The Circulatory System
Start with the complete cardiovascular system and learn what the heart, blood vessels, and blood are doing together.
What makes up the system?
The cardiovascular system consists of the heart, blood vessels, and blood. Together they transport substances such as oxygen, nutrients, hormones, and cellular waste throughout the body.
The cardiovascular system as a network
The heart provides the pumping force while the vessels provide the pathways through which blood travels.
The pump
The heart is a muscular organ that pumps blood through the pulmonary and systemic circulations.
The pathways
Arteries, capillaries, and veins form an extensive network through which blood travels.
The transport medium
Blood carries gases, nutrients, hormones, waste products, and cells involved in defense and clotting.
Constant adjustment
The cardiovascular system contributes to maintaining a stable internal environment.
Think of circulation as one continuous network.
The heart does not work independently from the vessels or the blood. Each part has a different job, but they operate as a single transport system.
Two major circulatory loops
Human circulation can be divided into pulmonary circulation, which connects the heart with the lungs, and systemic circulation, which carries blood between the heart and most of the body's tissues.
Follow the blood
A useful way to understand the system is to follow one drop of blood. It is pumped by the heart, sent through a circulatory loop, and returned to the heart so the cycle can continue.
The circulation is a loop, not a straight road.
Blood repeatedly travels through the heart and vessels as the cardiovascular system continuously moves materials around the body.