Heart Anatomy and Physiology

Building a Heart

The human heart is an extraordinary machine, and like any
machine it has several components enabling it to operate.
Let’s take a look at them!

The most basic component of the
heart is its role as a four-chambered
muscle.

The top two chambers are the atria and the
bottom two are the ventricles.

The right atrium receives deoxygenated blood
and empties it into the right ventricle; the left
atrium empties oxygenated blood into the left
ventricle.

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In order to pump blood in and out of the
chambers, the heart needs doors.

The heart’s valves open and shut, regulating the
amount of blood that enters and its destination.

At the bases of the pulmonary
artery and aorta are the
semilunar valves, which
support one-way flow of blood
out of the ventricles. The aortic
valve regulates blood flow
from the left ventricle into the
aorta, while the pulmonary
valve regulates the flow from
the right ventricle into the
pulmonary trunk.

The atrioventricular valves
control the blood flow from
the right atrium to the right
ventricle. They are attached
to papillary muscles by
fibrous cords called chordae
tendineae, which prevent the
AV valves from prolapsing back
into the atria as they close.

The external surface of the heart is also
known as epicardium, and is covered by
fat.

Factoid: It is completely normal to have some
fat on the surface of the heart. It’s when the fat
builds up on the surface or within the arteries that
there’s a problem.

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The great vessels connect the heart to
the arteries and veins, which distribute
blood throughout the body.

The great vessels are:
• The aorta
• The pulmonary trunk
• The vena cavae

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The aorta delivers oxygenated blood from
the left ventricle to the rest of the body.

Factoid: The aorta is approximately 2-3 cm
in diameter, making it thicker than a standard
garden hose!

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The pulmonary trunk delivers
deoxygenated blood from the right
ventricle to the lungs.

At the aortic arch, the pulmonary trunk splits
into the pulmonary arteries, which extend into
the lungs.

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The venae cavae deliver deoxygenated
blood from the top and lower halves of the
body, respectively, to the right atrium.

Factoid: The vena cavae are the largest veins in the
entire body.

The heart’s conduction system does
exactly what it sounds like: it conducts
electricity throughout the heart.

The pulses of electricity motivate the cardiac
muscle to contract, or beat.

The pathways of the conduction system are
made up of bundles and specialized muscle
fibers within the heart. Electrical signals move
down these pathways.

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Not only does the heart provide blood
for the body’s organs and tissues, but
also for itself. The coronary vessels
supply blood to the heart.

The arteries supply the heart with blood, while
the veins carry deoxygenated blood from the
heart tissue into the right atrium.

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Pulmonary vasculature manages
the passage of blood between the
heart and the lungs, as well as
gas exchange.

Pulmonary arteries move deoxygenated
blood
from the right ventricle to the lungs.

Pulmonary veins move oxygenated blood to
the
left atrium for distribution.

Factoid: The pulmonary arteries are the
only arteries in the body that carry venous
blood!

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Because the heart is super important,
it has a protective fibrous sac around it
called the pericardium.

There are several layers of pericardium: the
fibrous pericardium (the outer layer), the serous
pericardium (which has two layers of its own, the
parietal and visceral layers), and the fluid-filled
space between the serous pericardium’s layers.

Factoid: The fluid between the parietal and
visceral layers reduces friction on the heart as it
beats.

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Systemic vasculature manages
blood flow to other organs and tissues
throughout the body.

Factoid: Everyone has enough vasculature to
wrap around the Earth 2.4 times!

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