Anatomy, Arteries

Article Author:
Anthony Mercadante
Article Editor:
Avais Raja
Updated:
10/6/2019 8:00:28 AM
PubMed Link:
Anatomy, Arteries

Introduction

Arteries make up a major part of the circulatory system, with the veins and heart being the other main components. Arteries make up tubelike structures that are responsible for the transportation of fluid (i.e., blood for of the circulatory system, and lymph for the lymphatic system) to and from every organ in the body. Mainly, arteries manage the transportation of oxygen, nutrients, and hormones through our bodies. Arteries can dispense fresh oxygen to the body after it gets loaded onto the Fe 2+ found in the center of hemoglobin. The oxygen binds to hemoglobin and is carried by the arteries to areas that are lacking oxygen. Through a shift in affinity for the oxygen, it is then unloaded to specific areas through high surface areas knowns as capillaries.[1] Far from being a changeless structure, arteries adapt through signals received from the central nervous system, as they also react to an outer stimulus like pressure, temperature, and substances. Vascular nerves are responsible for innervating the arteries allowing them to change to their stimuli. As catecholamines get released into the blood, the nerves send signals to the arteries to either constrict or dilate, leading to changes in pressure.[2] 

Arteries are composed of smooth muscle allowing constriction and dilation through the parasympathetic nervous system.[3] Arteries differ from veins in the sense that they most often are carrying unoxygenated blood away from the heart and into the rest of the body system. This is not always the case; however, as the pulmonary artery moves unoxygenated blood from the heart to the lungs to complete the gas exchange in the alveoli.[4] Arteries play a crucial role in maintaining homeostasis in the body. As individuals age, health issues begin presenting themselves in the form of stiffening or thicking of the arteries; however, many different issues develop with age and poor diet. Additionally, arteries begin to clog with a thicking of plaque known as atherosclerosis.[5] As problems arise in the structure of the arteries, it begins leading to more strain on the heart, which develops congestive heart failure and which is often fatal. The arteries are vital to maintaining a healthy cardiovascular system, thus a healthy lifestyle.

Structure and Function

The arteries throughout the body are composed of three different layers. The first most inner layer of the artery is known as the intima, which is made up of a smooth muscle layer that contains one layer of endothelial cells, and the rest is smooth muscle and elastin. The tunica intima creates a tube for the oxygen-rich blood to move through to reach the appropriate site of perfusion. In this way, there is no leakage from the artery, and the nutrient-rich blood can move to the appropriate area before it unloads its oxygen and other nutrients. The second layer is known as the media or the middle layer. This media layer is made up of more smooth muscle that can dilate or constrict, which adjusted the pressures felt on the arterial walls during systolic pumping. As the muscle contracts, the walls will feel more pressure from the left ventricle, and similarly, as the vessels dilate, the pressure observed will drop.[6] The last layer is the outer most known as the adventitia. The adventitia is crucial for connecting the arteries to other tissues in the body, including the vascular nerves, which control the smooth muscles in the arteries. In this way, the arteries do not move freely throughout the body but instead are held in place to ensure a consistent and effective cardiovascular system. Usually, the arteries are under the most pressure as they are receiving blood from the left ventricle, the most powerful section of the heart. However, the pulmonary artery is different for two reasons. Not only does it move unoxygenated blood from the heart to the lungs, but it also handles much less pressure, as the right ventricle has less force than the left. The pulmonary artery leads to blood to the lungs while the rest of the arteries move blood to specific areas of the body. The blood from the left ventricle gets pumped through the largest artery known as the aorta. The aorta then split into four different sections, the ascending aorta, the aortic arch curves over the heart, descending thoracic aorta, and the abdominal aorta. The ascending aorta moves up from the heart and further divides in the carotid artery, which supplies the brain with blood.[7] The aortic arch is similar to the ascending aorta and carries blood up for the back and neck. The descending aorta is responsible for bringing blood from the heart to smaller vessels in the chest or ribs. Finally, the abdominal aorta carries blood to iliac arteries, which provides circulation for many of the organs in the abdominal region.[8]

Embryology

During development, the arteries constantly change to maintain balance in changing environments. The heart and arteries develop from the mesoderm germ layer as it is composed of smooth muscle. After the mesoderm begins to differentiate into sections of the circulatory system due to specific growth factor signaling, the arteries start to form, and circulation powered by the heart initiates. At the beginning of development, the arteries form from the pharyngeal arches. Each arch changes into a specific arterial section during the 9-month pregnancy. During pregnancy, the fetus has a sharded circulatory system with the mother, making the movement of blood unique. The uterine arteries carry blood from the mother to the placenta, where it then can perfuse and travel to the fetus to supply it with oxygen. Fetal hearts also have a unique blood flow as blood does not become oxygenated in its lungs, instead of by the mother. A fetus has a unique connection between the aorta and the pulmonary called the ductus arteriosus.[9] This connection allows blood to flow past the lungs of the fetus as they are not in use while in the fetus is in the amniotic sac.

Muscles

In all of these examples, arteries are comprised of smooth muscle. Meaning they are nonstriated muscles that encompass the vessels to provide support and integrity to the entire artery. This smooth muscle reacts to difference signals and nervations to constrict or dilate to maintain consistent blood pressure, such as epinephrine and angiotensin II. The sympathetic nervous system can use high levels of epinephrine, which affect alpha-adrenergic receptors to cause the arteries to constrict. This increase in pressure can aid in perfusion during both trauma or hormonal imbalance.[10] Furthermore, the kidney can indirectly affect blood pressure through its release of renin. Renin allows for the creation of angiotensin II, a powerful vasoconstrictor.[11] Therefore through the endocrine system, different hormones are released into the blood, which is then able to signal the vascular nerves to change to maintain homeostasis.  

Clinical Significance

There are many more ways that arteries aid in maintaining balance, including some vasodilators such as histamine or serotonin. This, however, can become dangerous if balance is not maintained. An angiogram, or inserting of a tube and dye into the artery, can be used to monitor the blood flow to identify and bleeds or blockages. However, environmental factors also play a role in the structure of arteries. For example, during anaphylaxis shock, massive amounts of histamine are released into the body, causing the arteries to dilate to an unsafe amount. This creates a lack of pressure for perfusion of the nutrient-rich blood. In an attempt to make up for this loss, the body begins entering a state of compensated shock by the heart rate. This does not work forever, and without dilation, the patient will soon go into a state of shock. In addition to having to be balanced, many medical issues may arise that would further complicate the situation. One of the most common medical problems concerning arteries is atherosclerosis; the arteries build up with plaque until it affects normal cardiovascular function. This compilation of plaque can form anywhere, meaning a blockage can develop in any area. If blood supply gets cut off from the heart, then, a myocardial infarction will occur.[12] Similarly, if there is a blockage of blood flow supplying the brain, this is known as a stroke. A lack of blood supply to any area of the body can cause permanent severe damage or even death. For example, if blood supply is cut off from the retina, then one may develop amaurosis fugax or blindness.[13] Transfats and bad cholesterol have been shown to affect arteries negatively, leading to atherosclerosis. Therefore it is crucial to maintain a healthy lifestyle through diet and exercise. The cardiovascular system is essential for keeping all of the other systems in the body. Arteries, in particular, have a vital role in supplying nutrients to the rest of the body. It is crucial to recognize the part that arteries play in the cardiovascular system to prevent medical obstacles in the future.



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      Contributed by Kelvin Ma, (CC By-S.A. 3.0 https://creativecommons.org/licenses/by-sa/3.0/deed.en) Image courtesy: https://commons.wikimedia.org/wiki/File:Artery.svg

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