Chronic kidney disease

Chronic kidney disease is a broad term that includes subtle decreases in kidney function that develop over a minimum of three months.

In contrast, acute kidney injury refers to any deterioration in kidney function that happens in less than three months.

Now the kidney’s job is to regulate what’s in the blood, so they might remove waste, or make sure electrolyte levels are steady, or regulate the overall amount of water, and even make hormones - the kidneys do a lot of stuff!

Blood gets into the kidney through the renal artery, and once inside it goes gets into tiny clumps of arterioles called glomeruli where it’s initially filtered, and the filtrate which is the stuff that gets filtered out, moves into the renal tubule.

The rate at which this filtration takes place is known as glomerular filtration rate or GFR. In a normal healthy person, this is somewhere around 100-120 milliliter of fluid filtered per minute per 1.73 m2 of body surface area. The value is slightly less in women than men and it decreases slowly in all of us as we grow older.

One of the most common causes of chronic kidney disease is hypertension.

In hypertension, the walls of arteries supplying the kidney begin to thicken in order to withstand the pressure, and that results in a narrow lumen. A narrow lumen means less blood and oxygen gets delivered to the kidney, resulting in ischemic injury to the nephron’s glomerulus.

Immune cells like macrophages and fat-laden macrophages called foam cells slip into the damage glomerulus and start secreting growth factors like Transforming Growth Factor ß1 or TGF-ß1.

These growth factors cause the mesangial cells to regress back to their more immature stem cell state known as mesangioblasts and secrete extracellular structural matrix. This excessive extracellular matrix leads to glomerulosclerosis, hardening and scarr, and diminishes the nephron’s ability to filter the blood - over time leading to chronic kidney disease.

The most common cause of CKD is diabetes, excess glucose in the blood starts sticking to proteins in the blood — a process called non-enzymatic glycation because no enzymes are involved.

This process of glycation particularly affects the efferent arteriole and causes it to get stiff and more narrow - a process called hyaline arteriosclerosis. This creates an obstruction that makes it difficult for blood to leave the glomerulus, and increases pressure within the glomerulus leading to hyperfiltration.