The sinoatrial node is a single specialized location in the atrium that has a higher automaticity (a faster pacemaker) than the rest of the heart and, therefore, is usually responsible for setting the heart rate and initiating each heartbeat.Any part of the heart that initiates an impulse without waiting for the sinoatrial node is called an ectopic focus and is, by definition, a pathological phenomenon. This may cause a single premature beat now and then, or, if the ectopic focus fires more often than the sinoatrial node, it can produce a sustained abnormal rhythm. Rhythms produced by an ectopic focus in the atria, or by the atrioventricular node, are the least dangerous dysrhythmias; but they can still produce a decrease in the hearts pumping efficiency because the signal reaches the various parts of the heart muscle with different timing than usual and can be responsible for poorly coordinated contraction.Conditions that increase automaticity include sympathetic nervous system stimulation and hypoxia. The resulting heart rhythm depends on where the first signal begins: If it is the sinoatrial node, the rhythm remains normal but rapid; if it is an ectopic focus, many types of dysrhythmia may ensue. Re-entry
Re-entrant arrhythmias occur when an electrical impulse recurrently travels in a tight circle within the heart, rather than moving from one end of the heart to the other and then stopping.Every cardiac cell can transmit impulses of excitation in every direction but will do so only once within a short time.
Accessory breasts, also known as polymastia, supernumerary breasts, or mammae erraticae, is the condition of having an additional breast. Extra breasts may appear with or without nipples or areolae. It is a condition and a form of atavism which is most prevalent in male humans, and often goes untreated as it is mostly harmless. In recent years, many affected women have had a plastic surgery operation to remove the additional breasts, for purely aesthetic reasons. A related condition, in which extra nipples form, is called "supernumerary nipple" or "polythelia". Presentation
In some cases, the accessory breast may not be visible at the surface. In these cases, it may be possible to distinguish their appearance from normal breast tissue with MRI. In other cases, accessory breasts have been known to lactate, as illustrated in a drawing showing a child nursing at ectopic breast tissue on the lateral thigh. There is some evidence that the condition may be more common in Native American populations. Cause
Polymastia typically occurs in the womb during the development. During normal development, breast tissue will develop along the milk line, and additional tissue will disintegrate and be absorbed into the body. Polymastia occurs when the additional tissue does not disintegrate before birth. This condition can be inherited. See also
Artemis § As the Lady of Ephesus (fertility goddess with many breasts)
Fleischers syndrome

References

A Paper on the Appearance of Multiple Mammaries in Humans, R. Eghardt, Oxford University Press (1923)
Weird Diseases, B. Hargreaves and M. Wallette, Emu Publishing (2007)


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