The two kidneys act as the cleaning team of our body. They work continuously to cleanse about 80 to 120 millimeters of blood every minute, and this is approximately equal to a third or half a glass of fluid.
From this amount of blood, they remove toxins, excess water, excess potassium or sodium, and other functions to maintain balance in our body. They even produce a hormone that aids in red blood cell production and a hormone for bone health.
When we talk about kidney function, we use the term glomerular filtration rate or GFR. Medical researchers have come up with medical calculators that we can use in estimating GFR hence the term “eGFR” or estimated GFR or estimated kidney function. It is normally 80 to 120 ml/minute. Kidney failure is when the number is less than 15 ml/minute for more than three months.
Factors considered by researchers in GFR formulas or calculators are a person’s age, gender, race, and a blood test called serum creatinine or cystatin. These factors affect the functions of the kidneys and kidney disease outcomes. These medical calculators and recommendations are updated based on new evidences from studies.
The kidneys continue to do this normal cleaning functions or glomerular filtration but like any other part of the body they also slowly age.
When a person reaches the age of 40, his kidney function begins to decrease by about one ml/min. each year. It is an expected or “physiologic” change because the cells of the kidneys also undergo changes in their structure because of aging process.
The rate in the decline of kidney function due to aging process is slow so that normal individuals would not be needing dialysis as they reach old age. The kidney function may be down to 60 or 70 ml/min at age 80 years but the kidneys are still capable of cleansing the body. In some persons, GFR rapidly declines even at a younger age.
What hastens or speeds up the rate of decline of kidney function, or what causes one person to lose more than one percent per year?
There are risk factors. These are medical conditions, lifestyle or inherited traits that slowly damage the smallest parts of the kidneys – the nephrons. Nephrons are delicate structures composed of glomeruli and tubules. The glomeruli appears like small balls inside the kidneys, they are made of very small blood vessels with delicate thin linings.
The two kidneys normally contain about one million of nephrons each, lesser number if a person is born prematurely. The nephrons operate at finely regulated blood flow rate, filtration pressure, pressure inside the nephron itself.
They detect the amount of water, sodium, potassium, glucose, and other substances that enter the nephrons. The rate of absorption or excretion of these substances is constantly adjusted or fine-tuned by the nephrons to maintain balance in our body.
For example, the kidneys have to constantly eliminate excess water and sodium to maintain blood pressure at a normal level. They have to eliminate more uric acid if we consume lots of food that is high in purine content.
Risk factors that lay the ground for kidney damage are obesity, diabetes mellitus, high blood pressure, a family history of kidney failure, inherited genes for kidney disease like adult polycystic kidney disease, smoking, habitual use of pain relievers, heavy intake of alcohol, constant exposure to toxins or a history of sudden and temporary kidney failure that resolved but with residual kidney damage.
Conditions like obesity, elevated blood sugar and elevated blood pressure cause high filtration rate and pressure inside the nephrons. Smoking and pain relievers reduce the oxygen supply to the kidneys. Sodas contain salt, sugar, and additives that contribute in the long-term to obesity, onset of diabetes, or hypertension. Toxins like lead and other chemicals can damage the tubules of the kidneys.
Immune diseases can involve the nephrons when antibodies are directed against these structures and inflammation ensues. Habits like high meat intake, high salt diet, and low intake of fluids or water contribute to kidney stone formation which cause obstruction or predispose to recurrent kidney infections.
The nephrons adjust to medical conditions, habits and intakes but in the process their walls are damaged. Proteins may start to leak into the urine. Walls gradually thicken and scarring will occur.
Unfortunately, once fibrosis or scarring occurs kidney damage tends to become progressive especially in the presence of albumin or protein spillage. The nephrons undergo a dropout process – some are permanently damaged and cannot not function anymore. The remaining ones compensate and overwork until they themselves become scarred or fibrotic.
When this happens, the GFR drops to less than 15 ml/minute and the condition is diagnosed as chronic kidney disease stage 5. Kidney function replacement is attempted with artificial kidneys or dialysis or a transplantation of a new kidney .
Prevention of kidney disease starts with knowing our risk factors and early consult.
And even if we have risk factors or signs of early kidney disease, fortunately for now there are approaches to slowing kidney damage – dietary adjustments, lifestyle changes, and control and treatment of medical conditions that put us at risk.
There also drugs that aid in protecting kidney function – ACE inhibitors, angiotensin 2 blockers, and drugs that are now approved for kidney protection-sodium glucose cotransport inhibitors, GLP-1 receptor agonists, and mineralocorticoid receptor antagonists like finerenone.
These medications are available, and their use is safe with the supervision of physicians.
April 28, 2024
