Questions: When a person moves from a sitting position to a standing position, blood pressure increases within a few minutes. What causes this increase in pressure? Multiple Choice - Fewer skeletal muscles are active while in a standing position thus more blood is circulating in the blood vessels - Blood is having to travel against gravity from the heart to the brain - More blood pressure is needed to carry oxygen rich blood to the brain while in a standing position - More skeletal muscles are active while in a standing position thus more pressure is needed to get oxygen rich blood to these active muscles - Less oxygen rich blood is need by the brain while standing

The answer is the second one: Blood is having to travel against gravity from the heart to the brain.

Explanation for each option:

• Fewer skeletal muscles are active while in a standing position thus more blood is circulating in the blood vessels: This is incorrect. When standing, more skeletal muscles are actually engaged to maintain posture, not fewer. The increase in blood pressure is not due to more blood circulating in the vessels because of inactive muscles.

• Blood is having to travel against gravity from the heart to the brain: This is correct. When a person stands up, the cardiovascular system must work against gravity to ensure that blood reaches the brain. This requires an increase in blood pressure to maintain adequate cerebral perfusion and prevent dizziness or fainting.

• More blood pressure is needed to carry oxygen-rich blood to the brain while in a standing position: This is partially correct but is essentially a restatement of the correct answer. The need for increased blood pressure is primarily due to the gravitational challenge of moving blood to the brain.

• More skeletal muscles are active while in a standing position thus more pressure is needed to get oxygen-rich blood to these active muscles: This is incorrect. While more muscles are active when standing, the primary reason for the increase in blood pressure is to ensure blood reaches the brain, not necessarily to supply active muscles.

• Less oxygen-rich blood is needed by the brain while standing: This is incorrect. The brain's demand for oxygen does not decrease when standing; in fact, maintaining adequate blood flow to the brain is crucial to prevent dizziness or fainting.

In summary, the increase in blood pressure when moving from sitting to standing is primarily due to the need to overcome gravity and ensure sufficient blood flow to the brain.