Cardiology

Anatomy

The Cardiovascular System

Your heart and circulatory system make up your cardiovascular system.
Your heart works as a pump that pushes blood to the organs, tissues, and cells
of your body. Blood delivers oxygen and nutrients to every cell and removes the
carbon dioxide and waste products made by those cells. Blood is carried from
your heart to the rest of your body through a complex network of arteries,
arterioles, and capillaries. Blood is returned to your heart through venules and
veins. If all the vessels of this network in your body were laid end-to-end,
they would extend for about 60,000 miles (more than 96,500 kilometers), which is
far enough to circle the earth more than twice!
The one-way circulatory
system carries blood to all parts of your body. This process of blood flow
within your body is called circulation. Arteries carry oxygen-rich blood away
from your heart, and veins carry oxygen-poor blood back to your heart.
In
pulmonary circulation, though, the roles are switched. It is the pulmonary
artery that brings oxygen-poor blood into your lungs and the pulmonary vein that
brings oxygen-rich blood back to your heart.
In the diagram, the vessels
that carry oxygen-rich blood are colored red, and the vessels that carry
oxygen-poor blood are colored blue.
Twenty major arteries make a path

through your tissues, where they branch into smaller vessels called arterioles.
Arterioles further branch into capillaries, the true deliverers of oxygen and
nutrients to your cells. Most capillaries are thinner than a hair. In fact, many
are so tiny, only one blood cell can move through them at a time. Once the
capillaries deliver oxygen and nutrients and pick up carbon dioxide and other
waste, they move the blood back through wider vessels called venules. Venules
eventually join to form veins, which deliver the blood back to your heart to
pick up oxygen.

The heart weighs between 7 and 15 ounces (200 to 425 grams) and is a little
larger than the size of your fist. By the end of a long life, a person's heart
may have beat (expanded and contracted) more than 3.5 billion times. In fact,
each day, the average heart beats 100,000 times, pumping about 2,000 gallons
(7,571 liters) of blood.

Click here for a Flash version of this illustration.
Your heart is located between your lungs in the middle of your chest, behind
and slightly to the left of your breastbone (sternum). A double-layered membrane
called the pericardium surrounds your heart like a sac. The outer layer of the
pericardium surrounds the roots of your heart's major blood vessels and is
attached by ligaments to your spinal column, diaphragm, and other parts of your
body. The inner layer of the pericardium is attached to the heart muscle. A
coating of fluid separates the two layers of membrane, letting the heart move as
it beats, yet still be attached to your body.
Your heart has 4 chambers. The
upper chambers are called the left and right atria, and the lower chambers are
called the left and right ventricles. A wall of muscle called the septum
separates the left and right atria and the left and right ventricles. The left
ventricle is the largest and strongest chamber in your heart. The left
ventricle's chamber walls are only about a half-inch thick, but they have enough
force to push blood through the aortic valve and into your body.
The Heart
Valves (illustration)
Four types of valves regulate blood
flow through your heart:
The tricuspid valve regulates blood flow between
the right atrium and right ventricle.
The pulmonary valve controls blood
flow from the right ventricle into the pulmonary arteries, which carry blood to
your lungs to pick up oxygen.
The mitral valve lets oxygen-rich blood from
your lungs pass from the left atrium into the left ventricle.
The aortic
valve opens the way for oxygen-rich blood to pass from the left ventricle into
the aorta, your body's largest artery, where it is delivered to the rest of your
body.
See also on this site: The Heartbeat
The Conduction System (illustration)
Electrical impulses from your heart
muscle (the myocardium) cause your heart to contract. This electrical signal
begins in the sinoatrial (SA) node, located at the top of the right atrium. The
SA node is sometimes called the heart's "natural pacemaker." An electrical
impulse from this natural pacemaker travels through the muscle fibers of the
atria and ventricles, causing them to contract. Although the SA node sends
electrical impulses at a certain rate, your heart rate may still change
depending on physical demands, stress, or hormonal factors.
The Circulatory
System (illustration)
Your heart and circulatory system
make up your cardiovascular system. Your heart works as a pump that pushes blood to the organs, tissues, and cells of your body.
Blood delivers oxygen and nutrients to every cell and removes the carbon dioxide
and waste products made by those cells. Blood is carried from your heart to the
rest of your body through a complex network of arteries, arterioles, and
capillaries. Blood is returned to your heart through venules and veins. If all
the vessels of this network in your body were laid end-to-end, they would extend
for about 60,000 miles (more than 96,500 kilometers), which is far enough to
circle the earth more than twice!