Cardiac function and BP

Question 1

skeletal muscle
(striated)

Answer 1

• muscle cells made up of sarcomeres that contain thick filaments (myosin)
  and thin filaments (actin)
• shortening of sarcomere occurs via sliding filament mechanism, where actin filaments slide along adjacent myosin filaments

Question 2

cardiac muscle

Answer 2

• acts like a syncytium
• a wave of depolarisation os followed by atrial and ventricular contraction

Question 3

syncytium

Answer 3

a single, multi - nucleated cell formed from many fused cells

Question 4

cardiac excitation

Answer 4

• 1% cardiac cells - with pacemaker activity
• 99% cardiac cells - contractile function -> within ventricular tissue

Question 5

SA node

Answer 5

• sinoatrial node - natural pacemaker of the heart
• a specialised region in the right atrial wall at the junction between the superior vena cava and the right atrium
• they generate heart beats
• they don’t have a resting potential

Question 6

SA Node phases

Answer 6

phase 0 : upstroke of action potential is less steep than myocyte
phase
phase 3 : plateau is not sustained
phase 4 : membrane potential deviates from K+ equilibrium potential

Question 7

cardiac excitation purpose

Answer 7

allows atria to contract and empty blood into ventricles

Question 8

why does excitation spread rapidly down the bundle of His & Purkinje fibres

Answer 8

to ensure almost simultaneous activation of ventricular cells

Question 9

4 events of cardiac excitation

Answer 9

only 3 are visible
1. atrial depolarisation (P wave)
2. Ventricular depolarisation (QRS complex)
3. Ventricular repolarisation (T wave)

Question 10

atrial systole

Answer 10

A-V valves open and atria empty blood into ventricles
- atrial excitation and contraction should be complete before onset of ventricular contraction

Question 11

ventricular systole

Answer 11

1. ventricles contract -> rise in pressure closes A-V valve
2. pressure in ventricle rises above aortic pressure -> aortic valve opens and blood is ejected from heart

Question 12

ventricular diastole

Answer 12

1. pressure in ventricles falls below aortic pressure -> aortic valve closes
2. pressure in ventricles falls below atrial pressure -> AV valve opes and filling begins

Question 13

stroke volume influences

Answer 13

1. end diastolic volume
2. aortic pressure
3. contractility

Question 14

end diastolic volume (preload)

Answer 14

• resting cardiac muscle stretched prior to contraction
• venous tone, blood volume, posture, intrathoracic pressure

Question 15

aortic pressure (after load)

Answer 15

• pressure against which the heart must work to eject blood during systole
• aortic stiffness, periooheral resistance , blood volume

Question 16

contractility

Answer 16

• strength and vigour of the heart’s condition during systole at a given preload and after load
• increased by sympathetic nerve stimulation and circulating catecholamines
• decreased by hypoxia, acidosis, infarction

Question 17

heart rate influences

Answer 17

intrinsic rate
SNS - increase in heart rate
PNS- decrease in heart rate

Question 18

intrinsic rate

Answer 18

heart can initiates own heart beat in the absence of any nervous or hormonal control

Question 19

systole

Answer 19

heart contracting
systolic blood pressure = 120 mmHg

Question 20

Diastole

Answer 20

heart relaxing
bp = 80mmHg

Question 21

what is systolic blood pressure (SBP) determined by

Answer 21

stroke volume(StV) -> increases in StV will increase in SBP
aortic elasticity -> decreases in elasticity will also increase SBP

Question 22

Diastolic blood pressure (DBP)

Answer 22

pressure within the arteries during the period when the heart is not beating, as the heart fills with blood

Question 23

what is DBP determined by

Answer 23

1. peripheral resistance (TPR) increases in TPR, increase DBP
2. Aortic elasticity -> decreases in elasticity will decrease DBP
3. heart rate -> decreases in HR will decrease DBP

Question 24

stroke volume =

Answer 24

end diastolic volume - end systolic volume

Question 25

pulse pressure =

Answer 25

systolic BP - diastolic BP

Question 26

mean BP =

Answer 26

diastolic BP + 1/3 pulse pressure

Question 27

resistance =

Answer 27

pressure difference/ flow

Question 28

vasoconstriction relationship w vessel radius

Answer 28

decrease in diameter increased resistance

Question 29

vasodilation relationship w vessel radius

Answer 29

increase in diameter decreased resistance

Question 30

what happens if bp is too low

Answer 30

inadequate supply of oxygen and nutrients to tissues

Question 31

what happens if bp is too high

Answer 31

excessive strain on the heart and increased risk of vascular damage

Question 32

how to effectively control bp

Answer 32

1. effector mechanisms -> ANS 2. pressure sensors -> baroreceptors 3. Central integration -> CNS cardiovascular centres

Question 33

what does sympathetic stimulation lead to

Answer 33

vasoconstriction and increased total peripheral resistance

Question 34

what is a baroreceptor

Answer 34

pressure sensors

Question 35

where are baroceptosr located

Answer 35

located in the walls of major arteries

Question 36

how does the body react to a fall in bp

Answer 36

- sensed by baroreceptors - afferent input to CNS CVS - info centrally integrated - efferent output via ANS - increased sympathetic drive to heart - increase heart rate abdominal TPR