Blood flow control

Question 1

What is total peripheral resistance (TPR)? [1 mark]

Answer 1

The total resistance to flow of blood in the systemic circuit.

Question 2

What is the inverse of resistance? [1 mark]

Answer 2

Conductance (G) = 1/TPR

Question 3

What is the formula for cardiac output? [3 marks]

Answer 3

Cardiac output (CO) = [Pressure gradient (Pa - CVP)]/Total peripheral resistance (TPR)

Question 4

What does TPR control? [2 marks]

Answer 4

• Blood flow

- Blood pressure

Question 5

What factors control TPR? [3 marks]

Answer 5

• Radius
• Pressure difference across vessels
• Length of vessel

Question 6

What happens to the arterioles and to TPR and BP to cause a higher blood flow? [2 marks]

Answer 6

• Arterioles dilate

- BP upstream and TPR decrease

Question 7

What happens to the arterioles and to TPR and BP to cause a lower blood flow? [2 marks]

Answer 7

• Arterioles constrict

- BP upstream and TPR increase

Question 8

What happens to the arterioles in hypertension? [1 mark]

Answer 8

Over constriction

Question 9

What happens to the superior mesenteric and common iliac post-prandial? [2 marks]

Answer 9

• Superior mesenteric dilates

- Common iliac constricts

Question 10

What happens to the superior mesenteric and common iliac during exercise? [2 marks]

Answer 10

• Superior mesenteric constriction

- Common iliac dilates

Question 11

What does the superior mesenteric arise from? [1 mark]

Answer 11

Anterior surface of the abdominal aorta

Question 12

What does the common iliac arise from? [1 mark]

Answer 12

The abdominal aorta

Question 13

What is Poiseuille’s law and what does it consider? [4 marks]

Answer 13

• Describes the volume flow rate of a liquid through a tube
• Viscosity decreases it
• Vessel length decreases it
• Radius increases it

Question 14

What is the formula for resistance? [4 marks]

Answer 14

Resistance = (8 x viscosity [η] x length)/(π x radius^4)

Question 15

What is the combined formula for Darcy’s and Poiseuille’s law?

Answer 15

CO = Pa - CVP x (πr^4)/(8ηL)

remember: conductance NOT resistance is in the equation

Question 16

What is the pressure like in capillaries? [1 mark]

Answer 16

Low (because of less resistance)

Question 17

What is the radius like in capillaries? [1 mark]

Answer 17

Constant (because of no innervation or smooth muscle)

Question 18

Why is there less resistance in capillaries? [1 mark]

Answer 18

Bolus flow (smooth flow)

Question 19

Why do vessels in parallel have less resistance? [1 mark]

Answer 19

If they were end to end, the total resistance would add up

Question 20

What are the two types of blood flow control? [2 marks]

Answer 20

• Central (from brain)

- Local

Question 21

What are the two types of LOCAL blood flow control? [2 marks]

Answer 21

• Intrinsic (within a tissue)

- Extrinsic (outside a tissue)

Question 22

What are examples of intrinsic blood flow control? [3 marks]

Answer 22

• Tissue metabolites
• Myogenic properties of muscle
• Endothelial factors

Question 23

What are examples of intrinsic blood flow control? [2 marks]

Answer 23

• Neural stimulation

- Hormones

Question 24

Why would having a linear relationship between blood flow and pressure be a bad thing? [1 mark]

Answer 24

There would be large differences in blood flow as pressure changes

Question 25

What happens in the Bayliss myogenic response? [2 marks]

Answer 25

- At low pressures, vessels open a lot | - At higher pressures, it closes more (so there's less fluctuation in blood flow)

Question 26

What does blood flow depend on? [3 marks]

Answer 26

- Viscosity of blood - Vessel diameter - Haematocrit

Question 27

What is viscosity? [1 mark]

Answer 27

A measure of internal friction opposing the separation of the lamina (circles in flow).

Question 28

What are the clinical implications for haematocrit? [2 marks]

Answer 28

HIGH: Polycythaemia LOW: Anaemia

Question 29

What are the clinical implications for RBC deformability? [3 marks]

Answer 29

- High haematocrit - Low blood flow - Sickle cell anaemia

Question 30

What are the clinical implications for velocity? [2 marks]

Answer 30

- Immobility (causes slow venous flow) | - Partial clotting (increases velocity)

Question 31

What happens to cardiac output when you breathe in? [3 marks]

Answer 31

- Increases a little bit - Diaphragm moves down - Increases pressure

Question 32

What happens to veins at low pressures? [1 mark]

Answer 32

They collapse

Question 33

What happens to veins at high pressures? [1 mark]

Answer 33

They distend

Question 34

What helps venous return? [2 marks]

Answer 34

- Thoracic pump | - Skeletal muscle contraction

Question 35

What does sympathetic venoconstriction increase? [3 marks]

Answer 35

- Venous retun - Central venous pressure (increases preload and SV) - End-diastolic pressure

Question 36

What is central venous pressure? [1 mark]

Answer 36

The pressure of blood in the right atrium

Question 37

What is Bernoulli's law? [1 mark]

Answer 37

Mechanical energy of flow is determined by pressure, kinetic and potential energies (ρ = fluid mass).

Question 38

What is the formula for Bernoulli's law? [3 marks]

Answer 38

Energy = Pressure (PV) + kinetic ((ρV^2)/2) + potential (pgh)

Question 39

When standing, where is there more pressure? [1 mark]

Answer 39

In the heart

Question 40

When standing, where is there more kinetic energy? [1 mark]

Answer 40

Heart

Question 41

When standing, where is there more potential energy? [1 mark]

Answer 41

Heart