👉 An atrium is a type of organ that contains blood vessels, called capillaries. It plays a crucial role in maintaining homeostasis by delivering oxygen and nutrients to various tissues throughout the body. The structure of an atrium is composed of two layers of cells - the epithelial layer and the mesenchymal layer. The epithelial layer is responsible for filtering out blood particles, while the mesenchymal layer contains blood vessels that facilitate nutrient delivery and oxygen exchange.