en españolEl corazón y el aparato circulatorio
About the Cardiovascular System
The heart and circulatory system (also called the cardiovascular system) make up the network that delivers blood to the body's tissues. With each heartbeat, blood is sent throughout our bodies, carrying oxygen and nutrients to all of our cells.
Every day, the approximately 10 pints (5 liters) of blood in your body travel many times through about 60,000 miles (96,560 kilometers) of blood vessels that branch and cross, linking the cells of our organs and body parts. From the hard-working heart, to our thickest arteries, to capillaries so thin that they can only be seen through a microscope, the cardiovascular system is our body's lifeline.
The circulatory system is composed of the heart and blood vessels, including arteries, veins, and capillaries. Our bodies actually have two circulatory systems: The pulmonarycirculation is a short loop from the heart to the lungs and back again, and the systemiccirculation (the system we usually think of as our circulatory system) sends blood from the heart to all the other parts of our bodies and back again.
The heart is the key organ in the circulatory system. As a hollow, muscular pump, its main function is to propel blood throughout the body. It usually beats from 60 to 100 times per minute, but can go much faster when it needs to. It beats about 100,000 times a day, more than 30 million times per year, and about 2.5 billion times in a 70-year lifetime.
The heart gets messages from the body that tell it when to pump more or less blood depending on a person's needs. When we're sleeping, it pumps just enough to provide for the lower amounts of oxygen needed by our bodies at rest. When we're exercising or frightened, the heart pumps faster to get more oxygen to our bodies.
The heart has four chambers that are enclosed by thick, muscular walls. It lies between the lungs and just to the left of the middle of the chest cavity. The bottom part of the heart is divided into two chambers called the right and left ventricles, which pump blood out of the heart. A wall called the interventricular septum divides the ventricles.
The upper part of the heart is made up of the other two chambers of the heart, called the right and left atria (pronounced: AY-tree-uh). The right and left atria receive the blood entering the heart. A wall called the interatrial (pronounced: in-tur-AY-tree-ul) septum divides the atria, and they're separated from the ventricles by the atrioventricular (pronounced: AY-tree-oh-ven-TRIK-yoo-lur) valves. The tricuspid valve separates the right atrium from the right ventricle, and the mitral (pronounced: MY-trul) valve separates the left atrium and the left ventricle.
Two other heart valves separate the ventricles and the large blood vessels that carry blood leaving the heart. These valves are called the pulmonic valve, which separates the right ventricle from the pulmonary artery leading to the lungs, and the aortic valve, which separates the left ventricle from the aorta, the body's largest blood vessel.
The Role of Blood Vessels
Blood vessels carrying blood away from the heart are called arteries. They are the thickest blood vessels, with muscular walls that contract to keep the blood moving away from the heart and through the body. In the systemic circulation, oxygen-rich blood is pumped from the heart into the aorta. This huge artery curves up and back from the left ventricle, then heads down in front of the spinal column into the abdomen. Two coronaryarteries branch off at the beginning of the aorta and divide into a network of smaller arteries that provide oxygen and nourishment to the muscles of the heart.
Unlike the aorta, the body's other main artery, the pulmonary artery, carries oxygen-poor blood. From the right ventricle, the pulmonary artery divides into right and left branches, on the way to the lungs where blood picks up oxygen.
Arterial walls have three layers:
- The endothelium (pronounced: en-doh-THEE-lee-um) is on the inside and provides a smooth lining for blood to flow over as it moves through the artery.
- The media is the middle part of the artery, made up of a layer of muscle and elastic tissue.
- The adventitia (pronounced: ad-ven-TIH-shuh) is the tough covering that protects the outside of the artery.
As they get farther from the heart, the arteries branch out into arterioles (pronounced: ar-TEER-ee-olz), which are smaller and less flexible.
Blood vessels that carry blood back to the heart are called veins. They are not as muscular as arteries, but they contain valves that prevent blood from flowing backward. Veins have the same three layers that arteries do, but they are thinner and less flexible. The two largest veins are the superior and inferior vena cavae (pronounced: VEE-nuh KAY-vee). The terms superior and inferior do not mean that one vein is better than the other, but that they are located above (superior) and below (inferior) the heart.
A network of tiny capillaries connects the arteries and veins. Even though they're tiny, the capillaries are one of the most important parts of the circulatory system because it is through them that nutrients and oxygen are delivered to the cells. In addition, waste products such as carbon dioxide are also removed by the capillaries.
What the Heart & Circulatory System Do
The circulatory system works closely with other systems in our bodies. It supplies oxygen and nutrients to our bodies by working with the respiratory system. At the same time, the circulatory system helps carry waste and carbon dioxide out of the body. Hormones — produced by the endocrine system — are also transported through the blood in our circulatory system. As the body's chemical messengers, hormones transfer information and instructions from one set of cells to another.
Did you ever wonder about the process behind your beating heart? A healthy heart makes a "lub-dub" sound with each beat. Here's what happens to make that sound: One complete heartbeat makes up a cardiac cycle, which consists of two phases. In the first phase, the ventricles contract (this is called systole, pronounced: SIS-tuh-lee), sending blood into the pulmonary and systemic circulation. To prevent the flow of blood backwards into the atria during systole, the atrioventricular valves close, creating the first ("lub") sound.
When the ventricles finish contracting, the aortic and pulmonic valves close to prevent blood from flowing back into the ventricles. This is what creates the second sound (the "dub"). Then the ventricles relax (this is called diastole, pronounced: dye-AS-tuh-lee) and fill with blood from the atria, which makes up the second phase of the cardiac cycle.
A unique electrical system in the heart causes it to beat in its regular rhythm. The sinoatrial (pronounced: sy-no-AY-tree-ul) or SA node, a small area of tissue in the wall of the right atrium, sends out an electrical signal to start the contracting of the heart muscle. These electrical impulses cause the atria to contract first; they then travel down to the atrioventricular or AV node, which acts as a kind of relay station. From here the electrical signal travels through the right and left ventricles, causing them to contract and force blood out into the major arteries.
In the systemic circulation, blood travels out of the left ventricle, to the aorta, to every organ and tissue in the body, and then back to the right atrium. The arteries, capillaries, and veins of the systemic circulatory system are the channels through which this long journey takes place. Once in the arteries, blood flows to smaller arterioles and then to capillaries.
While in the capillaries, the bloodstream delivers oxygen and nutrients to the body's cells and picks up waste materials. Blood then goes back through the capillaries into venules, and then to larger veins until it reaches the vena cavae. Blood from the head and arms returns to the heart through the superior vena cava, and blood from the lower parts of the body returns through the inferior vena cava. Both vena cavae deliver this oxygen-depleted blood into the right atrium. From here the blood exits to fill the right ventricle, ready to be pumped into the pulmonary circulation for more oxygen.
In the pulmonary circulation, blood low in oxygen but high in carbon dioxide is pumped out the right ventricle into the pulmonary artery, which branches off in two directions. The right branch goes to the right lung, and vice versa. In the lungs, the branches divide further into capillaries. Blood flows more slowly through these tiny vessels, allowing time for gases to be exchanged between the capillary walls and the millions of alveoli (pronounced: al-VEE-oh-lie), the tiny air sacs in the lung.
During the process called oxygenation, oxygen is taken up by the bloodstream. Oxygen locks onto a molecule called hemoglobin in the red blood cells. The newly oxygenated blood leaves the lungs through the pulmonary veins and heads back to the heart. It enters the heart in the left atrium, then fills the left ventricle so it can be pumped into the systemic circulation.
Things That Can Go Wrong
Problems with the cardiovascular system are common — more than 64 million Americans have some type of cardiac problem. But cardiovascular problems don't just affect older people — many heart and circulatory system problems affect teens, too.
Heart and circulatory problems are grouped into two categories: congenital, which means the problems were present at birth, and acquired, which means that the problems developed some time after birth.
Congenitalheart defects. Congenital heart defects are heart problems that babies have at birth. Congenital heart defects occur while a baby is developing in the mother's uterus. Doctors don't always know why congenital heart defects occur — some congenital heart defects are caused by genetic disorders, but most are not. A common sign of a congenital heart defect is a heart murmur. A heart murmur is an abnormal sound (like a blowing or whooshing sound) that's heard when listening to the heart. Lots of kids and teens have heart murmurs, which can be caused by congenital heart defects or other heart conditions.
Arrhythmia. Cardiac arrhythmias (pronounced: a-RITH-mee-uz), which are also called dysrhythmias or rhythm disorders, are problems in the rhythm of the heartbeat. Arrhythmias may be caused by a congenital heart defect or a person may develop this condition later. An arrhythmia may cause the heart's rhythm to be irregular, abnormally fast, or abnormally slow. But, some arrhythmias are not harmful. Arrhythmias can happen at any age and may be discovered when a teen has a checkup.
Cardiomyopathy. Cardiomyopathy (pronounced: kar-dee-oh-my-AH-puh-thee) is a long-lasting disease that causes the heart muscle (the myocardium) to become weakened. Usually, the disease first affects the lower chambers of the heart, the ventricles, and then progresses and damages the muscle cells and even the tissues surrounding the heart. Some kids and teens with cardiomyopathy may receive heart transplants to treat their condition.
Coronary artery disease. Coronary artery disease is the most common heart disorder in adults, and it's caused by atherosclerosis (pronounced: ah-thuh-ro-skluh-RO-sis). Deposits of fat, calcium, and dead cells form on the inner walls and clog up the body's arteries — in this case, the coronary arteries (the blood vessels that supply the heart) — and get in the way of the smooth flow of blood. A clot of blood may even form, which can lead to a heart attack. Heart attacks are very rare in kids and teens.
Hypercholesterolemia(high cholesterol).Cholesterol is a waxy substance that is found in the body's cells, in the blood, and in some of the foods we eat. Having too much cholesterol in the blood, also known as hypercholesterolemia (pronounced: high-pur-kuh-les-tuh-ruh-LEE-me-uh) or hyperlipidemia (pronounced: high-pur-lih-puh-DEE-me-uh), is a major risk factor for heart disease and can lead to a heart attack.
Hypertension (high blood pressure).Hypertension is when a person has blood pressure that's significantly higher than normal. Over time, it can cause damage to the heart and arteries and other body organs. Teens can have high blood pressure, which may be caused by genetic factors, excess body weight, diet, lack of exercise, and diseases such as heart disease or kidney disease.
Rheumatic heart disease. Teens who have had strep throat infection may develop rheumatic (pronounced: roo-MA-tik) fever. This type of infection can cause permanent heart problems, mostly in kids and teens between 5 and 15 years of age. People who've had strep throat and received antibiotics right away are unlikely to develop this problem.
So what can you do to halt heart and circulatory problems before they start? Getting plenty of exercise, eating a nutritious diet, maintaining a healthy weight, and seeing your doctor regularly for medical checkups are the best ways to help keep the heart healthy and avoid long-term problems like high blood pressure, high cholesterol, and heart disease.
The cardiovascular system (sometimes called the circulatory system) is practically the most vital part of the human body, without it humanity would’ve been extinct millennia ago. This system consists of the heart, blood vessels, and the veins and arteries that run through the entire human body. Responsible for transporting the nutrients, oxygen, hormones, and the cellular waste products all throughout the body, the cardiovascular system is fueled by the body’s hardest-working organ -the heart. Even at rest, the average human heart easily pumps over five liters of blood throughout the human body every minute. The heart is located just behind and slightly left of the breastbone, where the organs connection to the cardiovascular system keeps the human body alive. It is also the main key organ in the cardiovascular system.
The human heart receives commands from the body through the circulatory system, that tells it when to pump more or less blood depending on an individual’s needs. While people are exercising or terrified, the heart pumps even faster to increase the delivery of oxygen due to heightened emotion or activity. There are four chambers that enclose the heart with thick muscular walls. The bottom part of the organ is divided into two chambers called the left and right ventricles, which pump blood out of the heart and throughout the entire body. The interventricular septum is wall that divides the ventricles. The upper part of the heart consists of the other two chambers, called the right and left atria, which receive blood upon entering the heart. The left and right atria are separated from the ventricles by the atrioventricular valves a wall called the interatrial septum divides. These divides are separated by the tricuspid valve, while the mitral valve separates the left atrium and the left ventricle. Another two cardiac valves separate the ventricles and the large blood vessels that carry blood exiting the heart. This is the pulmonic valve, which separates the right ventricle from the pulmonary artery leading up to the lungs, and the aortic valve, which then separates the left ventricle from the aorta which is the body’s largest blood vessel. Arteries transport blood away from the heart. These are known as the thickest blood vessels, with muscular walls that need to contract to keep the blood moving away from the heart and through the body.
In the systemic circulation, oxygen-rich blood is pumped from the heart and into the aorta. The huge artery first curves up and back from the left ventricle, then it flows down in front of the spinal column into the abdomen. At the start of the aorta, two coronary arteries branch off and divide into a network of smaller arteries that administer oxygen and nourish the muscles of the heart. Contrary to the aorta, the pulmonary artery transports oxygen-poor blood. The pulmonary artery divides into left and right branches from the right ventricle, en route to the lungs where blood gains oxygen.
As arteries get farther from the heart, they begin to branch out into arterioles, which are smaller and less elastic than where they originate. Veins aren’t as muscular as arteries but they do carry blood back to the heart. They contain valves that are used to prevent blood from flowing backwards. Veins are less flexible and thinner than arteries, but they also have the same three layers as arteries do. The two largest veins are the inferior and superior vena cavae. The terms superior and inferior does not mean that one vein is better than the other vein, but that they are located above and below the heart. A network of tiny capillaries is what connects the arteries and veins. Although they are tiny, the capillaries are one of the most important parts of the cardiovascular system because through them, the nutrients and oxygen are delivered to the cells. In addition, the capillaries also remove waste products such as carbon dioxide.
Tissues in the cardiovascular system encompass arteries, the heart, pericardium, and veins. These tissues are handled by researchers for investigations in order to find better methods of diagnosing or remedying such disorders as congestive muscular dystrophy, heart failure, coronary artery disease, or cardiomyopathy. The major tissues of the system would be the muscle, nervous, epithelial, and connective tissues.
The epithelial tissue is a type of protective tissue that covers the entire human body. It is built from closely packed cells in one or more layers. The Epithelial tissue is found inside the body and is called endothelium. The tissue is usually positioned on top of a thin layer of connective tissue, which is called the “basement membrane.” In the cardiovascular system, epithelial tissue can be located in the structure of the veins, arteries, and capillaries, as it also protects and covers the heart. Epithelial cells are compacted tightly together, with little to none intercellular spaces and only a small amount of intercellular substance. Regardless of the type, epithelial tissue is usually separated from the underlying tissue by a thin sheet of connective tissue; basement membrane. The basement membrane provides structural support for the epithelium and also binds it to neighboring structures.
Muscle tissue is made up of muscle cells that are able to contract, whether it is involuntarily or on command. This tissue enables us to move our whole body, or just certain parts when we wish. Muscle tissue also creates involuntary movement inside our bodies in every organ system. The heart is considered the main organ of the circulatory system, and is considered a muscle, therefore is largely made up of muscle tissue. Such contractions may result in the movement of the whole body or a portion of it, which is if the muscles are attached to a movable part of the skeleton. If the muscle is located in the wall of a hollow organ, its contractions may cause the contents of the organ to move.
The main function of the nervous tissue is to react to stimuli and send impulses to various organs through the body. This type of tissue is made up a specialized type of cell called neurons. They cells are highly responsive which means that they react quickly to stimuli. The nerve cell fibers embedded in connective tissue makes up the nervous tissue. This tissue is detrimental to the cardiovascular system because it helps the brain to deliver messages to all of the components of the system. Without this tissue, the circulatory system would not function.
Connective tissue is sometimes referred to as the “glue” that holds the body together and is the most common and plentiful type of tissue in the entire human body. The connective tissue consists of widely spread cells and its job is to connect, support, or surround other tissues and organs. The connective tissue is what makes up the structure of not only the cardiovascular system, but all of the other organ systems as well. This tissue can be found in the walls of arteries, veins, and capillaries, and, of course, in the makeup of the heart.
The cardiovascular system works closely with other systems in our bodies. It supplies oxygen and nutrients to our bodies by working in rhythm with the respiratory system. Simultaneously, the cardiovascular system helps carry waste and carbon dioxide out of the body. Hormones are produced by the endocrine system and are also transported through the blood in the circulatory system. Hormones, as the body’s chemical messengers, transfer information and instructions from one set of cells to another. For example, one of the hormones that are produced by the heart helps control the kidneys’ release of salt from the body.
When red blood cells pass by the lungs, the carbon dioxide that they are carrying diffuses into the lungs and in return, some oxygen diffuses into the red blood cells. The red blood cells are then transported all throughout the body through the arteries and give nutrients to organs and tissues by using diffusion. Carbon dioxide from the organs and tissues diffuses into the red blood cells just as oxygen diffuses out of the red blood cells. The cells then carry the carbon dioxide back to the lungs where then diffusion occurs, and the cycle begins yet again. Red blood cells also contain a substance called hemoglobin. Hemoglobin are small molecules found within red blood cells that give the blood its rich red color. Red blood cells are first produced in the bone marrow and then released into the bloodstream once they have matured. The lifespan of the cells is about three or four months, once they have aged or become damaged they are subsequently removed from the bloodstream by the spleen. The most important job of the red blood cells is to transport oxygen and other nutrients to every of the part of the body and get rid of wastes in the body, such as carbon dioxide.
Blood doping is a performance enhancing process and is frowned upon in athletic competitions worldwide. It is when an athlete removes some of the blood from their body a few weeks prior to a large competition. During these weeks, their body replenishes the blood that they lost, and then just before the competition, they inject the blood back into their body, giving themselves an irregularly high level of red blood cells in the bloodstream. The more red blood cells mean more oxygen, which in turn gives the athlete a higher endurance, and more stamina. Blood doping is a very dangerous and unsanitary process that will result in immediate disqualification from competition due to the fact that it gives an individual an advantage over the other competitors.
The cardiovascular system is instrumental in the body’s ability to maintain homeostatic control of several internal conditions. Blood vessels help maintain a stable body temperature by manipulating the blood flow to the surface of the skin. Blood vessels near the skin’s surface open during times of overheating to allow hot blood to dump its heat into the body’s surroundings. When hypothermia occurs, these blood vessels constrict to keep blood flowing only to vital organs in the body’s core. Blood also helps balance the body’s pH balance due to the presence of bicarbonate ions that act as a buffer solution. Finally, the albumins in blood plasma help balance the osmotic concentration of the body’s cells by maintaining an isotonic environment.
Several functions of the cardiovascular system can control blood pressure. Autonomic nerve signals from the brain along with certain hormones affect the rate and strength of heart contractions. Greater contractile force and heart rate will lead to an increase in blood pressure, which can also affect blood pressure. Vasoconstriction decreases the diameter of an artery by contracting the smooth muscle in the arterial wall. The sympathetic division of the autonomic nervous system causes vasoconstriction, which leads to increases in blood pressure and decreases in blood flow in the constricted region. Vasodilation is the expansion of an artery as the smooth muscle in the arterial wall relaxes after the fight-or-flight response wears off or under the effect of certain hormones or chemicals in the blood. The volume of blood in the body also affects blood pressure. A higher volume of blood in the body will raise the blood pressure by increasing the amount of blood pumped by each heartbeat. Thicker and more viscous blood from clotting disorders will also raise blood pressure.
Hemostasis, the clotting of blood and formation of scabs, is managed by the platelets of the blood. Platelets normally remain inactive in the blood, that is until they reach damaged tissue or leak out of the blood vessels through a wound. Once they are active, platelets change into a spiny ball shape and become very sticky in order to latch on to damaged tissues. Then they release chemical clotting factors and begin to produce the protein fibrin to act as structure for the blood clot. After which they also begin sticking together to form a platelet plug. The platelet plug will serve as a temporary seal to keep blood in the vessel and keep foreign material out of the vessel until the cells of the blood vessel can repair the damage to the vessel wall.
The heart is a four-chambered ‘double pump,’ where each side (left and right) operates as a separate pump. The left and right sides of the heart are divided by a muscular wall of tissue known as the septum of the heart. The right side of the heart receives deoxygenated blood from the systemic veins and pumps it into the lungs for oxygenation. The left side of the heart receives oxygenated blood originating from the lungs and pumps it through the systemic arteries to the tissues of the body. Each heartbeat results in the simultaneous pumping of both sides of the heart, making the heart a very efficient pump. Thus making the cardiovascular system overall the most essential part of the body for a person to live.