Artery
Arteries are invulnerable enemies that act like obstacles found in 
Utero. They will peridoically spawn forth Blood Cells, either Mobile or Spinning, which will find their way to a Vein. They do not deal contact damage and cannot be flown over with flight.
They will continue spawning, even if the room is cleared, and will also persist and remain active even after leaving and re-entering the room. The only way to close an Artery and accompanying Veins is if they spawn in a room with 
Pressure Plates, which will deactivate them after the buttons are pressed.
Notes
- Depending on the room layout the Blood Cells spawn by Arteries will have specific designated Veins to travel to.
- This is determined by their variant type as 44.960.0 Arteries will only send Blood Cells to 44.962.0 Veins, and 44.960.1 to 44.962.1 etc.
- Multiple Arteries can send Blood Cells to a single Vein, but if there are multiple Veins designated to a single Artery, the Blood Cells will choose at random which Vein to travel to.
- Arteries will not spawn Mobile Blood Cells if there is no viable path towards a Vein, and will not spawn any types of Blood Cells if there are no Veins.
Vein
Veins are the exit counterpart to Arteries. Blood Cells will travel from Arteries and leave through Veins, but otherwise they will have all the same attributes as Arteries.
Blood Cells
Mobile Blood Cell
Mobile Blood Cells are enemies spawned endlessly from Arteries and will walk towards their designated Vein.
They can sometimes spawn at certain locations when entering a room, like regular enemies, but will still always spawn alongside Arteries and Veins.
Spinning Blood Cell
Spinning Blood Cells are flying versions of Mobile Blood Cells. They will be able to fly directly to their Veins over rocks and pits, but otherwise behave identically.
They can sometimes spawn at certain locations when entering a room, like regular enemies, but will still always spawn alongside Arteries and Veins.
Gallery
Artery's appearance in Utero.
