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
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.
3
Q
What percentage of blood is in the pulmonary circulation at any one time?
A
9%
4
Q
What percentage of blood is in the systemic circulation at any one time?
A
84%
5
Q
What percentage of blood is in the heart at any one time?
A
7%
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.
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.
8
Q
Use a diagram to describe the normal path of blood flow.
A
9
Q
Describe the structure of the aorta.
A
- Diameter = 25mm
- Wall = 2mm
10
Q
Describe the structure of a normal artery.
A
- Diameter = 4mm
- Wall = 1mm
11
Q
Describe the structure of a normal vein.
A
- Diameter = 5mm
- Wall = 0.5mm
12
Q
Describe the structure of the vena cava.
A
- Diameter = 30mm
- Wall = 1.5mm
13
Q
Describe the structure of an arteriole.
A
- Diameter = 30µm
- Wall = 6µm
14
Q
Describe the structure of a terminal arteriole.
A
- Diameter = 10µm
- Wall = 2µm
15
Q
Describe the structure of a capillary.
A
- Diameter = 8µm
- Wall = 0.5µm
16
Q
Describe the structure of a venule.
A
- Diameter = 20µm
- Wall = 1µm
17
Q
Describe the characteristics of arterioles.
A
- Smallest diameter
- Muscular walled arteries
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
Describe how muscle contraction affects the blood flow through a vein.
26
Describe what happens during orthostatic (postural hypotension).
* 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
Describe noncompliant vessels and give examples.
* Rigid tubes which resist expansion when internal pressure rises.
* Examples:
* Capillaries
* Arterioles
28
Describe compliant vessels and give examples.
* Tubes with elastic walls which swell when internal pressure rises.
* Examples:
* Arteries
* Veins
29
What is LaPlace's Law?
* 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
What is the consequence of LaPlace's Law on control of blood flow?
* 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
What is the consequence of LaPlace'sLaw on capillaries?
* Capillaries can be extremely thin and still withstand the pressure.
* Thin walls are essential for the exchange process.
32
Give another example of a practical consequence of LaPlace's Law?
Aneurysm
33
Describe the factors which affect blood flow through a vessel.
**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
Depict how viscosity affects blood flow through a vessel.
* 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
Describe how vessel length affects blood flow through the vessel.
* The shorter the vessel, the more blood flows through the vessel per unit time.
36
Describe how to calculate flow using the Poiseuille equation.
* 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
Describe how to calculate arterial pressure.
**Arterial pressure = cardiac output x total peripheral resistance**
38
Describe the neural regulation of arteriolar radius.
* Vasoconstrictor:
* Sympathetic nerves
* Vasodilator:
* NO-releasing nerves
39
Describe the hormonal regulation of arteriolar radius.
* Vasoconstrictor:
* Adrenaline
* Angiotensin II
* Vasopressin
* Vasodilator:
* Adrenaline
* Atrial-natriuretic peptide
40
Describe the local regulation of arteriolar radius.
* Vasoconstrictor:
* Myogenic response
* Endothelin-1
* Vasodilator:
* Decreased O2
* K+
* CO2
* H+
* Adenosine
* Nitric oxide
* Bradykinin
41
Decribe laminar fluid flow.
* 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
Describe the effect of turbulence on fluid flow through a vessel.
* 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
Describe how Reynold's number (Re) is used to describe flow.
* 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
Describe the trend in blood pressure and flow throughout the CVS.
