Posted in Psychology & Medicine

Viscera: Kidneys

(Learn more about the organs of the human bodies in other posts in the Viscera series here:

Despite being a vital organ that one cannot survive without, the kidneys are not very famous to the general populace. Not many people know what the kidneys do, let alone where exactly they lie in the body. The kidneys (of which there are two) are the major excretory organs of the human body. They are found in the back of the abdomen (in an area called the retroperitoneal space), tucked under the lower three ribs below the diaphragm. This is higher than where most people think the kidneys lie, because the abdomen extends quite high into the ribcage, as seen from the location of the liver.


The kidneys undertake many functions, but they can broadly be grouped into three groups: making urine, filtering blood and maintaining homeostasis.

Although the organ associated with urine is the bladder, it only stores urine, which is made by the kidneys and sent to the bladder via the ureters. Urine is the body’s main way of disposing excess water, salt and other byproducts such as urea. The kidneys fine-tune how much water we lose to urine depending on how much water is in the body. For example, if you drink a lot of water, the kidney senses the blood vessels being dilated and the blood being diluted, then allows more water to leave the body. Conversely, if you are dehydrated, the kidney does everything in its power to hold on to as much water as possible, resulting in concentrated urine.

The kidneys literally act as filters for the blood using a fine, intricate network of sieve-like blood vessels. These vessels have walls that have various sized holes that causes water and small molecules to pass into the kidney, while leaving large proteins in the blood. The filtered blood (containing water, various electrolytes and other metabolites) travel through a pipe network called nephrons, which reabsorb things the body needs (like water when you are dehydrated or salts like sodium), while leaving toxic products like urea and various medications.


Lastly, the kidneys maintain homeostasis (the status quo of the body) in various ways, such as fine-tuning the water and salt levels of the body. If you have renal failure where your kidneys do not function properly, you will retain too much water and may suffer a build-up of potassium, which can cause fatal changes in your heart rhythm. It is also involved in controlling the acidity of your blood and your blood pressure, through very complex mechanisms.

One way kidneys are famous is that they are popularly mentioned in the context of organ transplants. If you have renal failure, you may be able to get a kidney from a healthy, live donor as you can live with one kidney. When you take out a kidney from a healthy person, the remaining kidney will grow in size to compensate for the other kidney, while the transplanted kidney will go on to save the patient’s life by doing the many jobs mentioned above.


Posted in Psychology & Medicine


Despite the implied disgusting nature (especially smell) of urine, it is one of the most important types of “samples” used in medicine for diagnostic purposes. Like blood, urine can tell a lot about a person’s health and whether they have a certain disease or not.

One of the earliest recorded uses of urine as a medical test was for the detection of diabetes mellitus. People noticed that the urine of a diabetic would often smell quite sweet, and also taste sweet (it is uncertain how they came to test urine this way). This is because a diabetic has too much glucose (sugar) in their blood, causing it to spill over into the urine as the kidneys become saturated. In fact, the words diabetes mellitus stand for “passing through” (referring to the symptom of frequent urination) and “honey-sweet”. A completely unrelated disease called diabetes insipidus also causes frequent urination, but the urine does not taste sweet, hence “insipidus” (tasteless). This type of etymology is also seen in countries like Korea, China and Japan, where the word 당뇨(糖尿) literally stands for “sugar urine”. Although we no longer taste urine, it is still used to gauge the severity of diabetes by measuring the amount of protein in the urine (due to kidney damage).

There are many other tests one can do with urine to check for certain diseases. The chemical composition of urine tells us about the hydration status of a person, while giving away clues to diseases that cause electrolyte imbalance. It also gives some indication of how well the kidneys can do their job of concentrating urine. Certain markers such as white blood cells and bacteria in the urine can indicate a urinary tract infection. Antibodies in the urine can point towards a certain type of bacteria as the cause of a patient’s pneumonia, or whether a woman is pregnant (βhCG). Looking for proteins or sediments in the urine can be diagnostic of certain kidney diseases such as glomerulonephritis. Even rare diseases such as phaeochromocytomas can be diagnosed from the level of catecholamines in the urine (this is slightly too complex for our scopes).

A more interesting part of urinalysis is looking at the colour of the urine. Urine is usually a yellow colour, ranging in darkness depending on the concentration of urine. But when there are other things in the urine, the colour changes. Reddish urine suggests blood (which is not an indicator of kidney failure as TV shows say), which can be caused by trauma, UTIs, kidney stones or some other disease. Brown urine could be due to muscle breakdown somewhere in the body. Urine can appear very dark if the person has an illness called obstructive jaundice. Eating beetroots can cause your urine to turn bright red, while medications can change your urine colour from anywhere from red to orange to green. Murky or cloudy urine (with an offensive smell) may suggest a UTI.

Perhaps the most interesting urine colour known in medicine is purple. This unique colour is produced in a rare genetic disease called acute intermittent porphyria. If urine is collected from a patient suffering an attack of AIP (causes crippling abdominal pain) then left in the sun or under a UV light, it will turn purple due to certain proteins. Because of this, urine collected to test for AIP is wrapped in tinfoil before sending to the lab (where the chemicals are measured) to limit light exposure.

(Also read the article on how different colours of skin can be of diagnostic importance: