When the giraffe bends its head to drink water from the ground, there is a risk

Question

When the giraffe bends its head to drink water from the ground, there is a risk of increasing the arterial pressure in its brain even further (due to gravitational forces). An important recent finding was that the internal jugular vein (IJV) of the giraffe contains at least seven (7) valves, more than any other species (by comparison, the human IJV contains only one). Briefly explain the role of venous valves and how an increased number of valves within the IJV would affect the giraffe’s mean arterial pressure when it lowers its head. [2 marks].

This came up in some exam prep recently for my physiology exam (weird question, I know)
Please explain in thoroughly so I can understand the answer fully.

Explanation / Answer

As we consider the case of humans, it is rare that the blood flows back to the head from JV. It occurs only when there is a sharp increase in the pressure due to sneezing or on head stand position. The case is totally different in case of giraffe. As they bring their heads down, the blood to the head rushes due to two reasons. Firstly due to normal increase in arterial pressure due to gravitation, secondly due to flowback from jugular veins. In order to maintain this increase in pressure and prevent blood from entering into the head every time a giraffe bends down, there are present 7 IJV valves. They help in preventing reflow and decrease complications.

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