How Do the Reptile's Circulatory & Urinary System Work Together?

Water is necessary for any life form. It is like the fuel of an automobile. Humans use up this fuel and expel waste, just like an old-fashioned car. Reptiles, on the other hand, evolved in arid environments where water is less available. They use water almost like a hybrid engine, rationing it whenever they can and minimizing the waste they expel.

  1. Flow

    • In most animals, the circulatory system is a simple loop. Blood passes through the heart, down the arteries, throughout the body, then back to the heart via the veins. Along the way, the blood passes through the kidneys, where oxygen is taken from the blood vessels and waste is taken away. The urinary system is similarly straightforward. The kidneys produce two toxic chemicals as a by-product; urea and ammonia. These poisons are then dissolved in water, creating urine, which is collected in the bladder before being released.

    Reptile Urinary System

    • Many reptiles, especially species kept as pets, do things differently. Instead of using water to dissolve their waste, they create a third chemical called uric acid. That's why, in addition to clear urine, reptiles excrete a white, chalky substance.

    Renal Portal System

    • Whereas most animals have a unified circulatory system, reptiles have one that is segmented, like two vast highway systems that only intersect at one off ramp. When blood leaves the heart of a reptile, some of it goes to the regular circulatory system and some goes into the renal portal system. This second path winds through the lower half of the animal's body and through a vein that that splits in two directions.

    Paths

    • This vein determines the blood's flow through the final leg of the journey. One path enters the kidneys before returning to the heart. The other path is a direct line that bypasses the kidneys. A valve inside the vein determines the proportion of blood that goes through each path. If the reptile is dehydrated, only a small quantity of blood is passed into the kidneys, thereby minimizing the amount of water that will be lost to the production of uric acid.

    Sick Reptiles

    • The only time that the renal portal system impacts pet owners is in the application of drugs and medicines. Because the blood at the back half of the animal's body is closed off from the front half, anything injected there might be funneled straight into the kidneys, causing organ damage. Medicine for lizards and tortoises is injected in the front limbs so that it can be dispersed throughout the body before it reaches the kidneys.