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Cardiovascular > Introduction to CVS and Haemodynamics > Flashcards

Introduction to CVS and Haemodynamics Flashcards

1
Q

What are the main functions of the cardiovascular system?

A
  • Bulk flow of materials
    • Gases
    • Nutrients
    • Hormones
    • Waste
  • Temperature regulation
  • Homeostasis
  • Host defence
  • Reproduction
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2
Q

What are the components of the cardiovascular system?

A
  • Heart
    • Pump that generates blood flow around the system.
  • Arterial system
    • The conductance bessels that carry the blood around the body.
  • Microcirculation
    • Where transfer of nutrients, waste and water occurs.
  • Venous system
    • The capacity vessels, that store and return blood to the heart.
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3
Q

What percentage of blood is in the pulmonary circulation at any one time?

A

9%

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4
Q

What percentage of blood is in the systemic circulation at any one time?

A

84%

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5
Q

What percentage of blood is in the heart at any one time?

A

7%

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6
Q

Describe the organisation of cells as related to the organisation of capillaries.

A
  • Almost all cells are within a few cell diameters of a capillary.
  • ~10 billion capillaries; ~5L volume.
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7
Q

Why are vessels arranged parallel to one another?

A
  • Allows independent regulation of blood flow to different organs.
  • Adapts to the metabolic demands of the tissues.
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8
Q

Use a diagram to describe the normal path of blood flow.

A
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9
Q

Describe the structure of the aorta.

A
  • Diameter = 25mm
  • Wall = 2mm
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10
Q

Describe the structure of a normal artery.

A
  • Diameter = 4mm
  • Wall = 1mm
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11
Q

Describe the structure of a normal vein.

A
  • Diameter = 5mm
  • Wall = 0.5mm
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12
Q

Describe the structure of the vena cava.

A
  • Diameter = 30mm
  • Wall = 1.5mm
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13
Q

Describe the structure of an arteriole.

A
  • Diameter = 30µm
  • Wall = 6µm
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14
Q

Describe the structure of a terminal arteriole.

A
  • Diameter = 10µm
  • Wall = 2µm
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15
Q

Describe the structure of a capillary.

A
  • Diameter = 8µm
  • Wall = 0.5µm
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16
Q

Describe the structure of a venule.

A
  • Diameter = 20µm
  • Wall = 1µm
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17
Q

Describe the characteristics of arterioles.

A
  • Smallest diameter
  • Muscular walled arteries
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18
Q

Describe the characteristics of precapillary sphincters.

A
  • Rings of smooth muscle.
  • Control entry of blood from arteriole into each capillary.
19
Q

Describe the characteristics of capillaries.

A
  • Smallest dimeter blood vessel.
  • Simple tube
  • One cell thick
  • Flattened endothelial cells
  • Allows for diffusion of nutrients, waste etc. in/out tissues
20
Q

Describe the characteristics of venules.

A
  • Smallest diameter vessels
  • Drain blood back to the larger true veins
21
Q

What are the components of the cardiovascular system?

A
  • A pump (the heart).
  • A series of conducting pipes (the elastic arteries).
  • Smaller distributing pipes to radiators with thermostatic controls (the muscular arteries and arterioles).
  • Radiators for heat exchange (the capillary beds).
  • A system of return pipes that increase in diameter from the radiators back to the pump (the venules and veins).
  • It needs filled to the right volume to work (blood).
  • It works under pressure (blood pressure).
22
Q

Describe how to calculate pulse pressure.

A

Pulse pressure = systolic pressure - diastolic pressure

23
Q

Describe how to calculate mean arterial blood pressure.

A

MABP = diastolic pressure + 1/3 pulse pressure

24
Q

Describe what happens to venous pressure when standing completely still.

A
  • Pressure increases by 1mmHg for each 13.6mm below the surface.
    • By feet there is an increase of 90mmHg.
  • Mean arterial pressure at the level of the heart is ~100mmHg.
  • So, in the feet it is ~190mmHg
  • Leg oedema
    • 10-20% of blood volume within 15-30 minutes
25
Q

Describe how muscle contraction affects the blood flow through a vein.

26
Q

Describe what happens during orthostatic (postural hypotension).

A
  • Immediate effect in going from supine to upright.
  • Around 500ml of blood from the upper body moves to the legs.
  • There is decreased venous return, and therefore:
    • Decreased cardiac output
    • Decreased blood pressure
  • Reflex vasoconstriction in the legs and lower abdomen.
    • Takes a few seconds to kick in
27
Q

Describe noncompliant vessels and give examples.

A
  • Rigid tubes which resist expansion when internal pressure rises.
  • Examples:
    • Capillaries
    • Arterioles
28
Q

Describe compliant vessels and give examples.

A
  • Tubes with elastic walls which swell when internal pressure rises.
  • Examples:
    • Arteries
    • Veins
29
Q

What is LaPlace’s Law?

A
  • Distending pressure (P) produces an opposing force or tension (T) in the vessel wall, proportional to the radius (R) of the vessel:

T = PR

  • Think about pressure and vessel radius in:
    • Aorta
    • Arteriole
    • Capillary
30
Q

What is the consequence of LaPlace’s Law on control of blood flow?

A
  • Low tension required to oppose blood pressure in arterioles.
  • Smooth muscle control of arteriole and precapillary sphincters are the sites of tissue blood flow regulation.
31
Q

What is the consequence of LaPlace’sLaw on capillaries?

A
  • Capillaries can be extremely thin and still withstand the pressure.
  • Thin walls are essential for the exchange process.
32
Q

Give another example of a practical consequence of LaPlace’s Law?

33
Q

Describe the factors which affect blood flow through a vessel.

A

Flow is:

  • Directly proportional to:
    • the radius of the vessel
    • the pressure gradient along the vessel
  • Inversely proportional to:
    • the length of the vessel
    • the thickness of the fluid
34
Q

Depict how viscosity affects blood flow through a vessel.

A
  • Normal blood has a higher viscosity than plasma and higher viscosity than water.
  • Blood is a THIXOTROPIC FLUID:
    • Flow affects viscosity - static blood has 100x the viscosity of flowing blood.
35
Q

Describe how vessel length affects blood flow through the vessel.

A
  • The shorter the vessel, the more blood flows through the vessel per unit time.
36
Q

Describe how to calculate flow using the Poiseuille equation.

A
  • Viscosity and vessel length, plus vessel radius are all factors that generate resistance to flow by contributing to friction between blood and the walls of vessels.
  • As resistance increases, flow decreases.
37
Q

Describe how to calculate arterial pressure.

A

Arterial pressure = cardiac output x total peripheral resistance

38
Q

Describe the neural regulation of arteriolar radius.

A
  • Vasoconstrictor:
    • Sympathetic nerves
  • Vasodilator:
    • NO-releasing nerves
39
Q

Describe the hormonal regulation of arteriolar radius.

A
  • Vasoconstrictor:
    • Adrenaline
    • Angiotensin II
    • Vasopressin
  • Vasodilator:
    • Adrenaline
    • Atrial-natriuretic peptide
40
Q

Describe the local regulation of arteriolar radius.

A
  • Vasoconstrictor:
    • Myogenic response
    • Endothelin-1
  • Vasodilator:
    • Decreased O2
    • K+
    • CO2
    • H+
    • Adenosine
    • Nitric oxide
    • Bradykinin
41
Q

Decribe laminar fluid flow.

A
  • Vessels are lined with endothelial cells.
  • Fluid molecules touching the vessel wall adhere and move slowly.
  • The next layer slips over these; and the next slips over these.
  • The middle-most layers move most rapidly.
  • The centre is the most free-flowing part of the vessel.
42
Q

Describe the effect of turbulence on fluid flow through a vessel.

A
  • Turbulence disrupts flow, and increases resistance.
    • Poiseuille’s law doesn’t hold true during turbulence.
  • Reynold’s number (Re) is used to indicate whether flow is laminar or turbulent.
43
Q

Describe how Reynold’s number (Re) is used to describe flow.

A
  • Reynold’s number (Re) is used to indicate whether flow is likely to be laminar or turbulent.
    • For a given system, there will be a “critical value” for Re, above which turbulence is highly likely.
  • Turbulence is therefore likely with (because Re increases with):
    • high velocity flow
    • large diameter vessels
    • low blood viscosity
    • abnormal vessel wall
44
Q

Describe the trend in blood pressure and flow throughout the CVS.

Cardiovascular (12 decks)

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