‘Rete mirabile’ in Giraffe and other animals
Have you ever wonder how a giraffe pumps its blood all the way up its long neck?
Firstly- A giraffe heart is very powerful and can weigh up to 12kg (26.5 lbs)
Secondly- A series of non-return values located in the blood vessels travelling up the neck stop the blood from flowing back towards the heart in between beats.
Thirdly- The skin and muscle around the legs fit tightly, in effect increasing the blood pressure in the lower body, stopping blood draining down.
Due to these reasons a giraffe’s blood pressure is exceptionally high, compared to other animals. When a giraffe lowers its head to drink, it reduces the force of gravity and actually reverses it. This means that blood is forced towards the brain at very high pressures, possibly leading to major brain damage.
Luckily for the giraffe there is an organ specifically design to reduce the pressure before the blood enters the brain. Known as the ‘Rete mirabile’ or the blood sponge, this amazing organ ‘pools’ the blood at the base of the skull and regulates the amount of blood released into the brain. This works in reverse as the giraffe quickly lifts its head, stopping blood from draining out the brain too quickly, saving the giraffe from fainting.
This amazing organ is present in other antelope, and used for a very different function in species that live in hot arid climates. Most noticeable in the Gemsbok (Oryx) and the Springbok.
In these species it is actually used for ‘thermoregulation’. As it can help cool the blood before it enters the brain. Through a process of heat diffusion between blood vessels in the Rete mirabile, the blood is cooled to a sufficient temperature to enter the brain. This is very important firstly to protect brain cells for heat damage, but also to ‘trick’ the brain into believing that the rest of the blood in the body is in fact not that hot. This stops the animal losing precious water through sweating and panting.
This means these animals can stand out in the baking African Sun, with little visible effects.