William Harvey (1578–1657) was one of the early biologists who studied the bodies of humans and animals. He even dissected the bodies and did experiments with the heart and blood vessels. He concluded from his experiments that the blood leaves the heart through the arteries and returns via the veins. However, he could not explain how blood left the arteries to enter the veins. He said there must be some structure between arteries and veins but he could not find them. Marcello Malphigi (1628–1694) later discovered these structures while studying a dead frog's lungs under a microscope.
Which of the following statements about arteries and veins is TRUE?

Options

A. Arteries have thicker walls than veins.
B. Veins have thicker walls than arteries.
C. All arteries carry only oxygenated blood.
D. All veins carry only deoxygenated blood.

Answer

To determine which statement about arteries and veins is true, we will analyze the information provided in the question and the video transcript step by step.

### Step 1: Understanding the Function of Arteries
Arteries are blood vessels that carry blood away from the heart. Most arteries carry oxygenated blood, which is rich in oxygen and nutrients, to various parts of the body. The only exception is the pulmonary arteries, which carry deoxygenated blood from the heart to the lungs.

**Hint:** Remember that arteries generally carry oxygenated blood, except for the pulmonary arteries.

### Step 2: Understanding the Function of Veins
Veins are blood vessels that return blood to the heart. They typically carry deoxygenated blood, which is low in oxygen and high in carbon dioxide. The exception to this is the pulmonary veins, which carry oxygenated blood from the lungs back to the heart.

**Hint:** Keep in mind that veins usually carry deoxygenated blood, with the exception of pulmonary veins.

### Step 3: Analyzing the Thickness of Walls
The walls of arteries are thicker than those of veins. This is because arteries need to withstand the higher pressure of blood being pumped directly from the heart. The thicker walls help maintain the integrity of the arteries under high pressure.

**Hint:** Think about why arteries need to be thicker than veins in terms of blood pressure.

### Step 4: Evaluating the Statements
Now, let’s evaluate the statements provided:

1. **The arteries have thicker walls than the veins.** - This statement is true, as explained above.
2. **The veins are thicker than the arteries.** - This statement is false; veins have thinner walls.
3. **All the arteries carry oxygenated blood.** - This statement is false; pulmonary arteries carry deoxygenated blood.
4. **All veins carry only deoxygenated blood.** - This statement is false; pulmonary veins carry oxygenated blood.

### Conclusion
Based on the analysis, the true statement is: **The arteries have thicker walls than the veins.**

**Final Answer:** The correct statement is that arteries have thicker walls than veins.