Although mom controls the oxygen source, the fetus has a couple of clever tricks to get the most oxygen possible! Rishi is a pediatric infectious disease physician and works at Khan Academy.

Khan Academy learning modules include a Community space where users can ask questions and seek help from community members. Educators should consult with their Technology administrators to determine the use of Khan Academy learning modules in their classroom. Please review materials from external sites before sharing with students.

Learn how the needs of the fetus are met by the placenta, which is a special organ that belongs to both the mother and the fetus! Rishi is a pediatric infectious disease physician and works at Khan Academy.

Khan Academy learning modules include a Community space where users can ask questions and seek help from community members. Educators should consult with their Technology administrators to determine the use of Khan Academy learning modules in their classroom. Please review materials from external sites before sharing with students.

Using the stethoscope to check blood pressure is a technique thatŐs been used for >100 years! Blood pressure is one of the major vital signs frequently measured by health care workers, and it tells us a lot about our blood circulation. Learn what blood pressure is, how it relates to resistance in a tube, why it is necessary to get oxygen to your cells, and how it can change as you age. WeŐll finally put it all together by relating pressure, flow, and resistance in one awesome equation!

Khan Academy learning modules include a Community space where users can ask questions and seek help from community members. Educators should consult with their Technology administrators to determine the use of Khan Academy learning modules in their classroom. Please review materials from external sites before sharing with students.

The human body enjoys stability. For example, if your blood pressure changes, the body puts a couple of brilliant systems into motion in order to respond and bring your blood pressure back to normal. There are some quick responses using nerves and some slower responses using hormones. The system using hormones is sometimes called the renin-angiotensin-aldosterone-system (RAAS), which is the main system in the body for controlling blood pressure. When your blood pressure drops too low or gets too high, your kidneys, liver, and pituitary gland (part of your brain) talk to each other to solve the problem. They do this without you even noticing! Learn how the body knows when the blood pressure has changed, and how hormones like angiotensin 2, aldosterone, and ADH help return blood pressure to back to normal.

Khan Academy learning modules include a Community space where users can ask questions and seek help from community members. Educators should consult with their Technology administrators to determine the use of Khan Academy learning modules in their classroom. Please review materials from external sites before sharing with students.

No organ quite symbolizes love like the heart. One reason may be that your heart helps you live, by moving ~5 liters (1.3 gallons) of blood through almost 100,000 kilometers (62,000 miles) of blood vessels every single minute! It has to do this all day, everyday, without ever taking a vacation! Now that is true love. Learn about how the heart works, how blood flows through the heart, where the blood goes after it leaves the heart, and what your heart is doing when it makes the sound ŇLub DubÓ.

Khan Academy learning modules include a Community space where users can ask questions and seek help from community members. Educators should consult with their Technology administrators to determine the use of Khan Academy learning modules in their classroom. Please review materials from external sites before sharing with students.

Every time you take a breath, oxygen makes it way into your lungs. Follow along on that journey! Rishi is a pediatric infectious disease physician and works at Khan Academy.

Khan Academy learning modules include a Community space where users can ask questions and seek help from community members. Educators should consult with their Technology administrators to determine the use of Khan Academy learning modules in their classroom. Please review materials from external sites before sharing with students.

In this 14-minute video lesson, Sal gives an overview of the cycles of regulation, de-regulation and government in 20th century US capitalism. [History playlist: Lesson 13 of 26]

Khan Academy learning modules include a Community space where users can ask questions and seek help from community members. Educators should consult with their Technology administrators to determine the use of Khan Academy learning modules in their classroom. Please review materials from external sites before sharing with students.

In this 15-minute video lesson Sal gives an outline of the 1973 Allende Coup in Chile and Pinochet's Junta. [History playlist: Lesson 11 of 26]

Khan Academy learning modules include a Community space where users can ask questions and seek help from community members. Educators should consult with their Technology administrators to determine the use of Khan Academy learning modules in their classroom. Please review materials from external sites before sharing with students.

This 6-minute video lesson looks at the American Civil War from from Lee's Surrender to Grant to Lincoln's Assassination. [History playlist: Lesson 2 of 26]

Khan Academy learning modules include a Community space where users can ask questions and seek help from community members. Educators should consult with their Technology administrators to determine the use of Khan Academy learning modules in their classroom. Please review materials from external sites before sharing with students.

This 14-minute video lesson discusses the Bay of Pigs Invasion. [History playlist: Lesson 7 of 26]

Khan Academy learning modules include a Community space where users can ask questions and seek help from community members. Educators should consult with their Technology administrators to determine the use of Khan Academy learning modules in their classroom. Please review materials from external sites before sharing with students.

This 15-minute video lesson provides an overview Communism and the Marxist-Leninist States. [History playlist: Lesson 5 of 26]

Khan Academy learning modules include a Community space where users can ask questions and seek help from community members. Educators should consult with their Technology administrators to determine the use of Khan Academy learning modules in their classroom. Please review materials from external sites before sharing with students.

This 19-minute video lesson provides an overview of the Cuban Missel Crisis. [History playlist: Lesson 8 of 26]

Khan Academy learning modules include a Community space where users can ask questions and seek help from community members. Educators should consult with their Technology administrators to determine the use of Khan Academy learning modules in their classroom. Please review materials from external sites before sharing with students.

This 17-minute video lesson discusses Napoleon's disastrous invasion of Russia. [History playlist: Lesson 24 of 26]

Khan Academy learning modules include a Community space where users can ask questions and seek help from community members. Educators should consult with their Technology administrators to determine the use of Khan Academy learning modules in their classroom. Please review materials from external sites before sharing with students.

This 17-minute video lesson covers part 1 of Sal's series on the French Revolution: from the Convocation of the Estates General to the storming of the Bastille. [History playlist: Lesson 14 of 26]

Khan Academy learning modules include a Community space where users can ask questions and seek help from community members. Educators should consult with their Technology administrators to determine the use of Khan Academy learning modules in their classroom. Please review materials from external sites before sharing with students.

This 16-minute video lesson presents part 2 of Sal's series on the French Revolution. It covers the royals trying to escape, the Champ De Mars Massacre, the Declaration of Pillnitz, and the movement towards becoming a Republic. [History playlist: Lesson 15 of 26]

Khan Academy learning modules include a Community space where users can ask questions and seek help from community members. Educators should consult with their Technology administrators to determine the use of Khan Academy learning modules in their classroom. Please review materials from external sites before sharing with students.

This 23-minute video lesson presents part 3 of Sal's series on the French Revolution. It covers the Reign of Terror. [History playlist: Lesson 16 of 26]

Khan Academy learning modules include a Community space where users can ask questions and seek help from community members. Educators should consult with their Technology administrators to determine the use of Khan Academy learning modules in their classroom. Please review materials from external sites before sharing with students.

This 23-minute video lesson is Sal's 4th and final video on the French Revolution. It covers the rise of Napoleon. [History playlist: Lesson 17 of 26]

Khan Academy learning modules include a Community space where users can ask questions and seek help from community members. Educators should consult with their Technology administrators to determine the use of Khan Academy learning modules in their classroom. Please review materials from external sites before sharing with students.

This 27-minute video lesson is part 1 of Sal's overview of the Haitian Revolution. It covers the slaves rebellion in Saint-Domingue (Haiti) and the rise of Toussaint. L'Ouverture. [History playlist: Lesson 18 of 26]

Khan Academy learning modules include a Community space where users can ask questions and seek help from community members. Educators should consult with their Technology administrators to determine the use of Khan Academy learning modules in their classroom. Please review materials from external sites before sharing with students.

This 17-minute video lesson concludes Sal's overview of the Haitian Revolution. It covers Dessalines taking on Leclerc and Rochambeau. [History playlist: Lesson 19 of 26]

Khan Academy learning modules include a Community space where users can ask questions and seek help from community members. Educators should consult with their Technology administrators to determine the use of Khan Academy learning modules in their classroom. Please review materials from external sites before sharing with students.

This 16-minute video lesson gives an overview of the Korean War. [History playlist: Lesson 6 of 26]

Khan Academy learning modules include a Community space where users can ask questions and seek help from community members. Educators should consult with their Technology administrators to determine the use of Khan Academy learning modules in their classroom. Please review materials from external sites before sharing with students.