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Physiology- CP > Blood Flow > Flashcards

Blood Flow Flashcards

1
Q

What is the primary function of blood flow?

A
  • Bulk transport
  • Delivery of oxygen, nutrients and water to tissues
  • Removal of metabolic waste products from tissues
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2
Q

How long does it take a red blood cell to circulate for a normal adults at rest?

A
  • one minute
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3
Q

What does the vascular system comprise of?

A
  • 2 closed circuits in a series
  • Systemic circulation from left ventricle
  • Pulmonary circulation from right ventricle
  • Volume of blood ejected into each is the same
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4
Q

Describe the systemic circulation

A
  • Left heart –> aorta –> distributes blood all around body
  • Capillaries
  • Veins –> right heart –> lungs –> oxygenated blood –> left heart
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5
Q

What occurs at capillaries?

A
  • Gas exchange
  • Nutrient exchange
  • Movement across the capillaries
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6
Q

What is the general arterial structure?

A
  • Internal lining- endothelium
  • Elastic tissue- expansion and contraction of arteries
  • Smooth muscle found in lining
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7
Q

What is the general venous structure?

A
  • Fibrous tissue and collagen is found here

- Capacitants and elastin

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8
Q

Describe the structure of capillaries

A
  • Endothelial tube with pericytes
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9
Q

Describe the general structure of arterioles

A
  • Function involves directing/changing and driving blood flow
  • Proportionally more smooth muscle found in the small arterioles than the arteries
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10
Q

What is the impact of size on tension?

A
  • Law of Laplace
  • Tension = Pressure x Radius
  • Larger arteries experience more tension than the smaller arteries
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11
Q

What is the driving force of blood flow generated by?

A

Heart

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12
Q

What is the biphasic response in the aorta?

A
  • Blood ejected from the heart- peaks

- During diastole- drops

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13
Q

What is Darcy’s law?

A
  • Blood flow analogous to electrical current
  • Q = ∆P / R
  • Q = flow
  • ∆P = Pressure gradient
  • R= resistance
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14
Q

What varies flow?

A
  • Flow varies proportionally with pressure gradient

- Inversely with resistance

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15
Q

What determines systolic pressure?

A
  • Cardiac output (CO)

- Increased CO increases pressure

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16
Q

What happens to pressure across the vascular tree?

A
  • Drops
  • Aorta = ~100mgHg (biphasic mean)
  • Capillaries= ~25mmHg
  • Great veins= ~2mmHg
17
Q

What is Poiseuilles Law?

A
  • Describes resistance to flow through a cylinder

- R = nL/r⁴

18
Q

Describe the relationship between resistance and radius

A
  • Inversely promotional to the fourth power of the radius
  • 1/r⁴
  • This mains small changes in vessel diameter have large effects on resistance, and subsequently flow
19
Q

What is the relationship between flow and radius?

A

Flow is proportional to the fourth power of the radius

20
Q

What types of vessels will generate the largest amount of resistance?

A
  • Smaller arteries and arterioles
  • Large conductance arteries have limited capacity to vary diameter
  • Unlike smaller muscular arteries and arterioles
21
Q

Why do conduit arteries offer little resistance?

A
  • Large in size
  • 20% increase in diameter would be required to more than double the flow
  • Aorta 1cm, needs 0.2 cm increase
  • Arteriole 0.01 cm needs 0.002 cm increase for same flow change
22
Q

What happens if one arteriole is dilated in a network?

A
  • There will be a greater increase in flow because blood flows down the path of least resistance
23
Q

What is the relationship between viscosity and resistance?

A
  • Viscosity proportional to resistance
  • Inversely proportional to flow
  • Thicker solution = less flow
  • Blood is 2.5/3x more viscous than water
24
Q

Why is blood viscous?

A
  • Haematocrit
  • Proportion of blood volume occupied by red cells
  • Usually expressed as percentage
  • Females 37-47% and males 40-54%
  • Concentration and type of plasma protein will also have an effect
25
Q

What is the relationship between haematocrit and viscosity?

A
  • Haematocrit increases, relative viscosity increases

- Capillaries tend to have a lower viscosity

26
Q

What factors affect viscosity?

A
  • Generally, does not change
  • Anaemia and polycythaemia, decrease/increase viscosity respectively
  • Capillaries tend to have lower haematocrit due to axial streaming- higher flow
27
Q

What is meant by laminar blood flow?

A
  • Fastest at the centre of the vessel
  • As it flows through, the cells at the sides of the walls put at the wall of the artery
  • Silent
28
Q

What is shear stress?

A
  • Increased flow increases shear

- Slowed and pulled

29
Q

What is meant by non-laminar flow?

A
  • Turbulence
  • At high velocities, flow can become turbulent
  • Or at large diameter (like bronchial breathing)
30
Q

When does turbulent flow occur under normal conditions?

A
  • Asending aorta

- Around branch points

31
Q

Describe the sounds of turbulent flow

A
  • Not silent
  • Basis of Korotkoff sounds in measuring blood pressure
  • Tapping, cut off supply and then allow it to flow and there will be sound at that point
  • Basis of bruit in athermoa
32
Q

What is the equation for flow?

A

(∆P x πr⁴)/ 8nL

Physiology- CP (19 decks)

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