
basement membrane

Question 13

What do lymphatic vessels form from?

Answer 13

Cardinal vein (MAIN)

and mesenchymal stem cells

Question 14

Development of lymphatics

Answer 14

Lymphatic endothelial cells (LECs)
differentiate from venous endothelial cells on the cardinal vein

Expansion and maturation
of LECs proceed via growth factors and specific lymphatic genes

To form lymph sacs

Further expansion and differentiation
produces mature initial
and collecting lymphatics

Question 15

How do lymphatic vessels work?

Answer 15

Initial lymphatics are passive structures 
dependent on alternating changes
 in surrounding tissue hydrostatic 
and oncotic pressures to drive fluid 
(and proteins and cells) into 
and along the vessels 

process:
nitial- delicate vessels dependant on pressure changes for lymph formation and transport, pressure wave compresses initial lymphatic w lymph -> empties it and send fluid downstream to collecting vessel

once emptied it can open due to recoil generated by anchoring filaments outside of endothelial cells

recoil generates pressure difference between inside and outside lymphatic = neg pressure inside encouraging fluid to move from tissue into initial lymphatic through gaps between endothelial cells (primary valves)

fluid flows through lymphatic -> equilibirum -> flat valves close and nothing happens until another pressure wave comes along and cycle repeats

Question 16

How do collecting lymphatics work?

Answer 16

Collecting lymphatics receive lymph
from initial lymphatics and actively
pump lymph towards the lymph node.
Internal valves ensure flow is in one direction
Each section of collecting lymphatic
between two valves, known as a lymphangion, contracts like an individual heart

collecting lymphatics have valves- section between valves that contracts independently- lymph enters section (lymphangion) distends vessel aka muscle relaxes and section fills

then filling point reached -> valve closes and muscle contracts, valve to next section opens and so lymph passes along towards lymph node

this is why lymph can be pumped up a leg against gravity

Question 17

Process of lymph drainage- when is muscle involved?

Answer 17

Raised interstitial fluid pressure drives tissue fluid into initial lymphatics during relaxation of skeletal muscle.

Next wave of muscle contraction compresses full initial lymphatic and drives lymph drainage downstream towards collecting lymphatics.

Smooth muscle contractions of collecting lymphatics pump lymph towards lymph nodes

Lymph drainage without pumping collecting lymphatics depends on passive effect of skeletal muscle contractions and compression

Question 18

Main role of lymphatic system

Answer 18

Controls tissue and plasma volume homeostasis

Controls immune cell trafficking and adaptive immunity

Facilitates fat transport

Question 19

Tissue fluid is drained predominantly by the…

Answer 19

lymphatic NOT venous reabsoprtion

In the steady state all vascular filtrate/interstitial fluid drains via the lymphatic with only periods of transient reabsorption directly back into the blood circulation.

The clinical significance of this new physiology is that all chronic oedema represents lymphatic failure. If one accepts that the composition of lymph in pre-nodal lymphatics is not significantly different from interstitial fluid one could argue that chronic peripheral oedema is no different from lymphoedema (peripheral swelling with accumulation of lymph in the tissues due to inadequate lymph drainage).

Question 20

Microvascular filtration is governed by what?

Answer 20

Starling principle of fluid exchange

Question 21

In capillary fluid exchange what acts as a regulator?

Answer 21

The subglycocalyx acts as a regulator or stabiliser for filtration so
the default position is no reabsorption

Revised Starling principle includes interstitial forces as well as hydrostatic and osmotic pressures

Subglycocalyx- plasma proteins held and control osmotic pressure outside of blood and so gradient is controlled by it, acts as a regulator

Question 22

Process of pitting oedema

Answer 22

Tissue (interstitial) fluid is drained predominantly by the lymphatic and not by venous reabsorption

Blood capillary plasma filtrate becomes interstitial fluid and then lymph. The capillary filtration fluid is the lymph load

Oedema develops when lymph load exceeds lymph drainage

Lymph drainage is the rate limiting step for all oedema and so any chronic oedema is, in principle, a lymph drainage problem

Venous hypertension increases lymph load (fluid filtration from blood capillaries)

Venous oedema occurs when lymph load exceeds lymph drainage for a period of time

Lymphoedema occurs when the dominant fault is with the lymph drainage

Question 22

Process of pitting oedema

Answer 22

Tissue (interstitial) fluid is drained predominantly by the lymphatic and not by venous reabsorption

Blood capillary plasma filtrate becomes interstitial fluid and then lymph. The capillary filtration fluid is the lymph load

Oedema develops when lymph load exceeds lymph drainage

Lymph drainage is the rate limiting step for all oedema and so any chronic oedema is, in principle, a lymph drainage problem

Venous hypertension increases lymph load (fluid filtration from blood capillaries)

Venous oedema occurs when lymph load exceeds lymph drainage for a period of time

Lymphoedema occurs when the dominant fault is with the lymph drainage

Question 23

Lymphatics in immune system

Answer 23

Antigen arrives at lymph node and presents to dendritic cells in lymph which then presents to B and T cells –> generates immune response

From lymph node mature B lymphocytes leave bone marrow and T lymphocytes to infection

A tender lymph gland indicates immune response to infection

Question 24

Lymphatics and fat absorption

Answer 24

Intestinal lymphatics absorb fat

Lacteals - in walls of intestine, absorb fat as lymph and fatty lymph called chyle

Moves downstream through lymphatic vessels to lymph glands where its surveyed for unwanted materials -> goes to collecting point below diaphragm for distribution to organs

If absorption doesn’t happen = protein losing enteropathy (fat malabsorption)
gut becomes inflamed and loses fluid + protein –> diarrhoea

Question 25

Label the lymph node

Answer 25

Question 26

Why is an efficient lymphatic system is needed to overcome Covid-19 infection

Answer 26

Lymph vessels absorb the microbes responsible for an infection
and transport them to lymph glands for acquired immunity.

It is in lymph glands where immune cells become sufficiently developed to produce the specific resources to fight an infection such as Covid.

Question 27

Secondary lymphoid organs

Answer 27

Filters where foreign invaders like microbes are captured and lymphocytes activated

eg lymph nodes, tonsils, Peyer’s patches of small bowel,
MALT (mucosa-associated lymphoid tissue)
spleen

Question 28

How can lymphatics attract immune cells to site?

Answer 28

CCL21 can attract cells containing CCR7 (receptor) on immune cells

Question 29

Why does pulmonary oedema occur in heart failure?

Answer 29

Raised pulmonary venous pressure causing increased amounts of interstitial fluid which is not sufficiently cleared by lymph so congesting the lung.

This interstitial oedema spills out into the alveoli and interferes with O2 exchange

Question 30

Tissue fluid homeostasis

Answer 30

the blood vessels supply fluid, and the lymph drains it away

Tissue fluid is formed from plasma escaping through the blood vessel wall

Tissue (interstitial) fluid drains predominantly as lymph and NOT by venous reabsorption

Question 31

Left sided heart failure does what to pulmonary capillary pressure? And how does it lead to oedema?

Answer 31

The lung generates lymph even though
pulmonary capillary pressure (10mm Hg)
is much lower than plasma COP (25 mm Hg).

Pulmonary capillaries are in a filtration state because pulmonary interstitial protein concentration is high (70% of plasma). The COP gradient is therefore lower than the Hydraulic pressure gradient.

Left sided heart failure increases pulmonary capillary pressure, increasing filtration. Unless lymph drainage increases accordingly, oedema occurs in lung parenchyma.

Overflow of increased interstitial fluid into alveoli and impairment of O2 exchange

Question 32

Recommended staging investigation for breast cancer

Answer 32

Sentinel lymph node biopsy

Question 33

Preferential spread of cancer?

Answer 33

Via lymphatics

Question 34

Diseases where lymphatic dysfunction involved

Answer 34

Respiratory disease: Asthma, Chronic airways disease

CVS : Hypertension, Plasma volume homeostasis, Atherosclerosis

CNS: Glaucoma, Dementia

Infection: HIV, cellulitis, TB

Immunity: Organ rejection, autoimmunity, wound healing

GI: Crohn’s disease

Cancer Metastases

Obesity

Question 35

Pitting oedema

Answer 35

Indicates an excess of interstitial fluid

Results from too much fluid filtration from blood vessels overwhelming lymph drainage
or
too little lymph drainage

When plasma ultrafiltration (lymph load) exceeds lymph drainage for a sufficient period of time oedema develops

Question 36

Venous oedema

Answer 36

Varicose veins or venous engorgement e.g. heart failure, creates high venous pressure and increased microvascular fluid filtration into tissues.If lymph drainage adequate oedema can be avoided

Question 37

Lymphoedema

Answer 37

Lymphoedema is a chronic swelling due to lymph drainage failure

Lymphoedema occurs when the dominant fault is a failure of lymph drainage with no increase in capillary filtration (normal lymph load) e.g. breast cancer related lymphoedema, elephantiasis

Question 38

Primary lymphoedema

Answer 38

Primary lymphoedema is due to an inborn, presumed genetic, fault in lymph drainage. Basic science research in the form of genetic studies of patients’ DNA has opened up our understanding of the causes of primary lymphoedema. Identification of mutations in a specific gene provides a cause and a diagnostic test as well as revealing how that gene fault causes the disease. Understanding the mechanism of the disease provides guidance for new treatment.

eg. Milroy Disease due to mutations in the VEGFR3 gene
(Vascular Endothelial Growth Factor Receptor 3 Gene)

Question 39

Cellulitis

Answer 39

Cellulitis is a common complication of impaired lymph drainage and is often recurrent.

Impaired immune cell trafficking causes a failure to eradicate the infection

Recurrent cellulitis always means a problem with lymph drainage. Up to 50% lymphoedema patients suffer at least one attack of cellulitis

Question 40

3 lymph function failures causing certain diseases

Answer 40

Lymphoedema arises from a failure of lymph drainage which can be due to damage from external causes or inborn from genetic faults.

A failure of immune cell trafficking leads to infections particularly cellulitis

Disordered lymphatic fat transport can lead to intestinal malabsorption and excess peripheral fat deposition