blood flow Q's

[StayingSteady]

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Alright, I'm a little confused about the circulatory system...

1) When nutrients get absorbed into the intestinal capillaries in the small intestine, does all that blood go to the liver? or where else would it go?

2) does EVERY particle of blood flow to EVERY portion of the body? I know this seems like a silly question, but I ask this because of the kidneys. blood flows to the kidneys and gets filtered/reabsorbed to be excreted as urine. But does all blood get filtered? or just the blood that goes to the kidneys? and then does the other blood just stay dirty and contain wastes? also, kaplan says that 20% of the plasma from the glomerulus gets forced into the Bowman's capsule, but then what about the other 80%?

3) And how come vasoconstriction increases blood pressure? I know intuitively this makes sense, BUT... according to the continuity equation (A1v1=A2v2), vasoconstriction should increase blood velocity, and then according to Bernoulli's (?) conservation of energy equation, increased velocity should DECREASE pressure... so what's different in blood flow?

 

[FutureInternist]

Alright, I'm a little confused about the circulatory system...

1) When nutrients get absorbed into the intestinal capillaries in the small intestine, does all that blood go to the liver? or where else would it go?

2) does EVERY particle of blood flow to EVERY portion of the body? I know this seems like a silly question, but I ask this because of the kidneys. blood flows to the kidneys and gets filtered/reabsorbed to be excreted as urine. But does all blood get filtered? or just the blood that goes to the kidneys? and then does the other blood just stay dirty and contain wastes? also, kaplan says that 20% of the plasma from the glomerulus gets forced into the Bowman's capsule, but then what about the other 80%?

3) And how come vasoconstriction increases blood pressure? I know intuitively this makes sense, BUT... according to the continuity equation (A1v1=A2v2), vasoconstriction should increase blood velocity, and then according to Bernoulli's (?) conservation of energy equation, increased velocity should DECREASE pressure... so what's different in blood flow?

1. Yes, all the blood from the gut goes to liver first (since that's where your Kupffer cells can see what bad guys you brought in). All the nutrients also go to the liver, w/ the exception of chylomicron which, because of their big size, have to be absorbed thru the lymphatic system.

2. Yes....eventually. If a certain muscle only has a small requirement at a given time then you will have vasoconstriction so that excess blood does not go to places where it is not needed. With the next heart beat a "different" set of RBCs will go into the muscle. In the same way, all the blood eventually gets filtered. As for the 80%, it just goes out the efferent arteriole (but again, eventually, the 80% that "escaped" will get filtered down the line)

 

[fj4288]

1) Edit FutureInternist is right about this one 🙂.

2) NOT EVERY particle of blood goes to every single portion of the body. Perfect example is the Blood Brain Barrier (BBB) where only molecules of less than or equal to 500 D can enter (very SMALL). Substances like glucose and gases like oxygen or carbon dioxide can get through. But hormones or neurotransmitters or bacteria can't get through. All blood has to get filtered because you can't have excess waste building in the body or else you're going to become ill. Now in terms of the kidney blood is filtered where water and other solutes like Na, K, Cl, glucose, a.a. get filtered out BUT RBC's do not. Normally (99%) of filtrate will get reabsorbed by the end. The liver also filters blood in terms of destroying worn out RBC's or detoxifying your body (e.g. drinking alcohol). Bacteria are also phagocytozed in the liver. You have to remember blood is composed of BLOOD CELLS and PLASMA. If all the plasma was forced out into the bowman's capsule then all you would have is blood cells without any fluid to travel through. Since filtration is a constant process that other 80% will eventually get filtered too.

3) As far as this one goes I just think of the intuitive. I don't know how to explain this one using the physics because I think there more than just basic fluid dynamics going on.

 

[FutureInternist]

I didn't think of the brain as a body part, probably since mine has been lacking O2 for quite some time.

3. I THINK, it is because of a simultaneous constriction in the venous side as well --> inc blood volume in circulation --> inc pressure. Like the ideal gas laws etc, you can only get a predicted response if you keep ALL of the other factors constant, which is not the case in sympathetic stimulation of the CV system.

 

[StayingSteady]

1) Edit FutureInternist is right about this one 🙂.

2) NOT EVERY particle of blood goes to every single portion of the body. Perfect example is the Blood Brain Barrier (BBB) where only molecules of less than or equal to 500 D can enter (very SMALL). Substances like glucose and gases like oxygen or carbon dioxide can get through. But hormones or neurotransmitters or bacteria can't get through. All blood has to get filtered because you can't have excess waste building in the body or else you're going to become ill. Now in terms of the kidney blood is filtered where water and other solutes like Na, K, Cl, glucose, a.a. get filtered out BUT RBC's do not. Normally (99%) of filtrate will get reabsorbed by the end. The liver also filters blood in terms of destroying worn out RBC's or detoxifying your body (e.g. drinking alcohol). Bacteria are also phagocytozed in the liver. You have to remember blood is composed of BLOOD CELLS and PLASMA. If all the plasma was forced out into the bowman's capsule then all you would have is blood cells without any fluid to travel through. Since filtration is a constant process that other 80% will eventually get filtered too.

3) As far as this one goes I just think of the intuitive. I don't know how to explain this one using the physics because I think there more than just basic fluid dynamics going on.

Sorry, but so you're saying the brain blood does not get filtered before it reaches the brain because only those few substances can actually get through the BBB? but that blood gets filtered later on, correct?

thanks for the responses guys! really cleared things up

 

[fj4288]

Sorry, but so you're saying the brain blood does not get filtered before it reaches the brain because only those few substances can actually get through the BBB? but that blood gets filtered later on, correct?

thanks for the responses guys! really cleared things up

Well the blood that is going to the brain is prob. not 100% filtered..but that does not really matter because only certain particles can enter the CNS such as glucose. Now w/e waste that is made in the CNS I'm guessing just get broken down by lysosomes or phagocytozed and then transported back out of the CNS into the main circulatory system to eventually get filtered out.