C3.10 - Mammalian Heart

About the Heart

Pumps blood through 160,000 km of blood vessels
Beats 90k times / day, every day throughout person’s lifetime
Heartbeat consists of…
- systole: rhythmic contraction
- diastole: relaxation of myocardium
myocardium: entire cardiac muscle

Diagram of the heart incl. bloodflow

4-chambered heart: L/R atria and ventricles
atria: receive blood from veins and pumps them into ventricles
ventricle: receive blood from atria and pumps them away from heart
Two atria contract simultaneously
- little pressure generated
Two ventricles contract simultaneously shortly after
- high pressure generated
mitral / bicuspid valve: two-part valve that separates left atrium and l. ventricle
tricuspid valve: 3-part valve that separates right atrium and r. ventricle
atrioventricular valves: valves located between atria and ventricles
- two valves listed above
- soft “lub” sound
semilunar valves: 2 valves that prevent blood flowing back from…
- r. ventricle and pulmonary artery
- l. ventricle and aorta
- louder “dub” sound
- pulmonary valve between r. ventricle and pulmonary art.
- aortic valve: between l. ventricle and aorta
Deoxygenated blood from body collected by superior and inferior vena cava
R. atrium contracts pumping blood to r. ventricle
R. ventricle contracts and pumps blood to lungs through pulmonary artery
Oxygenated blood in pulmonary veins returns to heart via l. atrium
L. atrium contracts and sends oxygenated blood to l. ventricle
L. ventricle contracts and pumps blood out through aorta

Bloodflow circuits

pulmonary circuit: pathway of blood where blood travels from R. side of heart to lungs

R. atrium → R. ventricle → pulmonary artery → lungs → pulmonary vein → l. atrium

Here, artery has deox. blood and vein has ox. blood

L. atrium → l. ventricle → aorta → body → vena cava → r. atrium

coronary arteries: pair of arteries branching from the aorta to supply heart muscle with necessary nutrients

Pacemaker

Heart continues to beat when body is asleep / unconscious
Heartbeat self-regulated
sinoatrial (S-A) node: natural “pacemaker” of heart
- originates in bundle of fibres in r. atrium
- fires and contracts atria
- controlled by both nervous and endocrine system
- hormones: chemical messengers of the body
Impulse / cardiac action potential spreads to atrioventricular (A-V) node
Ventricles contract
Bundle of His and Perkinje fibres aid in spread of cardiac action potentials

Parts of an ECG

Parts of an ECG

electrocardiodiagram (ECG / EKG): graph that measures change in voltage between electrical signals of “pacemaker”
$P$ : contraction of atria
$Q$ to $S$ : contraction of ventricles, repolarization of atria (immeasurable)
$T$ : repolarization of ventricles before next firing
Random contractions of heart cause fibrillation
defibrillator: device that applies strong electrical current to heart which may reset the pacemaker
- WILL NOT start a stopped heart
Noradrenaline causes SA node to fire more rapidly
Acetylcholine slows SA node firing
Both released through impulses gen. in medulla oblongata

Defibrillator

Defibrillator