11 The cardiovascular system Flashcards
Why do we need a circulating blood supply?
- to maintain a supply of nutrients and signalling molecules and to remove waste from all bodily tissues
- to maintain pressure differences across tissues for capillary exchange
- to supply varying blood supplies to tissues depending on their need (e.g. digestion/exercise)
Blood flow (F) is determined buy which two factors?
- Resistance to flow (impedance)
- Pressure
F= P/R
What effects blood impedance
- length of vessel
- viscosity of blood (protein content)
- radius of the vessel (most important) - becasue small changes to the vessel radius have large impact on the flow rate
If the radius of the vessel is increased from 1cm to 2cm what happens to blood flow?
Impedance is reduced and blood flow increases from 1m/sec to 16ml/sec
(VR^4)
What is the intra cardiac systolic pressure in the left ventricle?
120mmHg
What is the intra cardiac systolic pressure in the right ventricle?
25mmHg
What is the average arterial systolic pressure in adults?
120mmHg
What is the average arterial diastolic pressure in adults?
80mmHg
How do we work out the mean arterial pressure?
diastolic pressure + 1/3 pulse pressure (syst pressure -diast pressure)
What is the Poiseuille-Hagen equation?
F=Change in pressure x (3.14r^4/Lñ)
radius^ x pi
Lenght x fluid viscosity
What is the intra cardiac diastolic pressure in the left ventricle?
0mmHg
What is the intra cardiac diastolic pressure in the right ventricle?
0mmHg
Why do we use mean arterial pressure instead of systolic pressure?
-Its a better measure with less variation across individuals
What is Darcys law?
describes the flow of fluid through a porous medium
F = P(difference)/R (blood flow)
Which factor affecting blood flow effects peripheral circulation?
Pressure
What happens in elastic arteries during diastole and systole?
-during systole they stretch as they fill with blood and during diastole the elastic fibres recoil/muscular contracaction pushing blood round the body therefore maintaining a constant blood flow despite pressure fluctuations in the heart
What happens to blood pressure?
it increases
What is the name of cardiac cells that contract themselves?
myogenic cells -these can cause arrythmia when some parts go freestyle
What are the electrical events in the cardiac cycle?
SA node - distribution by conducting system (generates ECG)
What are the timings/speeds of the electrical events in the heart?
Atria –> AV node 1 m/s
Av node –> bundle of his 0.5m/s
Bundle of his –> ventricular myocardium 5m/s
in the ventricular myocardium 1m/s
What is the basal rate of the SAN
spontaneous depolarisation causes basal rate of 80-100 beats per minute
What is our normal heart rate and why?
60-70 bpm
parasympathetic system acts on the heart to slow it down from 80-100bpm
via the vaygus nerve
What are the mechanical events of the heart?
systole and distole
What is the duration of the cardiac cycle?
800ms
What takes up the most of the cardiac cycle?
Diastole
What are the phases of ventricular contraction?
early - valves shut
late -blood forced out
