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Instruction 9-1
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Circulation | Digestive System | Digestive Enzymes | Kidney's Role | Respiratory System |
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| Circulation | ||||||
| CA HS Biology 9.a. | ||||||
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What is circulation? It is the movement of blood around
body: the continuous movement of blood through all parts of the body. The body's circulatory system really has three distinct parts: pulmonary circulation, coronary circulation, and systemic circulation. Or, the lungs (pulmonary), the heart (coronary), and the rest of the system (systemic). Each part must be working independently in order for them to all work together.
Pulmonary circulation Pulmonary circulation is the movement of blood from the heart, to the lungs, and back to the heart again. This is just one phase of the overall circulatory system. The veins bring waste-rich blood back to the heart, entering the right atrium throughout two large veins called vena cava. The right atrium fills with the waste-rich blood and then contracts, pushing the blood through a one-way valve into the right ventricle. The right ventricle fills and then contracts, pushing the blood into the pulmonary artery, which leads to the lungs. In the lung capillaries, the exchange of carbon dioxide and oxygen takes place. The fresh, oxygen-rich blood enters the pulmonary veins and then returns to the heart, re-entering through the left atrium. The oxygen-rich blood then passes through a one-way valve into the left ventricle where it will exit the heart through the main artery, called the aorta. The left ventricle's contraction forces the blood into the aorta and the blood begins its journey throughout the body.
The one-way valves are important for preventing any backward flow of blood. The circulatory system is a network of one-way streets. If blood started flowing the wrong way, the blood gases (oxygen and carbon dioxide) might mix, causing a serious threat to your body.
You can use a stethoscope to hear pulmonary circulation. The two sounds you hear, "lub" and "dub," are the ventricles contracting and the valves closing. The heart beats or contracts 70 times per minute. The human heart will undergo over 3 billion contraction cycles during a normal lifetime. The cardiac cycle consists of two parts: systole (contraction of the heart muscle) and diastole (relaxation of the heart muscle). Atria contract while ventricles relax. The pulse is a wave of contraction transmitted along the arteries. Valves in the heart open and close during the cardiac cycle. Heart muscle contraction is due to the presence of nodal tissue in two regions of the heart. The SA node (sinoatrial node) initiates heartbeat. The AV node (atrioventricular node) causes ventricles to contract. The AV node is sometimes called the pacemaker since it keeps heartbeat regular. Heartbeat is also controlled by the autonomic nervous system.
On average, your body has about 5 liters of blood continually traveling through it by way of the circulatory system. The heart, the lungs, and the blood vessels work together to form the circle part of the circulatory system. The pumping of the heart forces the blood on its journey. Coronary circulation While the circulatory system is busy providing oxygen and nourishment to every cell of the body, let's not forget that the heart, which works hardest of all, needs nourishment, too. Coronary circulation refers to the movement of blood through the tissues of the heart. This is done through the right and left coronary arteries. The circulation of blood through the heart is just one part of the overall circulatory system. Serious heart damage may occur if the heart tissue does not receive a normal supply of food and oxygen. The heart tissue receives nourishment through the capillaries located in the heart.
An anterior view of the heart shows the right coronary artery and the anterior decoding branch of the left coronary artery. Systemic circulation Systemic circulation supplies nourishment to all of the tissue located throughout your body, with the exception of the heart and lungs because they have their own systems. Systemic circulation is a major part of the overall circulatory system. The blood vessels (arteries, veins, and capillaries) are responsible for the delivery of oxygen and nutrients to the tissue. Oxygen-rich blood enters the blood vessels through the heart's main artery called the aorta. The forceful contraction of the heart's left ventricle forces the blood into the aorta, which then branches into many smaller arteries, which run throughout the body. The inside layer of an artery is very smooth, allowing the blood to flow quickly. The outside layer of an artery is very strong, allowing the blood to flow forcefully. The oxygen-rich blood enters the capillaries where the oxygen and nutrients are released. The waste products are collected and the waste-rich blood flows into the veins in order to circulate back to the heart where pulmonary circulation will allow the exchange of gases in the lungs. During systemic circulation, blood passes through the kidneys. This phase of systemic circulation is known as renal circulation. During this phase, the kidneys filter much of the waste from the blood. Blood also passes through the small intestine during systemic circulation. This phase is known as portal circulation. During this phase, the blood from the small intestine collects in the portal vein, which passes through the liver. The liver filters sugars from the blood, storing them for later.
Blood Vessels In a general sense, a vessel is defined as a hollow utensil for carrying something: a cup, a bucket, a tube. Blood vessels, then, are hollow utensils for carrying blood. Located throughout your body, your blood vessels are hollow tubes that circulate your blood. There are three varieties of blood vessels: arteries, veins, and capillaries. During blood circulation, the arteries carry blood away from the heart. The capillaries connect the arteries to veins. Finally, the veins carry the blood back to the heart. If you took all of the blood vessels out of an average child, and laid them out in one line, the line would be over 60,000 miles long! An adult's vessels would be closer to 100,000 miles long!
The arterial system Besides circulating blood, the blood vessels provide two important means of measuring vital health statistics: pulse and blood pressure. We measure heart rate, or pulse, by touching an artery. The rhythmic contraction of the artery keeps pace with the beat of the heart. Since an artery is near the surface of the skin, while the heart is deeply protected, we can easily touch the artery and get an accurate measure of the heart's pulse. When we measure blood pressure, we use the blood flowing through the arteries because it has a higher pressure than the blood in the veins. Your blood pressure is measured using two numbers. The first number, which is higher, is taken when the heart beats during the systole phase. The second number is taken when the heart relaxes during the diastole phase. Those two numbers stand for millimeters. A column of mercury rises and falls with the beat of the heart. The height of the column is measured in millimeters. Normal blood pressure ranges from 110 to 150 millimeters (as the heartbeats) over 60 to 80 millimeters (as the heart relaxes). It is normal for your blood pressure to increase when you are exercising and to decrease when you are sleeping. If your blood pressure stays too high or too low, however, you may be at risk of heart disease.
Arteries The heart pumps blood out through one main artery called the dorsal aorta. The main artery then divides and branches out into many smaller arteries so that each region of your body has its own system of arteries supplying it with fresh, oxygen-rich blood. Arteries are tough on the outside and smooth on the inside. An artery actually has three layers: an outer layer of tissue, a muscular middle, and an inner layer of epithelial cells. The muscle in the middle is elastic and very strong. The inner layer is very smooth so that the blood can flow easily with no obstacles in its path. The muscular wall of the artery helps the heart pump the blood. When the heart beats, the artery expands as it fills with blood. When the heart relaxes, the artery contracts, exerting a force that is strong enough to push the blood along, This rhythm between the heart and the artery results in an efficient circulation system. You can actually feel your artery expand and contract. Since the artery keeps pace with the heart, we can measure heart rate by counting the contractions of the artery. That's how we take our pulse. The arteries deliver the oxygen-rich blood to the capillaries where the actual exchange of oxygen and carbon dioxide occurs. The capillaries then deliver the waste-rich blood to the veins for transport back to the lungs and heart.
Veins Veins are similar to arteries but, because they transport blood at a
lower pressure, they are not as strong as arteries. Like arteries, veins
have three layers: an outer layer of tissue, muscle in the middle, and a
smooth inner layer of epithelial cells. However, the layers are thinner,
containing less tissue. The vein valves are necessary to keep blood flowing toward the heart, but they are also necessary to allow blood to flow against the force of gravity. For example, blood that is returning to the heart from the foot has to be able to flow up the leg. Generally, the force of gravity would discourage that from happening. The vein valves, however, provide footholds for the blood as it climbs its way up. Blood that flows up to the brain faces the same problem. If the blood is having a hard time climbing up, you will feel light-headed and possibly even faint. Fainting is your brain's natural request for more oxygen-rich blood. When you faint, your head comes down to the same level as your heart, making it easy for the blood to quickly reach the brain. Because it lacks oxygen, the waste-rich blood that flows through the veins has a deep red color, almost like maroon. Because the walls of the veins are rather thin, the waste-rich blood is visible through the skin on some parts of the body. Look at your wrist, hands, or ankles. You can probably see your veins carrying your blood back to your heart. Your skin refracts light, though, so that deep red color actually appears a little blue from outside the skin.
Capillaries
Unlike the arteries and veins, capillaries are very thin and fragile. The
capillaries are actually only one epithelial cell thick. They are so thin
that blood cells can only pass through them in single file. The exchange of
oxygen and carbon dioxide takes place through the thin capillary wall. The
red blood cells inside the capillary release their oxygen, which passes
through the wall and into the surrounding tissue. The tissue releases its
waste products, like carbon dioxide, which passes through the wall and into
the red blood cells. Heart The human heart is a pear-shaped structure about the size of a fist. The
heart is an amazing organ. It is responsible for supplying the body with
oxygenated blood. Each time the heart beats, it exerts a pressure on the
veins and arteries called blood pressure. Blood pressure is extremely
important and must be controlled if it is too high or low. Blood pressure
can be controlled by medication prescribed by your doctor, proper exercise
and a diet filled with plants and vegetables. The two upper chambers are called atrium; the bottom chambers are called
ventricles. The right side of the heart receives deoxygenated blood from all
parts of the body except for the lungs. The left side of the heart receives
oxygenated blood from the lungs and pumps it to the rest of the body. An
adult heart beats approximately 100,000 times a day, pumping about 2,000
gallons of blood. It has been estimated that the heart will beat about 3
billion times during a 70-year lifetime.
Blood The average adult has about five liters of blood living inside of their
body, coursing through their vessels, delivering essential elements, and
removing harmful wastes. Without blood, the human body would stop working.
Because it contains living cells, blood is alive. Red blood cells and white blood cells are responsible for nourishing and cleansing the body. Since the cells are alive, they too need nourishment. Vitamins and Minerals keep the blood healthy. The blood cells have a definite life cycle, just as all living organisms do. Approximately 55 percent of blood is plasma, a straw-colored clear liquid. The liquid plasma carries the solid cells and the platelets, which help blood clot. Without blood platelets, you would bleed to death. When the human body loses a little bit of blood through a minor wound, the platelets cause the blood to clot so that the bleeding stops. Because new blood is always being made inside of your bones, the body can replace the lost blood. When the human body loses a lot of blood through a major wound, that blood has to be replaced through a blood transfusion from other people.
But everybody's blood is not the same. There are four different blood types.
Red Blood Cells
Red blood cells perform the most important blood duty. A single drop of
blood contains millions of red blood cells, which are constantly traveling
through your body delivering oxygen and removing waste. If they weren't,
your body would slowly die. Over time, the red blood cells get worn out and eventually die. The average life cycle of a red blood cell is 120 days. Your bones are continually producing new blood cells, replenishing your supply. The blood itself, however, is re-circulated throughout your body, not being remade all of the time.
White Blood Cells
Whenever a germ or infection enters the body, the white blood cells snap
to attention and race toward the scene of the crime. The white blood cells
are continually on the lookout for signs of disease. When a germ does
appear, the white blood cells have a variety of ways by which they can
attack. Some will produce protective antibodies that will overpower the
germ. Others will surround and devour the bacteria. A consistently high number of white blood cells is a symptom of Leukemia, a cancer of the blood. A Leukemia patient may have as many as 50 000 white blood cells in a single drop of blood. Video Instruction
Experiments Measure your own pulse as you stand still and when you exercise. Explore what happens during the pumping action of your heart. Watch an interactive heart surgery.
Now let's do Practice Exercise 9-1 (top). |
