Contains the full lesson along with a supporting toolkit, including teachers’ notes.
What the Kidney Does
The kidneys form part of the human excretory system and are vital for homeostasis. They eliminate nitrogenous waste (urea,uric acid) and excess water, salts and H+. By reabsorbing the required amounts of water, salts and H+, they help maintain a constant body environment. Furthermore, they have an endocrine function, producing erythropoietin, renin and calcitriol. These hormones stimulate red blood cell production, regulate blood pressure and maintain blood calcium levels respectively.
Acute renal failure can occur rapidly as a result of bleeding, burns, crush injuries, infections or other causes. Nowadays it is treatable and most kidney function will be recovered. chronic renal failure occurs gradually and irreversibly. It can be caused by infections, diabetes, drug abuse or other mechanisms. Its slow onset means that symptoms may not be noticed until severe damage has been done.
If the kidneys have retained some function, a person may be able to stay healthy by monitoring fluid intake, following a regulated protein diet and lifestyle changes. Total renal failure (temporary or permanent) is lifethreatening. Now the challenge is to provide a replacement for the kidneys. There are several ways of doing this.
The process of cleaning wastes from the blood artificially is calledhaemodialysis. A patient is connected to a dialysis machine by tubes leading to and from blood vessels. The blood is pumped along a tube which has a semi-permeable membrane. On the other side of the membrane, the dialysate (an aqueous solution of sugars and salts with a concentration similar to that of healthy blood) is pumped in the opposite direction. This counterflow maximises the concentration difference between the two fluids, resulting in the diffusion of urea and salts out of the blood. Bicarbonate may be added to the dialysate in elevated concentrations and it diffuses into the blood, countering the acidosis which accompanies renal failure. A haemodialysissession takes a few hours and must be repeated a few times in a week. The process has 10% of the efficiency of the kidney, hence the need for regulated diets.