HEART AND BLOOD VESSEL BASICS

Transcription

1 HEART AND BLOOD VESSEL BASICS THE HEART What Does the Heart Do? The heart is a muscle about the size of a closed fist. The heart usually beats about times per minute. With each beat, your heart pushes blood throughout your body. Blood doesn't flow on its own; it needs the heart to beat (contract) and push the blood through your blood vessels. Each time your heart beats, your heart muscle is contracting. You might not think of your heart as a muscle that gets a big workout. But it does. Think about what the heart does every day in a healthy adult: It pumps about 1,900 gallons (7,200 liters) of blood. It beats 100,000 times. And it gets only a fraction of a second to rest between each beat! The term cardiac refers to the heart. Your heart's walls are made mostly of strong muscle called the myocardium. The myocardium is the strongest, hardestworking muscle in your body. It has to be your heart pumps blood from your head to your toes. None of your tissues or organs could survive without the oxygen and nutrients carried by your blood. Where Is the Heart Located? Your heart is located slightly to the left of the center of your chest. Your breastbone protects your heart. For further protection, your heart is positioned inside your ribcage, and between your lungs. Although not really shaped like a valentine heart, your heart is slightly pointed at the lower end. The lower end is called the apex. Heart and Blood Vessel Basics HEARTISTRY brought to you by Boston Scientific Corporation Page 1 of 9

2 HEART CHAMBERS What Do Heart Chambers Do? The inside of your heart is divided into four sections, or chambers. The chambers are like separate rooms that hold the blood before pumping it out to the body. Each chamber has doors (valves) that let blood pass in and out. The Atria Receiving Blood From the Body The two upper chambers in your heart are called the atria. (Just one of these chambers is called an atrium.) When blood flows into your heart from the body or lungs, it always flows into either the right or left atrium. When blood flows into your heart from the lungs, it always flows into the left atrium. Blood flows into both atria at the same time. When the atria are full with blood, they contract and push blood down into the ventricles at the same time. The Ventricles Pumping Blood Out to the Body The two lower chambers in your heart are called ventricles. The ventricles are known as the pumping chambers of your heart. When blood leaves your heart to go to your lungs, it is always pumped out from the right ventricle. When blood leaves your heart to go to the rest of your body, it is always pumped out from the left ventricle. The ventricles are larger than the atria. The ventricles are also very strong because they have to pump hard enough to push blood throughout your entire body. Your Heart's Right and Left Sides Sometimes the right and left sides of your heart are called your right heart and left heart. The right atrium and right ventricle are, of course, on the right side of your heart. (It's the same side as your right arm.) The left atrium and left ventricle are on the left side of your heart. However, when you look at a picture of the heart, the right heart is on the left. A wall called the septum separates the right and left sides of your heart. The septum also separates the oxygen-rich blood from the oxygen-poor blood in your heart. Blood that hasn't yet been to the lungs (oxygen-poor blood) stays on the right side of the septum. Blood returning from the lungs (oxygen-rich blood) stays on the left side of the septum. HEART VALVES What Do Heart Valves Do? Your heart has four valves that act like doors. Each valve has two jobs. They open to allow blood to flow in or out. They close to prevent blood from flowing where it shouldn t flow. The heart valves keep blood flowing in one direction through your heart. Heart and Blood Vessel Basics HEARTISTRY brought to you by Boston Scientific Corporation Page 2 of 9

3 Types of Valves There are two types of valves Atrioventricular valves These valves are at the base of the atria. They control blood flow between your heart's upper and lower chambers. The valve between the right atrium and the right ventricle is the tricuspid valve. The valve between the left atrium and the left ventricle is the mitral valve. Semilunar valves These valves are at the top of the ventricles. Semilunar valves control blood flow out of your heart. Blood flows out of the right ventricle to the lungs through the pulmonary valve. Blood flows out of the left ventricle to your body through the aortic valve. When you listen to your heartbeat through a stethoscope you hear "lubb-dubb, lubb-dubb." That sound is your heart valves closing. Although your heart has four valves, the valves open and close two at a time. In other words, the atrioventricular valves open and close at the same time. And the semilunar valves open and close at the same time. That's why you hear only two thumps ("lubb-dubb") per heartbeat, not four. CIRCULATORY SYSTEM (BLOOD FLOW) What Does It Do? Your circulatory system continuously delivers blood to all parts of your body, it also returns oxygen-poor blood to the lungs. The circulatory system consists of your: Heart, which pumps blood into blood vessels Blood vessels, a system of tubes that carry blood to your entire body and back to your heart Lungs, which supply oxygen to the blood You can compare your circulatory system to a figure eight. One loop routes blood from the heart to the lungs and back to the heart. On this loop carbon dioxide is removed from the blood, and oxygen is put into the blood. You fill your lungs with oxygen when you breathe in. And carbon dioxide is removed when you breathe out. The second loop delivers blood along with oxygen and nutrients to every other part of your body. The blood vessels then take away waste products (for example, carbon dioxide). Finally, the oxygen-poor blood returns to the heart for more oxygen. The cycle then repeats continuously. This second loop is large and very complex. To give you an idea, an adult has about 60,000 miles (96,560 kilometers) of blood vessels throughout the body! Heart and Blood Vessel Basics HEARTISTRY brought to you by Boston Scientific Corporation Page 3 of 9

4 Your circulatory system does more than carry oxygen and carbon dioxide, however. It carries nutrients from your intestines to your body's tissues. It carries hormones to the appropriate parts of your body from your glands. The circulatory system also carries waste products to your liver and kidneys to be removed. BLOOD VESSELS What Do Blood Vessels Do? 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. Types of 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. Heart and Blood Vessel Basics HEARTISTRY brought to you by Boston Scientific Corporation Page 4 of 9

5 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. Blood Vessels in Your Heart 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: Left anterior descending artery Left circumflex artery Left main artery Posterior descending artery Right coronary artery 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. Heart and Blood Vessel Basics HEARTISTRY brought to you by Boston Scientific Corporation Page 5 of 9

6 Blood Vessels Outside Your Heart 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: Brain (the carotid arteries, located in your neck) Arms (the subclavian arteries) Kidneys (the renal arteries) Lower abdomen (the iliac arteries) Upper legs (the femoral arteries) Lower legs (the popliteal arteries) 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: Internal mammary artery from inside the chest wall Radial artery which runs from your elbow to your wrist Saphenous vein which runs the length of your leg 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. Heart and Blood Vessel Basics HEARTISTRY brought to you by Boston Scientific Corporation Page 6 of 9

7 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. ELECTRICAL SYSTEM What Does the Electrical System Do? Just like your home, your heart needs electricity to work. The good news is that the heart creates its own electrical signals. The electrical system in your heart is what actually causes your heart to beat (contract). The electrical system also controls the speed of your heartbeat. Your heart's electrical system includes a network of pathways, similar to the electrical wiring in your home. The pathways carry electrical signals through your heart. As the signals travel through your heart tissue, they cause your heart to contract. When working properly, your heart's electrical system automatically responds to your body's changing need for oxygen. It slows down your heart rate when you sleep, for example. And it speeds up your heart rate as you climb stairs. When your heart rate speeds up, your heart pumps faster and your body gets more oxygen-rich blood. Your heart's electrical system is also called the cardiac conduction system. Parts of the Electrical System Heart and Blood Vessel Basics HEARTISTRY brought to you by Boston Scientific Corporation Page 7 of 9

8 Your heart's electrical system includes three important parts, or pathways. When the electrical signals travel down these paths as they should, your heartbeat is coordinated and occurs at a normal rate. S-A node (sinoatrial node) A-V node (atrioventricular node) His-Purkinje system The S-A Node: Your Heart's Natural Pacemaker The S-A node consists of special cells in your upper right atrium. These cells create the electrical impulses that start your heart beat. The S-A node normally produces electrical signals per minute. This results in a heart rate, or pulse rate, of beats per minute. Because the S-A node controls your heart rate, it is called your heart's "natural pacemaker." Electrical signals created by the S-A node travel down pathways to the A-V node. The A-V Node: Your Heart's Electrical Bridge The A-V node consists of special cells between your heart's upper and lower chambers. The A-V node allows the electrical signals to travel from the atria to the ventricles. You can think of the A-V node as the "electrical bridge" between the atria and ventricles. Some unusually slow heartbeats (called bradycardia) may be caused by problems in the A-V node. The His-Purkinje System Once in your heart's lower chambers, or ventricles, the electrical signals travel down a complex series of pathways called the His-Purkinje system. As this occurs, your ventricles contract. Once your S-A node has created an electrical signal, it takes less than a second for the signal to travel down to the A-V node and through the His-Purkinje system. Electrical Signals and Blood Flow Electrical signals created by the S-A node follow a natural electrical pathway through your heart walls. The movement of the electrical signals makes your heart's chambers contract. When a signal passes through a chamber wall, the chamber contracts. When the signal has moved out of the wall, the chamber relaxes. In a healthy heart, the chambers contract and relax in a coordinated way, or in rhythm. The Path of an Electrical Signal 1. The S-A node (natural pacemaker) creates an electrical signal. 2. The signal follows natural pathways through both atria. This causes the atria to contract, pushing blood into the ventricles. 3. The signal reaches the A-V node (electrical bridge). There, the signal pauses very briefly to give the ventricles time to fill with blood. 4. The signal spreads through the His-Purkinje system. This makes the ventricles contract, pushing blood out to your lungs and body. Heart and Blood Vessel Basics HEARTISTRY brought to you by Boston Scientific Corporation Page 8 of 9

9 Arrhythmias: Abnormal Heartbeats When your heart beats at a normal rate and rhythm it's called normal sinus rhythm. A problem in your heart's electrical system can disrupt your heart's normal rhythm. An abnormal heart rate (or heart rhythm) is called an arrhythmia. It's normal and healthy for your heartbeat to speed up or slow down during the day as your activity level changes. But it's not normal for your heart to beat out of rhythm. When your heart beats out of rhythm, it may not deliver enough blood to your body. Two types of arrhythmias in your atria are sinus tachycardia and atrial fibrillation. Two types of arrhythmias in your ventricles are ventricular tachycardia and ventricular fibrillation. Slow arrhythmias are called bradycardia. Many of these arrhythmias are serious enough to require treatment. To learn more about these arrhythmias, add them to your Education Rx (under Conditions). To check for a possible problem in your heart's electrical system, your doctor may order an electrocardiogram (ECG or EKG). An ECG records the electrical activity in your heart. The ECG also shows the timing of your heart's contractions. You've probably seen an ECG on television or when you visited someone in the hospital. The ECG monitor shows a line with peaks and valleys as the heart contracts and relaxes. Important Safety Information HEARTISTRY is provided for informational purposes only. It is not meant to replace any doctor s advice. Always talk to your doctor before starting any new treatment or program. Boston Scientific is a trademark and HEARTISTRY is a service mark of Boston Scientific Corporation. Heart and Blood Vessel Basics HEARTISTRY brought to you by Boston Scientific Corporation Page 9 of 9