Yesterday, a middle-aged man in his fifties, Lao Wang, came to see me, his face was haggard and anxious. As soon as he saw me, he said, ‘Doctor, it’s no good, my kidney is broken! Carefully inquired about the condition, it turned out that the patient in the past two weeks found that his two feet are swollen, and heavy and swollen, with a finger to press a puddle will be pressed out. The patient thought that his kidneys were broken, and the more he thought about it, the more afraid he was, so much so that he could not eat or drink. So what are the causes of swollen legs? Human tissues contain a lot of water, and if the tissues contain too much water, edema will form. Under normal circumstances, the water contained in the tissues is constantly exchanged with the water inside the blood vessels through the walls of the blood vessels, and a balance is maintained between the two. The main regulators of this balance are the osmotic pressure created by plasma albumin and the hydrostatic pressure created by intravascular water; the osmotic pressure caused by plasma proteins retains water within the blood vessels, while the hydrostatic pressure of the plasma forces the water to seep out of the blood vessels. Whether water is retained within the vasculature or leaks out of the vasculature into the tissues depends largely on who has more power between osmotic pressure and hydrostatic pressure. Thus, edema can be caused when hydrostatic pressure is too high (e.g., venous return obstruction from various causes) or when osmolality is low (low plasma protein concentration). Of course, too high vascular permeability (e.g., skin irritation) can also cause edema by causing too much water to enter the tissues. Based on the principle of edema formation mentioned above, let’s briefly analyze the possible causes of Wang’s leg swelling: Wang has been doing desk work for the last month, with very little activity. Since the lower limbs are in a low position in the body, it is presumed that their hydrostatic pressure will be relatively high, and the water will easily leak out into the tissue interstitial space, which will thus cause edema. Under normal circumstances, after walking and other activities, the regular contraction of the muscles of the lower limbs has a squeezing effect on the lower extremity veins, helping venous blood return. Since the old king is working at the desk and does not often walk around, in this case, the veins without muscle compression are more likely to dilate and congested, the venous pressure will rise, and the water in the blood vessels will seep out through the walls of the blood vessels and enter into the tissues. After listening to these analyses, Lao Wang understood and obviously relaxed a lot, and the subsequent examination also confirmed my analysis. Of course, swelling of the legs can not be completely excluded from other problems such as kidney disease, swelling of the legs should also beware of whether there are other diseases. 1, lower extremity venous thrombosis or valvular insufficiency: especially in one leg, and lying down can not completely subside need to be especially careful. 2, heart disease (such as heart failure or cardiac insufficiency): previous heart disease, edema in the afternoon or night swelling obvious, the next morning can be reduced. Liver disease: edema occurs due to the decrease of albumin produced by the liver, and ascites often occurs. Kidney disease: water retention caused by weakened drainage function of the kidneys leads to edema; at the same time, too much protein is lost in kidney disease, causing low albumin edema. Edema usually occurs in the loose tissues, mainly in the eyelids and lower limbs, and it is more serious in the morning and less in the afternoon or evening. 5.Allergy: there is a history of allergy, often accompanied by skin tingling. 6.Endocrine edema: it is common in women with endocrine diseases, and there is no obvious change in edema in 24 hours, and there is no obvious depression when pressed. 7.Dystrophic edema: for example, edema caused by advanced tumor.