Cardiac Cycle

Question 1

Cardiac Cycle Def

Answer 1

Start of 1 beat to the start of the next. Complete cycle of heart activity

Question 2

Systole Def.

Answer 2

Ventricular contraction. 2/5 of cycle at rest (increases during activity)

Question 3

Diastole Def.

Answer 3

Ventricular Relaxation. 3/5 of cycle at rest

Question 4

Cardiac Muscle (cardiomyocytes) Features

Answer 4

myogenically (involuntarily) active, irregular fibre shapes, mostly signle nucleate (some binucleated), straited, contain gap junctions (intercalated disks). Sponatneously active (operate seperate to extrinsic signalling)

Question 5

Intercalated disks function

Answer 5

Separate the heart into 2 syncytia. The 2 Atria and the 2 Ventricles. Current flows through interlacted disks after depolaristion to stimulate adjacent cell

Question 6

SA node outline

Answer 6

Cation leaky membrane keeps RMP at ~ -55mV. Gets depolarised by slow Na+ influx. Depolarises ar ~ -40mV opening Ca channels. 200 msecs later (time dependent) Ca channels close and K+ eflux occurs. Generates action potential sent onto rest of cells

Question 7

Extrinsic control of SA node

Answer 7

Autonomic nervous system

Question 8

SA node receptors

Answer 8

Beta1-ARs (sympathetic, increases cAMP) and M2 Receptors (parasympathetic, decreases cAMP)

Question 9

Relationship between cAMP and Na influx

Answer 9

Increased cAMP = Icreased Na influx

Question 10

Heart Conduction Pathway

Answer 10

Depolarisation starts at SA node in right atrium, depolaristaion flows through left and right atria, depolarisation reaches AV node and slows (no direct connectrion between atria and ventricles), depolarisation occurs in ventricles from AV nose down His bundles and Purkinje fibres, spreads slowly from endocardium to epicardium

Question 11

Reason why action potential travels through AV nose before

Answer 11

Delay allows for complete ventricular filling and limits transmission of abnormal rhythms

Question 12

Function of Ca channels opening during repolarisation

Answer 12

Creates plateau phase. Allows full contraction and relaxation of heart before next action potential (prevents tetanic contraction). This and period causes rhythmic contractions

Question 13

Cardiac Vessels Outline

Answer 13

Account for pressure changes in vessels and compartments of heart

Question 14

Diastole Ventricular Pressure Outline

Answer 14

Drops to 0mmHg, chamber enlarges (relaxes) counteracting pressure from atrium filling. As ventricle fills with blood from atrial systole, ventricular pressure rises

Question 15

Systole Ventricular Pressure Outline

Answer 15

Pressure rises as Ventricle contracts (AV valves close). Ventricle pressure exceeds atrial pressure and blood is ejected out of heart (higher volume out of left). Pressure drops until AV valves open beginning next cycle

Question 16

Diastole Ventricular Volume

Answer 16

Fills passively due to low ventricular pressure. Atria contraction occurs at end of diastole delivering final 25% of blood ventrical volume

Question 17

Systole Ventricular Volume

Answer 17

No ejection at systole start (hasn’t yet exceeded aortic/pulmonary pressure). Ejection begins rapid, slowing at systoles end. As pressure drops, filling begins again

Question 18

Electro-cardiogram (ECG) Outline

Answer 18

Shows electrical changes in heat over cycle

Question 19

ECG P-wave outline

Answer 19

Atria depolarisation. Starts at SA node moves through atria. Sinus rhythm

Question 20

ECG QRS complex

Answer 20

Ventricular depolarisation. Depolarisation spreads from epi to endocardium

Question 21

ECG T Wave

Answer 21

Ventricular repolarisation. Same direction as depolarisation (epi to endo cardium). Both charge and direction of current is reversed

Question 22

ECG PR Interval

Answer 22

Conduction through AV node. Conduction slows. Falls in range 0.2>x>0.12 secs

Question 23

ECG QT Interval

Answer 23

Ventricular Systole. Time taken for ventricular depolarisation and repolarisation. Heart rate dependent. Shorter at faster rates

Question 24

ECG ST Segment Outline

Answer 24

Interval between ventricular depolarisation and repolarisation

Question 25

1st Hear Sound

Answer 25

Lubb. Long and low. Closing of mitral and tricuspid valve

Question 26

2nd heart sound

Answer 26

Dub. Short. Closing of semilunar valves

Question 27

3rd heart sound

Answer 27

Transition between different rates of ventricle filling. Healthy

Question 28

4th sound

Answer 28

Stiff ventricle filling diring atrial systole. Elderly

Question 29

Murmurs Def

Answer 29

Outflow through narrowed (stentoic) valves and retrogade flow through leaky valves