The arteries and veins are the plumbing of the body and are responsible for moving blood to and from all of the vital organs. In most cases arteries are responsible for carrying oxygenated blood AWAY from the heart and to the specific organs, where the further away from the heart the arteries get the smaller they become (eventually forming arterioles). Whilst the arteries are typically responsible for taking blood away from the heart, the role of the veins is to return the de-oxygenated blood from the respective organ(s) back to the heart and lungs for re-oxygenation.
The exception to the rule (and there is always one) are the pulmonary and umbilical veins which carry oxygenated blood, whilst the arteries return them.
All of my “under the microscope” images are taken in a similar manner, and using the below equipment. In this case, focus stacking was conducted by capturing a video of the subject as I move through the planes of focus, and then software pulled the images out of that video and focus stacked them into the images below;
In the case of these samples, they were from a prepared university microscope slide collection and were from a rat I believe.