11 The cardiovascular system

Question 1

Why do we need a circulating blood supply?

Answer 1

• 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)

Question 2

Blood flow (F) is determined buy which two factors?

Answer 2

• Resistance to flow (impedance)
• Pressure

F= P/R

Question 3

What effects blood impedance

Answer 3

• 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

Question 4

If the radius of the vessel is increased from 1cm to 2cm what happens to blood flow?

Answer 4

Impedance is reduced and blood flow increases from 1m/sec to 16ml/sec
(VR^4)

Question 5

What is the intra cardiac systolic pressure in the left ventricle?

Answer 5

120mmHg

Question 6

What is the intra cardiac systolic pressure in the right ventricle?

Answer 6

25mmHg

Question 7

What is the average arterial systolic pressure in adults?

Answer 7

120mmHg

Question 8

What is the average arterial diastolic pressure in adults?

Answer 8

80mmHg

Question 9

How do we work out the mean arterial pressure?

Answer 9

diastolic pressure + 1/3 pulse pressure (syst pressure -diast pressure)

Question 10

What is the Poiseuille-Hagen equation?

Answer 10

F=Change in pressure x (3.14r^4/Lñ)
radius^ x pi
Lenght x fluid viscosity

Question 11

What is the intra cardiac diastolic pressure in the left ventricle?

Answer 11

0mmHg

Question 12

What is the intra cardiac diastolic pressure in the right ventricle?

Answer 12

0mmHg

Question 13

Why do we use mean arterial pressure instead of systolic pressure?

Answer 13

-Its a better measure with less variation across individuals

Question 14

What is Darcys law?

Answer 14

describes the flow of fluid through a porous medium

F = P(difference)/R (blood flow)

Question 15

Which factor affecting blood flow effects peripheral circulation?

Answer 15

Pressure

Question 16

What happens in elastic arteries during diastole and systole?

Answer 16

-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

Question 17

What happens to blood pressure?

Answer 17

it increases

Question 18

What is the name of cardiac cells that contract themselves?

Answer 18

myogenic cells -these can cause arrythmia when some parts go freestyle

Question 19

What are the electrical events in the cardiac cycle?

Answer 19

SA node - distribution by conducting system (generates ECG)

Question 20

What are the timings/speeds of the electrical events in the heart?

Answer 20

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

Question 21

What is the basal rate of the SAN

Answer 21

spontaneous depolarisation causes basal rate of 80-100 beats per minute

Question 22

What is our normal heart rate and why?

Answer 22

60-70 bpm
parasympathetic system acts on the heart to slow it down from 80-100bpm
via the vaygus nerve

Question 23

What are the mechanical events of the heart?

Answer 23

systole and distole

Question 24

What is the duration of the cardiac cycle?

Answer 24

800ms

Question 25

What takes up the most of the cardiac cycle?

Answer 25

Diastole

Question 26

What are the phases of ventricular contraction?

Answer 26

early - valves shut

late -blood forced out