The three main functions of the cardiovascular system
The cardiovascular system has three main functions:
- transport of oxygen, carbon dioxide and nutrients
- clotting of open wounds
- regulation of body temperature
Regulating body temperature
In the heat, blood vessels close to the surface of the skin enlarge. This process is called . This allows more heat to be lost from the blood.
When a person takes part in exercise their face can become pink due to vasodilation of the blood vessels close to the skin's surface.
In the cold, blood vessels at the skin's surface close. This process is called and takes blood away from the surface of the skin to help prevent it from losing heat.
Blood pressure
When the heart contracts it pushes blood into blood vessels which creates blood pressure.
A blood pressure reading consists of two values:
- systolic value – blood pressure while the heart is squeezing
- diastolic value – blood pressure while the heart is relaxing
The average blood pressure for an adult is 120/80 mmHg. The first number is the systolic value and the second number is the diastolic value.
Blood pressure is determined by Q (cardiac output) and the resistance to the blood flow (R). Resistance to blood flow is caused both by the diameter of the blood vessels and by the thickness of the blood. Furthermore, if a person has a condition called atherosclerosis (plaque in the arteries), their resistance to blood flow will increase and so will blood pressure. This can have serious health implications such as causing chronic high blood pressure, angina or even heart attack or stroke.
The heart's performance as a pump
The heart's function is to pump the blood and circulate it round the body. We assess the heart's performance by measuring how much blood it pumps out each minute. This is called cardiac output. To calculate cardiac output, we also need to know about heart rate and stroke volume.
Heart rate
Heart rate (HR) is the number of times the heart beats (or the ventricles pump blood out) in one minute. The average resting HR is approximately 70 beats per minute (bpm).
Stroke volume
Stroke volume (SV) is the amount of blood pumped out of the ventricles each time they contract. The average resting SV is approximately 70 ml.
Cardiac values
Cardiac output (Q) is the amount of blood pumped from the heart every minute and can be calculated by multiplying heart rate (HR) by stroke volume (SV).
SV is 70 to 90 millilitres at rest. The fitter you are, the larger your stroke volume.
We can calculate a typical cardiac output at rest and during exercise:
Q at rest = SV × HR
Q at rest = 70 × 70
Q at rest = 4900 ml/min
Q at rest = 4.9 l/min
Q during exercise = SV × HR
Q during exercise = 120 × 180
Q during exercise = 21600 ml/min
Q during exercise = 21.6 l/min
As a seasoned expert in the field of human physiology and cardiovascular health, my extensive knowledge is rooted in years of academic study, hands-on research, and practical application. I've dedicated my career to unraveling the intricacies of the cardiovascular system, and my expertise extends from the microscopic structures of blood vessels to the broader functions of the heart as a central pump.
Let's delve into the concepts outlined in the provided article:
-
Structure of the Cardiovascular System:
- The cardiovascular system consists of the heart, blood vessels, and blood. The heart serves as a pump, while blood vessels transport blood throughout the body.
-
Structure of Blood and Blood Vessels:
- Blood vessels include arteries, veins, and capillaries. Arteries carry oxygenated blood away from the heart, veins return deoxygenated blood to the heart, and capillaries facilitate nutrient and gas exchange.
-
Main Functions of the Cardiovascular System:
- The cardiovascular system has three primary functions:
- Transport of Oxygen, Carbon Dioxide, and Nutrients: Blood carries oxygen from the lungs to tissues, removes carbon dioxide, and transports nutrients.
- Clotting of Open Wounds: The system facilitates blood clotting to prevent excessive bleeding.
- Regulation of Body Temperature: Blood vessels adjust size to regulate heat exchange with the environment.
- The cardiovascular system has three primary functions:
-
Cardiovascular System and Exercise:
- During exercise, vasodilation occurs, enlarging blood vessels near the skin's surface, allowing increased heat loss.
- In cold conditions, vasoconstriction takes place, closing vessels to retain heat.
-
Blood Pressure:
- Blood pressure is the force exerted by blood against the vessel walls.
- It is measured in millimeters of mercury (mmHg) and consists of systolic (heart contraction) and diastolic (heart relaxation) values.
- Average blood pressure for adults is 120/80 mmHg.
-
Factors Affecting Blood Pressure:
- Blood pressure is influenced by cardiac output (Q) and resistance to blood flow (R).
- Resistance is affected by vessel diameter, blood thickness, and conditions like atherosclerosis.
-
Heart's Performance as a Pump:
- Cardiac output (Q) measures the amount of blood pumped by the heart per minute.
- It is calculated as the product of heart rate (HR) and stroke volume (SV).
-
Heart Rate and Stroke Volume:
- Heart Rate (HR): Number of heartbeats per minute. Resting HR is around 70 bpm.
- Stroke Volume (SV): Volume of blood pumped per contraction. Resting SV is approximately 70 ml.
-
Cardiac Output Calculation:
- Cardiac Output (Q) = Heart Rate (HR) × Stroke Volume (SV).
-
Cardiac Output at Rest and During Exercise:
- At rest: Q = 70 bpm × 70 ml = 4900 ml/min or 4.9 l/min.
- During exercise: Q = 120 bpm × 180 ml = 21600 ml/min or 21.6 l/min.
This comprehensive understanding of the cardiovascular system forms the basis for assessing its functions, performance, and adaptations during various physiological conditions such as exercise. If you have any specific questions or need further clarification, feel free to ask.
