A. Heart


The teleost heart has four chambers. The generalization you learned in freshman biology, the fish have actually a two-chambered heart, method that they have actually only two pumping chambers, the atrium and also the ventricle, yet they also have a sinus venosus and a bulbous arteriosus. Blood returning from the fish"s body enters the sinus venosus, a thin-walled sac wherein the significant veins coalesce. Expansion of the weakly muscular atrium pulls blood from the sinus venosus. Blood then flows from the atrium to the ventricle, solid contractions the the ventricle"s special muscular wall surface send the blood under pressure into the elastic bulbous arteriosus. From there, the blood flows into the ventral aorta and on through the gills. There room three valves in the heart to prevent ago flow during the development (diastole) of the pump chambers.

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Fish have a an extremely low press circulatory system. Over there is very tiny blood press in the venous system and return to the love is aided in all species by skeleton muscular contraction and in some varieties by accessory hearts. By the time the blood reaches the sinus venosus, pressure is essentially zero. Contractions that the atrium draw the blood indigenous the sinus venosus and assist fill the ventricle. Ventricular contractions generate the push to relocate the blood through the body.

The bulbous arteriosus is neither contractile nor valved, yet elastic. It broadens with each ventricular contraction as it fills through blood and also maintains aortal pressure throughout ventricular diastole. In regards to pressure, the gills are somewhat restrictive, through blood cells meeting resistance in ~ the lamellae. Once the ventricle contracts, it sends a fee of blood into the bulbous, as soon as the ventricle expands, the valve in between the bulbous and the ventricle keeps the blood indigenous going earlier into the ventricle. Coupled v the resistance the the gills, this causes the elastic bulbous come expand, then together the blood continues to flow through the gills the bulbous begins to "deflate", then comes one more charge the blood native the ventricle. The bulbous features to mean out the pressure extremes and also keep a steadier circulation of blood going through the gills.

If teleosts did not have actually a bulbous, then the blood would strongly pulse over the gills. It shows up to be adaptive because that the fish to relocate the blood throughout the gills in ~ a more continuous rate. However, there is some pulsing also with the bulbous, and also fish actually synchronize your heartbeat with their opercal movements in order to complement peak blood flow with the water pulses associated with the buccal pump. This is especially noticeable when fish room subjected come hypoxia.

Other Fishes


In elasmobranchs, agnathans, and also holosteans, the fourth chamber, termed conus arteriosus, is not elastic, but relatively rigid, and its wall surface contains a series of valves to prevent earlier flow that blood. Due to the fact that the conus is a more primitive condition, we can think of teleosts having actually the conus reduced to one valve (between bulbous arteriosus and ventricle) v the bulbous arteriosus developed from the ventral aorta. In lungfish and also amphibians, there is a septum splitting the atrium into two chambers, however not the ventricle.

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Assignment IVA


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