Chapter 20:

The Cardiovascular System:

The Heart

Video

■ Heart surgery in short -

https://youtu.be/MxP2cMgPx5s

■ Khan Academy The Heart:

https://youtu.be/7XaftdE_h60

Layers of the Heart Wall

1. Superior vena cava –

deoxygenated blood from the

anterior (head and chest).

2. Inferior vena cava –

deoxygenated blood from the

posterior (legs).

3. Right/left coronary artery –

oxygenated blood to the heart

muscle.

4. Cardiac veins –

deoxygenated blood from the

heart.

Pericardium and Heart Wall

Layers of the Heart Wall

1. Epicardium

(external layer)

2. Myocardium

❑ 95% of heart is

cardiac muscle

3. Endocardium (inner

layer)

❑ Smooth lining for

chambers of heart

Structure of the Heart

2 atria – receiving chambers

Auricles increase capacity

2 ventricles – pumping chambers

Internal Anatomy of the Heart

Right Atrium

❑ Receives blood from

■ Superior vena cava

■ Inferior vena cava

❑ Blood passes through

tricuspid valve (right

atrioventricular valve)

into right ventricle

Right Ventricle

■ Receives blood from

the right atrium.

■ Blood leaves through

pulmonary valve

(pulmonary semilunar

valve) into pulmonary

trunk and then right and

left pulmonary arteries

Left Atrium

❑ Receives blood from

the lungs through

pulmonary veins

❑ Passes through

bicuspid valve (aka

mitral valve aka left

atrioventricular valve)

into left ventricle

Left Ventricle

❑ Thickest chamber of the heart

❑ Blood passes through aortic valve (aortic semilunar valve) into ascending aorta

❑ Some blood flows into coronary arteries,remainder to body

Myocardial thickness

❑ Right ventricle pumps

blood to lungs

■ Shorter distance, lower

pressure, less

resistance

❑ Left ventricle pumps

blood to body

■ Longer distance,

higher pressure, more

resistance

Copyright 2009, John Wiley & Sons, Inc.

Fibrous skeleton

Copyright 2009, John Wiley & Sons, Inc.

Systemic and pulmonary

circulation - 2 circuits in series❑ Systemic circuit

■ Left side of heart

■ Receives blood from lungs

■ Ejects blood into aorta

Systemic and pulmonary

circulation - 2 circuits in series❑ Pulmonary circuit

■ Right side of heart

■ Receives blood from systemic circulation

■ Ejects blood into pulmonary trunk then to pulmonary arteries

■ Gas exchange in pulmonary capillaries

■ Pulmonary veins takes blood to left atrium

Autorhythmic Fibers

❑ Specialized cardiac

muscle fibers

❑ Repeatedly generate

action potentials that

trigger heart

contractions

❑ 2 important functions

1. Act as pacemaker

2. Form conduction

system

Conduction System

■ SA node acts as

natural pacemaker

❑ Faster than other

autorhythmic fibers

❑ Initiates 100 times per

second

Conduction System

■ Nerve impulses from

autonomic nervous

system (ANS) and

hormones modify

timing and strength

of each heartbeat

Heart Sounds

■ Auscultation

■ Sound of heartbeat

comes primarily from

blood turbulence

caused by closing of

heart valves

■ 4 heart sounds in each

cardiac cycle – only 2

loud enough to be

heard