how do nutrient get to cells of veins and arteries?

[phillybadboy]

capillaries are single and are in direct contact with blood. i know that some veins or arteries have capillaries running through them but some do not right? so for the veins and arteries that don't have veins and arteries running through them, these veins and arteries are composed of multilayered cells, the cells on the innermost layer is in direct contact with blood, but how do nutrients get to cell layers not in direct contact with blood? do nutrient reach other cell layers by going between paracellular by inner cell layers or transcellular through inner cell layers?

 

[Melmd]

I think they are called "vasa vasorum" which penetrates the outer (tunica adventitia) layer and middle (tunica media) layer almost to the inner (tunica intima) layer of large arteries/veins, this guys supply the needed nutrients for the viability of the blood vessels.

 

[phillybadboy]

but not all veins and arteries have capillaries going through them right? for the veins and arteries that don't have capillaries running through them, how do nutrient get to the inner layers that is not in the innermost layer?

 

[Melmd]

Yeah it inervates the tunica externa (outer layer of the vessel) as well as the tunica media (middle layer) of the vessels and by with diffusion thus nutrients are delivered. The tunica externa since it is directly in contact with blood it just diffuses directly. This is only true with large blood vessels but with specialized vessels in the body such as kidney and liver, they also have different mechanism of nutrient transport to the blood vessels.

 

[phillybadboy]

i know about the larger vessels and vasa vasorum, i'm actually asking about the smaller blood veins and arteries that don't have capillaries running though them, the smaller blood vessels (veins, arteries) are composed of multilayer cells, how do nutrient get to cells that are not in the innermost layer of the vessel? does it go between the spaces of the cells(paracellular)? or does it go through the cells(transcellular)?

 

[Melmd]

i know about the larger vessels and vasa vasorum, i'm actually asking about the smaller blood veins and arteries that don't have capillaries running though them, the smaller blood vessels (veins, arteries) are composed of multilayer cells, how do nutrient get to cells that are not in the innermost layer of the vessel? does it go between the spaces of the cells(paracellular)? or does it go through the cells(transcellular)?

It is still diffusion from one cell to the other, the plasma membrane have channels on each surface for the transfer of essential nutrients.

as you can see here the vasa vasorum still supplies the smooth muscle layer of an artery.

Picture is from http://www.rci.rutgers.edu/~uzwiak/AnatPhys/Blood_Vessels.html

 

[systemet]

i know about the larger vessels and vasa vasorum, i'm actually asking about the smaller blood veins and arteries that don't have capillaries running though them, the smaller blood vessels (veins, arteries) are composed of multilayer cells, how do nutrient get to cells that are not in the innermost layer of the vessel? does it go between the spaces of the cells(paracellular)? or does it go through the cells(transcellular)?

I think that both processes occur. I'm not sure as to the relative contribution of each.

Smooth muscle cells in the vessel wall are also connected by gap junctions, that would allow nutrients to flow from one cell to the next. How big a role this plays, I'm not sure.

The nutrient requirements of smooth muscle cells are also relatively low. Unlike the other muscle types, smooth muscle hydrolyses ATP at a slower rate, so there's less ATP consumed per unit time. They also have the ability to "latch", that is the cross-bridges can remain attached for a long period of time without dissociating, enabling smooth muscle cells to produce a constant level of isometric tension for a long period of time without consuming large amounts of ATP. This also minimises nutrient requirements.

 

[systemet]

Yeah it inervates the tunica externa

I think you want the word "supplies" or "perfuses" instead here, as "innervation" implies that neurons are involved. [I'm not trying to be picky, but this detracts from your responses.]

 

[phillybadboy]

systemet, not all veins and arteries have vasa vosorum right? and what do you mean when say smooth muscle cells have gap junctions and flow from on cell to another? do you mean these gap junctions allow nutrient out of one smooth muscle and into another?

 

[Melmd]

I think you want the word "supplies" or "perfuses" instead here, as "innervation" implies that neurons are involved. [I'm not trying to be picky, but this detracts from your responses.]

I stand corrected! yup innervate is for nerves! :beerchug:

 

[phillybadboy]

thanks fellas :beerchug:

 

[systemet]

systemet, not all veins and arteries have vasa vosorum right? and what do you mean when say smooth muscle cells have gap junctions and flow from on cell to another? do you mean these gap junctions allow nutrient out of one smooth muscle and into another?

There's a good resource for histology here:

http://www.courseweb.uottawa.ca/medicine-histology/english/cardiovascular/histologybloodvessels.htm

And this paper reviews vasa vasorum, but you may need a university computer to access it. Pm me, and I might be able to help.

http://cardiovascres.oxfordjournals.org/content/75/4/649.full
Ritman EL, Lerman A. The dynamic vasa vasorum. Cardiovascular Research (2007) 75(4):649-658.

* Ritman et al. say that vessels with diameters of < 0.5mm, or that have media <29 cell layers thick usually lack vasa vasorum.

* Gap junctions are channels between adjacent cells formed by groups of connexin proteins. They're regulated, i.e. they can close and open in response to certain stimuli. They allow movement of small molecules (I couldn't find a source for how small), just that it would allow movement of things like glucose-6-phosphate, or ATP.

* Flow is probably incorrect here, I admit, even though I introduced it, as it implies pressure differentials driving bulk movement. It would probably be more accurate to say that small molecules diffuse through the gap junctions.

 

[phillybadboy]

systemet, these gap junctions allow nutrient flow out of one smooth muscle cell directly into another smooth muscle cell?

 

[bstogner]

Simplistically, gap junctions are areas in the cell membranes of some adjacent sells that have small protein formed channels. Theses allow ions and some smaller molecules to flow from one cell to another. It is almost like their cytoplasm is continuous with just some of the bigger molecules and proteins blocked from moving through them.

Now all large veins and arteries have the vasa vasorum and only some of the smaller arterioles and venioles do not. Once they get small enough then the gap junctions combined with the interstitial fluid (the fluid around the outside of all the cells in the body which contains the nutrients from the capillaries) is enough to supply the outer layers of the arterioles and venioles with all of the needed nutrients and remove all of the waste under normal conditions.

 

[phillybadboy]

bstogner, these smaller arterioles and venioles that don't have vasa vasorum are directly connected to true capilaries? there are larger arterioles and venioles that have vasa vasorum? these larger arterioles and venioles that have vasa vasorum can they be directly connected to true capilaries? or they first connected to smaller aterioles and venules that don't have vasa vasorum and then to true capillaries? also for the arterioles and venioles that lack the vasa vasorum nutrients pass paracellularly to the different layers right? and even fo the arterioles and venioles that have vasa vasorum once the nutrients leave the capillaries nutrients move paracellularly to different cells also right? what is there more of in the human body arterioles and venioles that have vasa vasoum or arterioles and venioles that don't have vasa vasorum? thanks fellas you're not just helping me you're also helping other people who may stumble or search for these things

 

[bstogner]

The smaller ones are not connected to true capillaries but, the capillaries that branch off from them supply the interstitial fluid with more than enough nutrients. Since the outer layers of the arterioles and venioles that do not have the vasa vasorum are not too many cell layers thick then this interstitial fluid is enough to supply the outer layers with what they need.

The cells that are in the outer layers of these blood vessels do not form a water tight seal. This means that some of the interstitial fluid is also able to work its way into the middle layers also. This combined with the paracellular route is how these arterioles get their nutrients.

One important thing to remember here that might make this easier to understand is that capillaries do not provide nutrients directly to any cells in the body (cells of the capillaries themselves excluded). Instead they provide nutrients to the interstitial fluid. All the cells in the body are bathed in this fluid and they get their nutrients directly from it. And most cells are not connected with gap junctions so, paracellular rout of transmission is normally not possible. Most cells are not pressing tight enough together to make the spaces between them impermeable to the interstitial fluid. But, as someone mentioned earlier, smooth muscle cells and the cells of the inner lining of the arteries, veins, venioles, and arterioles are tight enough to exclude interstitial fluid or blood and do have gap junctions.

To answer the next question. The large arterioles that have the vasa vasorum do have true capillaries connected to them. But, the only ones that they have are the vasa vasorum. Any other capillaries must arise after the large arteries have branched into small arterioles then they can finally branch off into capillaries. These are the capillaries that supply the rest of the body's tissues.

As for the final question I am not sure. I would reason to guess that there are likely more that do not have vasa vasorum. This is just because there are no where near as many large arteries and veins as smaller ones. This is due to principals that are too difficult to get into in this already very long post. lol

 

[phillybadboy]

bstogner, so even if the cells of these blood vessels have gap junctions nutrients is still floating around in the interstitual and moves around to different cells in the areas between the cells and the cells takes in what it needs?

 

[phillybadboy]

bstogner, what i meant to say was the arteriols and veins that have vasa vasorum directly branch off to true capilaries? or does it have to become smaller arterioles and veins that don't have vasa vasorum first and then that branch off to true capilaries? the smaller arterioles and veins that don't have vasa vasorum do they directly branch of to true capillaries? or does it have to become something else first? these gap junctions that exist in the smaller arterioles and venioles, do the larger arteioles and venioles have gap junctions too? for the smaller arterioles and venioles that have the gap junctions the cells still also get nutrients from the interstitual fluids moving between the cells right? meaning that the nutrienst get to differnet cells not going directly through the cell but move in the space between the cells right? and even for the arterioles and venioles that have the gap junctions the cells still get nutrients from the interstitual space in this way? for the arterioles and venioles that have vasa vasorum the fluids from the vasa vasorum baths the cells of the different layers and the nutrients get to different cell layers by moving in th areas between the cells not directly through them right?

 

[bstogner]

Yes. That is exactly how it happens. The gap junctions are really more for the rapid transfer of signal molecules and ions than for nutrient transport. Although they are involved in that to a degree. But, you are exactly right.

 

[phillybadboy]

bstogner, could you also answer my question in post 18?