- Interatrial septum
Infobox Anatomy
Name = PAGENAME
Latin =
GraySubject = 138
GrayPage = 530
Caption = Interior of right side of heart. (labeled at right, as 'atrial septum')
Caption2 = Interior of dorsal half of heart of human embryo of about thirty-five days.
System =
MeshName = Heart+Septum
MeshNumber = A07.541.459
The interatrial septum is the wall of tissue that separates the right and left atria of theheart .Development
The interatrial septum forms during the first and second months of
fetal development . Formation of the septum occurs in several stages. The first is the development of theseptum primum , a crescent-shaped piece of tissue forming the initial divider between the right and left atria. Because of its crescent shape, the septum primum does not fully occlude the space between left and right atria; the opening that remains is called theostium primum . During fetal development, this opening allows blood to be shunted from the right atrium to the left.As the septum primum grows, the ostium primum progressively narrows. Before the ostium primum is completely occluded, a second opening called the
ostium secundum begins to form in theseptum primum . Theostium secundum allows continued shunting of blood from the right atrium to the left.To the right of the septum primum, the
septum secundum begins to form. This thick, muscular structure initially takes on the same crescent shape as the septum primum, except that it originates anteriorly, whereas the septum primum originates posteriorly. As the septum secundum grows, it leaves a small opening called theforamen ovale . The foramen ovale is continuous with the ostium secundum, again providing for continued shunting of blood.The ostium secundum progressively enlarges and the size of the septum primum diminishes. Eventually, the septum primum is nothing more than a small flap that covers the foramen ovale on its left side. This flap of tissue is called the valve of the foramen ovale. It opens and closes in response to
pressure gradient s between the left and right atria. When the pressure is greater in the right atrium, the valve opens; when the pressure is greater in the left atrium, the valve closes. Because thelung s are nonfunctional in fetal life, pressure in thepulmonary circulation is greater than that of thesystemic circulation . Consequently, the right atrium is generally under higher pressures than the left atrium, and the valve of the foramen ovale is normally open.At birth, there is a reversal in the pressure gradient between the atria, resulting in functional closure of the valve of the foramen ovale. Permanent anatomical closure of the foramen ovale occurs with time in normal infants. Inappropriate closure of the foramen ovale results in
patent foramen ovale .Disorders
*
Atrial septal defect is a relatively common heart malformation that occurs when the interatrial septum fails to develop properly.References
* Gray's Anatomy: The Anatomical Basis of Clinical Practice, 39th ed. (2005). ISBN 0-443-07168-3
* "Septum, interatrial." Stedman's Medical Dictionary, 27th ed. (2000). ISBN 0-683-40007-XExternal links
*
* [http://user.gru.net/clawrence/vccl/chpt1/iasept.gifDiagram]
* [http://www.indiana.edu/~anat550/cvanim/iasd/iasd.html Animation] , fromIndiana University
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