Edema, also called puffiness is a relatively common symptom. Some are swollen faces, some are swollen eyes, some are swollen feet, and the more serious are swollen stomachs. Swelling is different from fat, the latter is an increase in fat, the former is basically an accumulation of water, except for the relatively rare mucus edema. Where water accumulates, swelling occurs. The human body has a strict regulatory system for the distribution of water. The vast majority of water exists in the cells, followed by the tissue interstitium, and only a small portion is a component of the blood. Edema is an increase in water in the interstitial space of tissues. If it is cellular edema, because the number of cells is large and the amount of water is large, and because cells are the main component of organ function, a slight edema will produce serious symptoms and will not wait until the edema is visible to the naked eye. Tissue interstitial water in the balance of two kinds of pressure: a pressure is hydrostatic pressure, which is our usual understanding of the tap water pump to a high building water pressure; the other pressure is called osmotic pressure, generally did not read the biomedical may not know this pressure. Simply put: the factors that affect the hydrostatic pressure are the density and depth of the liquid, while the osmotic pressure is affected by the number of molecules or ions within the liquid, the more molecules and ions, the higher the osmotic pressure; the liquid flows from a place with high hydrostatic pressure to a place with low hydrostatic pressure, but from a place with low osmotic pressure to a place with high osmotic pressure. The amount of water in the tissue interstitial space depends on the balance of the two pressures within the capillaries and the tissue interstitial space. When the hydrostatic pressure within the blood increases and the osmotic pressure decreases, more water enters the tissue interstitium, producing edema. Extrapolating backwards from this mechanism, it is clear that any disease that raises tissue capillary pressure and lowers osmotic pressure within the blood will produce edema. Overall, diseases of the heart, liver, and kidneys account for the vast majority of diseases that can cause edema. Theoretically, chronic lung disease can also cause edema, but after lung insufficiency gradually leads to cardiac insufficiency, so it is put together with edema caused by heart disease. Most of the edema caused by heart disease is on the tops of the feet and calves, which is why doctors must look at the feet and calves when looking at cardiac function. Blood flow throughout the body from the veins back into the heart requires the heart to have a certain volume and also to be very elastic. The average person may think that good or bad heart function is like a muscle, the stronger the contraction, the better. But the heart’s job is not to carry an object or perform a set of movements. Between a strong heart and a long-lived heart, I think anyone knows what to choose. So a normal heart must not only contract strongly, but also spring back intact in order for blood to flow back into the heart. If the heart is not functioning, the blood has to temporarily exist in the veins, the capillaries that are upstream of the veins increase in pressure, and edema is created. A characteristic of the resulting cardiogenic edema is that the lower the part of the edema, the more obvious it is, such as the surface of the feet and calves. It is especially noticeable in the afternoon, after a day of standing. Unlike cardiogenic edema, which mainly affects hydrostatic pressure, edema caused by liver disease and kidney disease is due to a decrease in osmolarity. As mentioned at the beginning, the level of osmolarity is mainly influenced by the number of molecules or ions in the fluid. In the blood, the main molecule that affects the osmolarity is albumin. Both liver disease and kidney disease patients have a decrease in albumin in the blood, but in different ways. Liver disease is severe enough that albumin levels drop, and this is because the liver is the site of albumin production. In famine years and regions, because of severe malnutrition, not many amino acids are eaten and the liver does not have the raw material even if it is functioning normally, and hypoproteinemia is produced, but this situation is almost non-existent in China anymore. Theoretically hypoproteinemia is systemic, with edema easily occurring in all parts of the body, but patients with liver disease are predominantly ascites, why is this? The principle is similar to that of cardiogenic edema above. The veins of the digestive tract in the abdomen do not collect directly into large veins back to the heart like the veins of the body and extremities, but first have to collect in the liver through a portal vein. The raw nutritional materials collected from the GI tract are unloaded in the liver and loaded with finished or semi-finished products made by the liver before returning to the heart for transport to the whole body. When the liver is diseased, the normal structure of the liver is destroyed and the portal vein is blocked at one end of the liver, while the other end is still flowing in, creating a weir-like thing. The portal vein gets thicker and thicker, the upstream pressure gets higher and higher, and the viscera start to edema. Not much fluid could fit in the viscera, and it just so happened that there was a cavity with huge potential, the peritoneal cavity, close by, into which all the excess water was put, and ascites was formed. Some people will think they have gained weight. In fact, there is an easy distinction between the increase in abdominal circumference caused by ascites and obesity, and that is the belly button. No matter how overweight, the belly button is always sunken; but the pressure inside the abdomen increases when ascites, and the belly button is a weaker place on the belly, so it will jack up the belly button, and in serious cases, an umbilical hernia will be formed. The decrease in albumin in kidney disease patients is not due to a decrease in production, but a leakage from the urine. The human blood is filtered from the kidneys over and over again every day to filter waste into the urinary tract. Only very small molecules can pass through the sieve between the blood vessels and the urinary ducts. But if the kidneys become diseased, causing these sieve holes to become larger, albumin can pass through. When the sieve pores are not yet too large, only albumin can pass through and only protein can be detected in the urine. If the sieve pores increase further and red blood cells can pass through, then there will be not only urine protein but also hematuria. Because there are no local vascular changes like liver disease, the edema caused by kidney disease appears wherever the tissue is the most lax. The eyes and face are the most lax, so patients with kidney disease tend to have swollen eyes and face. If one leg or one arm is swollen and the other side is normal, it is often due to local obstruction of blood vessels or lymphatic vessels. In some patients, the cause of edema cannot be found, because no other disease can be found except edema. Idiopathic edema does not usually affect health, but it can only be determined if those diseases listed above are excluded.