Short answers, pulled from the story.
An average adult human carries five to six quarts of blood, which accounts for approximately 7% of their total body weight. This fluid consists of plasma, red blood cells, white blood cells, and platelets.
The first vascular system appeared over 600 million years ago in an ancestor of triploblasts. Fish possess a single circuit with a two-chambered heart pumping blood through gills and then body tissues.
Arches 3, 4, and 6 persist to become definitive structures while arch 5 disappears completely. The first and second aortic arches regress to form maxillary arteries and stapedial arteries respectively.
William Harvey published Exercitatio Anatomica de Motu Cordis et Sanguinis in Animalibus in 1628 demonstrating continuous blood circulation through minute connections. Marcello Malpighi discovered the capillary system connecting arteries and veins in 1661 completing Harvey's conceptual leap.
About 98.5% of oxygen in arterial blood combines chemically with hemoglobin molecules under normal sea-level pressure conditions. This chemical combination occurs within red blood cells circulating throughout the vascular system.