Editing Human body (section)

==== Heart ====
{{Main|Heart}}
The heart is an organ located in the [[thoracic cavity]] between the [[lung]]s and slightly to the left. It is surrounded by the [[pericardium]], which holds it in place in the [[mediastinum]] and serves to protect it from blunt trauma, [[infection]] and help lubricate the movement of the heart via [[pericardial fluid]].<ref>{{Cite journal|last1=Jaworska-Wilczynska|first1=Maria|last2=Trzaskoma|first2=Pawel|last3=Szczepankiewicz|first3=Andrzej A.|last4=Hryniewiecki|first4=Tomasz|date=2016|title=Pericardium: structure and function in health and disease|journal=Folia Histochemica et Cytobiologica|volume=54|issue=3|pages=121–125|doi=10.5603/FHC.a2016.0014|issn=1897-5631|pmid=27654013|doi-access=free}}</ref> The heart works by [[Circulatory system|pumping blood around the body]] allowing [[oxygen]], [[nutrient]]s, [[Metabolic waste|waste]], [[hormone]]s and [[white blood cell]]s to be transported.
[[File:Diagram of the human heart (cropped).svg|left|thumb|207x207px|Diagram of the human heart]]
The heart is composed of [[Atrium (heart)|two atria]] and [[Ventricle (heart)|two ventricles]]. The primary purpose of the atria is to allow uninterrupted venous blood flow to the heart during [[Systole|ventricular systole]]. This allows enough blood to get into the ventricles during [[Systole|atrial systole]]. Consequently, the atria allows a [[cardiac output]] roughly 75% greater than would be possible without them.<ref>{{Cite book|url=https://books.google.com/books?id=A3OmTSgtOgwC|title=The Gross Physiology of the Cardiovascular System|date=1999|first=Robert M. |last=Anderson|edition=2nd |chapter=Chapter 1: Normal Physiology |page=11}}</ref> The purpose of the ventricles is to [[Pulmonary circulation|pump blood to the lungs]] through the right ventricle and to [[Circulatory system|the rest of the body]] through the left ventricle.<ref>{{Cite web|title=Ventricle {{!}} heart|url=https://www.britannica.com/science/ventricle-heart|access-date=2021-08-07|website=Encyclopedia Britannica|language=en}}</ref>

The heart has an [[Cardiac conduction system|electrical conduction system]] to control the contraction and relaxation of the muscles. It starts in the [[sinoatrial node]] traveling through the atria causing them to [[Cardiac cycle|pump blood into the ventricles]]. It then travels to the [[atrioventricular node]], which makes the signal slow down slightly allowing the ventricles to fill with blood before pumping it out and starting the cycle over again.<ref>{{Cite web|title=How the Heart Works |url=https://www.nhlbi.nih.gov/health-topics/how-heart-works|access-date=2021-08-07|website=NHLBI, NIH |at="Your Heart's Electrical System" |url-status=live |archive-url= https://web.archive.org/web/20210813001819/https://www.nhlbi.nih.gov/health-topics/how-heart-works |archive-date= Aug 13, 2021 }}</ref>

[[Coronary artery disease]] is the [[List of causes of death by rate|leading cause of death worldwide]], making up 16% of all deaths.<ref>{{Cite web|title=The top 10 causes of death|url=https://www.who.int/news-room/fact-sheets/detail/the-top-10-causes-of-death |date=9 December 2020 |access-date=2021-08-07|website=WHO |language=en}}</ref> It is caused by the buildup of [[Atherosclerosis|plaque]] in the [[coronary arteries]] supplying the heart, eventually the arteries may become so narrow that [[Ischemia|not enough blood]] is able to reach the [[Cardiac muscle|myocardium]],<ref>{{Cite web|date=2021-07-19|title=Coronary Artery Disease |url=https://www.cdc.gov/heartdisease/coronary_ad.htm|access-date=2021-08-07|website=Centers for Disease Control and Prevention|language=en-us}}</ref> a condition known as [[Myocardial infarction|myocardial infarction or heart attack]], this can cause [[heart failure]] or [[cardiac arrest]] and eventually death.<ref>{{Cite web|date=2021-01-11|title=Heart Attack Symptoms, Risk Factors, and Recovery |url=https://www.cdc.gov/heartdisease/heart_attack.htm|access-date=2021-08-07|website=Centers for Disease Control and Prevention|language=en-us}}</ref> Risk factors for coronary artery disease include [[Obesity-associated morbidity|obesity]], [[Health effects of tobacco|smoking]], [[Hypercholesterolemia|high cholesterol]], [[Hypertension|high blood pressure]], [[Sedentary lifestyle|lack of exercise]] and [[diabetes]].<ref>{{Cite web|date=2019-12-09|title=Know Your Risk for Heart Disease |url=https://www.cdc.gov/heartdisease/risk_factors.htm|access-date=2021-08-07|website=Centers for Disease Control and Prevention|language=en-us}}</ref> [[Heart cancer|Cancer can affect the heart]], though it is exceedingly rare and has usually [[Metastasis|metastasized]] from another part of the body such as the [[Lung cancer|lungs]] or [[Breast cancer|breasts]]. This is because the [[Cardiac muscle|heart cells]] quickly stop dividing and all growth occurs through [[Hypertrophy|size increase]] rather than [[Mitosis|cell division]].<ref>{{Cite web|date=2009-02-10|title=Matters of the Heart: Why Are Cardiac Tumors So Rare? |url=https://www.cancer.gov/types/metastatic-cancer/research/cardiac-tumors|access-date=2021-08-07|website= National Cancer Institute|language=en}}</ref>