Blood flow Flashcards
What is the function of blood?
Transports:
Gases
Heat
Nutrients
Metabolites
Signals
Immune cells
The structure is adapted to its function.
What are the constituents of the blood?
Blood is a suspension of solid particles.
When coagulated and centrifuged the layers are:
Bottom - RBCs
Buffy coat, very thing late - white cells and platelets.
Plasma, made from proteins.
What is the cellular component of blood?
99% of the blood cells are red blood cells, which carry oxygen.
Platelets are small cell fragments for haemostasis.
White cells are for immunity and protection.
What are the constituents of plasma?
Na+ is most abundant cation then K+
Cl- and HCO3- are the most abundant anions.
Blood plasma is electroneutral
Na+, Cl- and HCO3- are the main osmotically active solutes.
What are the proteins in the plasma?
Albumin is the most abundant, made in the liver.
Then immunoglobulin, made by B cells.
Fibrinogen is also important.
What are the other components of plasma?
Lipids -
Cholesterol
Phospholipids
Triglycerides
Carbohydrates - mainly glucose, which is tightly regulated.
What is blood rheology?
The flow of matter, especially non-Newtonian flow of liquids and the plastic flow of solids.
Why is blood rheology studied?
It influences circulation.
It influences or is adapted to cellular function.
Abnormalities may relate to pathology
What properties are looked at in blood rheology?
Blood as a whole - resistance to flow and viscosity.
Cells in particular - deformability and adhesion.
How do the physical properties of vessels affect blood flow?
Small arteries are much bigger than RBCs, so blood is a liquid in arteries.
Arterioles - smaller, 10x bigger diameter than RBC. Cells and plasma flow change, RBCs go to centre, cell-free zone at the edges.
Capillaries are the same size or smaller than RBCs.
As vessels get smaller, the cells action have more of an impact.
How do the main drivers change with diameter?
When the diameter is much more than the blood cells, the blood component is blood viscosity.
When the diameter is less than the blood cells, the blood component is the cellular properties and plasma viscosity.
What is viscosity?
The characteristic resistance to flow, the friction within liquid.
What is the driving force for flow?
Flow is driven by the pressure gradient.
The heart pressurises that aorta.
As the elasticity squeezes in, blood moves around the body.
Blood moves from high pressure to low pressure.
What is the equation for flow?
Pressure gradient = the volumetric flow rate x resistance.
How is flow related to cardiac output?
Cardiac output = ABP / TPR
What is laminar flow?
A Newtonian fluid is a fluid where the viscosity does not change according to the flow rate.
The Newtonian fluid will flow through a straight tube at constant viscosity, but in layers.
Next to the wall, the liquid will have no velocity.
At the centre of the tube, the liquid will have very fast velocity.
What is the equation for resistance?
Resistance = 8 x viscosity x length / radius of the vessel ^4.
Resistance has 2 components:
Blood component - the blood viscosity.
Vascular component - the length of the vessel and the radius of the vessel.
Why is blood not a Newtonian fluid?
Blood is a non-Newtonian fluid because its viscosity changes depending on shear rate.
The blood vessels are not rigid and straight, instead curved and deform.
Blood flow is not constant but pulsatile.
What is the effect of increasing resistance?
If resistance increases (because blood viscosity increases) then to maintain flow rate pressure needs to increase.
If pressure doesn’t change and resistance increases, then cardiac output decreases.
What are the intrinsic factors controlling viscosity?
The structure of blood.
Major factors: Haematocrit - packed red cell volume
Plasma viscosity.
Minor factors: Red cell aggregation
Red cell deformation
What are the extrinsic factors controlling viscosity?
Flow conditions.
Viscosity depends on shear rate.
What is the relationship between haematocrit and viscosity?
As haematocrit increases viscosity increases, but is not linear.
Viscosity increases by 4% for each 1% increase in haematocrit.
What is the relationship between haematocrit and oxygen delivery?
The oxygen content is directly proportional to haematocrit, because this shows how many RBCs there are.
Proportional up to a certain point - because resistance goes up and flow becomes slower.
Haematocrit can become too high, and oxygen delivery inefficient = 40%, which is the value of haematocrit in healthy humans.
What are healthy haematocrit levels?
Men = 45%
Women = 40%
Neonates = 54%