week 5: cardiac physiology: cardiac output, blood pressure and flow

Question 1

cardiac output

Answer 1

volume of blood pumped out by each ventricle per unit time
most common unit: litres per min

Question 2

cardiac output (CO)=

Answer 2

heart rate (HR) x stroke volume (SV)

Question 3

stroke volume depends on

Answer 3

body size

Question 4

cardiac index

Answer 4

normalises SV to body surface area

Question 5

normal resting cardiac index

Answer 5

3.2 Lmin-1 m-2

Question 6

SA node innervated by both

Answer 6

sympathetic and parasympathetic branches of the autonomic nervous system

Question 7

noradrenaline

Answer 7

transmitter released by postganglionic S fibres

Question 8

what transmitters do P fibers release

Answer 8

acetylcholine (ACh)

Question 9

noradrenaline and acetylcholine action

Answer 9

act to change and regulate heart rate

Question 10

sympathetic effects are mediated via

Answer 10

B1 adrenoceptors

Question 11

Parasympathetic effects are mediated via

Answer 11

muscarine receptors

Question 12

increase in sympathetic nerve firing

Answer 12

increase in heart rate
tachycardia

Question 13

increase in parasympathetic nerve firing

Answer 13

decrease in heart rate
bradycardia

Question 14

dominant tone in resting state

Answer 14

parasympathetic

Question 15

intrinsic firing rate on SA node and therefore intrinsic frequency of a de-innervated heart

Answer 15

100 bpm

Question 16

what is heart rate determined by

Answer 16

pacemaker potential of the SA node cells

Question 17

stroke volume

Answer 17

vol of blood ejected out each ventricle per heartbeat
vol of blood in ventricle at end of diastole - volume og blood remaining at end of systole
end-diastolic vol - end systolic vol

Question 18

ejection fraction

Answer 18

fraction of the EDV ejected during the subsequent ventricular contraction
EF= SV/ EDV
(end-diastolic vol)
referred to as the pre-load

Question 19

end-systolic volume determined by

Answer 19

contractility of the ventricular muscle and the diastolic aortic blood pressure

Question 20

diastolic aortic blood pressure termed

Answer 20

afterload- resistance to blood ejection

Question 21

at the cellular level, strength of contraction depends on

Answer 21

initial sarcomere length and overlap of actin and myosin filaments

Question 22

The Frank Sterling law

Answer 22

strength of contraction depends on the initial degree of stretch: within the physiological range, stretching ventricular muscle leads to an increased force in contraction

Question 23

what does initial stretch depend on

Answer 23

end-diastolic volume (pre-load)

Question 24

determinants of end-diastolic volume

Answer 24

venous return

Question 25

what does venous return depend on

Answer 25

pressure in the large veins returning blood to the heart, the central venous pressure (CVP)

Question 26

central venous pressure can be influenced by

Answer 26

1. blood volume increased blood volume= increased CVP) 2. postural changes 3. respiratory and skeletal muscle pumps ( aid venous return and increase CVP) 4. vasoconstriction ( via increased sympathetic activity)

Question 27

extrinsic regulation of stroke volume comes from

Answer 27

autonomic nervous system

Question 28

what control is autonomic regulation of SV under

Answer 28

sympathetic: little parasympathetic innervation of the ventricular myocardium

Question 29

during action potential, B1 adrenoreceptors

Answer 29

increase level of cytosolic Ca2+ in ventricular myocytes (EC coupling)

Question 30

increasing levels of Ca2+ in ventricular myocytes

Answer 30

increases contractility of myocardium at any given length (starling curve shifted up) resulting in greater stroke volume from any given end diastolic volume

Question 31

blood flows down

Answer 31

pressure gradient

Question 32

pressure results

Answer 32

when flow is opposed by resistance

Question 33

steepest drop in pressure

Answer 33

occurs across arterioles, where the greatest resistance to blood flow occurs

Question 34

dicrotic notch (after phase 1)

Answer 34

closure of the aortic semilunar valve

Question 35

phase 1

Answer 35

diastole no blood enters aorta from left ventricle aortic vol and pressure decline to minimum

Question 36

typical systolic blood pressure (left)

Answer 36

120mmHg highest arterial pressure corresponds to the systolic phase of the cardiac cycle

Question 37

typical diastolic pressure (left)

Answer 37

80 mmHg lowest arterial pressure, corresponds to the diastolic phase of the cardiac cycle

Question 38

pulse pressure

Answer 38

40 mmHg systolic pressure- diastolic pressure

Question 39

mean arterial pressure

Answer 39

diastolic + (pulse pressure/3) typical 93mmHg

Question 40

Darcys law

Answer 40

in the steady state, fluid flow between 2 points is equal to the difference in pressure between the 2 points divided by resistance to flow flow=(p1-p2)/R analogous to OHms law for electrical current I=V/R

Question 41

Relating systemic circulation to Darcys law

Answer 41

flow= left ventricular output (ie CO) P1-P2= aortic pressure- right atrial pressure (effectively the MAP) R= The total resistance to flow imposed by all the blood vessels in the systemic circulation ( the total peripheral resistance, TPR, or systemic vascular resistance, SVR) hence CO=MAP/TPR can be rearranged

Question 42

what determines total peripheral resistance

Answer 42

resistance to a steady flow along a straight cylindrical tube is proportional to tube length and fluid viscosity and inversely proportional to tube radius ^4 the smaller the radius, the greater the resistance

Question 43

poiseuille's Law

Answer 43

combing P definition of resistance with Darcy's law of flow derive expression for flow throughout blood vessel flow=(P1-P2) X pi xr^4/ 8n xL

Question 44

arteriolar walls contain

Answer 44

high proportion of circularly arranged smooth muscle

Question 45

arteriolar radius under the influence of

Answer 45

sympathetic nervous system metabolic and myogenic autoregulatory influences

Question 46

what does metabolic autoregulation during exercise lead to

Answer 46

vasodilation in vascular beds of active skeletal muscle and heart leads to large increase in blood flow to skeletal muscle

Question 47

what is vasoconstriction mediated by

Answer 47

sympathetic nervous system

Question 48

what does vasoconstriction lead to

Answer 48

decrease in blood flow to the splanchnic and renal vasular beds

Question 49

active hyperaemia

Answer 49

diversion of blood to active muscles

Question 50

baroreceptors

Answer 50

receptors that are sensitive to changes in pressure

Question 51

what do arterial baroreceptors detect

Answer 51

degree of stretch in blood vessel wall mechano-receptor

Question 52

arterial baroreceptors are

Answer 52

sprays of non-encapsulated nerve endings in the adventitial layer of the arterial walls in the carotid sinus and the aortic arch

Question 53

baroreceptor afferents nerve fibers project to the

Answer 53

medulla oblongata main CV control centre

Question 54

increase in baroreceptor discharge firing rate leads to

Answer 54

increase in parasympathetic signalling decrease in sympathetic stimulation of heart decreased sympathetic stimulation of systemic arterioles and veins