Lymphatic

Question 1

What is the Lymphatic System?

what does it consist of? how does it act? what are the roles of the organs?

Answer 1

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

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

Question 2

Why is the lymphatic system important?

what are the main functions of lympkathic? (4)
what can dysfunction lead to?

Answer 2

• As the cleansing and recycling system of the body
• Lymphatic function is responsible for tissue fluid balance, immunity, and fat transport
• Lymphatic dysfunction contributes to many diseases including recurrent infection, cancer spread, obesity, dementia, HIV, atherosclerosis, poor wound healing, Crohn’s disease, glaucoma, pulmonary disease, autoimmunity, organ rejection, and arthritis
• Because of the lymphatic system’s various biological and physiological roles it can be implicated in some way in almost any pathology. Hence the lymphatic system is arguably as important as any body system but the evidence for its importance is only now being realised from genomic information

Question 3

Anatomy of lymphatic system

where is tissue fluid absorbed? what does it become here? where does this flow to?

where do all the lymph vessesl converge? where do they go from there?

Answer 3

A one-way drainage system like a river. Tissue fluid is absorbed by blind ending lymphatic capillaries (like the tentacles on sea anemones) to become lymph.

Lymph flows through small streams and ever bigger channels to lymph nodes

Peripheral (from superficial tissues) and central (within body) lymph draining channels converge on the thoracic duct where lymph exits the lymphatic system and enters the great veins of the neck

Question 4

what are lymphoid organs?

what do they do?

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

Primary lymphoid organs (2)

what do they do?

Answer 5

Primary lymphoid organs are the thymus and the bone marrow. They generate lymphocytes from immature progenitor cells.

Question 6

Secondary lymphoid organs (3)

What do they do?

Answer 6

Secondary lymphoid organs (SLOs) are defined structures comprising lymph nodes, spleen, and mucosa-associated lymphoid tissue (MALT) where lymphocytes are activated

Question 7

Tertiary lymphoid organs

Answer 7

Tertiary lymphoid organs (TLOs) are acquired loose lymph node-like immune cell clusters in tissues

Question 8

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

what is the RES resposnsible for? (2)
what are lymphoid organs responsible for? (2)

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

lymphatic vessesls
what are the two types?
describe their structure

Answer 9

2 types
absorbing lymphatic vessel -> blind ended, no smooth muscle and in-continous basement membrane
large collecting vessel -> drain into valve which have smooth muscles, basement membrane

Question 10

structure of lymphatic vessels

what does anchoring fibre do?

what do contractile vessels have for one way flow?

Answer 10

anchoring fibre - elastic fibre will open up initial lymphatic therefore material can gain entry and drain into pre-collecting
transform into big collecting vessel

contractile vessels as have smooth muscles + valves to allow 1 direction flow

Question 11

embryology + development

what do the vessesl form from? (2)

what do they differentiate from? what is needed for maturation and exapansion (2)? what does this form?
what does it eventually become?

Answer 11

Lymphatic vessels form from the cardinal vein and mesenchymal stem cells

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 12

How do lymphatic capillary vessels work?

what are initial lymphatics like? what do they depend on to drive fluid?

what leads to emptying of lymphatic downstream? what happens once it is emptied? what will stop this process and when does that happen? what happens when it reaches this process?

Answer 12

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

Tissue compression leads to emptying of lymphatic downstream. Once emptied, the lymphatic capillary will open up due to the recoil from the elastin in anchoring fibre which creates a pressure gradient of ocutside to inside so the valves open and interstitial fluid will move into the capillary. Valves will close once equilibrium of pressure gradient has been reached. A pressure wave will lead to tissue compression and squeeze the lymphatic down.

Question 13

How do collecting lymphatics work?

where do they receive their lymph from? where do they pump lymph to and where? what ensures one direction flow?

what is each section between 2 valves called? what happens here?

Answer 13

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

wave of contracting

Question 14

Movement + exercise for lymph drainage

what happens to raised interstiitial fluid? when does this occur?

what happen when muscles contract again? towards where? what happens here?

what happens without pumping collecting lymphatics ?

Answer 14

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 (once in collecting vessel, lymph will actively move)

Question 15

What does lymphatic system do? (3)

Answer 15

Controls tissue and plasma volume homeostasis

Controls immune cell trafficking and adaptive immunity

Facilitates fat transport

Question 16

Starling principle

what is tissue fluid drained predominantly by?
what does sum of straling priciple mean?

what is the regulator and stabiliser for filtration? what does this mean?

Answer 16

Tissue fluid is drained predominantly by the lymphatic and NOT by venous reabsorption.

Sum of starling principle results in net but decreased filtration along entire length of capillary

Subglycocalyx as a regulator or stabiliser for filtration so the default position is no reabsorption

Question 17

Physiological Principles of Pitting Oedema

what drains tissue fluid predominantly?
how does oedeoma develop?
what is the rate limiting step? so what is chronic oedema usual probem?

what can increase lymph load?
when does venous oedema occur?
when does lymph oedema occur?

Answer 17

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 18

Fat absroption

where? what? what moves downstream and to where? why?
where does it go after that?

Answer 18

intestinal lymphatic system -> called lacteals
becomes chyle which moves downstream through vessels and mesentry to lymph gland
surveyed to check for pathogen
goes to cysterna
lymphatic duct
blood stream
liver

Question 19

Fat Transport-mobilisation of peripheral fat

where is fat stored?
what has a part to play in its mobilisation?
what is lymph oedema? (2)

Answer 19

Fat stored in peripheral tissue
Lymph has part to play in mobilisation of fat when energy is required

Lymph oedoma - fat + fluid buildup

Question 20

cancer

how does it spread?

Answer 20

Cancer spreads preferentially through the lymphatic system

Question 21

Pulomonary oedema

in heart failure, why? what doesn’t clear it? what does this imterfere with?

compare pressure between pulmonary capillary pressure and plasma? why is pulomnary capillaries still in a filtration rate?

what does left sided heart failure increase? what needs to increase accordimgly?

Answer 21

Pulmonary oedema in heart failure is due to 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

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 22

Lymphatic system + immunity

what does lymphatics provide?
where do lymph glands exist? (3) what is taken here? what happens here?

Answer 22

Lymphatics provide the pathways by which information regarding infection is transported from the affected tissues to sites, namely lymphoid organs, where an appropriate immune response can be generated.

These are lymph glands fighting the infection. Lymph glands are connected to lymph vessels and exist all over the body but particularly in the neck, under the arms and in the groins. Lymph vessels absorb the microbes responsible for an infection and transport them to lymph glands. It is in lymph glands where immune cells become sufficiently developed to produce the resources to fight a specific infection such as Covid.

There are parallels with an army fighting a war. In a war, military intelligence uses information collection to provide guidance and direction to produce the most effective fighting force against the enemy. In an immune response to an infection this is what the lymphatic system does. The lymphatic vessels bring the intelligence (information about the infection) in the lymph to the lymph node. This enables the lymphocytes in the lymph node to develop the right weapons to fight the infection. B lymphocytes (B cells) produce antibody and T lymphocytes (T cells) develop the ability to kill other cells (in this case cells infected with Covid). Lymphocytes leave the lymph glands and depart for the war zone to kill off the infection. Ongoing information, like regular daily briefings from the war zone about the enemy, will refine and strengthen the capability of the lymphocytes to fight the Covid infection and result in the recruitment of more soldiers (lymphocytes) armed with the right weapons to fight the enemy. When ready the lymphocytes leave the lymph glands to kill off any virus they can find.

Question 23

Venous Oedema

what does it cause?
example of this case?

Answer 23

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 24

Lymphoedema

when does it occur? what is there no increase of?
example?

Answer 24

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 25

why does Primary lymphoedema occur?

Answer 25

Primary lymphoedema is due to an inborn, presumed genetic, fault in lymph drainage

Question 26

what is cellulitis?

what is a common complication of?
what does this lead to?

Answer 26

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

Impaired immune cell trafficking causes a failure to eradicate the infection