# How is blood able to circulate **URL:** \ **Category:** Factual Questions\ **Created:** [December 12, 2022, 8:01pm UTC](https://boards.straightdope.com/t/how-is-blood-able-to-circulate/976416 "2022-12-12T20:01:20Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![HoneyBadgerDC](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/honeybadgerdc/32/1033_2.png) [@HoneyBadgerDC](https://boards.straightdope.com/u/HoneyBadgerDC)\ **Post date:** [December 12, 2022, 8:01pm UTC](https://boards.straightdope.com/t/how-is-blood-able-to-circulate/976416/1 "2022-12-12T20:01:20Z")
Blood flow seems the opposite from river flow in that it goes from big to small. How do all the tiny little blood vessels make their way back into the return side of the blood stream? ---
**Author:** ![Qadgop\_the\_Mercotan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/qadgop_the_mercotan/32/83_2.png) [@Qadgop\_the\_Mercotan](https://boards.straightdope.com/u/Qadgop_the_Mercotan)\ **Post date:** [December 12, 2022, 8:08pm UTC](https://boards.straightdope.com/t/how-is-blood-able-to-circulate/976416/2 "2022-12-12T20:08:05Z")
> [@HoneyBadgerDC](#): > > How do all the tiny little blood vessels make their way back into the return side of the blood stream? Arteries turn into arterioles which turn into capillaries which turn into venules which turn into veins which return blood to the heart for pumping thru the lungs for oxygenation then back to the heart for pumping back to the rest of the body. The arterial side is high pressure, the venous side is low pressure, hence the flow. [![](https://i.postimg.cc/05TNYxyG/Overview-of-Blood-Circulation.jpg) ](https://i.postimg.cc/05TNYxyG/Overview-of-Blood-Circulation.jpg) [![](https://i.postimg.cc/PJgn1tbC/2101-Blood-Flow-Through-the-Heart.jpg) ](https://i.postimg.cc/PJgn1tbC/2101-Blood-Flow-Through-the-Heart.jpg) ---
**Author:** ![Bullitt](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bullitt/32/5725_2.png) [@Bullitt](https://boards.straightdope.com/u/Bullitt)\ **Post date:** [December 12, 2022, 8:17pm UTC](https://boards.straightdope.com/t/how-is-blood-able-to-circulate/976416/3 "2022-12-12T20:17:25Z")
Thanks for the diagrams, **Qadgop**. **HoneyBadger** , I recently had an MRI with contract done, and was told that when the contrast was injected, I would feel a sensation of warmth as the contrast spread. What’s really cool is that, as I felt that warmth sensation spread I could visualize the circulatory system at work in ways that pictures cannot describe. It was a slow progression of warmth spreading outward from my heart. I could visualize the speed at which my blood travels through my body. To anyone who will have that contrast injected, be prepared to have that sensation. It’s very interesting! ---
**Author:** ![Qadgop\_the\_Mercotan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/qadgop_the_mercotan/32/83_2.png) [@Qadgop\_the\_Mercotan](https://boards.straightdope.com/u/Qadgop_the_Mercotan)\ **Post date:** [December 12, 2022, 8:23pm UTC](https://boards.straightdope.com/t/how-is-blood-able-to-circulate/976416/4 "2022-12-12T20:23:21Z")
> [@Bullitt](#): > > I would feel a sensation of warmth as the contrast spread. AKA “the rush”. ;-D You really want to feel the rush, have a left ventriculogram performed during cardiac catheterization. That outdid all the previous rushes I’d had from CT or MRI contrast. IV dilaudid (which I got for some very nastily fractured ribs) gives a completely different type of rush, and one that I don’t recommend unless it’s really REALLY necessary. For me it was just TOO good. ---
**Author:** ![Seanette](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/seanette/32/9139_2.png) [@Seanette](https://boards.straightdope.com/u/Seanette)\ **Post date:** [December 12, 2022, 8:23pm UTC](https://boards.straightdope.com/t/how-is-blood-able-to-circulate/976416/5 "2022-12-12T20:23:33Z")
Also be ready to be VERY thirsty afterward. ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [December 12, 2022, 8:24pm UTC](https://boards.straightdope.com/t/how-is-blood-able-to-circulate/976416/6 "2022-12-12T20:24:54Z")
> [@Bullitt](#): > > To anyone who will have that contrast injected, be prepared to have that sensation. It’s very interesting! I had a pelvic arteriogram once, and the contrast agent created a very painful burning situation every time they injected it. It might not have been the same agent as what you had, since your procedure involved an MRI and mine involved X-rays. ---
**Author:** ![HoneyBadgerDC](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/honeybadgerdc/32/1033_2.png) [@HoneyBadgerDC](https://boards.straightdope.com/u/HoneyBadgerDC)\ **Post date:** [December 12, 2022, 8:40pm UTC](https://boards.straightdope.com/t/how-is-blood-able-to-circulate/976416/7 "2022-12-12T20:40:42Z")
Great replies, very interesting ---
**Author:** ![AskNott](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/asknott/32/5790_2.png) [@AskNott](https://boards.straightdope.com/u/AskNott)\ **Post date:** [December 12, 2022, 10:58pm UTC](https://boards.straightdope.com/t/how-is-blood-able-to-circulate/976416/8 "2022-12-12T22:58:12Z")
In addition to the higher to lower pressure thing, blood flow gets helped along by muscle contractions in your limbs, and the rhythmic squishing and relaxing that normal breathing creates in your chest and abdomen. Veins have little one-way valves to keep the flow from going backward. ---
**Author:** ![nearwildheaven](https://avatars.discourse-cdn.com/v4/letter/n/90db22/32.png) [@nearwildheaven](https://boards.straightdope.com/u/nearwildheaven)\ **Post date:** [December 12, 2022, 11:00pm UTC](https://boards.straightdope.com/t/how-is-blood-able-to-circulate/976416/9 "2022-12-12T23:00:50Z")
The blood cells also line up single-file in the smallest capillaries. Most of them are extremely flexible. ---
**Author:** ![TheCuse](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/thecuse/32/2854_2.png) [@TheCuse](https://boards.straightdope.com/u/TheCuse)\ **Post date:** [December 12, 2022, 11:05pm UTC](https://boards.straightdope.com/t/how-is-blood-able-to-circulate/976416/10 "2022-12-12T23:05:30Z")
> [@Bullitt](#): > > Thanks for the diagrams, **Qadgop**. > > **HoneyBadger** , I recently had an MRI with contract done, and was told that when the contrast was injected, I would feel a sensation of warmth as the contrast spread. What’s really cool is that, as I felt that warmth sensation spread I could visualize the circulatory system at work in ways that pictures cannot describe. It was a slow progression of warmth spreading outward from my heart. I could visualize the speed at which my blood travels through my body. > > To anyone who will have that contrast injected, be prepared to have that sensation. It’s very interesting! Yeah–it’s a pretty neat sensation. Not the feeling you need to piss though when your that area warms up, though. ---
**Author:** ![Fiveroptic](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/fiveroptic/32/8257_2.png) [@Fiveroptic](https://boards.straightdope.com/u/Fiveroptic)\ **Post date:** [December 12, 2022, 11:12pm UTC](https://boards.straightdope.com/t/how-is-blood-able-to-circulate/976416/11 "2022-12-12T23:12:30Z")
I understand that the return venous blood enters the right atrium and exits the right ventricle, then shoots through the pulmonary artery to the lungs. What I don’t get is why it’s necessary to have two chambers on each side. Is it for more efficient pumping? What about critters with two-chambered hearts, how does the heart pump blood out of the same chamber it’s entering? (I feel like I’m probably missing a major – and probably very blatant – step here…but luckily my heart has never relied on my intelligence to do its job.) ---
**Author:** ![Qadgop\_the\_Mercotan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/qadgop_the_mercotan/32/83_2.png) [@Qadgop\_the\_Mercotan](https://boards.straightdope.com/u/Qadgop_the_Mercotan)\ **Post date:** [December 12, 2022, 11:18pm UTC](https://boards.straightdope.com/t/how-is-blood-able-to-circulate/976416/12 "2022-12-12T23:18:37Z")
It’s more efficient. without the extra chambers, each beat would push blood both towards its intended target (lungs for R ventricle and rest of body for L ventricle) AND backwards from whence it came. Now two chambers is still enough forward progress for many animals, but for the more metabolically active ones. And of course some creatures have two atria and only 1 ventricle, which is more efficient than just having two ventricles ---
**Author:** ![Seanette](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/seanette/32/9139_2.png) [@Seanette](https://boards.straightdope.com/u/Seanette)\ **Post date:** [December 13, 2022, 12:44am UTC](https://boards.straightdope.com/t/how-is-blood-able-to-circulate/976416/13 "2022-12-13T00:44:15Z")
> [@TheCuse](#): > > Yeah–it’s a pretty neat sensation. Not the feeling you need to piss though when your that area warms up, though. I’d been warned about that, so availed myself of the nearest restroom just before going in. Definitely comforting to know that I was emptied out already. 🙂 ---
**Author:** ![DocCathode](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/doccathode/32/18773_2.png) [@DocCathode](https://boards.straightdope.com/u/DocCathode)\ **Post date:** [December 13, 2022, 12:45am UTC](https://boards.straightdope.com/t/how-is-blood-able-to-circulate/976416/14 "2022-12-13T00:45:47Z")
I say this seriously and not as a joke- For all your blood and vein questions, I HIGHLY recommend the film Hemo. It is VERY goofy in spots. It is also profoundly educational. ---
**Author:** ![Qadgop\_the\_Mercotan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/qadgop_the_mercotan/32/83_2.png) [@Qadgop\_the\_Mercotan](https://boards.straightdope.com/u/Qadgop_the_Mercotan)\ **Post date:** [December 13, 2022, 1:24am UTC](https://boards.straightdope.com/t/how-is-blood-able-to-circulate/976416/15 "2022-12-13T01:24:30Z")
> [@DocCathode](#): > > I HIGHLY recommend the film Hemo I agree. I saw this film in 9th grade around 1971 or so, and it got me thinking about going into medicine. ---
**Author:** ![StarvingButStrong](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/starvingbutstrong/32/335_2.png) [@StarvingButStrong](https://boards.straightdope.com/u/StarvingButStrong)\ **Post date:** [December 13, 2022, 2:16pm UTC](https://boards.straightdope.com/t/how-is-blood-able-to-circulate/976416/16 "2022-12-13T14:16:39Z")
> [@nearwildheaven](#): > > The blood cells also line up single-file in the smallest capillaries. Most of them are extremely flexible. If I look towards the sun with my eyes closed on a bright day, I can see little blobs moving along in single lines. I don’t know if I’m seeing capillaries in my eyelids, or some deeper level of the eyeball, but it always amazed me that I could see single cells without microscopes or any other technology. (Possibly this is aided by the fact that I’ve been extremely near-sighted even before school age.) ---
**Author:** ![HoneyBadgerDC](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/honeybadgerdc/32/1033_2.png) [@HoneyBadgerDC](https://boards.straightdope.com/u/HoneyBadgerDC)\ **Post date:** [December 13, 2022, 4:52pm UTC](https://boards.straightdope.com/t/how-is-blood-able-to-circulate/976416/17 "2022-12-13T16:52:30Z")
> [@DocCathode](#): > > I say this seriously and not as a joke- For all your blood and vein questions, I HIGHLY recommend the film Hemo. It is VERY goofy in spots. It is also profoundly educational. I watched it, it was good. ---
**Author:** ![Bootb](https://avatars.discourse-cdn.com/v4/letter/b/e19b73/32.png) [@Bootb](https://boards.straightdope.com/u/Bootb)\ **Post date:** [December 14, 2022, 2:34am UTC](https://boards.straightdope.com/t/how-is-blood-able-to-circulate/976416/18 "2022-12-14T02:34:55Z")
> [@nearwildheaven](#): > > The blood cells also line up single-file in the smallest capillaries. Most of them are extremely flexible. Which is why sickle cell anemia is painful. ---
**Author:** ![Bullitt](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bullitt/32/5725_2.png) [@Bullitt](https://boards.straightdope.com/u/Bullitt)\ **Post date:** [December 14, 2022, 8:29am UTC](https://boards.straightdope.com/t/how-is-blood-able-to-circulate/976416/19 "2022-12-14T08:29:39Z")
Learning here that they line up in single file, and flexibility is key,… now I understand why SCA is painful. Thanks for this discussion. > **[Sickle cell disease](https://en.m.wikipedia.org/wiki/Sickle_cell_disease)** > > Sickle cell disease (SCD) is a group of blood disorders typically inherited. The most common type is known as sickle cell anaemia. It results in an abnormality in the oxygen-carrying protein haemoglobin found in red blood cells. This leads to a rigid, sickle-like shape under certain circumstances. Problems in sickle cell disease typically begin around 5 to 6 months of age. A number of health problems may develop, such as attacks of pain (known as a sickle cell crisis), anemia, swel Sickle cell... ---
**Author:** ![outlierrn](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/outlierrn/32/3005_2.png) [@outlierrn](https://boards.straightdope.com/u/outlierrn)\ **Post date:** [December 14, 2022, 6:40pm UTC](https://boards.straightdope.com/t/how-is-blood-able-to-circulate/976416/20 "2022-12-14T18:40:35Z")
The venous return side of the system has one way valves, muscle contractions and breathing provide additional pumping force. [Next page](https://boards.straightdope.com/t/how-is-blood-able-to-circulate/976416.md?page=2)