Morphological and Morphometric Studies on the Prenatal Development of the Heart of the Dromedary (Camelus dromedarius)

Abstract

The aim of this study to investigate the morphology and morphometry of the pre-natal development of dromedary heart. Forty eight hearts of camel foetuses obtained from Al-Ssalam and Tamboul slaughterhouses, Sudan, were used in histological, histometric, ultrastructural and morphometric studies. Samples were collected during the period (December 2014-March 2015). The foetuses were divided into three age groups: first trimester (1-130 days), second trimester (131-260 days) and third trimester (261- 426 days). At the early stages the pericardium was associated with the diaphragm, liver and thoracic vertebrae. The atrial outlines were irregularly showing many undulations, whereas the ventricular outlines were relatively regular. The epicardium appeared as a thin layer which showed a gradual increase in thickness and amount of adipose tissue. As foetal age increased, a gradual increase was also observed in the myocardial thickness of the ventricular wall and atrial pectinate muscles. Sinoatrial node (SAN) in the second and third trimesters had the same location as in the adult and also had two types of cell as in other animal species. Atrioventricular node (AVN) was found close to the atrioventricular opening in the first trimester and close to the opening of the coronary sinus in the second and third trimesters. It generally appeared as a group of large-sized and lightly stained cardiac muscle cells. Atrioventricular bundle (AVB) was embedded in myocardium in the second trimester either between the endocardium and myocardium or within the myocardium in the third trimester. Purkinje fibres (PF) were embedded in the myocardium in the first trimester and either between the endocardium and myocardium or within the myocardium in the second and third trimesters. Myocardial bridges (MBs) were observed only histologically in the second and third trimesters. They appeared as bundles of fibres of cardiac muscle which covered the interventricular branch of coronary artery either partially or completely. The thickness of MBs and the interventricular branch of coronary artery in the third trimester was significantly higher than that in the second trimester. Type II MBs were observed in the late stages of first trimester with SEM. MBs had a less developing transverse tubular system than the myocardium in the same stages. The heart during the first third of first trimester had approximately similar dimensions. The length increased more than the width during the late stages of the first trimester. The longitudinal groove started gradually as a shallow groove and the coronary groove was not observed until the end of the first trimester. The atrial pectinate muscles showed a wavy appearance at the early stages of first trimester and gradually developped and appeared as large branching and anastomosing plexiform cords at the second and third trimesters. Pectinate muscles were thicker in the second trimester than in the third trimester. There were no intercalated discs in the first and second trimester, whereas Z lines with irregular striations were present. They were first appeared in the third trimester. Mitochondria were numerous around the nuclei and between the fibrils. No significant differences were detected in ultrastructural morphometric measurements in the length of myofibrils in the first, second and third trimesters. The length and width of mitochondria in the second and third trimesters were constant. This was also true for the width of connective tissue nuclei and of myocardium in the three trimesters and connective tissue nuclei of MBs. Mitochondria in the first trimester was longer than that in the second and third trimesters. The sarcomere in the third trimester was significantly thicker. Connective tissue nuclei in the first trimester were longer than those of second and third trimesters. Connective tissue cells nuclei of MBs were longer in the third trimester than those of myocardium. It is concluded that the development of camel heart is fully achieved through the three gestational ages (first, second and third trimesters).