The advantage to this arrangement is that high pressure in the vessels pushes blood to the lungs and body. The mixing is mitigated by a ridge within the ventricle that diverts oxygen-rich blood through the systemic circulatory system and deoxygenated blood to the pulmocutaneous circuit. For this reason, amphibians are often described as having double circulation. Figure 2. The blood is pumped from a three-chambered heart with two atria and a single ventricle.
Most reptiles also have a three-chambered heart similar to the amphibian heart that directs blood to the pulmonary and systemic circuits, as shown in Figure 3a. The ventricle is divided more effectively by a partial septum, which results in less mixing of oxygenated and deoxygenated blood. Some reptiles alligators and crocodiles are the most primitive animals to exhibit a four-chambered heart.
Crocodilians have a unique circulatory mechanism where the heart shunts blood from the lungs toward the stomach and other organs during long periods of submergence, for instance, while the animal waits for prey or stays underwater waiting for prey to rot. One adaptation includes two main arteries that leave the same part of the heart: one takes blood to the lungs and the other provides an alternate route to the stomach and other parts of the body.
Two other adaptations include a hole in the heart between the two ventricles, called the foramen of Panizza, which allows blood to move from one side of the heart to the other, and specialized connective tissue that slows the blood flow to the lungs. Together these adaptations have made crocodiles and alligators one of the most evolutionarily successful animal groups on earth. In mammals and birds, the heart is also divided into four chambers: two atria and two ventricles, as illustrated in Figure 3b.
The oxygenated blood is separated from the deoxygenated blood, which improves the efficiency of double circulation and is probably required for the warm-blooded lifestyle of mammals and birds.
The four-chambered heart of birds and mammals evolved independently from a three-chambered heart. The independent evolution of the same or a similar biological trait is referred to as convergent evolution.
The circulatory systems is a network of blood vessels supplying the body with oxygen and nutrients, while removing carbon dioxide and waste. Most animals are complex, multicellular organisms that require a mechanism for transporting nutrients throughout their bodies and for removing waste products.
The circulatory system has evolved over time from simple diffusion through cells, in the early evolution of animals, to a complex network of blood vessels that reach all parts of the human body. This extensive network supplies the cells, tissues, and organs with oxygen and nutrients, while removing carbon dioxide and waste, the byproducts of respiration. The circulatory system can be thought of as a highway system that runs throughout the body.
Circulatory system is analogous to a highway system : Just as highway systems transport people and goods through a complex network, the circulatory system transports nutrients, gases, and wastes throughout the animal body. At the core of the human circulatory system is the heart. The size of a clenched fist, the human heart is protected beneath the rib cage. Made of specialized and unique cardiac muscle, it pumps blood throughout the body and to the heart itself.
Heart contractions are driven by intrinsic electrical impulses that the brain and endocrine hormones help to regulate. Human heart : The heart is central to the human circulatory system, as it pumps blood throughout the body. Gas exchange is one essential function of the circulatory system. A circulatory system is not needed in organisms with no specialized respiratory organs, such as unicellular organisms, because oxygen and carbon dioxide diffuse directly between their body tissues and the external environment.
However, in organisms that possess lungs and gills, oxygen must be transported from these specialized respiratory organs to the body tissues via a circulatory system. Therefore, circulatory systems have had to evolve to accommodate the great diversity of body sizes and body types present among animals.
The circulatory system can either be open or closed, depending on whether the blood flows freely in a cavity or is contained in vessels. The circulatory system is effectively a network of cylindrical vessels the arteries, veins, and capillaries that emanate from a pump the heart. In all vertebrate organisms, as well as some invertebrates, this is a closed-loop system in which the blood is not moving freely in a cavity.
In a closed circulatory system, blood is contained inside blood vessels, circulating unidirectionally in one direction from the heart around the systemic circulatory route, then returning to the heart again. Closed and open circulatory systems : a In closed circulatory systems, the heart pumps blood through vessels that are separate from the interstitial fluid of the body. Most vertebrates and some invertebrates, such as this annelid earthworm, have a closed circulatory system.
Hemolymph returns to the blood vessel through openings called ostia. Arthropods, such as this bee and most mollusks, have open circulatory systems. In contrast to a closed system, arthropods including insects, crustaceans, and most mollusks have an open circulatory system. In an open circulatory system, the blood is not enclosed in the blood vessels, but is pumped into a cavity called a hemocoel. The blood is called hemolymph because it mixes with the interstitial fluid.
As the heart beats and the animal moves, the hemolymph circulates around the organs within the body cavity, reentering the heart through openings called ostia singular: ostium.
This movement allows for gas and nutrient exchange. An open circulatory system does not use as much energy to operate and maintain as a closed system; however, there is a trade-off with the amount of blood that can be moved to metabolically-active organs and tissues that require high levels of oxygen.
In fact, one reason that insects with wing spans of up to two feet wide 70 cm are not around today is probably because they were outmatched by the arrival of birds million years ago. However, gas exchanges in the respiratory organs are facilitated by a low BP, which must be provided by a different circulation.
The differentiation between a low- and a high-pressure circulation appears first in octopus. It is most pronounced in birds. A separate low-pressure circulation appears when the systemic pressure exceeds 50 mmHg cephalopods, some reptiles, mammals, and birds.
In humans, it is interesting to note that 50 mmHg is also the limit of PAP beyond which appear serious clinical problems. A pulsatile ventricle is the most common pumping system among animals, because it affords high output under high pressure, but pulsatility is a hindrance for capillaries, where flow must be as continuous as possible.
Therefore, large arterial vessels have developed an increased elastin content to absorb systolo-diastolic pulsations. All branches of the evolutionary tree, although independent from each other, tend to evolve in the same direction, a phenomenon called convergence.
Each type of heart seems the best-fit for the needs of each phylum. The top performer is probably the bird's heart, but the human heart appears well-adapted for a medium-sized creature, which main achievement is its brain. Google Scholar. Google Preview. Oxford University Press is a department of the University of Oxford.
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Search Menu. Article Navigation. Close mobile search navigation Article Navigation. Volume Article Contents Abstract. The tree of evolution. Lower invertebrates. Anatomic evolution of the circulatory system.
Intracardiac haemodynamics. The stress of gravity. Birds and mammals. The evolution of haemodynamics. Is our heart a well-designed pump? The heart along animal evolution. Bettex , Dominique A. Email: dominique. Oxford Academic. Pierre-Guy Chassot. Revision received:. Cite Cite Dominique A. Select Format Select format. Permissions Icon Permissions. Abstract A carrier system for gases and nutrients became mandatory when primitive animals grew larger and developed different organs.
Animal evolution , Heart anatomy , Haemodynamics. Translational perspective. Figure 1. Open in new tab Download slide.
Figure 2. Figure 3. Figure 4. Figure 5. Figure 6. Figure 7. Figure 8. Google Scholar Crossref. Search ADS. Google Scholar PubMed. The cephalopod heart: the evolution of a high-performance in vertebrate pump. The decapod crustacean circulatory system: a case that is neither open nor closed. Evidence for endothermic ancestors of crocodiles at the stem of archosaur evolution. Cardiac embryology: understanding congenital heart disease for the noncardiac anesthesiologist.
Myocardial fiber and connective tissue architecture in the fish heart ventricle. Proliferation and differentiation processes in the heart: muscle elements in different phylogenetic groups. Gravity, blood circulation, and the adaptation of form and function in lower vertebrates. Heart ventricle pump in teleosts and elasmobranchs: a morphodynamic approach. Regulation of cardiac function in the horn shark by changes in pericardial fluid volume mediated through the pericardioperitoneal canal.
Ontogeny of cardiovascular and respiratory physiology in lower vertebrates. Scaling of anaerobic metabolism during exercise in the estuarine crocodile Crocodylus porosus.
Functional morphology and patterns of blood flow in the heart of Python regius. How the python heart separates pulmonary and systemic blood pressure and blood flows.
Ventricular haemodynamics in Python molurus : separation of pulmonary and systemic pressures. The physiological and evolutionary significance of cardiovascular shunting in reptiles.
On being the right size: heart design, mitochondrial efficiency and lifespan potential. Animal models of human cardiovascular disease, heart failure and hypertrophy. Published on behalf of the European Society of Cardiology. All rights reserved.
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