Edema is an alteration of the skin that is mainly caused by the presence of large amounts of body fluid retained in the tissue spaces, resulting in local or generalized skin swelling, decreased elasticity, and reduced tone. So the key is the retention of large amounts of body fluids. The basic pathophysiological change of nephrogenic edema is mainly water and sodium retention. Why is there a large amount of fluid retention? Let’s hear how Wang Rui understands it! Different types of edema are caused by different causes of fluid retention. And edema can be roughly divided into two categories: Nephrotic edema: large amount of proteinuria leads to hypoproteinemia, blood colloid osmotic pressure decreases, and water flows from the blood vessels to the tissue interstitial space to appear edema. At this time, the tissue interstitial protein content is low, and due to the influence of gravity, it is first manifested in the sagging areas, mainly in the lower limbs. When the intravascular load increases, some substances will be leaked through the vessel wall, just like the transmembrane transport of cells, leaking small molecules. When kidney disease occurs, a large amount of albumin is lost with the urine, the lack of albumin in the blood vessels, the plasma colloid osmotic pressure decreases, and fluid leaks from the vessels into the tissue interstices, resulting in edema. Because of the difficulty of venous return, it mostly swells up from the lower limbs. Edema in nephritis: The lesion of nephritis is mainly in the glomerulus, and the glomerular filtration rate decreases while the tubular reabsorption function is relatively normal, which leads to globular-tubular imbalance, which is the main cause of water and sodium retention. In nephritis there is no significant hypoproteinemia and the tissue interstitial protein content is high, so the starting site of such edema is in the relatively lax eyelids and face. As the disease progresses the edema can spread rapidly throughout the body. We can simply imagine our human beings as a pocket, usually drinking water is to fill the pocket, urination is to pour the water out of the pocket, drinking water and urination these two acts maintain the water balance of our pocket. If this pocket only has water in without water out, then the pocket will be propped up, which is the mechanism of nephritis edema. This kind of edema is due to too little kidney drainage and too much water retention in the body, resulting in an absolute increase in the intravascular volume load, causing the water inside the blood vessels to leak out to the outside of the blood vessels – that is, in the tissue interstices. In cases like this, where does the water flow to? To where the pressure is low, of course. And our human skin tissue where the lowest pressure? The thin skin (less muscle composition) where the pressure is low! And the face just meets these two, so this kind of edema first swell face. However, when it is particularly severe, other parts of the edema may also appear.