This week I was talking to an anatomist about the piece of bone present in cattle hearts. He told me that cows, and other ruminants, have bone (actually a piece of hard cartilage but described as bone) in the aorta to help support it, this is called the os cordis. I had the chance to feel it in a dead cows heart and it got me thinking about how other animals hearts may vary from the human heart, so here is an interesting selection of animals with hearts that have unique characteristics to suit their different environments.
While mammals and birds have hearts with four chambers, frogs have hearts with just three. One ventricle and two atria. The heart pumps deoxygenated blood from the body to the lungs and skin for oxygen, back to the heart and then back through the body to take oxygen to the organs. To keep the oxygenated blood separate from the deoxygenated blood in the one ventricle, frogs have small grooves within the heart, called trabeculae, which are partitions formed by bands/columns of connective tissue. The reason the blood goes to the skin is because frogs can get oxygen from their skin as well as the lungs.
The blue whale is the largest animal in the world, some can measure over 90 ft long and weigh over 180 tons. So it’s no surprise that a blue whales arteries and heart are also enormous to pump the blood throughout the whole of the body. A blue whales heart can weigh up to 600kg and can be the size of a small car. The aorta can measure over 23 centimetres and some arteries can be so large that an adult human could swim through them. Because of the size of a blue whales heart it only needs to beat at a rate of 8 – 10 beats per minute due the sheer volume of blood it can pump out. Each beat can be heard from over 2 miles away!
Earthworms don’t have hearts, so to keep the blood circulating around the body worms have five ‘pseudohearts’ which are blood vessels that can contract. These do not pump the blood, instead they squeeze the blood along the vessels to help keep it moving along the worm’s body. Like frogs, worms can also get oxygen from their moist skin as they do not have lungs. Air can dissolved in the skins mucous and then the oxygen is absorbed into the blood where it is squeezed around the body. Like humans worms have the protein haemoglobin in their blood which carries the oxygen but they have what’s called an ‘open circulatory system’ which means the haemoglobin simply floats along with the all other fluids.
Octopuses have three hearts. Two ‘brachial’ hearts on either side of its body which pump the blood through each of an octopuses two gills and a ‘systemic’ heart in the centre of the body which circulates blood round the body. The ‘brachial’ hearts are responsible for oxygenating the blood by pumping it through the blood vessels of the gills and then the systemic heart is responsible for pumping this oxygenated blood from the gills through the rest of the body. Like in frogs, the systematic heart of the octopuses has two atria but only one ventricle. Octopuses have copper in their blood so, unlike in humans where oxygenated blood turns red, oxygenated blood in octopuses is blue.
Cheetahs are famous for their speed and so it’s no wonder they have a powerful heart to get the oxygen to the muscle cells fast. Even their resting heart rate is about 120 beats per minute while a humans can be around 60-80 beats per minute. And while the human heart rate reaches a maximum of 220 beats per minute the cheetah’s heart can reach 250 beats per minute in a only few seconds. Because this heart rate is so high it limits the cheetah’s sprinting time to around 20 seconds, after this its organs will become too hot and be permanently damaged.