Cardiac output (Pt1): Electrical events and heart rate

Question 1

CO =

Answer 1

HR x SV

Question 2

Heart rate is driven by

Answer 2

waves of electrical activity that induce cardiac muscles to contract

Question 3

2 types of pacemaker cells

Answer 3

ones in the AV node and SA node

Question 4

AV node

Answer 4

connects atria and ventricles and delays the signal for 0.1ms- allows atria to contract before ventricles

Question 5

Bundle of His

Answer 5

Fast conducting myocytes that connnect to the Purkinje fibres, only way activity can pass to the ventricles

Question 6

Myocyte

Answer 6

cardiac muscle cell

Question 7

Purkinje fibres- why are they wide

Answer 7

Wide allowing rapid conduction throughout the ventricle and simultaneous contraction of ventricles

Question 8

Purkinje fibres are

Answer 8

nerves

Question 9

Atrial excitation involves

Answer 9

SA node

Question 10

ventricular excitation involves

Answer 10

AV node

Question 11

what causes pacemaker cells of the SA node to trigger an AP

Answer 11

Low RMP

Na+ leakage, leading to depolarisation

Question 12

Mechanism for APs in pacemaker cells of the SA node

Answer 12

sodium ions leaking in through the F type channels and calcium ions moving in through the T type (transient) channels cause a threshold graded depolarisation.
Rapid opening of calcium L-type channels responsible for rapid depolarisation
Reopening of K+ channels and closing o calcium channels responsible for repolarisation.

Question 13

What is the overall driver of heart rate

Answer 13

SA node, overrides AV and purkinje fibres

Question 14

Mechanism for contraction of ventricular myocytes

Answer 14

Rapid opening of VGNC responsible for rapid depolarisation phase
Prolonged ‘plateau’ of depolarisation (contraction) due to slow but prolonged opening of VGCCs and closure of K+ channels
Opening of K+ results in repolarisation

Question 15

How does calcium produce contraction of cardiac muscle

Answer 15

excitation-contraction coupling

Entry of extracellular ca ions causes release of Ca from sarcoplasmic reticulum by binding to ryanodine receptors

Question 16

Why does cardiac muscle have a long refractory period

Answer 16

Allows ventricles to fill prior to pumping

Question 17

vagus nerve (parasympathetic)

Answer 17

decr heartbeat

Innervates just SA and AV nodes

Question 18

Sympathetic ganglia

Answer 18

incr heartbeat (also regulate force/SV)
Innervates whole heart

Question 19

What do parasympathetic and sympathetic nervous system regulate

Answer 19

rate of depolarisation in the SA node

Question 20

At rest which one dominates

Answer 20

Parasympathetic

Question 21

Parasympathetic mechanism

Answer 21

Parasympthetic neurones release Ach
acts upon m2 muscarinic receptors of SA node
Incr K+ efflux, decr Ca influx
Hyperpolarises cell and decr rate of depolarisation
decr HR - bradycardia

Question 22

Sympathetic mechanism

Answer 22

Release noradrenaline
acts upon B1 adrenergic receptors of SA node
Incr NA+ and Ca2+ influx 
Incr rate of depolarisation
Incr heart rate
Tachycardia

Question 23

ECG

Answer 23

measures electrical activity of the heart

Summation of the spread of APs throughout the heart

Question 24

P

Answer 24

atrial depolarisation

Question 25

QRS

Answer 25

ventricular depolarisation

Question 26

T

Answer 26

ventricular repolarisation

Question 27

PQ

Answer 27

length of atrial contraction

Question 28

QT

Answer 28

length of ventricular contraction

Question 29

ECG provides info on

Answer 29

``` HR rhythm disturbances of rhythm and conduction (arrhythmia, pacemaker) conduction velocity orientation of heart relative size of chambers Condition of tissue within the heart Damage to myocardium Drugs ```

Question 30

Inspiration

Answer 30

faster PQRST closer together decr in vagal parasympathetic activity> incr in heart rate

Question 31

Expiration

Answer 31

Slower PQRST further apart Vagal paraympathetic activity increase> heart rate decrease

Question 32

sinus arrythmia

Answer 32

bnormal heart rhythms that start at the sinus node

Question 33

Third degree

Answer 33

complete failure of conduction atria to ventricles | beat independently

Question 34

Ventricular etopic beat

Answer 34

Aberrant firing of myocytes in ventricles-ill synchronised and fails to eject blood Common after heart attacks

Question 35

ventricular fibrillation result

Answer 35

Random firing Fibrillating ventricles can't pump blood Fatal

Question 36

Ventricular fibrillation caused by

Answer 36

Myocardial infarction Electric shock Drug intoxication Impaired cardiac metabolism