Blood Pressure and its Regulation
When we think about blood pressure it is the mean arterial pressure that is monitored and regulated by the body. It is the force of blood pushing against the walls of the arteries as the heart pumps blood to the systemic tissues of the body. It is not the arterial systolic or diastolic or pulse pressure nor the pressure found in any other part of the vascular tree.
When you go to the doctor to get your pressure checked however, those measurements record the arterial systolic and diastolic pressures, which are used as markers to assess mean arterial pressure.
The limit for normal blood pressure as designated by the National Institutes of Health (NIH) is less than 120/80 mmHg. So to put it simply, blood pressure is the force exerted on the blood vessels by blood being pumped by the heart, during contraction and relaxation.
Determinants of Blood Pressure
There are four major determinants of blood pressure. They are:
Blood Volume – the more volume of blood present means that the vessels and heart have to work hard to pump that blood through the Circulatory system.
- Overall Compliance – the elastic characteristics of the vessels contribute to the overall pressure in the vessels. When the vessels have expanded the blood pressure is lowered and if it recoils blood pressure will increase.
- Cardiac Output – CO is related to two other factors: heart rate and stroke volume. When the heart rate is fast, CO is increases and when stroke volume is high, CO also increases. Therefore when CO increases, then the arterial pressure will also increase.
- Peripheral Resistance – the resistance of the arteries is related to the Overall Compliance Characteristic. When peripheral resistance increases, the overall compliance decreases and thus the arterial blood pressure increases.
Why is Regulation Needed?
As blood is pumped from the heart to the various blood vessels, enough pressure is generated in order to send blood to all parts of the body. As the blood travels further from the heart, they branch off and gradually decrease in size, much like the branches of the tree. One branch may travel to the stomach, while another may transport blood to the muscle and yet another to the brain, etc.
When the heart contracts, pressure built up in the blood vessels increases as the blood passes through, while the opposite is true when the heart relaxes in between heart beats. For the blood to be able to reach all of the vitals organs, healthy, elastic blood vessels that will stretch and recoil as the pressure goes up and down respectively, are needed.
Persons who suffer from hypertension, their small blood vessels in vitals organs are most often affected over time. These vessels become scarred, harden and inelastic, which means they are more likely to get blocked or worse rupture which could lead to organ damage and even the failure of these organs in some cases. So it is important to regulate hypertension to reduce the risks of:
In the case of hypotension, the blood pressure is abnormally low. When the pressure is this low, blood is not pumped effectively through the systemic circuit of the body. This leaves the body with a lack of blood supply getting to major/vital organs. With organs not receiving optimal blood supply, it’s cells do not receive the proper amounts of oxygen and cannot carry out fundamental metabolic processes efficiently, which reduces the amount of energy the cells produce to power the body, this will lead to a host of problems such as, fainting, dizziness, seizures etc.
So, we see regulation of blood pressure is of utmost importance for our survival!
How is Blood Pressure Regulated?
Both divisions of the Autonomic Nervous system, the Parasympathetic and Sympathetic Nervous systems regulate blood pressure. They act like the gas and brake pedals in a vehicle by increasing and decreasing the blood pressure when it begins to move outside of the bounds of normalcy, the Sympathetic being the gas pedal and the Parasympathetic being the brake.
This subtopic will be explained more in depth in the next article, Blood Pressure Regulation at a Glance: How Determinants Affect Blood Pressure.