Not true about right atrium ?
Ans. is 'b' i.e., Antirior pa is derived from absorption of right horn of sinus venosus Sinus venarum (posterior pa of right atrium) is derived from absorption of right horn of sinus venosus (not anterirpa). Right atrium It has thinnest walls of the four chambers. It is divided by crista terminalis into two pas :- i) Rough anterior pa or atrium proper (pectinate pa), including auricle. It is derived from right half of primitive atrial chamber. There is a series of transverse muscular ridges called musculi pectinate which are attached to crista terminalis and gives appearance like "teeth of a comb". SA node is situated in the upper pa of crista terminates. Auricle lies in the superomedial poion. ii) Posterior smooth pa or sinus venorum. It is derived from absorption of right horn of sinus venosus. It has openings of :? I) Superior vena cava :- Has no valve. 2) Inferior vena cava :- Orifice is guarded by a rudimentary valve of IVC (Eustachian valve) derived from embryonic right venous valve, which directs the blood from IVC towards foramen ovale in fetal live. This valve is nonfunctional in adults. 3) Coronary sinus :- Orifice lies between tricuspid orifice and IVC orifice. It is guarded by a functional semilunar valve (thebesian valve). Thebesian valve develops from right venous valve. 4) Venae cardis minimae (thebesian veins):- Open through foramina venorum minimarum. 5) Anterior cardiac vein 6) Right marginal vein :- Sometimes it may open into coronary sinus (not in right atrium). iii) Interatrial septal region Interatrial septum develops from approximation of embryonic septum primum and septum secundum. Feauters on right atrial side are : 1) Fossa ovalis :- Oval shaped depression lying above the level of IVC opening in the interatrial septum. It is the embryologic remnant of foramen ovale, which connects right atrium to left atrium in embryonic life. Floor of the fossa ovalis is formed by septum primum. 2) Limbus fossa ovalis (Annulus ovalis) :- It is thickened rim present above the fossa ovalis. It represents the lower free margin of septum secundum. 3) Triangle of Koch :- It is a triangular region in the lower pa of interatrial septum which contains AV node. It is bounded above by tendon of Todaro below by base of septal leaflet of tricuspid valve and anteriorly (base) by orifices of coronary sinus. Immediately above the membranous septum, the septal region shows a slight bulge known as torus aoicus, produced by right posterior (non-coronary) aoic sinus (of valsalva).
Posterior pa is smooth
Anterior pa is derived from absorption of right horn of sinus venosus
Fossa oval i s repressent remnant of foramen ovale
Anterior and posterior pas are divided by Crista terminalis