Going by outward appearance, the Upyri are almost indistinguishable when standing next to your average Sol Human. The differences, though, lie in the teeth and eyes of the Upyri. Upyri cuspids are significantly sharper than a human's, and are slightly longer in length. As for their eyes, their pupils tend to be naturally dilated, and appear to have tapeta lucida which humans normally lack. This results in Upyri eyes being near black at times, with very little iris to speak of, and appear to flash a bright blue or red when light is cast on them. The appearance of tapeta lucida would suggest that they have a heightened sense of night vision, as its commonly found in most nocturnal and carnivorous creatures. Traditionally, if an Upyri would like to blend in with a human population, they would acquire contacts or shades to mask their eyes' appearance. Some Upyri have even gone to other lengths, having their cuspids removed and replaced with those similar to a human's.
Internally, it is a drastically different story. Upyri seem to lack some of the organs that humans naturally possess, and are equipped with an elongated stomach shaped more like a tube. Upyri are not able to ingest and digest normal solid foods due to this layout, and are forced to ingest liquid foods. Their primary source of food traditionally is serum, a special fluid gathered from the blood of other creatures and beings. This can be acquired through the filtering of the blood through a special machine that most Upyri carry on their person, or through the direct ingestion of blood. Ingesting it directly tends to not work as well as filtering it just for the serum in blood, though, as they also ingest all the gunk and nasty stuff that the creature/being may have had floating around in their blood. Most forms of blood will satisfy an Upyri, be it Human/Kanad/Ayr/Malmarian/Khergian/etc or animals. An Upyri has trouble drinking another Upyri's blood, though, as it forces a violent, convulsive reaction. The body will attempt to expel the Upyri blood from the stomach, usually resulting in the Upyri puking the blood right back up. Some Upyri have built a tolerance to the blood, but it isn't as fulfilling to the appetite as blood from other organic species.
They are equipped with two functioning hearts, though both are smaller than a normal human heart. Each has two chambers, and they are stacked neatly atop one another on the right side of the body. Their lungs, liver, and kidneys are similar to humans, though of slightly different sizes. They seem to be missing the pancreas, which suggests that all the digestion of food occurs in the stomach itself before moving on to the intestines. They also lack an appendix naturally.
Similar to that of a Malmarian, the Upyri have naturally long lifespans compared to a Human. Most Upyri tend to live to around the age of 250. The oldest an Upyri has ever lived was recorded at 341 years.
Upyri and other Human-like races are able to breed together, but the actual physical form of the child is based off the species of the mother. If the mother is Upyri, then the child will be Upyri physiologically. If the mother is of another race, then the child will be of that race physiologically. The child does gain traits from the father, and thus becomes a hybrid of the two races. A hybrid of Human and Upyri genetics is called a Humyri (a blending of Human and Upyri.)