Morphology and morphometric features of the heart of the domestic horse (Equus ferus caballus)

Abstract

The article presents the results of studies of the macro- and microscopic structure, features of organo- and cytometry of the heart of the domestic horse – Equus ferus caballus Linnaeus, 1758. The obtained data are of great importance for fundamental and applied research in veterinary morphology, cardiology, and pathology. The results obtained significantly expand and supplement the information on the morphological structure of the horse's heart in relation to the species characteristics of domestic mammals in the relevant sections of histology, zoology, comparative anatomy, etc. According to the results of morphometry, the absolute mass of the heart of a physiologically mature horse was 2988 ± 97 g, the relative mass was 0.59 ± 0.01%, and the net mass of the heart was 2807 ± 93 g. According to linear measurements of the heart (height – 30.26 ± 0.74 cm, width – 20.52 ± 0.55 cm, thickness – 12.84 ± 0.39 cm, circumference – 54.16 ± 2.05 cm), the development index (shape) of the horse’s heart is 147.5 ± 8.1%, therefore the horse’s heart is defined as of the dilated-shortened type. The more developed components of the heart are its ventricles – left and right, then the left and right atrium. According to such absolute values, the ratio of the mass of the horse’s ventricles to its net mass was 1:0.8, the ratio of the mass of the atria to its net heart mass was 1:0.2, and the ratio of the mass of the atrial myocardium to the mass of the ventricular myocardium was 1:0.24. According to the results of cytometry, the left ventricular cardiomyocytes had a larger volume – 12554 ± 878 μm3 , the right ventricular cardiomyocytes had a slightly smaller volume – 8402 ± 681 μm3 , and the atrial cardiomyocytes had the smallest volume – 5729 ± 513 μm3 . The volumes of the cardiomyocyte nuclei were similar: in the left ventricle, 133 ± 9 μm3 ; in the right ventricle, 132 ± 8 μm3 ; and in the atrial cardiomyocytes, 129 ± 8 μm3 . And so, the smallest nuclear-cytoplasmic ratio was characteristic of cardiomyocytes of the left ventricle (0.0107 ± 0.0007), significantly higher is the value of cardiomyocytes of the right ventricle (0.0159 ± 0.0010), and significantly higher is the value of cardiomyocytes of the atrium (0.0230 ± 0.0007). We associate such ambiguous organo- and cytometric parameters of the ventricles and atria of the heart with the activity of their work – the functional features of the muscular tissue of the myocardium, capable of spontaneous rhythmic contractions, as a result of which blood moves through the vessels: the left ventricle (its cardiomyocytes) mainly performs the function of a pump, promoting the movement of blood through the vessels of the large circle of blood circulation, carrying out a correspondingly greater load; right ventricle (cardiomyocytes) – performs a predominantly volumetric function, promoting blood movement only through the vessels of the small circle of blood circulation, while performing a smaller load.