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Circulatory System of a Rattlesnake and a Human

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Published: 23rd Sep 2019 in Biology

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Circulatory System of a Rattlesnake and a Human

A comparison of the circulatory system of a Homo sapiens (human) to that of a Crotalus durissus (rattlesnake) reveals that the circulatory system of both organisms is made up of three systems that work together: the cardiovascular system, the pulmonary system and the systemic circuit. The circulatory system functions as a way of delivery oxygen and nutrients to cells and taking away wastes and has evolved over millions of years. It does this through an intricate network of arteries, veins and capillaries. It also involves the kidney, which regulates the blood pressure and removes the body’s wastes.

Humans have a double pumped four-chambered heart, one of the most complex in living organisms. The four chambers are made up of a left atrium, left ventricle, right atrium and a right ventricle. The right atrium takes in deoxygenated blood, filled with carbon dioxide, and squeezes it through the one-way valve into the right ventricle, where the blood is pumped to the lungs, through another valve, where the carbon dioxide is excreted and replaced with oxygen, see Figure 1 (Better Health Channel, 2018). The now oxygenated blood travels back to the heart, where it enters the left atrium and is pumped into the left ventricle which has a thicker muscular wall, to withstand the high blood pressure, and then into the aorta (Better Health Channel, 2018). From the aorta the blood travels through arteries and then through the capillaries. The heart has one-way valves to stop backflow of blood. The left side of the heart and the right side of the heart are separated by a wall of muscle called a septum. The septum ensures there is no mixing of the deoxygenated and the oxygenated blood. Due to the four-chambered heart mankind is homeothermic, meaning we can maintain our own body temperature, this is essential to our survival as we are very active terrestrial organisms and need to be able to control our body temperature. The snake heart is less evolved than the human heart but is showing evolution in its complexity. The snake heart is three-chambered and consists of two atria and one incompletely divided ventricle, see Figure 2 (There is no diagrams of a snake heart). The incomplete ventricle causes slight mixing of oxygenated and deoxygenated blood (Johansen and Hol, 1960). The ventricle is separated into a systemic and a pulmonary chamber (cavum arteriosum and cavum pulmonale) and a third smaller chamber, cavum venosum. Blood that enters the cavum pulmonale during diastole must first pass through the cavum venosum and blood ejected from the cavum arteriosum during cardiac contraction must flow through the cavum venosum. It was found that there was a division between of the systemic and pulmonary inflows meaning that the snake heart is divided during both filling and ejection. The blood pressure in the systemic system were much higher than those in the pulmonary circuit. Snakes have adapted to their environments by losing limbs and staying low to the ground, their elongated, horizontal body means that the heart must pump harder for the blood to reach its destination. The hear may pump the blood but without capillaries the circulatory system would not function.



Capillaries are very small, very thin blood vessels, only 5 micrometers in diameter that are found in both humans and snakes. They consist of two layers of cells, an inner layer of endothelial cells and outer layer of epithelial cells, see Figure 2. They are so small that red blood cells slow down to flow through them single file, this allows gases to diffuse into the blood. Capillaries facilitate the exchange of gasses, fluids and nutrients in the body and remove carbon dioxide and wastes from the body. In the lungs, oxygen diffuses from the alveoli into the capillaries to be carried around the body and carbon dioxide diffuses from the capillaries back into the alveoli. Fluids and nutrients diffuse through selectively permeable capillaries in the villi and into body tissue and waste is transported to the kidneys and liver to be removed from the body. Human capillaries are no different from the capillaries found in snakes. The capillaries only have low blood pressure but through the body there are different blood pressures all regulated by the kidney.

Figure 3: Capillary Structure                      Source: https://www.shutterstock.com/image-vector/capillary-blood-vessel-labelled-vector-diagram-235549774

The kidney’s function is to regulate the balance of water, salt and blood pressure in the body and by doing this it ensures that the body maintains homeostasis. The kidneys are made up of a system                                                                              of millions of nephrons. The nephrons have two parts: the glomerulus and the tubule. The glomerulus strains blood cells and large molecules from the toxins and fluids passing through the kidney. The glomerulus uses tubuloglomerular feedback mechanism to know when to filtrate the fluids, this helps to maintain homeostasis. The fluids and toxins pass through the tubule and are reabsorbed or go back into the bloodstream and are filtered out of the body (National Institute of Diabetes and Digestive and Kidney Diseases). Kidneys also produce hormones that help regulate blood pressure, make red blood cells and promote bone health (National Institute of Diabetes and Digestive and Kidney Diseases). The Renin-Angiotensin System is a group of hormones that act together to regulate the body’s blood pressure. When renal blood flow is low the renin angiotensin system activates and begins processes to increase blood pressure around the body, see Table 1 (Weber, 2018). These systems and mechanisms are essential to maintaining homeostasis. The kidneys developed and evolved over thousands of years just like the human heart.

Table 1: The components of the Renin-Angiotensin System and their function and place of origin



Where it comes from

Juxtaglomerular Cells

To convert prorenin into renin when renal blood flow is low



To convert inactive Angiotensin into Angiotensin I

Inactive angiotensin is produced in the liver

Renin comes from the kidneys

Angiotensin I

Has small effect on blood pressure

To be converted into Angiotensin II

Is converted from inactive Angiotensin

Angiotensin II

Directly affects blood pressure by acting on blood vessels to increase blood pressure

Stimulates the release of Aldosterone

Is converted from Angiotensin I

Angiotensin Converting Enzyme

To convert Angiotensin I into Angiotensin II

The lungs


Strong vasoconstrictor can cause a big increase in blood pressure

Makes the kidney retain both salt and water, so as time passes the amount of fluid in the body increase

The adrenal cortex in the adrenal gland

The evolution of the heart can be traced back millions of years. Mammals evolved from other classes of vertebrates and as the organism got more complex so did the heart (Walia, et.al, 2010). The more chambers a heart has the more complex the organism is. Humans have a four-chambered heart as we are currently one of the most complex organisms, snakes however, have a three-chambered heart that is slowly starting to evolve into a four-chambered heart. The evolutionary history of the heart began with invertebrates having a simple circulatory system that pumped blood and fluid around the body through muscle contractions (The University of Melbourne). This then evolved into a fish heart that had two chambers, an atrium and a ventricle, and developed a closed circulatory system (University of Melbourne). To increase the efficiency of oxygen distribution a double circulatory system developed (University of Melbourne). After that a 3-chambered heart developed and then a four-chambered heart, the most complex heart.

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The comparison of the Homo sapiens (human) circulatory and the Crotalus durissus (rattlesnake) circulatory system shows both similarities and differences. Both systems have evolved over millions of years, the human system, however, is now more complex but snakes are slowly evolving from a three-chambered heart to a four-chambered heart. Although they are drastically different organisms both snakes and humans have virtually the same capillaries. Concluding sentence

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