Function of the urinary organs
Blood reaching the kidney is filtered in the capillary tuft of the nephron capsule: small substances – water, salts, glucose, urea – pass into the capsule cavity and form primary urine (about 150–180 litres a day), while blood cells and large proteins do not pass. In the tubule useful substances – glucose, much of the water, needed salts – are reabsorbed into blood, harmful substances remain and final (secondary) urine forms (about 1–1.5 L per day). Urine contains water, urea, uric acid and salts; in a healthy person there is almost no glucose or protein. The kidney regulates water–salt balance and blood osmotic pressure (under hormones, including a pituitary hormone) and helps regulate blood pressure. Kidney and urinary tract health: drink enough water, keep the body and lower back warm in cold, do not hold urine for long, keep personal hygiene, avoid very salty food, alcohol and smoking. If there is pain in the lower back, pain when urinating or colour changes, tell adults and see a doctor; do not take medicines on your own.
Water diary: write when and what you drink in a day; discuss drinking when thirsty and more during exercise and heat. Do not draw conclusions about urine colour on your own – ask adults if you have a question.