Primitive atrium
Encyclopedia
The primitive atrium is a term used to describe a stage in the embryonic development of the human heart
. It grows rapidly and partially encircles the bulbus cordis
; the groove against which the bulbus cordis lies is the first indication of a division into right and left atria
.
The cavity of the primitive atrium becomes subdivided into right and left chambers by a septum, the septum primum
, which grows downward into the cavity.
For a time the atria communicate with each other by an opening, the ostium primum of Born, below the free margin of the septum.
This opening is closed by the union of the septum primum with the septum intermedium, and the communication between the atria is reëstablished through an opening which is developed in the upper part of the septum primum; this opening is known as the foramen ovale
(ostium secundum of Born) and persists until birth.
A second septum, the septum secundum
, semilunar in shape, grows downward from the upper wall of the atrium immediately to the right of the primary septum and foramen ovale.
Shortly after birth it fuses with the primary septum, and by this means the foramen ovale is closed, but sometimes the fusion is incomplete and the upper part of the foramen remains patent. The limbus fossæ ovalis denotes the free margin of the septum secundum.
Issuing from each lung is a pair of pulmonary veins; each pair unites to form a single vessel, and these in turn join in a common trunk which opens into the left atrium
.
Subsequently the common trunk and the two vessels forming it expand and form the vestibule
or greater part of the atrium, the expansion reaching as far as the openings of the four vessels, so that in the adult all four veins open separately into the left atrium.
Heart
The heart is a myogenic muscular organ found in all animals with a circulatory system , that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...
. It grows rapidly and partially encircles the bulbus cordis
Bulbus cordis
The bulbus cordis lies ventral to the primitive ventricle after the developing heart assumes its S-shaped form...
; the groove against which the bulbus cordis lies is the first indication of a division into right and left atria
Atria
Atria may refer to:*Atrium , an anatomical structure of the heart*Atrium , a large open space within a building*Atria or Alpha Trianguli Australis, a star in the constellation Triangulum Australe...
.
The cavity of the primitive atrium becomes subdivided into right and left chambers by a septum, the septum primum
Septum primum
In the developing heart, the cavity of the primitive atrium becomes subdivided into right and left chambers by a septum, the septum primum, which grows downward into the cavity. The increasingly smaller gap below it is known as the ostium primum...
, which grows downward into the cavity.
For a time the atria communicate with each other by an opening, the ostium primum of Born, below the free margin of the septum.
This opening is closed by the union of the septum primum with the septum intermedium, and the communication between the atria is reëstablished through an opening which is developed in the upper part of the septum primum; this opening is known as the foramen ovale
Foramen ovale
There are multiple structures in the human body with the name foramen ovale :* In the fetal heart, the foramen ovale is a shunt from the right atrium to left atrium....
(ostium secundum of Born) and persists until birth.
A second septum, the septum secundum
Septum secundum
The septum secundum, semilunar in shape, grows downward from the upper wall of the atrium immediately to the right of the primary septum and ostium secundum....
, semilunar in shape, grows downward from the upper wall of the atrium immediately to the right of the primary septum and foramen ovale.
Shortly after birth it fuses with the primary septum, and by this means the foramen ovale is closed, but sometimes the fusion is incomplete and the upper part of the foramen remains patent. The limbus fossæ ovalis denotes the free margin of the septum secundum.
Issuing from each lung is a pair of pulmonary veins; each pair unites to form a single vessel, and these in turn join in a common trunk which opens into the left atrium
Left atrium
The left atrium is one of the four chambers in the human heart. It receives oxygenated blood from the pulmonary veins, and pumps it into the left ventricle, via the mitral valve.-Foramen ovale:...
.
Subsequently the common trunk and the two vessels forming it expand and form the vestibule
Vestibule (architecture)
A vestibule is a lobby, entrance hall, or passage between the entrance and the interior of a building.The same term can apply to structures in modern or ancient roman architecture. In modern architecture vestibule typically refers to a small room or hall between an entrance and the interior of...
or greater part of the atrium, the expansion reaching as far as the openings of the four vessels, so that in the adult all four veins open separately into the left atrium.