Thank you for visiting nature. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser or turn off compatibility mode in Internet Explorer. In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript. MOST text-books of elementary zoology contain an account of the circulation of the frog. The mixed blood is sent through the systemic arches to the hinder part of the body.
Meanwhile the head region is supplied through the carotid vessels with pure arterial blood, while the greater part of the venous blood is sent through the pulmo-cutaneous vessels to the lungs and skin. Google Scholar. Sabatier, A. Robertson, J. Evans, F. O'Donoghue, C. Article Google Scholar. Baxter, E. Ozorio de Almeida, M. Paris , 89 , Noble, G. It drives blood through the closed circulatory system. External features: Heart lies mid-ventrally inside the anterior trunk region.
It is protected by the pectoral girdle. It is reddish in color. It is somewhat conical or triangular in shape. It has the broad base which is directed anteriorly and the narrow apex posteriorly. Pericardium: Pericardium encloses the heart. It is thin, transparent, two-layered sac. The outer wall of pericardium is termed as parietal pericardium. The inner wall of pericardium is termed as visceral pericardium. Visceral pericardium closely invests the heart. Chambers of heart: There are 3 chambers in a heart of frog.
Heart is made up of: Two atria or auricles right and left : It is dark colored and lies anteriorly. One ventricle: It is pink colored, conical and lies posteriorly. A very faint longitudinal inter-auricular groove demarcates the two auricles externally. However, a narrow transverse auriculo-ventricular groove or coronary sulcus clearly marks off the two auricles from ventricle.
Two additional chambers are present in the heart of the frog i. Sinus venosus: It is dark colored, thin-walled and triangular chamber. It is attached dorsally to heart. Truncus arteriosus: It is a tubular chamber that arises anteriorly from the right ventral side of ventricle.
It immediately bifurcates anteriorly into two branches, each again breaks into three arches i. It is hollow and muscular.
In order to keep the unidirectional flow of blood, the various chambers are separated by valves. Auricles: There are two auricles, left and right. Examples of animal circulatory systems : a Fish have the simplest circulatory systems of the vertebrates: blood flows unidirectionally from the two-chambered heart through the gills and then to the rest of the body.
The blood is pumped from a three-chambered heart with two atria and a single ventricle. The heart is three chambered, but the ventricles are partially separated so some mixing of oxygenated and deoxygenated blood occurs, except in crocodilians and birds.
In amphibians, reptiles, birds, and mammals, blood flow is directed in two circuits: one through the lungs and back to the heart pulmonary circulation and the other throughout the rest of the body and its organs, including the brain systemic circulation. Amphibians have a three-chambered heart that has two atria and one ventricle rather than the two-chambered heart of fish figure b. The two atria receive blood from the two different circuits the lungs and the systems.
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 where gas exchange occurs in the lungs and through the skin.
For this reason, amphibians are often described as having double circulation. Most reptiles also have a three-chambered heart similar to the amphibian heart that directs blood to the pulmonary and systemic circuits figure c. 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 successfully-evolved animal groups on earth.
In mammals and birds, the heart is also divided into four chambers: two atria and two ventricles figure d. 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.
Privacy Policy. Skip to main content. The Circulatory System. Search for:. Overview of the Circulatory System. The Role of the Circulatory System The circulatory systems is a network of blood vessels supplying the body with oxygen and nutrients, while removing carbon dioxide and waste. Learning Objectives Describe the basic properties of the circulatory systems.
Key Takeaways Key Points The heart is central to the circulatory system as it is the fist-sized pump that circulates the blood throughout the body. As animals became more complex and multicellular, the circulatory system evolved because simple diffusion was insufficient to supply all of the cells with nutrients. The coordination of the circulatory system and the respiratory system to ensure proper gas exchange is very important in animals that have lungs and gills.
Key Terms respiration : the process by which cells obtain chemical energy by the consumption of oxygen and the release of carbon dioxide; the process of inhaling and exhaling; breathing cardiac : pertaining to the heart.
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