Arteries and Veins: Key Concepts

Arteries are commonly drawn in red, and veins are drawn in blue, leading to the idea that:
- Arteries carry oxygenated blood.
- Veins carry deoxygenated blood.
This is not always correct.
Deoxygenated blood is often thought to be blue due to the appearance of veins under the skin.
- Veins appear blue due to the optics of light passing through the skin, not the color of the blood itself.
- Deoxygenated blood is actually a deeper red.

Blood is pumped from the heart through the aorta, which branches to supply the body.
- Some blood flows towards the head.
- Most blood flows down to the rest of the body.
Arteries branch into smaller vessels, eventually reaching capillaries.
- Capillaries: Small vessels that bridge arteries and veins where gas and nutrient exchange occurs.
Blood loses oxygen in the capillaries and becomes deoxygenated.
Deoxygenated blood flows from capillaries into veins.
Veins carry the blood back to the heart, entering the right atrium, then the right ventricle.
The blood is then pumped towards the lungs.

Pulmonary Artery: Carries deoxygenated blood away from the heart to the lungs.
- Exception to the idea that arteries always carry oxygenated blood.
In the lungs, gas exchange occurs, and the blood becomes oxygenated.
Pulmonary Veins: Carry oxygenated blood from the lungs back to the heart.
- Exception to the idea that veins always carry deoxygenated blood.
Oxygenated blood enters the left atrium, then the left ventricle, and is pumped to the rest of the body via the aorta.

Arteries:
- High Pressure: Blood is pumped directly from the heart.
  - Cutting an artery results in blood spurting out.
- Low Volume: Approximately 15% of total blood volume.
Veins:
- Low Pressure: Blood is not directly pumped by the heart; it moves sluggishly back.
  - Valves ensure blood flows in one direction.
- High Volume: Approximately 65% of total blood volume.