Circulatory



**Dixie and Bryce on the Blood** **Marygrace and Jacob on the Vessel System ** **Anqi on the Heart **



Introduction: ===**The Circulatory System is a multi-part architecture of cells, including the heart, the vessel system, and the blood. The purpose of this system is to maintain the human body and act as its subway system, transporting an assortment of cargo, from calcium to the spongy marrows, oil to the fatty brain, oxygen to the respiratory system and even the dingy rainbow colored waste. **===

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//First and foremost, it is important to remember that the blood (or hemoglobin) that runs throughout the human body is infinitely more important and more complex than oil in a car. For although blood is to the body as oil is to the gears of a machine, blood does more than just lubricate and drive the gears into motion. It (blood) carries nutrients throughout the body, renews and replaces the cells/tissue in the body so as to keep it running, lets the eyeballs see when the brain decided for some reason to cut itself, etcetera etcetera. It is for this reason that we (Bryce and Dixie) are devoting our work and time on this topic.// //Blood, an essential part to the cardiovascular sytem, is also part of the hematologic system, which consists of the blood and the bone marrow.// //Blood consists of various formed elements, or blood cells, suspended in a fluid called plasma. Formed elements in the blood would include// //1) red blood cells (RBC's), or erythrocrytes 2) white blood cells (WBC's), or leukocytes// //and 3) platelets, or thrombocytes.// (//Red Blood Cells and platelets function entirely within blood vessels; White blood cells act mainly in the tissues outside the blood vessels.)//

RED BLOOD CELLS (FM and AI: First Mentioned and Always Important)
Red Blood cells transport oxygen and carbon dioxide to and from body tissues. They contain //hemoglobin,// the oxygen carrying substance that gives blood its red color. Red blood cells have an average life span of 120 days (about four months). Bone marrow releases red blood cells into circulation in immature form as //reticulocytes.// The reticulocytes mature into red blood cells in about 1 day. The spleen sequesters, or isolates, old, worn-out red blood cells, removing them from circulation. The rate of reticulocyte release usually equals the rate of old red blood cell removal. When red blood cell depletion occurs (for example, with hemorrhage), the bone marrow increases reticulocyte production to maintain the normal red blood cell count.

WHITE BLOOD CELLS (The Big, the Bad and the Immune System's Calvalry)
Five types of white blood cells participate in the body's defense and immune systems. These five types of cells are classified as //granulocytes// (neutrophils, //eosinophils//, and basophils) and //agranulocytes// (monocytes and lymphocytes). Granulocytes include //neutrophils, eosinphils,// and //basophils--//collectively known as //polymorphonuclear leukocytes.// All granulocytes contain a single //multilobular nucleus// and //granules// in the cytoplasm. Each cell type exhibits different properties and each is activated by different stimuli. //Neutrophils//, the most numerous granulocytes, account for fifty to seventy-five percent of circulating white blood cells. These phagocytic cells engulf, ingest, and digest foreign materials. They leave the bloodstream by passing through the capillary walls into the tissues ( a process called //diapedesis//) and then migrate to and accumulate at infection sites. Neutrophils are the first cells to arrive at the site of injury. Meanwhile, worn-out neutrophils form the main component of pus. Bone marrow produces their replacements, immature neutrophils called //bands//. In response to infection, bone marrow must produce many immature cells and release them into circulation, elevating the band count. //Eosinophils// account for 0.3% to 7% of circulating white blood cells. These granulocytes also migrate from the bloodstream by diapedesis but do so as a response to an allergic reaction. Eosinophils account for 0.3% to 7% of circulating white blood cells. These granulocytes also migrate from the bloodstream by diapedesis but do so as a response to an allergic reaction. Eosinophils accumulate in loose connective tissue, where they become involved in the ingestion of antigen-antibody complexes. Basophils, the last of the granulocytes, usually constitutes for fewer than 2% of the white blood cells in circulation. They also possess liitle or no phagocytic ability. Their cytoplasmic granules secrete someting called //histamine// that makes the blood vessels more permeable and eases the passage of fluids from the capillaries into body tissues. Meanwhile, the white blood cells in the agranulocyte category--//monocytes// and //lymphocytes//--lack specific cytoplasmic granules and even have nuclei (plural for //nucleus//) without lobes. //Monocytes//, an angronulocyte //and// the largest of the white blood cells, constitutes for only 1% to 9% of white blood cells in circulation. Like neutrophils, monocytes are phagocytic and enter the tissues by diapedesis. Outside the bloodstream, monocytes enlarge and mature, becoming tissue //macrophages// (also called //histiocytes//). As macrophages, monocytes may roam freely through the body when stimulated by inflammation. Usually, they remain immobile, populatinng most organs and tissues. Collectively, they serve as components of the //reticuloendothelial system//, which defends the body against infection and disposes of cell breakdown products. Macrophages concentrate in structures that filter large amounts of body fluid, such as the liver, spleen, and lymph nodes, where they defend against invading organisms. Macrophages are efficient phagocytes (cells that ingest microorganisms, cellular debris like worn-out neutrophils, and necrotic tissue. When mobilized at the site of infection, they phagocytize cellular remnants and promote healing of the wound/site of infection. Meanwhile, another kind of angranulocyte, lymphocytes are the last of white blood cells and also the least when it comes to size. However, lymphocytes are the second most numerous type of white blood cell (20%-43%), making up for their size with their numbers. They derive from stem cells that are located in the bone marrow. There are three types of lymphocytes: 1) //T lymphocytes// directly attack an infected cell 2) //B lymphocytes// produce antibodies against specific antigens 3) //Natural killer cells// provide immune surveillance and resistance to infection.

PLATELETS (The last, but not quite the greatest)
//Platelets// are small, colorless, disk-shaped cytoplasmic fragments split from cells in bone marrow called //megakaryocytes.// These fragments have a life span of about ten days. Platelets perform three vital functions, which would be: to initiate contraction of damaged blood vessels to minimize blood loss, form //hemeostatic plugs// in injured blood vessels, and, with plasma, provides materials that accelerate the process of blood coagulation.

As the Circulatory System can be referred to as a delivery track, you may wonder how everything is delivered. The answer is through the blood vessels, your body's ducts or hoses. They divide into three categories: arteries, veins, and capillaries, and come together to perform the vital task of keeping your organs in good health.

Your own vessel system, just as anyone else's, uses blood as its pack mule to distribute or circulate nourishment, hormones, and other things throughout your body's organs. Pretty generous, right? Truthfully, the Vessel system does ask a little in return from time to time. It takes waste and carbon dioxide and flushes it from your system. You've most likely heard of a pulse at some time or another. Well your pulse has lots to do with the Vessel System- it is the contraction of your arteries, triggered by the beat of your heart. So by touching an artery, you can also easily feel and check on your heart rate. Talk about multi-tasking! Still not sure about what this whole deal's about? Read on. Arteries are the monstrous "pipes" in your Vessel System. They are solely responsible for the job of pumping oxygen-rich blood from your heart to your capillaries (paragraph four) to be distributed to your different tissues and cater to their health. Arteries even have their own special setup to do precisely this: the main dorsal aorta pumps blood directly from your heart, to smaller tubes that branch out into smaller networks.

There are many large and important arteries which do jobs for the heart. These include:

**Aorta: same as dorsal aorta** **Pulmonary Artery: through this artery, oxygen-less blood is transferred from the heart (its right ventricle), to the lungs for oxygen restoration.** **Coronary Arteries: a network of arteries that branch off from the Aorta to different parts of the heart muscle to distribute blood to its tissues.** ** Pulmonary Vein: this vein is the carrier of the newly oxygenated blood back to the heart and straight into its left atrium. **

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Arteries have the same design as veins, with an outer layer of tissue, a middle layer of stretch-tastic muscle, and a super smooth inner layer comprised of epithelial cells. Their structure is actually a quite important factor in their job. Their smooth inside means flowing blood won't be held back, and muscles enable the artery to contract and push blood through for steady circulation. ======

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As a small child, I always assumed that it was just veins that carried the blood throughout my body. Let's just say that if my two-year-old self had assumed correctly, I would not be sitting here, gracing you with my very nice and unnecessarily extensive knowledge. I would not be able to retain my life for very long with just veins, because these parts of the Vessel System deal with oxygen-depleated blood, whereas the blood organs need is oxygen-rich. This oxygen-less blood is naturally maroon. ======

A vein's precise function is to carry the oxygen-less and waste-rich blood back to the heart to be restored and reused. Though they do this very gently, utilizing valves stationed throughout to close up their hollow i nsides and prevent the blood from flowing backwards.

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There is no doubt that every part of the vessel system is vital, but capillaries are what make it possible for the other parts of the system to perform their job. Embedded in tissue, these tubes connecting the veins and arteries are very fragile and so thin that blood cells have to travel single-file through them! In side the capillaries stationed in the lungs, a gas exchange takes place. They receive oxygen rich blood from arteries on one end, and the oxygen in the blood is released through the capillary's wall into the tissue. The tissue exchanges this oxygen for waste (carbon dioxide). This carbon dioxide is transferred to the blood still sitting inside of the capillary, which then travels out the other end and into a vein. On the subject of capillaries, they are the reason your skin gets flushed and red as a tomato when you get too hot. When capillaries receive this heat, they send it out to the skin tissue, turning it an embarassingly vibrant red. ======



The heart is a complex muscle that rests just over to the left from the center of your body. While the vessel system and blood help transport and store the energy that you eat or drink, the heart provides the power and ability for these simple, unconcious things to happen every single day. This engine work-house not only is able to perform these various actions, but remains active for all hours of each day!

Think about it. As you sit and read a book, or run a mile out in the neighborhood, your heart is always working with the other parts of this system to keep the nutrients that you need circulating throughout your body, even if it has to work extra hard to keep up with the nutrients you're using. As you've probably noticed before, whenever you are under stress, nervous, or just exercising, your heart rate speeds up compared to the rate when you are resting. This rate is usually measured in BPM, or beats per minute. But why does the heart make its significant and well-known galumphing beat?

The beat of your heart all has to do with the circulation of blood throughout it. It starts when blood surges into the atriums of the heart, which you can locate on the diagram above. The atriums are split into the right atrium and left atrium, and both hold different types of blood that flow from different kinds of vessels. The right atrium holds oxygen-free blood, which is blood that doesn't hold any oxygen at all, while the left holds oxygen-rich blood, blood that is obviously filled with oxygen.

The second thing the heart does is activate the node, a small, biologial button that will send an electrical impulse to start the blood pumping through the valves, a one way vessel that connects the atriums to the ventricles. Both types of blood will now flow into their respective ventricles, the right or left ventricle. (The left atrium's blood will flow into the left ventricle, as is the same idea for the right atriums and ventricles.) When the blood flows through, the valves connecting the ventricles and atriums snap shut, maintaining the heart so that it doesn't flow back into the atriums. TThe snapping sound of the valve closing is actually what causes the thumping sound of our hearts!

Once the blood has flowed through to the ventricle, another node is activated so that the blood will flush out of the heart and into the rest of the body. The vessels that carry the blood out of the heart are called the Pulmonary Artery and the Aorta, as more descriptively described in the section of the vessel system. Once this happens, the process starts over again to carry a new group of blood cells to different parts of the body, allowing your body to receive the nutrients you need. The heart can repeat this procedure up to 100,000 times a day!

Although you may think the heart acts on its own and does not need any help from you as an involuntary muscle, the heart, though it may not rely on you to keep it running, fully expects for you to maintain your health so it can keep on pumping away. Avoiding cardiovascular diseases such as coronary heart disease can happen when you eat only the intended amount of fat and cholesterol, and exercise certainly helps to prevent many of these illnesses. Find out more about coronary heart disease and coronary arteries below in an article about heart attacks.

Believe it or not, the Circulatory System is pretty popular with all its cousin body systems. In fact, the Crculatory, Respiratory, and Digestive Systems are quite the rebellious posse. This "oh-so-tight" relationship is due to multiple variables. the Respiratory System is a friend who has many frivolous connections, one of which is most commonly known as the act of breathing. At a simple breathing lesson, one of the core concepts is the exhale, which is a goodbye to the carbon dioxide byproduct of Cellular Respiration. In order to make this carbon dioxide easily accessible, it is your beloved Circulatory System (the veins to be precise) which carries this carbon dioxide from the site of CR. Also on the subject of the Respiratory System and its most necessary elements, lungs are in the running. As mentioned above, blood is on the subway to and from these lungs nonstop to be re-oxygenated. Like the Respiratory System, the Digestive System's waste or digested food substances, nutrients, and numerous other products are also carried by the blood system, but in addition, the Digestive System connects to the Circulatory in one of its accessory organs. The Liver readies all blood that arrives by way of digestion for the rest of the body, sorting out both the good and bad. There is no doubt that hundreds more connections exist between all of these body systems, for nothing less can be expected of such a renowned celebrity as the Circulatory System. Almost everyone has heard of the pair of words- heart attack- and many more have experienced one. One of the many reasons for countless heart attacks is called coronary heart disease. Coronary heart disease is when someone has either an unhealthy amount of fat or of cholesterol in their system, causing coronary arteries to get blocked with plaque. This plaque builds up in the arteries' weak spot. In order to keep a steady flow of blood going o the heart, arteries can widen tremendously, but the plaque will eventually rupture. When blood clots to seal the wound in the plaque, it totally cuts off the artery and the heart ends up receiving no blood, causing the all important muscle will weaken and eventually cease to work because of lack of nutrients.

Map of Cardiovascular diseases around the world. Darker colors signify larger percentage of diseased population. Picture obtained from Wikimedia Commons



=== WEBTRIBUTIONS: //Your Gross and Cool Body // //National Geographic // //Medtropolis // //The Franklin Institute Wikimedia Commons flickrCC //  ===