Structure and working mechanism of heart of frog

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Structure and working mechanism of heart of frog

The heart of frog is conical and its end is directed backward and is made up of five chambers i.e

  • Two auricles
  • One sinus venos
  • One ventricle
  • One truncus arteriosus

Two auricles One ventricle One sinus venosus One truncus arteriosus Two auricles are separated by an inter-auricular septum’ In the larger right auricle, a large sinu-auricular aperture is situated near the septum; which is guarded by two flap of sinu-auricular valves’ These valves allow the blood to enter from the sinus venosus into the right auricle but prevent the backward flow into the sinus venosus’ In left auricle’ the pulmonary veins open by an apefiure which is situated near the inter-auricular septum obliquely’ The two auricles communicate with ventricle by a common large auriculo- ventricular aperture. The opening is guarded by two thin flaps: one dorsal and one ventral which are the auriculo-ventricular valves’ The two flaps extend to the ventricle and are attached to the wall of the ventricle by firm fibrous cords’ known as chordae tendinae’ The ventricle is thick walled muscular chamber and its inner wall is provided with large number of projections’ the columnae cornea’ which divide the cavity into numerous fissures’ The ventricle opens into the truncus arteriostls and the opening is guarded by three semilunar valves whose edges project towards the tl’uncus arteriosus’

The truncus is divided into two part a thick walled proximal conus arteriosus or pylangium and a thin walled distal bulbus arteriosus or synangium. The pylangium is a short tubular structure and is provided with a row of semilunar valves at its both ends and its cavity is incompletely divided by a longitudinal spiral valve into two chambers’ a right cavum aorticum and a left cavum pulmocutanium’ The cavum aorticum opens into the synangtum which is divided by a principal septum into a dorsal and a ventral charnber. The cavum pulmo-cutaneum opens into the dorsal chamber of synangium which opens anteriorly into the pulmo-cutaneous arteries’ 3t :1]:i aofticum opens into the ventral chamber of synangium which further opens ln front into the systemics and carotid trunk’ In the anterior part of the cavum pulmonary cutaneum, theie is the aperture of pulmo-cutaneous trunks which is guarded by a small pulmo-cutaneous valve.

wren the sinus venosus contracts, the blood is pushed into the right auricle through sinu-auricular-ap6rture’ The left auricle receives the blood from the lungs by pulmonary veins’ When the two auricles contract’ the sinu- auricular valve and the opening of pulmonary vein are closed’ The blood flom both auricles passes into the ventricles’ According to old theory’ the two bloods in the ventricle were not aliowed to mix due to presence of septa’ short stay and viscous nature of blood’ But according to foxon’ the blood gets completely mixed in the ventricle and mixed blood is distributed through the carotid, systemic and pulmo cutaneous trunks to all parts of the body’

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