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Circulatory System - Latest Research

January 21, 2019

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Quiz
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Simplified diagram of the human Circulatory system in anterior view.Graphic credit: Wikipedia Commons

Blood vessels are the part of the circulatory system, and microcirculation, that transports blood throughout the human 1) ___. These vessels are designed to transport nutrients and oxygen to the tissues of the body. They also take waste and carbon dioxide and carry them away from the tissues and back to the heart. Blood vessels are needed to sustain life as all of the body's tissues rely on their functionality. There are three major types of blood vessels: the arteries, which carry the blood away from the heart; the capillaries, which enable the actual exchange of water and chemicals between the blood and the tissues; and the 2) ___, which carry blood from the capillaries back toward the heart. The word vascular, meaning relating to the blood vessels, is derived from the Latin vas, meaning vessel. A few structures (such as cartilage and the lens of the eye) do not contain blood vessels.

Blood vessels function to transport 3) ___. In general, arteries and arterioles transport oxygenated blood from the lungs to the body and its organs, and veins and venules transport deoxygenated blood from the body to the lungs. Blood vessels also circulate blood throughout the circulatory system. Oxygen (bound to hemoglobin in red blood cells) is the most critical nutrient carried by the blood. In all arteries apart from the pulmonary artery, hemoglobin is highly saturated (95-100%) with oxygen. In all veins apart from the pulmonary vein, the saturation of hemoglobin is about 75%. (The values are reversed in the pulmonary circulation.) In addition to carrying 4) ___, blood also carries hormones, waste products and nutrients for cells of the body.

Blood vessels do not actively engage in the transport of blood (they have no appreciable peristalsis). Blood is propelled through arteries and arterioles through pressure generated by the 5) ___. Blood vessels also transport red blood cells which contain the oxygen necessary for daily activities. The amount of red blood cells present in your vessels has an effect on your health. Hematocrit tests can be performed to calculate the proportion of red blood cells in your blood. Higher proportions result in conditions such as dehydration or heart disease while lower proportions could lead to anemia and long-term blood loss. Permeability of the endothelium is pivotal in the release of nutrients to the tissue. It is also increased in inflammation in response to histamine, prostaglandins and interleukins, which leads to most of the symptoms of inflammation (swelling, redness, warmth and pain).

Blood vessels play a huge role in virtually every medical condition. Cancer, for example, cannot progress unless the tumor causes formation of new blood vessels, which is called 6) ___, to supply the malignant cells' metabolic demand. Atherosclerosis, the formation of lipid lumps (atheromas) in the blood vessel wall, is the most common cardiovascular disease, the main cause of death in the Western world.

Blood vessel permeability is increased in inflammation. Damage, due to trauma or spontaneously, may lead to hemorrhage due to mechanical damage to the vessel endothelium. In contrast, occlusion of the blood vessel by atherosclerotic plaque, by an embolized blood clot or a foreign body leads to downstream ischemia (insufficient blood supply) and possibly necrosis. Vessel occlusion tends to be a positive feedback system; an occluded vessel creates eddies in the normally laminar flow or plug flow blood currents. These eddies create abnormal fluid velocity gradients which push blood elements such as cholesterol or chylomicron bodies to the endothelium. These deposit onto the arterial walls which are already partially occluded and build upon the blockage. The most common disease of the blood vessels is hypertension or high blood pressure. This is caused by an increase in the 7) ___ of the blood flowing through the vessels. Hypertension can lead to more serious conditions such as heart failure and stroke. To prevent these diseases, the most common treatment option is medication as opposed to surgery. Aspirin helps prevent blood clots and can also help limit inflammation.

Scientists have managed to grow perfect human blood vessels as organoids in a petri dish for the first time. The breakthrough engineering technology dramatically advances research of vascular diseases like diabetes, identifying a key pathway to potentially prevent changes to blood vessels -- a major cause of death and morbidity among those with diabetes. The breakthrough engineering technology, outlined in a new study published this week in Nature, dramatically advances research of vascular diseases like diabetes, identifying a key pathway to potentially prevent changes to blood vessels -- a major cause of death and morbidity among those with diabetes. An organoid is a three-dimensional structure grown from stem 8) ___ that mimics an organ and can be used to study aspects of that organ in a petri dish. Being able to build human blood vessels as organoids from stem cells is a game changer.

Every single organ in our body is linked with the circulatory system. This could potentially allow researchers to unravel the causes and treatments for a variety of vascular diseases, from Alzheimer's disease, cardiovascular diseases, wound healing problems, stroke, cancer and, of course, diabetes.“ Diabetes affects an estimated 420 million people worldwide. Many diabetic symptoms are the result of changes in blood vessels that result in impaired blood circulation and oxygen supply to tissues. Despite its prevalence, very little is known about the vascular changes arising from diabetes. This limitation has slowed the development of much-needed treatment. To tackle this problem, a scientific team developed a groundbreaking model: three-dimensional human blood vessel organoids grown in a petri dish. These so-called “vascular organoids“ can be cultivated using stem cells in the lab, strikingly mimicking the structure and function of real human blood vessels. When researchers transplanted the blood vessel organoids into mice, they found that they developed into perfectly functional human blood vessels including arteries and capillaries. The discovery illustrates that it is possible not only to engineer blood vessel organoids from human stem cells in a dish, but also to grow a functional human vascular system in another species. What is so exciting about this research, is that there was success in making real human blood vessels out of stem cells. The resulting organoids resemble human capillaries to a great extent, even on a molecular level, which can now be used to study blood vessel diseases directly on human tissue. One feature of 9) ___ is that blood vessels show an abnormal thickening of the basement membrane. As a result, the delivery of oxygen and nutrients to cells and tissues is strongly impaired, causing a multitude of health problems, such as kidney failure, heart attacks, strokes, blindness and peripheral artery disease, leading to amputations. When the authors exposed the blood vessel organoids to a “diabetic“ environment in a petri dish, a massive expansion of the basement membrane in the vascular organoids was observed. This typical thickening of the basement membrane is strikingly similar to the vascular damage seen in diabetic patients. The authors searched for chemical compounds that could block thickening of the blood vessel 10) ___. They found none of the current anti-diabetic medications had any positive effects on these blood vessel defects. However, they did discover that a secretase inhibitor, a type of enzyme in the body, prevented the thickening of the blood vessel walls, suggesting, at least in animal models, that blocking secretase could be helpful in treating diabetes. This research could enable the identification of underlying causes of vascular disease, and has the potential to develop and test new treatments for patients with diabetes. Sources: Nature, 2019 DOI: 10.1038/s41586-018-0858-8; ScienceDaily.com; Wikipedia

ANSWERS: 1) body; 2) veins; 3) blood; 4) oxygen; 5) heartbeat; 6) angiogenesis; 7) pressure; 8) cells; 9) diabetes; 10) walls

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