7.3 Heart Beat & Contraction

Heart beats are generated by

Action potentials

Heart beats are generated at

the SA node (right atrium)

We use ______ to record electrical impulses/changes of the heart

EKG

EKG’s have 3 parts

• P waves = depolarization/contraction of atria

• QRS = Ventricular depolarization/contraction

• T = ventricular repolarization/ventricles relax

Cardiac cycle consists of

systole and diastole

• these are used to help take your blood pressure

Systole

phase of contraction

Diastole

phase of relaxation

Steps of cardiac cycle

1. relaxation

2. Atrial Systole

3. Ventricular Systole

Heart beat sounds consist of

lub and dub

lub

first sound, its the closing of the AV valves (tricuspid and mitral), which starts as systole

Dub

2nd sound, its short and its the closing of the pulmonary and aortic valves which starts diastole.

Pulse

is the ejection of blood from the left ventricle of the heart during each contraction, you feel it in your arteries

• can be used to determine heart rate.

• easiest to find are radial artery at wrist and carotid artery

Heart rate is determined

at rest

Tachycardia

rapid rest rate (more than 100 bpm)

Bradycardia

slow rest rate (less than 50 bpm)

Fetal Circulation

• breathing and digestion are carried out by the mother till birth

• gas exchange is delivered through the placenta

• lungs are collapsed in womb, open at birth

• fetal heart has a fossa ovale which allows blood to bypass the lungs

  • closes at birth.