Information about Four Chambered Heart

The heart is a muscular organ responsible for pumping blood through the blood vessels by repeated, rhythmic contractions, or a similar structure in the annelids, mollusks, and arthropods.^[1] The term cardiac (as in cardiology) means "related to the heart" and comes from the Greek καρδία, kardia, for "heart." The heart is composed of cardiac muscle, an involuntary muscle tissue which is found only within this organ.^[2] The average human heart beating at 72 BPM, will beat approximately 2.5 billion times during a lifetime of 66 years.

Early development

Main article: Heart development

The human embryonic heart begins beating about 21 days after conception, or five weeks after the last normal menstrual period (LMP), which is the date normally used to date 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 linearly for the first month of beating, peaking at 165-185 BPM during the early 7th week, (early 9th week after the LMP). This acceleration is approximately 3.3 BPM per day, or about 10 BPM every three days, an increase of 100 BPM in the first month.^[3]

After peaking at about 9.5 weeks after the LMP, it decelerates to about 152 BPM (+/-25 BPM) during the 15th week after the LMP. After the 15th week the deceleration slows reaching an average rate of about 145 (+/-25 BPM) BPM at term. The regression formula which describes this acceleration before the embryo reaches 25 mm in crown-rump length or 9.2 LMP weeks is Age in days = EHR(0.3)+6

There is no difference in male and female heart rates before birth.^[4]

Structure

In the human body, the heart is usually situated in the middle of the thorax with the largest part of the heart slightly offset to the left (although sometimes it is on the right, see dextrocardia), underneath the breastbone (see diagrams). The heart is usually felt to be on the left side because the left heart (left ventricle) is stronger (it pumps to all body parts). The left lung is smaller than the right lung because the heart occupies more of the left hemithorax. The heart is enclosed by a sac known as the pericardium and is surrounded by the lungs. The pericardium comprises of two parts: the fibrous pericardium, made of dense fibrous connective tissue; and a double membrane structure containing a serous fluid to reduce friction during heart contractions (the serous pericardium). The mediastinum, a subdivision of the thoracic cavity, is the name of the heart cavity.

The apex is the blunt point situated in an inferior (pointing down and left) direction. A stethoscope can be placed directly over the apex so that the beats can be counted. It is located posterior to the 5th intercostal space in the left mid-clavicular line. In normal adults, the mass of the heart is 250-350 g (9-12 oz), or about three quarters the size of a clenched fist, but extremely diseased hearts can be up to 1000 g (2 lb) in mass due to hypertrophy. It consists of four chambers, the two upper atria (singular: atrium ) and the two lower ventricles. On the left is a picture of a fresh human heart which was removed from a 64-year-old male.

Functioning

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 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 a passive process called 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. 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.

Starting in the right atrium, the blood flows through the tricuspid valve to the right ventricle. Here it is pumped out 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 bicuspid valve to the left ventricle and on to through the aortic semilunar valve to the aorta. The aorta forks, and the blood is divided between major arteries which supply the upper and lower body. The blood travels in the arteries to the smaller arterioles, then finally to the tiny capillaries which feed each cell. The (relatively) deoxygenated blood then travels to the venules, which coalesce into veins, then to the inferior and superior venae cavae and finally back to the right atrium where the process began.

The heart is effectively a syncytium, a meshwork of cardiac muscle cells interconnected by contiguous cytoplasmic bridges. This relates to electrical stimulation of one cell spreading to neighboring cells

First aid

See cardiac arrest for emergencies involving the heart

If a person is encountered in cardiac arrest (no heartbeat), cardiopulmonary resuscitation (CPR) should be started and help called. If an automated external defibrillator is available, this device may automatically administer defibrillation if this is indicated. Usually, if there is enough time, the person can be rushed to the hospital where he or she will be cared for by a cardiologist, a doctor who specializes in the heart and lungs.

Food use

The hearts of cattle, sheep, pigs, chickens and certain fowl are consumed in many countries. They are counted among offal, but being a muscle, the taste of heart is like regular meat. It resembles venison in structure and taste.

As a symbol

For more details on this topic, see Heart (symbol).

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For more details on this topic, see Heart (Anthropology).

The heart was historically seen by some as the seat of the soul and the organ responsible for human thought. The Romans for example noticed that changing heart rates often corresponded with emotions such as fear, love and excitement. While it is now known that those changes in heartbeat rate are reactions rather than causes of thoughts or emotions, the term "heart" is widely used metaphorically when talking about love. When used in this metaphorical sense, the heart is often illustrated as an icon (♥).

The term "heart" can also refer to the core or center of anything e.g. "The heart of the matter". The center of the world, the core, is the "heart of the world."

The Aztec civilization used the heart as a sacrificial token during the sacrifice of a human being. The priest used a stone knife to cut into the thoracic cavity and remove the heart, upon which it would be placed on a stone altar as an offering to the gods. The greatest sacrifice under the reign of Montezuma involved the removal of the hearts of over 12,000 enemy soldiers.

References

www.3pic.com

External links

• eMedicine: Surgical anatomy of the heart
• Very Comprehensive Heart Site
• Self Improvement Wednesday - ABC 702 Drive audio
• The circulatory system
• The position of the heart
• Interactive 3D heart This realistic heart can be rotated, and all its components can be studied from any angle.

•  • [ e] Anatomy of torso, cardiovascular system: heart
Structures	atria (interatrial septum, musculi pectinati) • ventricles (interventricular septum, trabeculae carneae, chordae tendinae, papillary muscle) • valves • cusps
Regions	base • apex • grooves (coronary/atrioventricular, interatrial, anterior interventricula, posterior interventricular) • surfaces (sternocostal, diaphragmatic) • borders (right, left)
Right heart	(vena cavae, coronary sinus) → right atrium (auricle, fossa ovalis, limbus of fossa ovalis, crista terminalis, valve of the inferior vena cava, valve of the coronary sinus) → tricuspid valve → right ventricle (conus arteriosus, moderator band/septomarginal trabecula)  → pulmonary valve → (pulmonary artery and pulmonary circulation)
Left heart	(pulmonary veins) → left atrium (auricle) → mitral valve → left ventricle → aortic valve (aortic sinus) → (aorta and systemic circulation)
Layers	pericardium  (sinus) • epicardium • myocardium • endocardium • cardiac skeleton (fibrous trigone, fibrous rings)
Conduction system	Cardiac pacemaker • SA node • AV node• bundle of His • Purkinje fibers

•  • [ e] Cardiovascular system
Blood  |  Heart → Aorta → Arteries → Arterioles → Capillaries → Venules → Veins → Vena cava → Heart → Pulmonary arteries → Lungs → Pulmonary vein