applied animal and health welfare - conduction system and output

cardiac cycle

Contraction and relaxation of heart muscle

Systole –

contracting causing chamber to empty

Diastole –

relaxing and repolarising following contraction allowing chamber to fill with blood

impulse for

heartbeat comes from sinoatrial (SA) node

located in wall of right atrium

pacemaker

charged atoms - cation

positively charged -

sodium (na+)

potassium (k+)

calcium (ca++)

anions

negatively charged

chloride (cl-)

polarisation

A SA node generates electrical current

-by movement of cations across the outer membranes of its cells

Cations are pumped out of the cell in a process called polarisation

• results in outside of the cell having more positive charge than the inside

depolarisation- gates in

cell wall opened

cations fow into cell to equalise charge on either side of cell membrane

depolarisation generates an electrical current

-causes heart muscle to contract

systole

repolarisation

SA node automatically repolarises itself

then depolarises again

diastole

cardiac cycle - 1) pacemaker generates

wave of signals to contract

2 signals are delayed

at AV node

3)signals pass

to heart apex

4) signals spread

throughout ventricles

electrocardiogram (ECG/EKG)

Cardiac currents are the result of an electrical impulse

An instrument that detects electrical currents may be used to measure electrical activity of the heart

Electrocardiograph

Measures electrical current using metal electrodes attached to the skin

To produce an electrocardiogram

Correct lead placement vital

RED-

yellow-

green

black

N.B. In the UK, most commonly:

Red = Right forelimb

Yellow = Left forelimb

Green = Left hindlimb

Black = Right hindlimb

heart rate

Heart has to move adequate amount of blood to tissues in body

•To deliver oxygen and nutrients

•To remove waste products

heart must maintain sufficient

cardiac output to adequately perfuse tissues and meet these aims

heart rate and cardiac output

stroke volume

cardiac output

heart rate

calculation including

Cardiac Output (CO) = Stroke Volume (SV) x Heart Rate (HR)

larger animals have

larger stroke

slower

much greater tissue

larger hearts

volumes

-more blood pumped per beat

heart rates

mass to supply

heart rate based

in part on rate which SA node spontaneously depolarises

many factors can influence cardiac output and heart rate

stroke volume is a measure of

the volume of blood ejected from the left ventricle during one   contraction or sytole

. If the cardiac output and stroke volume both decrease what has happened to the heart rate to maintain equilibrium?

  it will increase

How could mitral valve stenosis affect the stroke volume?

Mitral valve stenosis impairs left ventricular filling, so there is a decrease in diastolic volume. This leads to a decrease in stroke volume.