Click image to open full size
Human Circulatory System
Human Circulatory System
Related Tools
Related Labs
Related Worksheets
The human circulatory system is the transport network that moves blood throughout the body. It delivers oxygen and nutrients to cells, carries away carbon dioxide and other wastes, and helps maintain stable internal conditions. This system is essential for survival because every organ depends on a steady blood supply. The heart, blood vessels, and blood work together as one coordinated system.
The heart acts as a muscular pump, sending blood through two main circuits. In pulmonary circulation, blood travels between the heart and lungs to exchange carbon dioxide for oxygen. In systemic circulation, oxygen-rich blood leaves the heart and reaches the rest of the body before returning oxygen-poor blood back to the heart. Valves, pressure differences, and vessel structure help keep blood moving in the correct direction.
Key Facts
- The circulatory system has three main parts: heart, blood vessels, and blood.
- Pulmonary circulation path: right ventricle -> pulmonary arteries -> lungs -> pulmonary veins -> left atrium.
- Systemic circulation path: left ventricle -> aorta -> body tissues -> venae cavae -> right atrium.
- Arteries carry blood away from the heart, and veins carry blood toward the heart.
- Cardiac output = heart rate x stroke volume.
- Blood pressure is written as systolic/diastolic, such as 120/80 mmHg.
Vocabulary
- Atrium
- An atrium is an upper chamber of the heart that receives blood returning to the heart.
- Ventricle
- A ventricle is a lower chamber of the heart that pumps blood out of the heart.
- Capillary
- A capillary is a tiny blood vessel where gases, nutrients, and wastes are exchanged with tissues.
- Oxygenated blood
- Oxygenated blood is blood that contains a high concentration of oxygen, usually after leaving the lungs.
- Valve
- A valve is a flap of tissue that prevents blood from flowing backward in the heart or veins.
Common Mistakes to Avoid
- Saying all arteries carry oxygen-rich blood, because this ignores the pulmonary arteries, which carry oxygen-poor blood from the heart to the lungs.
- Saying all veins carry oxygen-poor blood, because this ignores the pulmonary veins, which carry oxygen-rich blood from the lungs to the heart.
- Mixing up the right and left sides of the heart, because the right side pumps blood to the lungs while the left side pumps blood to the body.
- Thinking blood in arteries moves slowly because arteries are large, which is wrong because blood leaving the heart is under high pressure and moves rapidly through arteries.
Practice Questions
- 1 A person has a heart rate of 72 beats per minute and a stroke volume of 70 mL per beat. What is the cardiac output in mL per minute and in L per minute?
- 2 If 5000 mL of blood is pumped by the heart each minute and the heart rate is 80 beats per minute, what is the stroke volume in mL per beat?
- 3 Explain why the wall of the left ventricle is thicker than the wall of the right ventricle.