A morphological study on sinus and atrioventricular nodes in saanen goats*

In mammals, the sinus node and atrioventricular node are defined as the heart's specific stimulus and conduction systems. The electrical stimulation that starts in the sinus node continues with the atrioventricular node, and the rhythmic stimulation occurs in this way. There are differences in the sinus and atrioventricular nodes' location, size, and cell structures between species. In this study, which was carried out to determine the morphological structures and locations of the sinus and atrioventricular nodes in Saanen goat hearts, nine hearts from healthy goats were used. After performing the routine tissue follow-up procedure for histological examinations, 5 μm-thick serial sections taken from paraffin-blocked samples were stained with Crossman Trichrome and Periodic Acid Schiff (PAS) and photographed. It was determined that the sinus node was in a subepicardial position near where the cranial vena cava opens up to the right atrium. The sinus node, with an average length of 8-10 mm was crescent-shaped. The atrioventricular node was located in the subendocardium layer in the right half of the interatrial and the interventricular septum, where the coronary sinus opened into the right atrium. An atrioventricular node with an average length of 4.5-5 mm was observed to be roughly oval. Two types of cells were identified in both nodes: cells with small, rounded with empty cytoplasm and rather large nuclei, and cells with thin, elongated structures and darker staining.