Frog: two atria, one ventricle
Both mammals and birds have a four-chambered heart, made up of a right atrium, right ventricle, left atrium, and left ventricle, but a frog’s heart has only three chambers—two atria and one ventricle.
In humans, a four-chambered heart stores oxygenated and deoxygenated blood in separate chambers, but in a frog’s three-chambered heart, there is a groove called a “trabecula” that allows one of the ventricles to Separate oxygenated blood from deoxygenated blood. Frogs can get oxygen not only from their lungs, but also from their skin, and the frog’s heart survives based on this weird evolutionary phenomenon.
According to a 1989 study published in the American Journal of Physiology, the frogs with the strangest heart structures were hardy frogs, such as tree frogs. When a tree frog hibernates, its body freezes and its heart stops beating completely, but when the body thaws, the heart starts beating again.
Octopus, squid and cuttlefish: 3 hearts
Octopuses, squid and cuttlefish are all cephalopods, or tentacled sea creatures, and they all have three hearts.
On both sides of the body of cephalopods, there are two arm-shaped hearts that can send blood to their carps to absorb oxygen, and the systemic heart in the center of the body pumps oxygenated blood from the carps to the body other parts.
The blood of cephalopods is blue because of the copper in their blood. Human blood is red because hemoglobin contains iron. Just like rust is red, the iron element in human hemoglobin also appears red when combined with oxygen molecules. But in cephalopods, oxygenated blood turns blue.
Blue Whale: Owner of Earth’s Largest Heart
The blue whale heart is the largest heart structure among species on Earth today. The blue whale’s heart is the size of a small car and weighs about 430 kilograms. Like other mammals, the whale’s heart has four chambers, and the heart is responsible for extending to twice the length of a school bus. The body of the whale that transports blood has a wall thickness of at least 15 centimeters in the aorta, a very thick blood vessel.
When blue whales dive deep, their heart rates drop to four beats per minute, a phenomenon that helps them prolong their dives and even alleviate decompression sickness. In 2021, a study reported that a lower heart rate in blue whales reduces blood flow to pressurized lung passages, and that reduced nitrogen intake may alleviate decompression sickness.
Cockroach: 13 chambers in one heart
Like other insects, the cockroach has an open body circulatory system, which means its blood vessels don’t fill up. Cockroach blood flows through a single structure with 12-13 chambers. The cockroach’s dorsal sinuses are located on the top of the body. The dorsal sinuses can send oxygenated blood to the chambers of the heart, but the heart cannot send oxygenated blood to the rest of the body.
Cockroaches and other insects breathe and transport oxygen throughout the body through vents (openings on the surface of the body) rather than mammalian lungs, so the cockroach’s blood doesn’t need to carry oxygen from one place to another.
Instead, cockroaches have a bloody substance called hemolymph, which contains nutrients and is white or yellow in color. The cockroach’s heart cannot beat “independently”, and must expand and contract through the muscles in the body cavity, thereby helping the heart to transport hemolymph to other parts of the body. Usually the hearts of wingless cockroaches are smaller than those of winged cockroaches, and the heart rate of cockroaches is very close to that of humans.
Earthworms: 5 fake hearts
The earthworm does not have a heart, but it has five false hearts around its esophagus. Instead of pumping blood, these false hearts squeeze blood vessels to promote blood circulation in the earthworm.
Also, earthworms do not have lungs, but absorb oxygen through their moist skin. The air in the soil, or the moist air outside the soil after a rain, dissolves in the mucus in the earthworm’s skin, and the oxygen in it is drawn into the earthworm’s cells and blood system and pumped throughout the body.
Earthworm blood is red and contains hemoglobin, the protein that carries oxygen, but unlike humans, earthworms have an open circulatory system, and the hemoglobin in their blood merely floats.
Zebrafish: A broken heart can regenerate
The head of the fish is small and pointed, the body of the fish is small and exquisite like a spindle, and its body is like a zebra, covered with golden yellow and dark blue vertical stripes. This is the zebrafish, commonly known as “flower striped fish” and “blue striped fish”, which is native to South Asian countries such as India, Pakistan, Bangladesh, and Nepal at the southern foot of the Himalayas.
Because this tropical fish is highly similar to human genes, and the embryo is transparent, it is easy to observe the effects of drugs on its internal organs and other factors, so this fish is favored by scientists. Some of these scientists are fascinated by the zebrafish’s amazing ability to regenerate most organs and tissues, including the heart. Some scientists have discovered a gene switch in zebrafish. After a heart attack, this switch will be activated by itself, allowing cells to divide and multiply rapidly, and promote the complete regeneration and healing of damaged heart muscle. After the heart is completely healed, The switch will automatically turn off again.