The Anatomy of the Kidneys
There are different parts of the kidneys that have specific roles in their function.
- The cortex: This is the outer layer and is where some of the processing happens.
- The medulla: This is the middle layer of the kidney and is also where some processing happens.
- The pelvis: This is where the urine collects to leave the kidney via the ureters.
The Function of the Kidneys
The kidney produces urine through the processes of filtration, reabsorption, secretion, and elimination. If you are unfamiliar with how this works, see my Urinary System Introduction lesson. This helps the body to maintain homeostasis.
The Blood Supply to the Kidneys
The cardiac output from the heart is approximately 5.6 liters per minute. Of that, 1.2 liters go to the kidneys every minute. That’s about 20% of all the blood.
From that 20%, we produce around 125 mL of filtrate per minute. This adds up to around 180 L every day. All this filtrate doesn’t become urine, or we’d be in the restroom all day. That wouldn’t be fun.
When the filtrate is produced, it contains waste, but it also contains usable stuff (i.e. water, ions, etc). The bulk of this gets reabsorbed back into the bloodstream to be used by the body.
The end result is that we produce around 1 L of urine on a daily basis.
Looking at a cross-section of a kidney under a microscope, you will see little structures. These are nephrons and are the functional units of the kidneys.
This is where most of the processes happen to produce urine. There are approximately 1 million nephrons in a kidney. The urine produced by these nephrons collects via the collecting ducts. From there, it drains into the urinary pelvis.
The urine then travels via the ureters down to the bladder and leaves the body via the urethra.
The kidney consists of the cortex, medulla, and pelvis. One of the major functions is filtering the blood. The functional unit of the kidney is the nephron. If you understand these basic concepts, you are ready to dive into the blood supply of the kidneys.