HA32 is an EM of a similar section of a cardiac muscle cell as that shown in HA31 but shown at a different angle. In addition to the mitochondria at the end of the nucleus (N), there is a centriole (microtubule organizer) in cross section and several vesicles containing an atrial natriuretic factor that can be exocytosed to aid in blood pressure regulation (arrowheads). Tertiary lysosomes (3) stain very darkly. Identify the cell membrane (PM) and mitochondria (m). Two cellular junctions, gap junctions (GJ) and spot desmosomes (D) are labeled in HA32L. These will be described in the Epithelium chapters.