You may have remarked that your heart comes to your mouth while entering the examination hall. Does that actually mean your heart leaves its place and reaches for your mouth? No, it doesn’t. It’s an expression that we use when we can literally feel and hear the blood pounding in our ears. Similar to this, many people experience fainting spells when they see blood; does this imply that they are allergic to the sight of blood? No, of course not! The reason behind both these situations is the dramatic change in their blood pressure.
The blood pounding in the ears and the sensation that your heart is about to burst out of your chest occurs due to the dramatic rise in one’s blood pressure. Conversely, when you feel like fainting or nauseous, it is due to a sudden huge drop in blood pressure.
So now the question arises of what blood pressure is and how on this earth it is affecting our bodies so much. Let us understand it today!
Content: Blood Pressure
What is Blood Pressure?
The human heart comprises 4 chambers – 2 atriums and 2 ventricles. Among them, the left ventricles push the deoxygenated, i.e., impure blood, to the lungs to pick up oxygen. Whereas the left ventricles pump the oxygenated, i.e., pure blood to the whole body.
Definition of Blood Pressure
When the blood is pumped out of the heart and into the arteries, it exerts a certain amount of force on the walls of an artery. This force occurring in the artery because of the blood pressing against its wall is blood pressure. Basically, arterial blood pressure is the result of the pumping of blood from the heart into the already full aorta. This pressure ensures that the blood reaches each and every part with the same intensity.
“The pressure or force exerted by the blood per unit area on the walls of the arteries is referred to as blood pressure”.
For easy understanding, you can imagine our body is like a factory with lots of pipes running through it. Similarly, your blood arteries are comparable to the steam pipes in industries, and your heart is in place of the furnace. These pipes transport the essentials from one part to another with the help of blood.
So, just like the steam pipes, if the internal pressure is very high, they may burst. Or if the pressure is too low, then it will not be enough to move the blood and eventually, the furnace is backed up. Our body’s homeostatic control tries to tightly regulate the blood pressure by making fine or dramatic adjustments in order to maintain the BP within safe limits.
Factors Affecting Blood pressure
There are many factors that affect the pressure of the blood inside your arteries. Here we will discuss some of the major factors:
- Cardiac Output
- Total blood volume
- Nervous control of the blood vessels (Vasomotion)
- Systemic vascular resistance (SVR)
1. Vessel length
2. Blood viscosity
3. Diameter of the blood vessel
Cardiac Output
The cardiac output refers to the volume of blood pumped out of the ventricle per minute. It is measured in litres per minute. The cardiac output is the product of heart rate and the stroke volume, i.e., the amount of blood ejected out by the ventricles during each beat.
For instance, if the heart rate of a person measures 72 beats/min and the stroke volume is 80 ml, then the cardiac output can be:
CO = 72 beat/min X 0.08 Litres/beat
Cardiac output = 5.5 litres/min
Thus, the cardiac output determines the amount of blood that comes out of the heart. From this, it is evident that any factor that raises cardiac output, either by increasing heart rate or stroke volume or by elevating both, will ultimately elevate the BP.
In contrast, any given factor that lowers the cardiac output, by reducing heart rate or stroke volume or both, will eventually decrease the cardiac output.
The factors that aid the elevation of the cardiac flow are:
- Thyroid hormone
- Increased calcium level
- Catecholamines epinephrine and epinephrine
- Sympathetic stimulation
- Increased calcium level
Conversely, the factors that degrade the cardiac output are:
- Decreased calcium levels
- Rise or fall in potassium ion level
- Parasympathetic stimulation
- Acidosis
- Anoxia
- Lowered calcium levels
Total Blood Volume
Our body must have a sufficient amount of blood circulating through our blood vessels so as to maintain a healthy being. The blood volume refers to the total amount of blood flowing in the body. This volume highly impacts BP.
If by any means the volume of the blood inside the body increases, the vessels will overstretch to pass the extra blood, which ultimately will raise your BP. On the other hand, if the volume decreases, then the transport via blood vessels will partly collapse as the walls will be unable to press strongly against the blood to move them further. Consequently, lowering blood pressure.
Vasomotion
In a closed circulation system, BP not only relies on heart rate and total blood volume but also on the nervous control of the blood vessels.
The medulla oblongata region of the brain has a vasomotor centre present near the heart rate centre.
The motor nerves carry the impulse from the vasomotor centre to the smooth muscles in the artery walls.
There are two such motor nerves – vasoconstrictor and vasodilator.
Vasoconstriction
The vasoconstrictor causes the narrowing of the blood vessels. Vasoconstriction occurs when the blood vessel receives more constrictor impulses and lesser dilator impulses. As the vessel contracts, the blood pushes harder on the walls of arteries to move further, thereby raising BP.
Vasodilation
The vasodilator causes the widening of the blood artery. Vasodilation occurs when the vessel gets more of the dilating impulses and less of the constricting impulse. As the vessel dilates, the blood slowly moves forward, and the BP dramatically falls.
Systemic Vascular Resistance (SVR)
If any factor is working against the blood flow, then we say it is increasing the resistance. The resistance is actually the amount of friction that blood encounters while travelling through the blood vessels. Thus, we refer to it as the opposite of blood flow. Most of the resistance is found in the peripheral circulatory system. Thus, it is also known as peripheral resistance.
This resistance significantly determines the compliance of the blood vessel, i.e., its ability to expand and accommodate more content. The more the artery’s compliance, the more it will be able to expand to accept blood surges without significantly raising blood pressure or resistance. In this way, the resistance determines the pressure of blood inside our arteries. There are three main sources which decide the level of resistance:
- Blood Viscosity
- Blood Vessel Length
- Blood Vessel Diameter
Blood Viscosity
The blood viscosity is itself a resisting factor for its flow. As we all know that the thicker the fluid is, the more difficult it becomes for its molecules to move. Similar is with the blood. The viscosity of the blood depends upon its constituents like the number of blood cells, plasma protein and some other elements like fats etc.
Thus, the viscosity of the blood has a dramatic impact on BP. Usually, the thickness of the blood remains constant in the body. But at the time of diseases like polycythaemia which cause a drastic increase in the blood cells, or with the issues like anaemia, where the blood cell count falls, in such cases, the viscosity of the blood changes.
This implies that the thicker the blood will be, the more will be the resistance. As a result, the heart will have to pump the blood with increased force, thereby increasing the blood pressure.
Blood Vessel Length
As the length of the blood vessel increases, the resistance also increases. You can understand it as having a pipe of 10 m and 20 m. Even when you pump the water into both pipes with the same intensity, the pressure from the 10 m pipe will be much higher than that of the 20 m pipe. Similarly happens with our bodies.
Persons who gain weight and are obese need to build miles of arteries and arterioles to vascularise all the extra tissues, which increases peripheral resistance. Consequently, the heart has to apply more force to move the blood within the body. This eventually increases blood pressure.
Blood Vessel Diameter
Conversely, if your body experiences cold, your hypothalamus signals the blood arteries to contract. It reduces the blood flow to the periphery, which ceases the cold blood entering the core of the body from limbs.
The blood vessel diameter is the factor that has the greatest impact on the resistance. When the blood vessel diameter changes, the resistance changes too, and so does the blood pressure. The diameter of your blood vessel often changes to regulate the internal cues. For instance, if the body feels hot, your hypothalamus sends the message that you need to get away from the heat. Resultantly, your peripheral blood arteries will dilate so as to increase the blood flow of your limbs.
How the diameter of the vessel alters the blood pressure?
When the radius of a pipe is just halved, what do you think will happen? You might say that it is simple and the volume coming out of the pipe will also be reduced to half. But it’s not true at all!
When you decrease the radius by half, the flow inside is decreased by 1/24, i.e., 1/16 times. That means 1/16 times the blood from the original blood. By this, you can imagine that blood flow from the artery is slow, less and insufficient. Thereby the heart pushes the blood intensity and the blood tries to move from a smaller passage. this leads to an increase in blood pressure.
Other Factors influencing Blood Pressure
There are certain factors that impact the level of blood pressure in our bodies:
- Gender: In adult males, the blood pressure can be 10 to 20 mm higher than the female of the same age. This implies that generally, males have elevated blood pressure than females.
- Obesity: Extremely fat people face the problem of higher blood pressure compared to that of a normally weighed person.
- Physical fitness: Individuals who are physically fit and sound tend to have normal and maintained blood pressure than those who are out of shape. However, individuals with heart-healthy habits may feel just fine even at an older age.
- Pain: Our brain often responds to pain by increasing the rate and strength of the heart rate, ultimately elevating blood pressure.
- Age: Blood pressure tends to rise with growing age. As one grows older, the network of the blood vessels changes. This is because the arteries get stiffer with time, thereby raising the blood pressure level.
- Gravity: Gravity also plays a part in determining the pressure of blood inside our arteries. For instance, while we are standing, the blood pressure of the lower body is greater in comparison to the upper because of the gravitational pull.
- Emotions: Our emotion has a great impact on the blood pressure level of the body. Fear, hatred, anger, worry, and excitement are some of the emotions that can drastically alter blood pressure.
- Exercise: While you are exercising, your body requires more amount of oxygen for cellular respiration. Thus, in order to cater for this increased demand, the heart pumps the oxygenated blood with more force, thereby increasing the pressure of blood in arteries.
- Diseases: Mainly, diseases that affect the arteries and the renal system causes high blood pressure. In contrast, a disease that hampers the heart in any way will lead to lower blood pressure.
- Intoxicants: Several chemicals are designed to strengthen the action of the heart, contract the arteries, and expand the arteries. They are also known as vasoconstrictors and vasodilators. The vasodilators increase the artery’s diameter, due to which the arteries become large in diameter, lowering the body while the vasoconstrictors contract the blood vessel, which increases the blood pressure.
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