This lesson explores chronic kidney disease and the metabolic disorders that affect kidney function. We'll delve into diabetes mellitus, hypertension, and glomerulonephritis and learn what your urine can tell you about your health.
When everything is hunky-dory, your kidneys do an excellent job of ensuring what needs to be filtered or absorbed gets done right, right on time. However, there are conditions outside of the kidney's control that can overwhelm the kidney's ability to do its job. These conditions may be a symptom of a metabolic disorder that causes kidney damage. In addition, there are times when the kidneys themselves are sick, and this causes trouble for them and the rest of the body. We'll delve into some of these interesting but terrible diseases in this lesson.
Structures of a kidney nephron
What Shouldn't Be in Urine
As we move on, you must keep in mind that while there are some small deviations from this rule, under normal conditions, there shouldn't be any glucose or any large structures such as proteins and cells in the urine. If there is glucose, proteins like albumin and hemoglobin, or cells such as leukocytes (white blood cells) or erythrocytes (red blood cells) in the urine, that means there is something wrong in the kidneys, or something along the rest of the urinary tract, or both.
One example of a metabolic disorder that can affect kidney function is diabetes mellitus. This is a disease whereby the body stops producing or responding to insulin, which is a hormone that drives glucose into the cells and out of the bloodstream. If a person with diabetes doesn't have their body properly controlled through medication, there can be deadly consequences. One of the many clues physicians can use to diagnose diabetes is the presence of glucose in the urine, something we call glucosuria.
If we have glucose in the urine, it means we have exceeded something called the 'renal threshold.' This means that the level of glucose in blood is so high that when the glomerulus filters the glucose into the tubules, the proximal convoluted tubule's reabsorptive capacity of glucose is breached, and it dumps what it cannot hold back into the urine. Think of the proximal tubules as a dam. If there is a massive amount of water behind a dam that wasn't built to control such a high amount of water in the first place, the dam will be breached and will send the excess water into the river below. In our case, that river is the rest of the renal tubule.
Structure of a normal glomerular capillary
In contrast to diabetes, which can secondarily cause kidney problems, there is an affliction which may be primarily due to issues within the kidneys themselves. This disorder is called primary glomerulonephritis, which is the inflammation of the kidney's glomerulus. If a disorder occurring outside of the kidneys, such as diabetes, is causing the inflammation, the disease is known as secondary glomerulonephritis.
It's easy to remember what glomerulonephritis means because you can easily spot the word glomerulus in the term. The word 'nephro' refers to the kidney, while the ending '-itis' refers to the inflammation of something. Hence, we get inflammation of the kidney's glomerulus, or glomerulonephritis.
In this disease, inflammatory factors begin to tick off your glomerular capillaries by damaging them. The capillaries normally have cells which are joined in a formation just big enough to let small molecules through but not porous enough to let large structures through. However, if the cells get really mad, due to inflammatory mediators hurting them, they begin to break down and move apart from one another, like you would break down and cry or move away from someone you're angry with. As these cells get damaged and move away from one another in anger, the capillary walls become even more porous than before!
This is a problem, as large structures can now freely pass through the glomerulus and into the urine. In cases of glomerulonephritis, we may see red blood cells in the urine, something called hematuria, or proteins like albumin in the urine, something we call proteinuria. Since albumin is the main protein of human blood plasma, it should make sense why it is often found in the urine in cases of glomerulonephritis.
The problem with proteinuria is that it may, by itself, cause further damage to the kidney. So, you get a wicked circle of damage causing more damage in the case of glomerulonephritis. It's like that old saying: 'Negativity breeds more negativity.' It couldn't be more true in this case.
Inflammation of the glomerular capillaries weakens their walls.
Chronic Kidney Disease
Unfortunately, both diabetes and glomerulonephritis, as well as high blood pressure, may cause another issue called chronic kidney disease (CKD).
In cases of advanced stages of chronic kidney disease, the kidneys may no longer be able to secrete enough of a hormone called erythropoietin, or EPO for short. If this happens, your bone marrow will no longer be stimulated to produce red blood cells, a process called erythropoiesis. This will lead to a condition whereby your body does not have enough red blood cells or hemoglobin, something we term anemia.
In addition, high blood pressure, also known as hypertension, not only causes chronic kidney disease but is like glomerulonephritis in a sense. The high blood pressure in the body also means high blood pressure in the glomerulus. This increased pressure in the glomerulus causes the walls of the capillaries to engorge with blood to the point where they, like in glomerulonephritis, become very porous. The increased porous nature of the capillary walls can lead to, once again, proteinuria.
Overall, I anticipate that these few examples have given you a taste for how interdependent all of our body's systems are on one another. If any one part breaks down, everything will be affected one way or another. I'm sure you can tell that sometimes one disease can cause another and vice versa, and there's collateral damage everywhere in between.
Regardless, I truly hope neither you nor anybody you know has the terrible conditions we went over. At the very least, however, you can understand a little bit more of the reasons as to why certain problems arise due to these diseases. Let's review these conditions one more time to help refresh your memory.
Diabetes mellitus is a disease where the body stops producing or responding to insulin and may cause glucosuria, which is glucose in the urine.
While diabetes may secondarily affect kidney function, there is a disorder that starts in the kidneys themselves. This affliction is called primary glomerulonephritis, which is the inflammation of the kidney's glomerulus, and this may lead to proteinuria, or protein in the urine.
Since albumin is the main protein of human blood plasma, it should come as no surprise that albumin will be found in the urine of patients who have proteinuria.
Unfortunately, both diabetes and glomerulonephritis can by themselves eventually cause chronic kidney disease, which can lead to a condition whereby your body does not have enough red blood cells or hemoglobin; we call this malady anemia.
At the end of this lesson, you should be able to:
- List items found in the urine that could signal health problems
- Explain what causes diabetes mellitus and why it leads to glucose in the urine
- Describe the problems that result from the inflammatory factors found in glomerulonephritis
- Understand how chronic kidney disease can lead to anemia
- Summarize how hypertension can affect the kidneys