Your blood vessels are a vast network of tubes that carry blood throughout your entire body. The blood vessels “drop off” oxygen and nutrients to all of the cells in your body. The blood vessels then “pick up” waste products like carbon dioxide—and return the oxygen-poor blood to the heart and lungs. When the blood passes through your lungs, oxygen moves once again into the blood.
You might sometimes hear the terms vascular or vasculature. These terms refer to your blood vessels.
Three types of blood vessels carry blood through your body: arteries, capillaries and veins.
Arteries
Arteries carry blood rich in oxygen from your heart to the tissues and organs in your body, like your brain, kidneys, and liver. Because arteries carry oxygen, they appear red. Artery walls are thick and flexible. And they need to be. The heart pumps with enough force, or pressure, to deliver blood throughout the body. The thicker walls help protect the arteries against damage from the high pressure.
(Here’s a good tip to remember the difference between arteries and veins. The “a” in “artery” can also refer to the blood being carried “away” from your heart.)
Arteries get smaller as they get farther from your heart. At their smallest point, arteries become capillaries.
Capillaries
Capillaries are the body’s tiniest blood vessels. They carry blood to and from every cell in your body. In an adult, that amounts to trillions of cells.
Capillaries are where the “exchange” takes place. Capillary walls are so thin that oxygen and nutrients can pass right through them into your body’s cells. Waste products from the cells, like carbon dioxide, can also pass through the capillary walls and into your bloodstream before returning to the heart. Capillaries connect arteries to veins.
Veins
Capillaries get larger as they leave each cell and soon become veins. Veins carry the oxygen-poor blood back to your heart. Because they carry blood without oxygen, veins appear blue. Vein walls are much thinner than artery walls. That’s because blood flows through them at a lower pressure. The word venous refers to veins.
Coronary Arteries
Like the other muscles in your body, your heart needs oxygen to survive. The blood vessels that deliver oxygen to your heart muscle are the coronary arteries. They have that name because they encircle and sit on the surface of your heart like a crown. (The word “coronary” means crown.)
The coronary arteries are divided into two systems. The left coronary artery system supplies blood mostly to the left side of your heart. The right coronary artery system supplies blood mostly to the right side of your heart.
Commonly Blocked Coronary Arteries
Maybe someone you know has coronary artery disease (CAD), or heart disease. A person with CAD has at least one coronary artery that’s clogged with plaque. Plaque results when fatty substances, like cholesterol, build up in your arteries. Over time the arteries become hard and narrowed. In the coronary arteries, plaque buildup can slow blood flow to the heart muscle.
These larger coronary arteries are the ones that are most likely to become blocked or affected by CAD:
Coronary Veins
Coronary veins are found only in your heart. And like other veins in your body, coronary veins carry oxygen-poor blood. Coronary veins collect the oxygen-poor blood from your heart muscle—not from inside the heart chambers, but from the muscle of the heart wall.
Coronary veins empty blood directly into the right atrium through the coronary sinus. The coronary sinus is a small opening in the right atrium that’s protected by a flap of tissue.
Peripheral Vascular System
Outside your heart, blood vessels deliver oxygen and nutrients to the rest of your body. These blood vessels make up the peripheral vascular system.
Commonly Blocked Peripheral Arteries
Like the heart’s coronary arteries, peripheral arteries can become clogged with plaque. Plaque results when fatty deposits, like cholesterol, build up in your arteries. Over time the arteries can become hard and narrowed. In the peripheral arteries, this plaque can slow blood flow to vital areas such as the brain.
This problem with blocked arteries is called peripheral vascular disease (PVD). You may also hear it called peripheral artery disease. Some of the arteries that are especially prone to PVD supply blood to your:
Vessels Used for Bypasses
If you have a blocked artery, your doctor may fix the problem by re-routing the blood through part of a healthy blood vessel. A section of healthy blood vessel is often taken from your chest, arm, or leg. Your doctor sews—or “grafts”—one end of the healthy blood vessel below the blocked artery. The doctor then grafts the other end of the healthy blood vessel above the blocked artery. Blood flows through the new blood vessel around the blockage. This “detour” is called a bypass graft.
Your doctor chooses which blood vessels to use for a graft. That choice depends on the size and location of your blocked artery. And on the size of your other blood vessels available for grafts. Doctors usually choose from among these three options when taking the healthy vessel for the graft:
When portions of these blood vessels are removed for grafts, other blood vessels take over for them. Surgeons more often choose arteries, rather than veins, for grafts. Veins sewn to the heart arteries may become clogged again. Arteries are less likely to get clogged again, meaning that the patient is less likely to need another surgery in the future.
What Is Blood Pressure?
Blood pressure is the force of your blood pushing against your artery walls. When your heart is relaxed, it is in diastole. When contracted, it is in systole. The force, or blood pressure, is stronger when your heart contracts and weaker when your heart relaxes. In addition, the force or pressure is stronger in your arteries and weaker in your veins.
Your doctor or nurse reports your blood pressure with two numbers—a higher number “over” a lower number. Normal blood pressure for an adult is about “120 over 80” or 120/80 mm/Hg. Blood pressure is measured in millimeters of mercury, or mm/Hg.
So what do the numbers mean?
The bigger number (on the top) refers to the systolic pressure. This is the pressure when your heart contracts.
The smaller number (on the bottom) refers to the diastolic pressure. This is the pressure when your heart relaxes between beats.
The blood pressure reading tells your doctor how hard your heart is working. If one or both numbers are higher than normal, you may 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.
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