The kidneys are essential for cleansing the blood and eliminating urine waste from the body. They also have other important functions that maintain homeostasis in the body including regulating acid-base balance, the concentration of electrolytes, controlling blood pressure, and secreting hormones.
Kidney failure causes a very serious and possibly fatal disruption of homeostasis in the body. Complications include weakness, shortness of breath, widespread swelling (edema), metabolic acidosis, and heart arrhythmias.
Along with the lungs, the kidneys are the main organs for regulation of pH in the body. They do this by recovering and regenerating bicarbonate (HCO3–) from urine and excreting hydrogen ions (H+) into the urine. The kidneys use the enzyme carbonic anhydrase to catalyze reactions involving bicarbonate. This is the same enzyme used in acid-base balance functions in the red blood cells, the stomach, and pancreas.
Some of the electrolytes the kidney helps to keep in homeostasis are sodium, potassium, chloride, bicarbonate, magnesium, copper, and phosphate. For example, the hormones aldosterone and angiotensin II regulate the reabsorption of sodium from the renal filtrate and the excretion of sodium into the renal collecting tubule, respectively.
Blood Pressure- Extracellular Fluid Volume
The kidneys don’t directly sense blood pressure, but they act to regulate blood pressure over the long term. They do this via the renin-angiotensin system that regulates the amount of extracellular fluid in the body, which, in turn, is regulated by the levels of sodium in the blood plasma. Over time, untreated high blood pressure can damage the arteries around the kidneys leading to kidney disease.
The kidneys synthesize two important hormones that help support homeostasis—erythropoietin and renin. Erythropoietin stimulates the production of red blood cells in the bone marrow. This happens in response to the normal turnover rates (life spans) of these cells, and in response to cellular hypoxia when the tissues aren’t getting enough oxygen.
Renin is both a hormone and an enzyme, also known as angiotensinogenase. It is used to help synthesize angiotensin II that has several effects on the body, ultimately leading to increased blood pressure.