![]() The vast inner part is myocardium, composed of cardiac muscle, specialised conductive tissue, valves, blood vessels and connective tissue. The right AV valve is a single, spiral plane of myocardium, in remarkable contrast to the fibrous structure characteristic of the mammalian tricuspid valve. ![]() ![]() In the avian heart the right and left AV valves are in close proximity to the conduction system. The inside layer is endocardium, also covering valves. The heart histologically consists of three layers, which resemble their structure in blood vessels. Ĭhicken atrioventricular (AV) heart valve (A, B), ventricle longitudinal (C, D) and transverse (E, F) views, and the atrium (G, H). Similarly, the right ventricle has a thinner wall than the left as blood is only pumped to the lungs, whereas the left ventricle pumps blood around the body. Thinner walls are found in the atria as the blood is only pumped to the ventricles, which does not require as much muscle as that required to pump blood to the entire body. The atria receive the blood from the veins and then pump the blood through to the ventricles. The heart is also subdivided into atria cranially and ventricles caudally (see Figure 1 for the histology of these structures). Finally, the heart is primarily supplied by two coronary arteries branching from the ascending aorta, whilst cardiac veins drain blood from the heart tissue into the right atrium, via the coronary sinus. The septum itself contains a conduction system for the initiation and propagation of action potentials, allowing stimulation and consequent contraction of the myocardium. The septum separates the heart into right and left halves, with the left side sending blood to the systemic circulation and the right side routing blood to the pulmonary circulation. The cardiac fibrous skeleton called the annulus fibrosus comprises of four connective tissue rings acting to separate the atria and the ventricles. The cardiac muscle acts to contract rhythmically via coordination of the cardiomyocytes, potentiating movement of blood around the body. The heart itself it made up of multiple structural components. The mammalian heart lies just into the left hand side of the thoracic cavity, whilst the avian heart lies slightly to the right of the midline. The chambers effectively function as two separate pump systems to circulate blood around the body, with cardiac valves ensuring unidirectional flow of blood through the chambers and blood vessels. Similar to mammals, birds have a four-chambered heart surrounded by pericardium. Structure and function of the avian heart With the availability of more reference genomes, increases in the number and magnitude of avian studies and more advanced technologies, the genetics behind avian cardiovascular disorders is being unravelled.ġ.1. This review investigates a range of avian cardiovascular disorders in order to highlight their pathologies, epidemiology and genetics in addition to avian models of heart disease. By 2018, the Avian Genomes Consortium had published the sequences of 45 species/34 orders. In 2015, Nature published news on the ‘Bird 10K’ project, which aims to sequence 10,500 extant bird species. This work is assisted by the growing number of avian genomes being published. Increasingly, the avian genome is being analysed in its own right. Birds have also been used to model cardiovascular disease and therefore knowledge has become enriched due to this endeavour. Previously much work was undertaken in mammals with information extrapolated and transferred to birds. Research into avian cardiovascular genetics has rapidly accelerated. This in turn has highlighted the importance of breeding, genetic testing and possibilities for future prognostic and diagnostic testing. Cardiovascular disease is common in avian species and increasing commercial economic losses and demand for healthcare in the household/smallholding veterinary sector has resulted in increased research into these disorders.
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