Blood flow control Flashcards
What is total peripheral resistance (TPR)? [1 mark]
The total resistance to flow of blood in the systemic circuit.
What is the inverse of resistance? [1 mark]
Conductance (G) = 1/TPR
What is the formula for cardiac output? [3 marks]
Cardiac output (CO) = [Pressure gradient (Pa - CVP)]/Total peripheral resistance (TPR)
What does TPR control? [2 marks]
- Blood flow
- Blood pressure
What factors control TPR? [3 marks]
- Radius
- Pressure difference across vessels
- Length of vessel
What happens to the arterioles and to TPR and BP to cause a higher blood flow? [2 marks]
- Arterioles dilate
- BP upstream and TPR decrease
What happens to the arterioles and to TPR and BP to cause a lower blood flow? [2 marks]
- Arterioles constrict
- BP upstream and TPR increase
What happens to the arterioles in hypertension? [1 mark]
Over constriction
What happens to the superior mesenteric and common iliac post-prandial? [2 marks]
- Superior mesenteric dilates
- Common iliac constricts
What happens to the superior mesenteric and common iliac during exercise? [2 marks]
- Superior mesenteric constriction
- Common iliac dilates
What does the superior mesenteric arise from? [1 mark]
Anterior surface of the abdominal aorta
What does the common iliac arise from? [1 mark]
The abdominal aorta
What is Poiseuille’s law and what does it consider? [4 marks]
- Describes the volume flow rate of a liquid through a tube
- Viscosity decreases it
- Vessel length decreases it
- Radius increases it
What is the formula for resistance? [4 marks]
Resistance = (8 x viscosity [η] x length)/(π x radius^4)
What is the combined formula for Darcy’s and Poiseuille’s law?
CO = Pa - CVP x (πr^4)/(8ηL)
remember: conductance NOT resistance is in the equation
What is the pressure like in capillaries? [1 mark]
Low (because of less resistance)
What is the radius like in capillaries? [1 mark]
Constant (because of no innervation or smooth muscle)
Why is there less resistance in capillaries? [1 mark]
Bolus flow (smooth flow)
Why do vessels in parallel have less resistance? [1 mark]
If they were end to end, the total resistance would add up
What are the two types of blood flow control? [2 marks]
- Central (from brain)
- Local
What are the two types of LOCAL blood flow control? [2 marks]
- Intrinsic (within a tissue)
- Extrinsic (outside a tissue)
What are examples of intrinsic blood flow control? [3 marks]
- Tissue metabolites
- Myogenic properties of muscle
- Endothelial factors
What are examples of intrinsic blood flow control? [2 marks]
- Neural stimulation
- Hormones
Why would having a linear relationship between blood flow and pressure be a bad thing? [1 mark]
There would be large differences in blood flow as pressure changes
What happens in the Bayliss myogenic response? [2 marks]
- At low pressures, vessels open a lot
- At higher pressures, it closes more (so there’s less fluctuation in blood flow)
What does blood flow depend on? [3 marks]
- Viscosity of blood
- Vessel diameter
- Haematocrit
What is viscosity? [1 mark]
A measure of internal friction opposing the separation of the lamina (circles in flow).
What are the clinical implications for haematocrit? [2 marks]
HIGH: Polycythaemia
LOW: Anaemia
What are the clinical implications for RBC deformability? [3 marks]
- High haematocrit
- Low blood flow
- Sickle cell anaemia
What are the clinical implications for velocity? [2 marks]
- Immobility (causes slow venous flow)
- Partial clotting (increases velocity)
What happens to cardiac output when you breathe in? [3 marks]
- Increases a little bit
- Diaphragm moves down
- Increases pressure
What happens to veins at low pressures? [1 mark]
They collapse
What happens to veins at high pressures? [1 mark]
They distend
What helps venous return? [2 marks]
- Thoracic pump
- Skeletal muscle contraction
What does sympathetic venoconstriction increase? [3 marks]
- Venous retun
- Central venous pressure (increases preload and SV)
- End-diastolic pressure
What is central venous pressure? [1 mark]
The pressure of blood in the right atrium
What is Bernoulli’s law? [1 mark]
Mechanical energy of flow is determined by pressure, kinetic and potential energies (ρ = fluid mass).
What is the formula for Bernoulli’s law? [3 marks]
Energy = Pressure (PV) + kinetic ((ρV^2)/2) + potential (pgh)
When standing, where is there more pressure? [1 mark]
In the heart
When standing, where is there more kinetic energy? [1 mark]
Heart
When standing, where is there more potential energy? [1 mark]
Heart
