Biology / Unit 13 Bio 3205 short lesson, about 20 seconds
Vein Structure
Captions available
The idea
A vein carries blood toward the heart through a thinner wall than an artery, relying on one-way valves and surrounding muscle to keep low-pressure flow moving.
In practice
Valves inside leg veins stop blood pooling backward under gravity while a person stands.
Where people slip
"Vein" names a direction of flow, toward the heart — it does not specify what the blood contains.
Your place on the trail
Every lesson rests on earlier ones and opens later ones. Tap any to jump.
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