A question for all the doctors ..

[Toshiba]

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Where is the highest viscosity blood in the body

A Aorta
B Pulmonary artery
c Vena cava
D Vasa recta
E Pulmonary vein

Plz help me with this question, I 'll rally appreciate

 

[nutmegs]

nutmegs says vena cava

 

[Ramoray]

i would say aort since it is the vessl with the greatest radius. if you rearranged the pouselle equation you would have viscosity is proportional to radius^4 , so increasing radius should increase viscosity which makes sense since the blood with highest radius will move the slowest, and somethign slow to me sounds viscous.

 

[idq1i]

i would say aort since it is the vessl with the greatest radius. if you rearranged the pouselle equation you would have viscosity is proportional to radius^4 , so increasing radius should increase viscosity which makes sense since the blood with highest radius will move the slowest, and somethign slow to me sounds viscous.

Changes in blood viscosity are negligible once the vessel exceeds a certain diameter (~2-3 cm ?). Your answer can't detect a difference between 4 of the choices (aorta is one of them)

My best guess is D - vasa recta. Are they not relatively polycythemic?

 

[nutmegs]

where do the lymphatics dump back in again? that's why I picked vena cava over pulm

and radius and viscosity are not related, they just both happen to be related to flow

 

[idq1i]

and radius and viscosity are not related,

They are for imperfect fluids (blood is a good example).

 

[Chandler]

Good Job Idq1. The answer is indeed vasa recta.

 

[driedcaribou]

i would say aort since it is the vessl with the greatest radius. if you rearranged the pouselle equation you would have viscosity is proportional to radius^4 , so increasing radius should increase viscosity which makes sense since the blood with highest radius will move the slowest, and somethign slow to me sounds viscous.

This is either a question of semantics or understanding of the variable.

Is the original poster asking about vessel resistance or actual viscosity?

Viscosity is the property of a fluid and a variable independent of radius.
It really doesn't change much in a substance like blood. Someone polycythemic would have a higher viscosity of blood than someone who is well hydrated.

A fluid that is higher in solute would be more viscous than a fluid lower in solute.


Viscosity = [Frictional Force x thickness x time] / [(Area of plate) x (distance)]
http://xtronics.com/reference/viscosity.htm

http://www.cvphysiology.com/Hemodynamics/H003.htm

 

[Toshiba]

Hi Guys from all this discussion even I think it should be vasa recta . It can't be a vessel with a bigger diameter .

 

[Idiopathic]

where do the lymphatics dump back in again? that's why I picked vena cava over pulm

This is, in fact, the only thing that would alter the viscosity (a property of the fluid itself) of the blood.

 

[BlackNDecker]

This is, in fact, the only thing that would alter the viscosity (a property of the fluid itself) of the blood.

Changes in hematocrit alter the viscosity of the blood...

Incr. Hct => Incr. Viscosity

So, the answer is definitely Vasa Recta? The Aorta would have the highest turbulence, not viscosity...makes sense that it would be the vasa recta since fluid is reabsorbed thus increasing the Hct.

 

[BlackNDecker]

where do the lymphatics dump back in again? that's why I picked vena cava over pulm

I remember this drawing from the Moore & Dalley Anatomy text:

The Chyle Cisterna feeds the Right Lymphatic Duct >>> Right Subclavian Vein (drains 75% of body lymph)...Upper Left Quadrant Lymphatics drain into Thoracic Duct >>> Left Subclavian Vein.

I don't recall the IVC receiving a major flow of lymph...anybody know the specifics on this?

 

[uclabruins47]

i remember R subclavian drains only right head + right body above diaphragm and thoracic duct drains everything else. not 100% sure.

 

[omores]

The major factor affecting blood viscosity is red blood cell concentration. The thoracic duct dumps into the left subclavian, which is upstream from the superior vena cava. So the blood will be more dilute (and less viscous) there. But if you "average" both VCs (since the question doesn't specify which one), that'll be ~the viscosity of the pulmonary artery -- no concentrational or dilutional effects are happening within the heart. Rule out both those answers.

By the same token, the pulmonary vein ~the viscosity of the aorta. Rule out both.

That leaves the vasa recta. The vasa recta help maintain the intertitial concentration gradient. They lose water as they descend (thus RBC concentration and viscosity increase), but they gain water as they ascend (normalizing RBC concentration). Thus the average viscosity is probably not significantly different from anywhere else. But I'm assuming the question is asking where the point of highest viscosity is located, and that'd be at the bottom of the hairpin turn of the vasa recta.

 

[Idiopathic]

The major factor affecting blood viscosity is red blood cell concentration. The thoracic duct dumps into the left subclavian, which is upstream from the superior vena cava. So the blood will be more dilute (and less viscous) there. But if you "average" both VCs (since the question doesn't specify which one), that'll be ~the viscosity of the pulmonary artery -- no concentrational or dilutional effects are happening within the heart. Rule out both those answers.

By the same token, the pulmonary vein ~the viscosity of the aorta. Rule out both.

That leaves the vasa recta. The vasa recta help maintain the intertitial concentration gradient. They lose water as they descend (thus RBC concentration and viscosity increase), but they gain water as they ascend (normalizing RBC concentration). Thus the average viscosity is probably not significantly different from anywhere else. But I'm assuming the question is asking where the point of highest viscosity is located, and that'd be at the bottom of the hairpin turn of the vasa recta.

Ok, this makes more sense now.

 

[Ramoray]

damn i was way off, mjakes sense now. that was a good response thanks

 

[Spiff]

Blood is a complicated fluid. Most of the basic fluid-dynamics stuff applies to Newtonian or near-Newtonian fluids, not to blood which is a suspended particle medium. With regard to blood viscosity, the diameter of the tube through which the blood is flowing and the flow rate will alter the apparent viscosity of the fluid: At higher flow, as the shear rate increases, RBCs will deform to a larger extent and the blood becomes less viscous, at low flow rates, RBCs deform less but they also stack together and form small fibrinogen bonds to become Rouleauxs -- this significantly increase apparent viscosity. To add even more complications, there is also a phenomenon called the Fahraeus-Lindqvist effect where the apparent viscosity will actually decrease in small diameter tubes. I am not sure what the explanation is for this effect but the bottom line is that blood viscosity mainly depends on three things: hematocrit, cell deformability, and aggregation. The last two factors are heavily influenced by flow rate, so the highest apparent viscosity will be in areas of high hematocrit and/or low flow.