Crocodilians have a unique valve in their heart that enables blood to bypass the lungs while they are diving. This feature is called the Foramen of Panizza and helps them remain underwater for long periods of time when they are threatened by man or other intruders. The Foramen of Panizza connects the left and right aorta. Deoxygenated blood from the right ventricle can flow into the right aorta. When the heart is relaxed, some oxygenated blood from the left ventricle can flow into the left aorta across the Foramen of panizza. Some species of crocodilians have regulatory sphincters that prevent unwanted flow of blood through the Foramen of Panizza while at the surface. This connection of the left and right aorta presents a difficult problem for evolutionists to explain as it contains several unique anatomical parts and is far to complex to have evolved over time by small mutational errors. It is also presents another problem because other diving animals including other reptiles, whales and birds would benefit from such an adaptation, yet they do not have it. Once again those pesky facts keep getting in the way of good evolution dogma and the evidence of design is obvious for anyone with an open mind.
Key Words: Alligator mississippiensis, Foramen of Panizza, diving bradycardia, prolonged diving, right to left cardiac shunt.
The circulatory system of vertebrates is complex and transports blood throughout the body. It is a closed system with the blood remaining in blood vessels through the journey. In contrast, most invertebrates have an open circulatory system and blood leaves the blood vessels to diffuse into the body cavities eventually making its way back to the heart. In both groups the flow of blood provides several important functions. It transports oxygen from the lungs or gills to the rest of the body and removes carbon dioxide. Nutrients are transported from the gut to where it is needed and waste products are removed by the kidneys for expulsion. The flow of blood to the skin helps regulate body temperature in endothermic (warm blooded) birds and mammals by releasing excess heat to the environment and is reduced to conserve body heat under cold environmental conditions. The skin also provides important thermal insulation during cold weather along with hair or feathers.
The early work of Scholander showed that certain seals slow their hearts when forcible submerged (Scholander, 1940). Their heart rate dropped from 125 to 10 beats per minute when submerged. This response was soon called “diving bradycardia” and was found to occur widely in humans, certain snakes, whales and several other diving mammals. The slowing of the heart was thought to help conserve energy resulting in longer survival underwater.
The structure of the heart varies widely among the various vertebrate groups. Fish have the simplest heart with two pumping chambers consisting of a thin walled atrium and the more muscular ventricle. Blood enters the atrium from the sinus venous with a valve preventing backflow when the atrium contracts sending blood to the ventricle. Blood leaves the ventricle by way of the cornus arteriosus and again backflow is prevented by valves. Blood then flows to the gills and on to the entire body. Systemic blood pressure is low in fish, because most of the blood pressure is reduced as the blood passes through the gills. Amphibians have a more complex heart with three muscular chambers consisting of two atria and a single ventricle. It was thought to be inefficient with unoxygenated blood from the body mixing with oxygenated blood from the lungs. Farther research showed the complex series of valleys and ridges in the ventricle wall keeps the oxygenated and unoxygenated blood from mixing and it is now seen as a highly efficient organ. Crocodilians, birds and mammals have four chambered hearts, but the crocodilian heart is unique and has a special feature that extends diving time in part by bypassing the lungs during extended diving when no oxygen would be available. It has long been known that for birds and mammals that blood from the body enters atrium then goes to the right ventricle and the lungs and returns to the left atrium and left ventricle where it is pumped throughout the body. Let’s look more closely at the unique crocodilian heart.
Alligators and other reptiles have lungs and breathe air. Crocodilians are classified as semiaquatic animals and spend most of their life in and around water. They often sleep underwater only coming to the surface to breath. The Nile crocodile, Crocodylus niloticus has been observed submerged for two hours and the Australian salt water crocodile can stay underwater even longer. The saltwater crocodile, Crocodylus porosus is the largest living reptile with the record of 21 feet long and weighing 2,370 pounds caught in the Philippines. The heart rate response of several species of crocodilians was tested in the labortory by tying them to a board and forcing them underwater. In each case the heart slowed and the response was described as diving bradycardia.
Accidental Discovery Provides Insight
Several important scientific discoveries were made by accident. Perhaps the best know is the discovery of Penicillin by Alexander Fleming. He observed a growth free zone around the contamination of penicillin mold in a bacterial culture. The discover led to the use of antibiotics and is said to have changed world history forever. Another important accidental discovery was X-rays discovered by Wilhelm Roentgen while working with cathode rays. That discovery changed medical diagnosis. Although certainly of less importance, I also made an accidental discovered that changed our view of what happens when animals dive underwater.
When forcefully submerged in the laboratory the heart rate of alligators and other crocodilians slows dramatically and this was thought to be a response to diving. The response was even called “diving bradycardia” and had been observed in many other diving animals including seals. I have studied alligators and other animals for over 45 years (Smith, 1979; Smith, et. al., 1978, Smith et. al., 1984) and made the surprising accidental discovery that this is not the case. Using radio telemetry, (Smith, 1974 and Smith, 1975) I found alligators normally dive underwater without a significant slowing of their heart rate. The response observed in the laboratory was the result of fear and not submergence. I made a surprising accidental discovery that changed that simplistic view. I was studying a large free ranging alligator under natural conditions at the Welder Wildlife Refuge in South Texas and the alligator spent time underwater without a significant slowing of the heart. The telemetered alligator was submerged and occasionally surfacing to breathe. It was displaying the same heart rate observed when it was out of the water. The heart rate did not slow when it voluntarily went underwater.
A fellow graduate student studying the hatching success of the Least Bittern approached “my” submerged alligator. In spite of my vigorous hand gestures and verbal protests, he continued directly over the submerged alligator. The alligator’s heart rate dropped dramatically to less than half the previous value as the canoeist came near. It was obvious the alligator’s heart rate slowed in response to fear and not to diving. The accidental observation was tested several times using carefully designed experiments. Each time the alligator slowed its heart in response to fear or disturbance, but not to voluntary diving. What had been called diving bradycardia was instead a response to fear. My discovery forced other scientists to look more closely at what had been wrongly called, “diving bradycardia.” This discovery has been documented for numerous other species including seals under natural conditions makes a strong case against drawing conclusions from studies conducted in the artificial environment of the laboratory.
The Foramen of Panizza
Crocodilians have the most complex circulatory system of any vertebrate. It includes a unique anatomical structure called the Foramen of Panizza that allows blood to bypass the lungs while submerged. It was first described in 1833 by Bartolomeo Panizza. When under water, blood pressure in the lungs increases, causing the blood to flow through the Foremen of Panizza and to the systemic circulation without going to the lungs. The foramen of Panizza functions much like the foramen ovale in unborn mammals by reducing the work load of the heart. Prior to birth, mammals obtain oxygen from the placenta by way of the unbilical cord. At this time it would be of no value for all the blood to go through the lungs. This bypass saves energy and reduces the work load of the heart. The foramen ovale provides a path for blood to flow directly from the right atrium to the left atrium of the heart, bypassing the lungs. With a newborn mammal's first breath the pulmonary blood pressure decreases and the left atrial pressure exceeds the right atrial pressure closing foramen ovale forcing all the blood to flow to the lungs. Shortly after birth the foramen ovale heals in the closed position as it is no longer needed. In sharp contrast the foramen of Panizza of crocodilians remains functional throughout their life and helps them occupy their unique ecological niche by allowing them to remain safely submerged sometimes for hours. Many crocodilians also have a special sphincter that prevents blood from flowing in this pathway while they are not diving.
Here is yet another example of design from nature for which the evolutionists have no rational theory as to its origin. What is particularly troublesome for evolutionists is its uniqueness to crocodilians. Other diving animals such as turtles, birds, seals or even whales lack all of these special features. Since the bypass provides a useful feature in crocodilians, why has such a structure not evolved for other diving animals? Evolutionists are at a loss to explain its origin in crocodilians and the lack of such a useful device in other diving animals. It is obvious such a complex specilized feature could not have developed by random mutational errors.
With the avalanche of such new information, it is becoming increasingly difficult to remain a committed evolutionist! Those pesky facts continue to stand in the way of good evolution dogma. The cracks in the foundation of evolution are widening each year as we discover more about the complexity, beauty and sheer wonder of God’s creation. It requires a huge amount of blind faith to remain a devoted evolutionist. As Christians, we know in Whom we believe and understand it was HE who created the marvels that make up all living things. In the near future evolution will be relegated to the dust bin of history as yet another failed theory. Many will marvel at the large number of scientists and others who accepted the unsupported dogma for over a century.
Great is the LORD and most worthy of praise; his greatness no one can fathom. (Ps 145:3, NIV)
The fool says in his heart, "There is no God." (Ps 14:1a, NIV)
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Wikipedia: diving bradycardia
Wikipedia: Saltwater crocodile