Heart is a muscular organ and acts as pump. It's main function is to pump blood. It is located at the level of forelimbs in body Cavity in between two lungs. It is roughly triangular, reddish dark Coloured structure. It lies inside pericardium which is double layered sac like Structure.
It's inner layer is Called visceral layer which lies on the Surface of heart while space is present in between inner layer and outer layer or parietal layer Called pericardial Cavity which remains filled with pericardial fluid which absorbs mechanical shock , Injuries and protects heart and creates frictionless environment during heart beat.Frog's heart is 3 chambered ; two auricles and one ventricle.
The two auricles are right auricle and left auricle. They are upper Chambers and remain demarcated with each other by a vertical groove Called inter auricular groove. They receive blood. The Rt. atrium receives blood from sinus venosus while Lt. atrium receives blood from lungs by pulmonary Veins.
The ventricle is lower Chamber.The auricles and Ventricle remain demarcated by a deep horizontal groove Called auriculo-ventricular groove or Coronary sulcus. It pumps blood into truncus arteriosus.
Two additional chambers are found on the surface of Frog's heart which are sinus venosus and truncus arteriosus.
The sinus venosus is roughly triangular chamber on dorsal surface of heart and is formed by the union of two pre cavals and one post Caval. It opens into Rt. atrium.
The truncus arteriosus is a tubular structure on ventral surface of heart. It is large sized blood vessel arising from top right region of ventricle.
* Internal structure of heart: It is studied with the help of vertical section from ventral side. The auricles are thin Walled Chambers and remain Separated with each other by interauricular septum. The Rt. atrium is larger in Size and has opening of sinus venosus called sino-atrial aperture which remains guarded by a pair of sino_atrial valves to maintain one way flow of blood or to prevent back flow of blood. This sino-atrial aperture is present near to interauricular septum at middle level.
The left auricle has opening of common pulmonary vein near to interauricular septum below the level of sino-atrial aperture. This opening is without valves, as it is oblique , get Closed automatically on Contraction of Lt. atrium.
Both auricles open into ventricle by a Common opening called
auriculo-ventricular aperture which remains guarded by two pairs of
auriculo-ventricular valves(AV-valves). They allow blood to pass from auricles into ventricle while prevent back flow of blood.
The flaps of these Av-valves remain connected with wall of ventricle by fine fibers Called Chordae tendinae. Their function is to keep AV-valves in their own position specially during ventricular systole.
The ventricle is thick walled chamber and its inner surface has a number of folds or ridges also Called columnae Carneae. Due to the presence of folds; fissures or depressions are present in between the successive folds. Due to the presence of these folds and fissures, Cavity of ventricle is highly reduced.
The Ventricle opens into truncus arteriosus from it's top right region and this opening remains guarded by 3 semilunar valves to prevent back flow of blood. [ However, 4 - Valves according to sharma an Indian biologist]
The truncus arteriosus is large sized blood Vessel arising from top right region of ventricle Which ascends, get curved towards left and bifurcates into right and left aortic trunk. Each aortic trunk further divides into
3-aortic arches which are Carotid arch, systemic arch and pulmocutaneous arch.
In the cavity of thuncus arteriosus , 3 - semilunar valves are present. Due to their presence , truncus arteriosus remains differentiated into
long-proximal pylangium or conous arteriosus and short-distal synangium or bulbous arteriosus.
In the Cavity of pylangium, a spiral valve is present through out its length which remains attached dorsally while is free ventrally. Due to the presence of this spiral valve Cavity of pylangium remains differentiated into right- ventral Cavum aorticum and left - dorsal Cavum pulmocutaneum. The Cavumpulmocutaneum Contains Common opening of pulmocutaneous arch.
The synangium is short distal Part and Contains separate openings of Carotid and systemic asch. All these openings remain guarded by a pair of valves to prevent back flow of blood.
