Can someone explain role of interstitial fluid and how it is transported around the body?

[mrh125]

what is it interstital fluid? where does it come from? from what i understand when the heart undergoes a systole and blood is pump out of the heart interstitial fluid is deposited in tissue and must be returned to the blood (?) via the lymphathetic system via lymph nodes and the thoracic duct. How does this process work? particularly what sort of pressure is involved? hydrostatic pressure forces interstital into lymph tissues, what pushes it out of lymph tissues?

my understanding of the lymphathetic system is the most fuzzy out of all body systems.

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[Czarcasm]

what is it interstital fluid? where does it come from? from what i understand when the heart undergoes a systole and blood is pump out of the heart interstitial fluid is deposited in tissue and must be returned to the blood (?) via the lymphathetic system via lymph nodes and the thoracic duct. How does this process work? particularly what sort of pressure is involved? hydrostatic pressure forces interstital into lymph tissues, what pushes it out of lymph tissues?

my understanding of the lymphathetic system is the most fuzzy out of all body systems.

I'll explain things from the tissue to lymphatics perspective as my knowledge of the cardiovascular system is a little limited right now since I haven't reviewed in a long time. I understand the basic idea, but don't want to mix up the terminology (hydrostatic pressure, oncotic pressure, osmotic pressure, etc).

On a very fundamental level, your body is constantly pumping fluid to the organs of your body. This "blood" is essentially blood plasma, a foggy liquid -- which also contains several other components: blood cells, proteins, platelets, unwanted pathogens and 'intruders', white blood cells to target those intruders, etc.

As blood passes from your heart through your arteries and to a capillary bed, essential nutrients are taken up to our tissues from the capillaries, a slightly porous membrane (1 cell thick -- 'endothelial cells') compared to the thick wall of the arteries, while at the same time, wasteful products are take from the tissues into the capillaries to be removed in some fashion: excreted via kidney filtration, exhaled, or processed in other ways (like in the liver). It is estimated that of the blood that exits the capillaries, only 90% is taken back up to your veins and recirculated throughout your body. We have about ~5L of blood in our bodies, and over time, this 10% of excess fluid would accumulate. Without any system evolved to return this fluid back to our bodies, not only would our tissues swell up, but we would undergo cardiovascular shock due to loss of so much plasma.

That's where the lympathics come in. The lympathics are two-fold. Not only do they pick up excess fluid from tissues, but they pick up pathogens and unwanted byproducts that may have been exposed to the area. This is an essential component to our immune system! While this fluid is picked up from our tissues (along with other materials), they pass through a series of valves, much like the ones present in our veins. However, there are a few significant differences. As opposed to being a continuous system (like arteries --> capillaries --> veins --> heart -->) the lymphatic system is a 1-way system meaning it's closed at one end and continuous on up to the jugular vein, where that excess liquid is reintroduced into our circulatory system. Secondly, the valve system was evolved as a way to constantly push up fluids through the lympathics. Unlike our veins which have some muscular tissue attached, there is less framework surrounding lympathic tissue. However, both veins and lympathic vessels require the movement of our muscles to push that fluid up -- the is very important! There is no pressure influence here guiding the fluid back to the heart (perhaps just a little for the veins, but definitely not for the lympathics). One consequence of individuals who've been bed prone for sometime is accumulation of liquid in tissues because of lack of muscular movement. This is generally why individuals in hospitals have various limbs lifted up and every so often are asked to move around if possible.

So that's basically lympathics summarized. One other thing worth noting, is that while the excess fluid (termed "lymph") is picked up, it goes through a series of security "check points" where lymph nodes scan for pathogens and unwanted toxins and elicit an immune response -- just something to keep in mind.

Flow of Lymph: multiple lymph capillaries ---fuses---> multiple collecting vessels ---fuses---> 6 lympathic trunks ---fuses---> 2 collecting ducts --dumps into--> subclavian veins

Hope this helps.

 

[inasensegone]

Your question requires a really long answer, and to be honest, my physiology is a bit rusty and I haven't finished that part of my content review yet, so I will answer what I can.

The water in the body is made up of Intracellular fluid (ICF - fluid inside of cells) and Extracellular fluid (ECF - fluid NOT inside of cells). OK so far pretty basic. Interstitial fluid is a type of ECF. It bathes the cells and represents their external environment. When the sodium potassium pump is working (which is always) it is pumping 3 sodium ions into the interstitial fluid, and 2 potassium ions into the ICF.

So when the heart undergoes systole, the ventricles of the heart are contracting. The right ventricle pumps blood through the pulmonary (lung) circuit and the left ventricle pumps blood through the systemic (rest of the body) circuit. [The blood itself is majority (~55%) plasma. Plasma is another type of ECF.] The lymphatic system is another circuit that runs parallel to the blood. The 2 are only connected at the Thoracic duct (left lymph duct) and the Right lymph duct, where these 2 ducts dump into the venous system. The lymph system deals with transferring absorbed dietary fat from the digestive system to the circulatory system, returning fluid and proteins to the circulatory system, and acting as a filter working with the immune system.

OK while I was typing this, Czarcasm posted a pretty good description of the lymphatic system, so let me describe hydrostatic pressure and osmotic pressure. Notice how Czarcasm pointed out that the circulation goes from Arteries, (to arterioles), to capillaries, (to venules), to veins. Between the transition from arteries to veins there exists a transition in direction of net pressures (which occurs in the capillaries because this is the point where arterial system becomes venous). On the arterial side (and the venous side) we have 2 types of pressures: Hydrostatic pressure and Colloid osmotic pressure. Colloid osmotic pressure is also called Oncotic pressure, or even just Osmotic pressure. Osmotic pressure is created by the presence of large proteins in the blood. There aren't a bunch of large proteins in the interstitial fluid, so the Oncotic pressure pulls fluid into the circulatory system (you might recall your basic biology lab experiment with the Osmosis and Diffusion through a dialysis bag). The hydrostatic pressure can be thought of as the pressure exerted by the force of blood flowing through the circulatory system. This means that the Hydrostatic pressure pushes fluid out of the circulatory system.

So, recap: Hydrostatic pushes fluid out of the arteries and veins, and Oncotic pulls fluid in. On the arterial side, the hydrostatic pressure exceeds the Oncotic pressure, so you have a net flow of fluid and nutrients out of the artery and the arterial side of the capillary beds. On the venous side, there is less hydrostatic pressure because fluid has left circulation, and now Oncotic pressure exceeds hydrostatic. This causes fluid to be picked up from the interstitial fluid. When you see alcoholics with giant bellies, this is called ascites. A lot of these guys (or gals) will have poor liver function. The liver is the main site of plasma protein synthesis, which means that they have less proteins in their plasma. This means that they have less Oncotic pressure. This means that they pull less fluid out of the interstitial fluid, and it accumulates, causing ascites (a type of edema). Same thing with those poor starving little kids from Africa that they used to have on TV (the ones with the big pot bellies). They have a low protein diet and this causes them to have a low Oncotic pressure. The net result is that their hydrostatic pressure exceeds their Oncotic, and fluid accumulates. Congestive heart failure works similarly and can result in peripheral edema. You probably don't need that much info on circulatory pressures for the MCAT, but I find it pretty interesting and once you become a doctor, a lot of these patients will be your bread and butter anyway.

Edit: Since a picture is worth a thousand words, and since I just learned how to upload pictures on here, here ya go:

 

[dudewheresmymd]

I'll explain things from the tissue to lymphatics perspective as my knowledge of the cardiovascular system is a little limited right now since I haven't reviewed in a long time. I understand the basic idea, but don't want to mix up the terminology (hydrostatic pressure, oncotic pressure, osmotic pressure, etc).

On a very fundamental level, your body is constantly pumping fluid to the organs of your body. This "blood" is essentially blood plasma, a foggy liquid -- which also contains several other components: blood cells, proteins, platelets, unwanted pathogens and 'intruders', white blood cells to target those intruders, etc.

As blood passes from your heart through your arteries and to a capillary bed, essential nutrients are taken up to our tissues from the capillaries, a slightly porous membrane (1 cell thick -- 'endothelial cells') compared to the thick wall of the arteries, while at the same time, wasteful products are take from the tissues into the capillaries to be removed in some fashion: excreted via kidney filtration, exhaled, or processed in other ways (like in the liver). It is estimated that of the blood that exits the capillaries, only 90% is taken back up to your veins and recirculated throughout your body. We have about ~5L of blood in our bodies, and over time, this 10% of excess fluid would accumulate. Without any system evolved to return this fluid back to our bodies, not only would our tissues swell up, but we would undergo cardiovascular shock due to loss of so much plasma.

That's where the lympathics come in. The lympathics are two-fold. Not only do they pick up excess fluid from tissues, but they pick up pathogens and unwanted byproducts that may have been exposed to the area. This is an essential component to our immune system! While this fluid is picked up from our tissues (along with other materials), they pass through a series of valves, much like the ones present in our veins. However, there are a few significant differences. As opposed to being a continuous system (like arteries --> capillaries --> veins --> heart -->) the lymphatic system is a 1-way system meaning it's closed at one end and continuous on up to the jugular vein, where that excess liquid is reintroduced into our circulatory system. Secondly, the valve system was evolved as a way to constantly push up fluids through the lympathics. Unlike our veins which have some muscular tissue attached, there is less framework surrounding lympathic tissue. However, both veins and lympathic vessels require the movement of our muscles to push that fluid up -- the is very important! There is no pressure influence here guiding the fluid back to the heart (perhaps just a little for the veins, but definitely not for the lympathics). One consequence of individuals who've been bed prone for sometime is accumulation of liquid in tissues because of lack of muscular movement. This is generally why individuals in hospitals have various limbs lifted up and every so often are asked to move around if possible.

So that's basically lympathics summarized. One other thing worth noting, is that while the excess fluid (termed "lymph") is picked up, it goes through a series of security "check points" where lymph nodes scan for pathogens and unwanted toxins and elicit an immune response -- just something to keep in mind.

Flow of Lymph: multiple lymph capillaries ---fuses---> multiple collecting vessels ---fuses---> 6 lympathic trunks ---fuses---> 2 collecting ducts --dumps into--> subclavian veins

Hope this helps.

Your question requires a really long answer, and to be honest, my physiology is a bit rusty and I haven't finished that part of my content review yet, so I will answer what I can.

The water in the body is made up of Intracellular fluid (ICF - fluid inside of cells) and Extracellular fluid (ECF - fluid NOT inside of cells). OK so far pretty basic. Interstitial fluid is a type of ECF. It bathes the cells and represents their external environment. When the sodium potassium pump is working (which is always) it is pumping 3 sodium ions into the interstitial fluid, and 2 potassium ions into the ICF.

So when the heart undergoes systole, the ventricles of the heart are contracting. The right ventricle pumps blood through the pulmonary (lung) circuit and the left ventricle pumps blood through the systemic (rest of the body) circuit. [The blood itself is majority (~55%) plasma. Plasma is another type of ECF.] The lymphatic system is another circuit that runs parallel to the blood. The 2 are only connected at the Thoracic duct (left lymph duct) and the Right lymph duct, where these 2 ducts dump into the venous system. The lymph system deals with transferring absorbed dietary fat from the digestive system to the circulatory system, returning fluid and proteins to the circulatory system, and acting as a filter working with the immune system.

OK while I was typing this, Czarcasm posted a pretty good description of the lymphatic system, so let me describe hydrostatic pressure and osmotic pressure. Notice how Czarcasm pointed out that the circulation goes from Arteries, (to arterioles), to capillaries, (to venules), to veins. Between the transition from arteries to veins there exists a transition in direction of net pressures (which occurs in the capillaries because this is the point where arterial system becomes venous). On the arterial side (and the venous side) we have 2 types of pressures: Hydrostatic pressure and Colloid osmotic pressure. Colloid osmotic pressure is also called Oncotic pressure, or even just Osmotic pressure. Osmotic pressure is created by the presence of large proteins in the blood. There aren't a bunch of large proteins in the interstitial fluid, so the Oncotic pressure pulls fluid into the circulatory system (you might recall your basic biology lab experiment with the Osmosis and Diffusion through a dialysis bag). The hydrostatic pressure can be thought of as the pressure exerted by the force of blood flowing through the circulatory system. This means that the Hydrostatic pressure pushes fluid out of the circulatory system.

So, recap: Hydrostatic pushes fluid out of the arteries and veins, and Oncotic pulls fluid in. On the arterial side, the hydrostatic pressure exceeds the Oncotic pressure, so you have a net flow of fluid and nutrients out of the artery and the arterial side of the capillary beds. On the venous side, there is less hydrostatic pressure because fluid has left circulation, and now Oncotic pressure exceeds hydrostatic. This causes fluid to be picked up from the interstitial fluid. When you see alcoholics with giant bellies, this is called ascites. A lot of these guys (or gals) will have poor liver function. The liver is the main site of plasma protein synthesis, which means that they have less proteins in their plasma. This means that they have less Oncotic pressure. This means that they pull less fluid out of the interstitial fluid, and it accumulates, causing ascites (a type of edema). Same thing with those poor starving little kids from Africa that they used to have on TV (the ones with the big pot bellies). They have a low protein diet and this causes them to have a low Oncotic pressure. The net result is that their hydrostatic pressure exceeds their Oncotic, and fluid accumulates. Congestive heart failure works similarly and can result in peripheral edema. You probably don't need that much info on circulatory pressures for the MCAT, but I find it pretty interesting and once you become a doctor, a lot of these patients will be your bread and butter anyway.

Edit: Since a picture is worth a thousand words, and since I just learned how to upload pictures on here, here ya go:

View attachment 178349

Great posts guys. Can one of you clarify what are the main regions of lymphoid/lymphatic tissue/organs are in the body? Of the major internal organs which ones are considered to contain lymhpoid tissues/organs per se? The pancreas, kidney, small intestine etc. are not considered lymphoid tissue right? Only stuff like thymus, liver?


I tried googling but only was able to find encylopedia/general answers. Thanks!

 

[inasensegone]

Great posts guys. Can one of you clarify what are the main regions of lymphoid/lymphatic tissue/organs are in the body? Of the major internal organs which ones are considered to contain lymhpoid tissues/organs per se? The pancreas, kidney, small intestine etc. are not considered lymphoid tissue right? Only stuff like thymus, liver?

I tried googling but only was able to find encylopedia/general answers. Thanks!

The 2 organs that are generally considered part of the lymphatic system are the Thymus gland and Spleen, however there is lymph tissue ALL OVER the body of course because it is part of out immune system. I haven't reviewed the immune system yet in regards to the MCAT, so I'm going to keep this short because my knowledge is limited. The bone marrow and Thymus gland are primary lymph tissues meaning that immune cells form there (like T-cells from the Thymus gland and various leukocytes/WBCs from red bone marrow). There is also secondary lymphoid tissues like the spleen (involved in filtering the blood), lymph nodes (filter the lymph), gut-associated lymphoid tissue (GI immune response), the tonsils of the pharynx (1st contact of GI foreign bodies and respiratory), and a few other places like the skin, liver, respiratory, and urinary tracts. Interestingly enough, the gut-associated lymphoid tissue (GALT) may be largest contributor to lymphoid tissue overall due to size.

In GALT: Macrophages and lymphocytes will analyze foreign bodies in the interstitial fluid of the small intestine and can trigger an immune cascade that involves flushing the system (increased chloride ion secretion, fluid loss, and mucus secretion - i.e. diarrhea). GALT is also connected to liver lymphoid tissue which receives, filters, and cleans the incoming GI blood.

My memory is kind of fuzzy on additional details. Perhaps I will update this post in the future when I cover immunology.

And also, here is a picture:

 

[Czarcasm]

Great posts guys. Can one of you clarify what are the main regions of lymphoid/lymphatic tissue/organs are in the body? Of the major internal organs which ones are considered to contain lymhpoid tissues/organs per se? The pancreas, kidney, small intestine etc. are not considered lymphoid tissue right? Only stuff like thymus, liver?


I tried googling but only was able to find encylopedia/general answers. Thanks!

They categorize lympathic tissues in 3 broad categories: Primary Organs, Secondary Organs, and Peripheral Tissues (scattered in various locations of the body but lack the fibrous capsule present in primary and secondary organs).

To understand the distinction given to both primary and secondary organs, you need to know a little more about their developmental history and their associated functions.

ALL Leukocytes, Red Blood Cells, and Platlets originate in the Bone Marrow via a hematopoetic stem cell which inturn gives rise to different precurors. Once these cells are made, they exit the bone marrow and enter the bloodstream. These cells include B and T cells, both of which are apart of our adaptive ("specific") immunity. However, while T cells are originally produced in the bone marrow, they leave it in an immature state and are directed to the Thymus where they undergo a "bootcamp" to weed out ~98% of T Cells. This "bootcamp" eliminates T cells that recognize our own self antigens. The survivors are known as immunocompotent naive T cells (immunocompotent meaning they passed the test). Once they pass the test, they exit the Thymus and re-enter various lympathic tissues and organs (Spleen, Lymph Nodes, associated tissues, etc). Eventually these naive cells become activated when an antigen is present. And while T Cells undergo "bootcamp" training in the Thymus, B Cells reside still in the bone marrow and this is where they are checked for self antigens and eliminated. Likewise, once they pass the test, they reorganize in various lympathic tissues of the body in a naive but immunocompotent state.

Therefore, our primary organs are simply: bone marrow (where B cells become immunocompotent) and Thymus (where T cells become immunocompotent).

Our secondary organs include basically all the other lympathic organs you are familiar with: Spleen, Lymph Nodes, Tonsils, Appendix, etc. In these tissues, this is where our adaptive immunity is activated in the presence of an antigen. Here, B cells proliferate and differentiate into plasma cell secreting antibodies with the assistance of activated T Helper Cells (activated in the presence of an antigen; this can occur in the bone marrow, but to a lesser degree; activation does not happen in the thymus). Cytotoxic T Cells (also activated in the presence of an antigen), leave these tissues to fight off the infected areas directly.

And finally, various areas in our body have scattered lympathic tissues which complete the same exact task as our secondary organs, but lack an encapsulated tissue. This includes the tissues underlying our mucuous associated membranes digestive tract, our respiratory tract, and our reproductive linings (urinary, vaginal, etc).

 

[dyspareunia]

what is it interstital fluid? where does it come from? from what i understand when the heart undergoes a systole and blood is pump out of the heart interstitial fluid is deposited in tissue and must be returned to the blood (?) via the lymphathetic system via lymph nodes and the thoracic duct. How does this process work? particularly what sort of pressure is involved? hydrostatic pressure forces interstital into lymph tissues, what pushes it out of lymph tissues?

my understanding of the lymphathetic system is the most fuzzy out of all body systems.

Nice walls of texts for a very simple topic. Interstitial fluid is fluid inbetween cells and is essentially equivalent to blood without the cells and proteins.

At the arteriole end of the capillary fluid is filtered (leaks out) into the interstitium. Most of this fluid is reabsorbed at the venule end of the capillary, but the capillary itself is not capable of reabsorbing all of the filtered fluid. What the venule can't reabsorb, the lymphatics take care of.

Filtration pressure is hydrostatic pressure. Reabsorption pressure is oncotic pressure.

Fluid flows through the lymphatics and eventually drains into the venous system at the left subclavian vein.