Intro to Blood Vessels

What Do Blood Vessels Do?

Blood flows through your body in a complex system of tubes called blood vessels. Blood vessels carry blood to every part of your body. At each tissue or organ in your body, blood makes an exchange—it "drops off" oxygen and nutrients and "picks up" waste products (toxins and carbon dioxide). After the exchange, blood returns to your heart.

A similar exchange takes place in your lungs. When blood flows through your lungs, it "drops off" carbon dioxide from your body and "picks up" oxygen. You fill your lungs with oxygen by breathing in. You get rid of the carbon dioxide in your lungs by breathing out.

Your blood vessels, heart, and lungs make up the circulatory system (Figure 1). In healthy adults, the heart pumps approximately 1,900 gallons (7,200 liters) of blood through about 60,000 miles (96,560 kilometers) of blood vessels every day.

Figure 1

Circulatory System Enlarge

Types of Blood Vessels

Three types of blood vessels carry blood through your body (Figure 2):

If you hear or read the word vascular or vasculature, it means your blood vessels.

Figure 2

Types of Blood Vessels Enlarge

Arteries

Arteries carry oxygen-rich blood from your heart to the tissues and organs in your body, like your brain, kidneys, and liver. Because they carry blood with oxygen, arteries appear red. Blood flows through arteries with great force. So the walls of arteries are thick and flexible. The thicker walls help protect the arteries against damage from the high pressure.

Arteries get smaller and smaller as they get farther from your heart. At their smallest point, arteries become capillaries.

Capillaries

Capillaries connect arteries to veins. As the tiniest blood vessels, capillaries carry blood to and from every cell in your body. In an adult body, that means trillions of cells.

Capillary walls are so thin that oxygen and nutrients can pass right through them into your body's cells. Waste products and carbon dioxide from the cells can also pass through the walls of capillaries back into your bloodstream.

Veins

Capillaries get larger and larger as they leave each cell and quickly become veins. Veins carry the oxygen-poor blood back to your heart. Because they carry blood without oxygen, veins appear blue. The walls of veins are much thinner than artery walls—they don't have to be as thick because blood flows through veins at a lower pressure.

Q. What type of blood vessel carries oxygen-rich blood from the heart to your body?

 Capillaries

 Arteries

 Veins

The Largest Blood Vessels

The Venae Cavae

The two largest veins in your body are the inferior vena cava and the superior vena cava (Figure 3). These two veins empty blood into your heart's right atrium:

Figure 3

The Largest Blood Vessels Enlarge

The Aorta

The aorta is your body's largest artery (Figure 4). It's attached directly to the left ventricle of your heart. The left ventricle pumps blood out of your heart through the aortic valve into the aorta. All other major arteries branch from the aorta and carry blood to the rest of your body.

Figure 4

The Aorta Enlarge

Q. What is the largest artery in your body?

 Inferior vena cava

 Superior vena cava

 Aorta

What is Blood Pressure?

Blood pressure is the force of your blood pushing against the walls of your arteries. The force is stronger when your heart contracts, and weaker when your heart relaxes. Also, the force is stronger in your arteries, and weaker in your veins.

Your nurse reports your blood pressure with two numbers—a higher number "over" a lower number. Normal blood pressure for an adult is "120 over 80" or 120/80.

So what do the numbers mean?

Blood pressure tells your doctor how hard your heart is working. If one or both numbers are higher than normal, you have high blood pressure. High blood pressure means your heart is working extra hard to push blood through your arteries. It also means you may be at higher risk for developing heart problems.

Next: Blood Vessels in Your Heart

Q. If a patient's blood pressure is 120/80, does the patient have high, low, or normal blood pressure?

 High blood pressure

 Low blood pressure

 Normal blood pressure