Q.Describe the structure of the heart of a frog.

A frog's heart is three-chambered - two atria and one ventricle - with a sinus venosus behind and a conus arteriosus in front; the single ventricle causes partial mixing of oxygenated and deoxygenated blood.

Structure of the heart of a frog:

• The heart of a frog is a muscular organ situated mid-ventrally in the anterior part of the body cavity, enclosed in a two-layered membrane called the PERICARDIUM.
• It is THREE-CHAMBERED, consisting of two atria (auricles) and one ventricle, together with two accessory chambers - the sinus venosus and the conus arteriosus.

Chambers:

1. Atria (auricles) - two:

• The RIGHT ATRIUM is larger and receives DEOXYGENATED blood from the body through the sinus venosus.

• The LEFT ATRIUM is smaller and receives OXYGENATED blood from the lungs and skin (through the pulmocutaneous veins / left precaval).

• The two atria are separated by an inter-atrial septum and open into the ventricle by a common auriculo-ventricular aperture guarded by valves.

2. Ventricle - one (single):

• A single, thick-walled, muscular chamber with spongy inner walls (columnae carneae) that reduce the mixing of the two kinds of blood to some extent.
• Since there is only ONE ventricle, oxygenated and deoxygenated blood get PARTIALLY MIXED here.

Accessory chambers:

3. Sinus venosus: …