Why does the human body lack potassium

In fact, in life, many people suffer from potassium deficiency, but the causes are different. The most common reason is reduced potassium intake, that is, often being picky eaters in daily diet and not paying attention to eating foods rich in potassium may lead to lack of potassium intake. Another reason is excessive potassium excretion, such as severe diarrhea and vomiting, and a large loss of digestive fluids, which may lead to potassium deficiency.

1. Reduced potassium intake

Generally, the diet is rich in potassium. Therefore, as long as the body can eat normally, the body will not be deficient in potassium. Patients with digestive tract obstruction, coma, and long-term fasting after surgery cannot eat. If these patients are given intravenous nutrition without potassium supplementation or insufficient potassium supplementation, potassium deficiency and hypokalemia may occur. However, if insufficient intake is the only reason, the degree of potassium deficiency may not be very serious within a certain period of time due to the potassium conservation function of the kidney. When potassium intake is insufficient, urinary potassium excretion can be reduced to below 20mmol/L within 4 to 7 days, and can be reduced to 5 to 10mmol/L within 7 to 10 days (normal urinary potassium excretion is 38 to 150mmol/L).

2. Potassium loss through the gastrointestinal tract

This is the most important reason for children to lose potassium, which is common in patients with severe diarrhea, vomiting and other conditions accompanied by a large loss of digestive fluid. The concentration of K+ in feces can reach 30~50mmol/L during diarrhea. At this time, the potassium lost with feces can be 10~20 times more than normal. The reason why the fecal potassium content increases is that, on the one hand, diarrhea reduces the absorption of potassium in the small intestine, and on the other hand, the decrease in blood volume caused by diarrhea can increase the secretion of aldosterone, and aldosterone can not only increase the excretion of urinary potassium, but also enhance the secretion of potassium in the colon. Since the potassium content of gastric juice is only 5~10mmol/L, the loss of gastric juice is not the main cause of potassium loss during severe vomiting, and a large amount of potassium is lost through the kidney with urine, because the metabolic alkali poisoning caused by vomiting can increase the excretion of potassium by the kidney (details later), and the decrease in blood volume caused by vomiting can also promote the excretion of potassium by the kidney through the secondary increase of aldosterone.

3. Certain kidney diseases

For example, in distal renal tubular acidosis, due to the dysfunction of hydrogen secretion in the distal convoluted tubule, H+-Na+ exchange is reduced and K+-Na+ exchange is increased, resulting in potassium loss. In proximal renal tubular acidosis, the reabsorption of HCO3- in the proximal convoluted tubule is reduced, and the increase of HCO3- reaching the distal convoluted tubule is an important reason for the increase of potassium excretion in the distal convoluted tubule (see below). In the polyuric stage of acute tubular necrosis, due to the osmotic diuresis caused by the increase of urea in the tubular fluid and the insufficient reabsorption of water and electrolytes by the new renal tubular epithelium, potassium excretion may increase.