Learn about the components of blood and their functions in the human body.

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Khan Academy

The video explains the circulatory system and the heart, covering their structure and function.

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Test your knowledge of the endocrine system with these practice questions from Khan Academy.

Learn about the relationship between pressure, flow, and resistance in the circulatory system.

If you're seeing this message, it means we're having trouble loading external resources on our website. If you're behind a web filter, please make sure that the domains *.kastatic.org and …

If you're seeing this message, it means we're having trouble loading external resources on our website. If you're behind a web filter, please make sure that the domains *.kastatic.org and …