Topic of the week: Kidneys

What are the kidneys?

The kidneys are a pair of organs within the abdominal cavity and are the start of the urinary tract. The medical term for referring to the kidneys is renal. Their main jobs include filtering blood, reabsorbing essential nutrients, helping maintain blood pressure, and producing certain hormones.

The kidneys filter blood and excrete toxins to be urinated out of the body. Inside the kidneys there are millions of tiny filtration structures called nephrons. The blood must pass through the first section of the nephron called the glomerulus. Here the blood's liquid portion, the plasma, separates and crosses over a barrier from the glomerulus and is collected in the Bowman's Capsule. This liquid is called ultrafiltrate (it will soon turn into urine). 

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From the Bowman's Capsule, the ultrafiltrate journeys to the proximal renal tubules. The proximal tubules are long filtering tubes allowing electrolytes and nutrients like amino acids and glucose, to return back into the bloodstream.

Along with toxins like blood urea nitrogen (BUN) produced by the body's metabolism, drugs can also cross the barrier into the ultrafiltrate so they can be excreted by the body.

The next section is called the Loop of Henle, and this is where water is reabsorbed back into the bloodstream. Sodium and chloride are also reabsorbed to help maintain electrolyte balance. 

A special function of the Loop of Henle is the production of a hormone called erythropoietin. This hormone helps stimulate the production of red blood cells and helps prevent early red blood cell death. 

The next section is the distal convoluted tubule where the ultrafiltrate has even more water filtered out of it, concentrating the waste produced by the body into what we call urine.  The balance of how much water is absorbed or excreted is essential for maintaining a healthy blood pressure.

The urine passes into a collection duct system and is then into the pelvis of the kidneys. It then leaves the kidneys through the ureters, to the bladder, and then out of the body through the urethra.

Kidney Animation

Check out the video below for an animation about how kidneys work

As you can tell, the kidneys have a very important function in the body and mammals would not be able to survive without them.

I hope this helps you understand what the kidneys are. We'll discuss kidney disease in a different post.

Author

Yvonne Brandenburg, RVT, VTS (SAIM) is a Registered Veterinary Technician practicing in California and obtained her Veterinary Technician Specialty in Small Animal Internal Medicine in 2016. She is the founder of InternalMedicineForPetParents.com. For more about Yvonne visit her author page here.

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