There are two types of human blood vessels, one is called artery and the other is called vein. If the blood in the blood vessels is ejected from the heart, you can feel the blood vessels will beat, called arteries; if the blood in the blood vessels is flowing back to the heart, you can not feel the blood vessels beat, called veins. Blood clot, is the clotted blood, similar to the pig red we see in the vegetable market. If blood clots in a vein, it is called a venous thrombosis. Under normal circumstances, the blood in the veins is not clotted and can flow; when the blood becomes solid and becomes thrombus, it will block the blood vessels, resulting in poor blood flow, and the blood cannot return to the heart, which will cause the body fluids to gather in the feet, resulting in swollen feet like elephant legs. So, the blood in the veins clots and becomes a blood clot, which is called venous thrombosis. What are the manifestations of venous thrombosis in the lower extremities? The most typical manifestation of lower extremity vein thrombosis is the sudden swelling of one leg, most commonly when you wake up and find that one leg is much swollen than the other, and there is a small indentation when you press it with your finger, and it may be accompanied by pain, and the pain is more obvious when you walk. Sometimes you can also see some bruises on the calf, which are actually small dilated veins. Why do you see small dilated veins? Because the large veins in the lower extremities are blocked by blood clots, and blood cannot flow through them, so it flows through the smaller veins next to them. Similar to a city where the main road is blocked, some of the cars will pass through the small road next to it. When the blood flow through the small vein next to it increases, it naturally expands, and when it is normally invisible, it bulges as if it is a bruise.