Cardiac Output

Question 1

what is cardiac output, CO

Answer 1

the RATE at which a ventricle pumps blood out (L/min)

Question 2

what is heart rate

Answer 2

the NUMBER of contractions per min

Question 3

what is the equation for CO

Answer 3

CO= HR X SV

Question 4

what affects CO

Answer 4

intrinsic (affecting SV)= ventricular contractility, EDV, ESV, afterload
extrinsic (affecting HR)= hormones, autonomic innervation

Question 5

where is the autonomic headquarter for cardiac control

Answer 5

medulla oblongata

Question 6

what cardiac structures/ tissues do the para/symp divisions of the autonomic nervous system innervate

Answer 6

1. SAN/ AVN
2. atrial muscle cells
3. ventricular muscle cells

Question 7

what is another word for parasympathetic fibres and why

Answer 7

cranio-sacral

they are innervated by cranial nerves 3,7,9,10

Question 8

why is another word for sympathetic fibres and why

Answer 8

thoracolumbar

ganglia are located on either side of spine

Question 9

describe the effect of parasympathetic activity on the HR

Answer 9

parasympathetic neurones release Ach, opens chemically gated Na+ channels, decrease rate of depolarisation, increase length of repolarisation= decrease HR

Question 10

describe the effect of sympathetic activity on the HR

Answer 10

sympathetic neurones release NE, bind to beta 1 receptors, open na/cl ion channels, influx of +ve ions, decrease rate of depolarisation, shorten length of repolarisation= increase HR

Question 11

what is the affect of parasympathetic activity on the conducting system

Answer 11

decrease SPEED OF CONDUCTION, ventricles contract a longer while after atria contract, systole is longer

Question 12

what is the affect of sympathetic activity on the conducting system

Answer 12

increase the SPEED OF CONDUCTION, ventricles contract ASAP after atria, systole is shorter

Question 13

which hormones affect the HR

Answer 13

adrenaline

thyroid hormones: insulin, glucagon

Question 14

what is the affect of adrenaline on the HR

Answer 14

increase HR because….

• increases AP at SAN
• increases speed/ velocity of AP since its linked with sympathetic NS

Question 15

what is the affect of the thyroid hormones on the HR

Answer 15

increase HR because…

- increase the force of contraction

Question 16

what factors are affecting the HR

Answer 16

autonomic nervous system (para/sympathetic nerve fibres)

hormones (adrenaline and thyroid hormones)

Question 17

what factors affect the SV

Answer 17

ventricular contractility
EDV
afterload

Question 18

what is ventricular contractility

Answer 18

how forcefully the ventricle contracts

Question 19

what is afterload

Answer 19

the pressure the ventricle is contracting against (atrial pressure)

Question 20

which factors influence ventricular contractility

Answer 20

1. adrenaline
2. sympathetic NS
3. Ca2+ (linked with sympathetic NS stimulating alpha/beta receptors of cardiac cell membrane)

Question 21

which factors influence EDV

Answer 21

starlings law of heart

Question 22

what is the starling’s law of heart

Answer 22

when the RATE of which blood flows INTO the heart from the veins changes, the heart automatically ADJUSTS its OUTPUT to match INFLOW

(adjust the SV, so that CO matches the venous return)

Question 23

what are the affects of a high EDV on the cardiac muscle cell

Answer 23

1. increase in troponin affinity for ca2+, increases cross-bridges
2. a high EDV increases the length of cardiac muscle cells to optimum length for contraction

Question 24

what is the affect of sympathetic activity on the starlings curve

Answer 24

moves upwards, at any EDV

Question 25

what influences the EDV

Answer 25

pre-load aka end-diastolic-pressure

EDV is directly proportional to pre-load

Question 26

what is pre-load/ end-diastolic pressure

Answer 26

the pressure of blood inside the heart before a contraction

Question 27

which determines the pre-load/ end - diastolic pressure

Answer 27

• filling time

- atrial pressure (which is determined by atrial contraction, venous return)