What: " The frog heart differs from the mammalian heart anatomically in that they are three chambers rather than four chambers. As mentioned above, the pacemaker in the amphibian heart is in the sinus venosus, a thin-walled sac that receives blood from the anterior and posterior veins and empties blood into the right atrium. Similarly, the left atrium receives oxygenated blood from the pulmonary veins returning from the lungs. The single ventricle receives blood from both atria and pumps blood out through the large artery called the truncus arteriosus (Figure 1). In contrast, the mammalian ventricle has separate left and right chambers, which completely prevent mixing of the venous and arterial blood. Obviously, the frog heart will have a small amount of mixing of oxygenated and deoxygenated blood. However, the mixing is not very thorough. This stems from the fact that the pressure, and thus turbulent flow, in the frog circulation is low. Also, the ventricle is like a sponge with spaces called trabeculae that separate arterial and venous blood. Finally, the blood leaving the heart through the conus arteriosus contains a ridge of material called a spiral valve, which allows for the shunting of the appropriate blood volumes to the pulmonary circuit and the systemic circuit."

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Date: Mar 4 2014 12:50 PM