Final answer:
Blood flows through the different organs in parallel, with each organ receiving oxygenated blood directly from the heart. Many arteries and veins run parallel and may change names, and anastomoses in veins and some arteries provide alternative pathways for circulation.
Step-by-step explanation:
Blood flows through the different organs in parallel. Unlike a single circuit system like that found in fish, where blood travels in a unidirectional manner through a single circuit (gills, organs, then back to the heart), the human cardiovascular system, including the systemic veins, allows blood to flow to different organs simultaneously. In this parallel system, each organ receives freshly oxygenated blood directly from the heart, which then travels through arteries and branches out, reaching the organ's capillaries. After the exchange of gases and nutrients, the deoxygenated blood is collected by veins and returned to the heart.
Within the body, many arteries and veins run parallel to each other and share names; they may change names upon reaching certain landmarks. Anastomoses, which are connections between blood vessels, are especially frequent in veins, providing alternative pathways for blood flow in the event of a blockage, though certain arteries also feature anastomoses. Hence, understanding blood flow can sometimes be as complex as charting a river with many interconnected tributaries.