Why is there So Much Variation in Blood Pressure?
The blood is distributed to different body parts in varying amounts, whether your blood pressure is low or high, depending on your actions. For instance, your digestive system may need a larger blood flow after your meals. Your brain requires a higher blood flow when you are thinking something very deeply and your blood flow will enormously increase when you are running.
Normal Total Blood Flow:
In a normal woman and man, when at rest the total blood flow is nearly six liters per minute, with about 24% going to your gut, 13% to the brain, 21% to the large muscles, 4% to the heart muscles and 19% to the kidneys. The flow of the blood to your brain may remains the same, even if you run as fast as you can. But, the total flow of the blood through your body will increase more than four times to 25 liters per minute. The blood flow to your heart muscles increases four times, while the blood flow to other large muscles may increase tenfold. But, the blood flow to your kidneys falls to four times lower than that and five times lesser to your digestive system.
All these changes start even when you think of running. By redistributing blood flow, your body can prepare for action. Similarly, your blood pressure responds quickly to any emotional states like simple curiosity,embarrassment, sexual interest and fear, even for only a short time.
Small Capillaries Blood Pressure:
Between the network of arteries(high pressure) and veins(low-pressure), lies a huge mesh of small microscopically capillaries. The walls of these small capillaries are made up of extremely small cells in which the molecules of nutrients,oxygen and waste products can be easily interchanged. Therefore, the pressure within these small capillaries should remain unchanged within very narrow limits. You can maintain this constancy only by maintaining the flow of blood through your arterioles and arteries.
In fact, the major reason for the variable of blood pressure in your arterial vessels is to maintain a constant blood pressure within the capillaries. The control is mostly exerted through tension changes in the muscles of the spiral surrounding the arterioles, which cause a big changes or variations in arterial blood pressure.