Structure and working of Frog's heart

Structure and working of  Frog's heart

Structure of  Frog's Heart


It is a muscular organ and acts as pumping station and pumps blood.

External structure

it lies mid-ventrally in the anterior region of body cavity. It is reddish in colour and is triangular in shape with broad anterior and narrow prosterior end.
It lies inside thin, transparnent, two layered sac called as pericardium. The cavity between two pericardial layers contains pericardial fluid which postects heart from friction or shocks and keeps it moist.
It consists of 3 chambers, two auricles and one ventricle. The auricles are two anterior dark coloured chambers and are right auricle and left auricle. Two auricles remain demarcated by a longitudinal inter-auricular groove. The ventricle is posterior, comical pink colour chamber. The auricles and ventricle remain demarcated with each other by transverse auricular-ventricular groove or coronary sulcus.
The frog's heart has two additional chambers, sinus venosus and truncus arterious. The sinus venosus is dark coloured, thin walled and triangular chamber present on dorsal surface of heart. It is formed by union of two anterior precavels and one posterior postcarvel. The truncus arterious arises from anterior right ventral side of ventricle and is a tubular structure. It bifurcates anteriorly into two branches or trunks, each further divides into three arches; carotid, systemic and pulmocutaneous.

Internal structure



its internal structure is studied with the help of vertical section. It is hollow, muscular with different chambers. The different chambers remain seperated by values to keep one way flow of blood.
The two auricles are thin walled and remain separated from each other by a thin vertical inter-auricular septum. Right buriale is larger than left. The sinus venosus opens into dorsal wall of right buriale by a large oval aperture, sinu auricular aperture. It kids at middle close to inter-auricular septum and remains guarded by a pair of flap like values. The common pulmonary vein opens into left auricle, near inter-auricular septum, by a small opening without values. Both auricles open into ventricle by a common large auriculo ventricular aperture guarded by two pairs of flap like auriculo-ventricular values.
The ventricle is thick walled, muscular and spongy in nature. Its inner surface has irregular ridges or folds, the columnae carneae with depressions called as fissures. These folds reduce cavity of ventricle. The flaps of auriculo-ventricular values remain connected with wall of ventricle by thread like chordae tendineae.
The opening of ventricle into truncus anteriosus is guarded by 3 semilunar values (4 according to sharma) which prevent back flow of blood from truncus into ventricle. The spirally twisted cavity of truncus anteriosus remains divided by 3 semilunar values into a long thick walled proximal conus arteriosus or pylangium and a short distal, thin walled bulbous aorta or synangium. A longitudinal spiral valve is present on pylangium which remain attached dorsally while free ventrally. It divides cavity of pylangium into left dorsal cavum pulmoutaneum and right ventral cavum aorticum. The common opening of two pulmocutaneous arches lies in cavum pulmocutaneum while seperate openings of carotid and systemic arches lie in synangium. Sharma describes a joint opening of carotid and systemic. All there openings are guarded by values.


Working of heart
Heart constantly beats during life time under nervous control to pump blood into blood vessels. Contraction of heart is called systole, while relaxation is called as diastole. When shots venosus contracts, its non oxygencted blood passes into right auricle through sinu auricular aperture the blood from lungs come into left auricle through pulmonary vein. The two auricles now contract almost simultanadously forcing their blood into ventricle through auriculo-ventricular aperture.

A ) old view : according to the older they the ventricle contained only deoxygenated blood in its right side received from right auricle and only oxygencted blood in its left side received from left auricle, with some mixed blood in the middle region. The two lines of blood could not mix to any great extent because of their viscous nature and also because of the network of columnae carneane. When ventricle starts contraction, first the deoxygenated blood from the right side being nearer flows into the truncus arterious and directed by the spiral valve into the common opening of pulmocutaneous arches and carried to lungs and skin for oxygenction. Spiral valve now closes the opening of pulmocutaneous arches. Next follows the mixed blood which is pushed through cavum aorticum into the systemic arches and sent to the body and limbs. Finally enters the oxygeneated blood of left side and directed through carotid arches to the head. Thus, spiral value in truncus plays an important sold in directing blood into different arches.

B ) modern view: Recent experimental studies conducted mostly by vandervael and foxon show trav it is actually campelety mixed blood in ventricle and truncus which flows simultaneously through the three pairs of arches to all parts of the body. The blood received from skin an buccal cavity into sinus venosus and right buriale is in fact more oxygencted than that received from lungs to left auricle. According to this view he interauricular serum and spiral value in truncus have become functionless in frogs. Studies by delong indicate that the carotid arches receive highly oxygencted blood, the pulmocuataneous archer with atleast oxygen, and the systemic arches mixed blood. The precise mechanism is not understood.