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Human heart
External view
Surface view of the heart
Latin	cor humanum
Gray's	subject #135 506
System	Circulatory
Artery	Right coronary artery, left coronary artery, anterior interventricular artery
Vein	Superior vena cava, inferior vena cava, right pulmonary veins, left pulmonary veins
MeSH	Heart
Dorlands/Elsevier	Heart

The human heart is a muscular organ that provides a continuous blood circulation through the cardiac cycle and is one of the most vital organs in the human body.^[1] The heart is divided into four main chambers: the two upper chambers are called the left and right Atrium and two lower chambers are called the right and left Ventricle. There is a thick wall of muscle separating the right side and the left side of the heart called the septum. Normally with each beat the right ventricle pumps the same amount of blood into the lungs that the left ventricle pumps out into the body. Physicians commonly refer to the right atrium and right ventricle together as the right heart and to the left atrium and ventricle as the left heart.^[2]

The electric energy that stimulates the heart occurs in the sinoatrial node, which produces a definite potential and then discharges, sending an impulse across the atria. In the atria the electrical signal moves from cell to cell^[3] while in the ventricles the signal is carried by specialized tissue called the Purkinje fibers^[4] which then transmit the electric charge to the myocardium.

At 21 days after conception, the human heart begins beating at 70 to 80 beats per minute and accelerates linearly for the first month of beating.

The human embryonic heart begins beating at around 21 days after conception, or five weeks after the last normal menstrual period (LMP). The first day of the LMP is normally used to date the start of the gestation (pregnancy). The human heart begins beating at a rate near the mother’s, about 75-80 beats per minute (BPM).

The embryonic heart rate (EHR) then accelerates by approximately 100 BPM during the first month to peak at 165-185 BPM during the early 7th week afer conception, (early 9th week after the LMP). This acceleration is approximately 3.3 BPM per day, or about 10 BPM every three days, which is an increase of 100 BPM in the first month.^[5][6][7] The regression formula, which describes this acceleration before the embryo reaches 25 mm in crown-rump length, or 9.2 LMP weeks, is: the Age in days = EHR(0.3)+6. .^[8]

After 9.1 weeks after the LMP, it decelerates to about 152 BPM (+/-25 BPM) during the 15th week post LMP. After the 15th week, the deceleration slows to an average rate of about 145 (+/-25 BPM) BPM, at term. There is no difference in female and male heart rates before birth. The human heart and its disorders (cardiopathies) are studied primarily by cardiology.

Real-time MRI of the human heart

Human-heart

Real-time MRI - Human Heart (short-axis view)

Structure[link]

Heart

anterior view, coronal section.

The blood supply of the heart is provided by the coronary circulation. Coronary arteries labeled in red text and other landmarks in blue text.

The human heart has a mass of between 250 and 350 grams and is about the size of a fist.^[9]

It is enclosed in a double-walled protective sac called the pericardium.^[10]The double membrane of pericardium consist of the pericardial fluid which nourishes the heart and prevents shocks. The superficial part of this sac is called the fibrous pericardium. The fibrous pericardial sac is itself lined with the outer layer of the serous pericardium (known as the parietal pericardium). This composite (fibrous-parietal-pericardial) sac protects the heart, anchors its surrounding structures, and prevents overfilling of the heart with blood. The inner layer also provides a smooth lubricated sliding surface within which the heart organ can move in response to its own contractions and to movement of adjacent structures such as the diaphragm and lungs.

The outer wall of the human heart is composed of three layers. The outer layer is called the epicardium, or visceral pericardium since it is also the inner wall of the (serous) pericardium. The middle layer of the heart is called the myocardium and is composed of muscle which contracts. The inner layer is called the endocardium and is in contact with the blood that the heart pumps. Also, it merges with the inner lining (endothelium) of blood vessels and covers heart valves.^[11]

The human heart has four chambers, two superior atria and two inferior ventricles. The atria are the receiving chambers and the ventricles are the discharging chambers.

The pathways of blood through the human heart is part of the pulmonary and systemic circuits. These pathways include the tricuspid valve, the mitral valve, the aortic valve, and the pulmonary valve.^[12] The mitral and tricuspid valves are classified as the atrioventricular (AV) valves. This is because they are found between the atria and ventricles. The aortic and pulmonary semi-lunar valves separate the left and right ventricle from the pulmonary artery and the aorta respectively. These valves are attached to the chordae tendinae (literally the heartstrings), which anchors the valves to the papilla muscles of the heart.

The interatrioventricular septum separates the left atrium and ventricle from the right atrium and ventricle, dividing the heart into two functionally separate and anatomically distinct units.

Functioning[link]

Blood flow diagram of the human heart. Blue components indicate de-oxygenated blood pathways and red components indicate oxygenated pathways.

Blood flows through the heart in one direction, from the atria to the ventricles, and out of the great arteries, or the aorta for example. Blood is prevented from flowing backwards by the tricuspid, bicuspid, aortic, and pulmonary valves.

The heart acts as a double pump. The function of the right side of the heart (see right heart) is to collect de-oxygenated blood, in the right atrium, from the body (via superior and inferior vena cavae) and pump it, via the right ventricle, into the lungs (pulmonary circulation) so that carbon dioxide can be dropped off and oxygen picked up (gas exchange). This happens through the passive process of diffusion.

The left side (see left heart) collects oxygenated blood from the lungs into the left atrium. From the left atrium the blood moves to the left ventricle which pumps it out to the body (via the aorta).

On both sides, the lower ventricles are thicker and stronger than the upper atria. The muscle wall surrounding the left ventricle is thicker than the wall surrounding the right ventricle due to the higher force needed to pump the blood through the systemic circulation. Atria facilitate circulation primarily by allowing uninterrupted venous flow to the heart, preventing the inertia of interrupted venous flow that would otherwise occur at each ventricular systole.^[13]

Starting in the right atrium, the blood flows through the tricuspid valve to the right ventricle. Here, it is pumped out of the pulmonary semilunar valve and travels through the pulmonary artery to the lungs. From there, blood flows back through the pulmonary vein to the left atrium. It then travels through the mitral valve to the left ventricle, from where it is pumped through the aortic semilunar valve to the aorta and to the rest of the body. The (relatively) deoxygenated blood finally returns to the heart through the inferior vena cava and superior vena cava, and enters the right atrium where the process began.

Lifestyle and heart health[link]

Obesity, high blood pressure, and high cholesterol can increase the risk of developing heart disease. However, half the number of heart attacks occur in people with normal cholesterol levels. Heart disease is a major cause of death.

It is generally accepted that factors such as exercise, diet, and overall well-being, including both emotional and physiological components, affect heart health in humans.^{[14][15][16][17]}

See also[link]

• Electrocardiography
• Heart rate
• Blood pressure

References[link]

External links[link]

• Prenatal human heart development
• Anatomy of the Human Heart - Texas Heart Institute
• The Gross Physiology of the Cardiovascular System (2nd Ed., 2012)
• Dissection review showing vessels of the heart as well as internal and external features
• The Human Heart: An Online Exploration from The Franklin Institute
• Blood Flow Through the Human Heart

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Hamza Yusuf
Hamza Yusuf at Doha Academy Education Conference in Qatar, 2010.
Born	Mark Hanson 1958 (age 53–54) Walla Walla, Washington, United States
Residence	Northern California, United States
Occupation	Islamic scholar
Religion	Sunni Islam[1][2]
Spouse	Liliana (Umm Yahya) Hanson
Website
Sandala.org

Hamza Yusuf Hanson is an American Islamic scholar^[3][4], and (with Zaid Shakir and Hatem Bazian) is co-founder of Zaytuna College in Berkeley, California, United States. He is a convert to Islam, and is one of the signatories of A Common Word Between Us and You, an open letter by Islamic scholars to Christian leaders, calling for peace and understanding. He has described the 9/11 attacks as "an act of 'mass murder, pure and simple'". Condemning the attacks, he has also stated "Islam was hijacked ... on that plane as an innocent victim".^[5] The Guardian newspaper in the United Kingdom reported that he "is arguably the west's most influential Islamic scholar" and added that "many Muslims find his views hard to stomach."^[6]

Biography[link]

Hamza Yusuf was born to two academics^[7] in Washington State and raised in Northern California. In 1977, he became Muslim and subsequently traveled to the Muslim world and studied for ten years in the United Arab Emirates, Saudi Arabia, as well as North and West Africa.^[8] Hamza Yusuf spent four years studying in the United Arab Emirates and elsewhere in the Middle East. Later he traveled to West Africa and studied in Mauritania, Medina, Algeria, and Morocco under such scholars as Murabit al Haaj; Baya bin Salik, head of the Islamic court in Al-'Ain, United Arab Emirates; Muhammad Shaybani, Mufti of Abu Dhabi; Hamad al-Wali; and Muhammad al-Fatrati of Al Azhar University in Cairo, Egypt.^{[citation needed]} After more than a decade abroad, he returned to the United States and earned degrees in nursing from Imperial Valley College and religious studies at San José State University.^{[citation needed]}

Hamza Yusuf is a co-founder of Zaytuna College, located in Berkeley, California. He is an advisor to Stanford University's Program in Islamic Studies and the Center for Islamic Studies at Berkeley's Graduate Theological Union.^{[citation needed]} He also serves as a member of the board of advisors of George Russell's One Nation, a national philanthropic initiative that promotes pluralism and inclusion in America. In addition, he serves as vice-president for the Global Center for Guidance and Renewal, which was founded and is currently presided over by Abdallah Bin Bayyah, one of the top jurists and masters of Islamic sciences in the world.^{[citation needed]}

Hamza Yusuf has promoted Islamic sciences and classical teaching methodologies throughout the world. He has also been an advocate for social justice, peace, and conviviality among peoples and places. For several years, he has argued that the "them versus us" problem is fundamentally flawed, and, in R. D. Laing’s term, a “knot” that will destroy people if they do not extricate themselves from it.^{[citation needed]}

Hamza Yusuf has served as an advisor to many organizations, leaders, and heads of state.^{[citation needed]} He has been an innovator in modern Islamic education^{[citation needed]}, founding the highly imitated Deen Intensives, and with Ibrahim Osi-Efa, he started the first Rihla program in England, which has been running for over fifteen years. Dozens of young Muslims who were influenced by his call to reviving traditional Islamic studies in the West went to the Muslim lands in the nineties and early part of the current decade to study, many of who are now teachers in their own right.^{[citation needed]}

With Eissa Bougari, Hamza Yusuf initiated a media challenge to the Arab world that resulted in a highly successful cultural religious program that he hosted for three years and was one of the most watched programs in the Arab world during Ramadan.^{[citation needed]} Cambridge Media Studies stated that this program had a profound influence on subsequent religious programming in the Arab world. He has also been interviewed on BBC several times and was the subject of a BBC documentary segment The Faces of Islam, ushering in the new millennium, as it aired at 11:30 pm on December 31, 1999. Hamza Yusuf has been an outspoken critic of American foreign policy as well as Islamic extremist responses to those policies.^{[citation needed]}

He has drawn criticism from both the extreme right in the West and Muslim extremists in the East.^[9] He told The Guardian: "Many people in the west do not realise how oppressive some Muslim states are – both for men and for women. This is a cultural issue, not an Islamic one. I would rather live as a Muslim in the west than in most of the Muslim countries, because I think the way Muslims are allowed to live in the west is closer to the Muslim way. A lot of Muslim immigrants feel the same way, which is why they are here."^[10]

He and colleagues founded the Zaytuna Institute in 1996, which has established an international reputation^{[citation needed]} for presenting a classical picture of Islam in the West and which is dedicated to the revival of traditional study methods and the sciences of Islam. Hamza Yusuf currently resides in Northern California with his wife and five children.^{[citation needed]}

Hamza Yusuf has also authored several encyclopedia articles and research papers. His published books include The Burda (2003), Purification of the Heart (2004), The Content of Character (2004), The Creed of Imam al-Tahawi (2007), Agenda to Change our Condition (2007), and Walking on Water (2010). Forthcoming are The Prayer of the Oppressed, and The Helpful Guide.^{[citation needed]}

Hamza Yusuf is the first American lecturer to teach in Morocco's prestigious and oldest university, the University of Al-Karaouine in Fes.^[11] He is married and has five children, all boys.

Critical reception[link]

Jordan's Royal Islamic Strategic Studies Centre placed him on its list of the top 50 most influential Muslims in the world.^{[citation needed]} The magazine Egypt Today described him as a kind of theological rock star, "the Elvis Presley of western Muslims."^[12] Recently, Hamza Yusuf was ranked as "the Western world's most influential Islamic scholar" by The 500 Most Influential Muslims, edited by John Esposito and Ibrahim Kalin, (2009).^[13]

Publications[link]

Books Authored[link]

• The Burda The Burda (2003)
• Purification of the Heart: Signs, Symptoms and Cures of the Spiritual Diseases of the Heart (2004)
• The Content of Character (2004)
• The State We Are In: Identity, Terror, and the Law of Jihad (contributing Author) (2006)
• The Creed of Imam al-Tahawi The Creed of Imam Al-Tahawi (2007)
• Agenda to Change our Condition co-authored with Zaid Shakir (2007)
• Walk on Water: The wisdom of Jesus Walk on Water: The wisdom of Jesus (2010)
• Educating your Child in Modern Times

Books with Foreword or note[link]

• Instruction of the Student: The Method of Learning
• The Prophetic Invocations By Mostafa Al-Badawi

Book Edited with Zaid Shakir[link]

• Submission Faith and Beauty Submission Faith and Beauty, The Religion of Islam by Joseph Lumbard (2009)

Papers[link]

• Caesarean Moon Births Part 1
• Caesarean Moon Births Part 2
• Climbing Mount Purgatorio
• Religion, Violence, and the Modern World
• Generous Tolerance in Islam and its Effects on the Life of a Muslim
• Chess in the Light of the Jurist
• Who are the Disbelievers?

References[link]

External links[link]

Wikimedia Commons has media related to: Hamza Yusuf

Websites[link]

• Sandala.org – Official website of Hamza Yusuf
• Zaytuna.org – Zaytuna College
• Sheikhhamza.com – Contains list of books recommended by Hamza Yusuf and a biography

See also[link]

• Zaytuna College
• Zaid Shakir