Why does one person's body return to the resting heart rate faster than another persons? Explain why there is a difference. (Use Vocabulary: heart, circulatory system, pump, oxygen, arteries, veins, muscles, lungs, respiratory system.)

The heart is a pump, usually beating about 60 to 100 times per minute. With each heartbeat, the heart sends blood throughout our bodies, carrying oxygen to every cell. After delivering the oxygen, the blood returns to the heart. The heart then sends the blood to the lungs to pick up more oxygen. This cycle repeats over and over again.

What Does the Circulatory System Do?
The circulatory system is made up of blood vessels that carry blood away from and towards the heart. Arteries carry blood away from the heart and veins carry blood back to the heart.

The circulatory system carries oxygen, nutrients, and hormones to cells, and removes waste products, like carbon dioxide. These roadways travel in one direction only, to keep things going where they should.

What Are the Parts of the Heart?
The heart has four chambers — two on top and two on bottom:

The two bottom chambers are the right ventricle and the left ventricle. These pump blood out of the heart. A wall called the interventricular septum is between the two ventricles.
The two top chambers are the right atrium and the left atrium. They receive the blood entering the heart. A wall called the interatrial septum is between the atria. The atria are separated from the ventricles by the atrioventricular valves:

The tricuspid valve separates the right atrium from the right ventricle.
The mitral valve separates the left atrium from the left ventricle.
Two valves also separate the ventricles from the large blood vessels that carry blood leaving the heart:

The pulmonic valve is between the right ventricle and the pulmonary artery, which carries blood to the lungs.
The aortic valve is between the left ventricle and the aorta, which carries blood to the body.
What Are the Parts of the Circulatory System?
Two pathways come from the heart:

The pulmonary circulation is a short loop from the heart to the lungs and back again.
The systemic circulation carries blood from the heart to all the other parts of the body and back again.
In pulmonary circulation:

The pulmonary artery is a big artery that comes from the heart. It splits into two main branches, and brings blood from the heart to the lungs. At the lungs, the blood picks up oxygen and drops off carbon dioxide. The blood then returns to the heart through the pulmonary veins.

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