Primary function 1 of arteries
Act as rapid-transit passageways for blood due to their larger radius
Primary function 2 of arteries
Act as pressure reservoirs to make sure a pressure gradient exists even when heart is relaxing
Structural features of major arteries
- Have thick walls
- The connective tissue layers on both sides of the smooth muscle cells contain a significant amount of elastin fibres
- These elastin fibres allow arteries to act as a pressure reservoir
Systole
- The left ventricle contracts and ejects pressurized blood into the aorta
- The volume of the blood that enters the arteries is greater than the rate at which blood is flowing through the capillaries, this ejected blood stretches the artery walls outward
- The pressure generated is stored in artery walls to help maintain pressure during diastole
Systolic pressure
- Maximum blood pressure occurs during systole when blood is ejected from the heart
- In a healthy individual is around 120 mmHg
Diastole
- During diastole, the aortic valve is closed so blood is not flowing into the aorta but blood flow to the capillaries is still occurring
- This is possible because the arterial walls were stretched during systole
- During diastole, the arterial walls undergo passive recoil to propel blood forward
What role does elastic recoil play during diastole?
- Stretched elastic fibres return to their normal shape
- They exert a squeezing force on the arterial blood
- Helps maintain arterial pressure and a pressure gradient for continuous blood flow even when the heart is not pumping
Diastolic pressure
- During diastole, blood leaves arteries and pressure gradually falls
- Pressure reaches its minimum level, known as diastolic pressure
- Around 80 mmHg in a healthy adult
How can blood pressure be measured?
By using an automated blood pressure monitor or by using a sphygmomanometer
How does a sphygmomanometer work?
- Its an inflatable cuff with a pressure gauge and a stethoscope
- The inflatable cuff is inflated with air to create pressure above systolic pressure
- This pressure is transferred through the arm to the brachial artery
What is the brachial artery?
The major artery carrying blood to the forearm
What are the sounds of blood flow while using a sphygmomanometer called?
Korotkoff sounds
When does turbulent flow occur during blood pressure measurement?
- Turbulent flow occurs whenever arterial blood pressure exceeds cuff pressure between systolic and diastolic pressures
- (approx. 120–80 mmHg)
When is the first sound heard when using a sphygmomanometer?
- At peak systolic pressure
- Intermediate sounds then follow
What happens when cuff pressure is less then 80 mmHg using a sphygmomanometer?
- It is below blood pressure and blood flows through the vessel in a laminar fashion
When is the last sound heard when using a sphygmomanometer?
- Heard at minimum diastolic pressure
- No sounds to follow because of smooth, uninterrupted, laminar flow
Pulse pressure
Difference between the systolic and diastolic pressures and represents the pressure change during that cardiac cycle
Mean Arterial Pressure (MAP)
- Average pressure during the cardiac cycle
- Represents the mean driving force for blood flow throughout the rest of the vascular system
During a cardiac cycle of a person at rest, how long does the heart spend in diastole?
2/3 of the time
During a cardiac cycle of a person at rest, how long does the heart spend in systole?
1/3 of the time
Pulse pressure equation
= systolic pressure - diastolic pressure
MAP equation
=diastolic pressure + 1/3 pulse pressure
Pressure Changes from Heart to Capillaries
- The heart creates large pressure swings in the ventricles each heartbeat, which transfer to the large arteries where cyclical changes (pulse pressure) still occur
- At the arterioles, this cyclical pressure becomes non-pulsatile before entering the capillaries, improving nutrient/waste exchange efficiency
- From the capillaries to the venules and large veins, blood pressure steadily drops
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Module 1: Section 1 + 256
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Module 1: Section 316
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Module 1: Section 413
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Module 1: Section 531
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Module 2: Section 120
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Module 2: Section 216
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Module 2: Section 332
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Module 2: Section 451
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Module 2: Section 511
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Module 4: Section 127
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Module 4: Section 235
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Module 4: Section 333
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Module 4: Section 426
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Module 4: Section 59
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Module 4: Section 628
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Module 5: Section 115
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Module 5: Section 234
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Module 5: Section 352
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Module 5: Section 47
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Module 5: Section 533
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Module 5: Section 67
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Module 6: Section 121
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Module 6: Section 223
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Module 6: Section 344
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Module 6: Section 428
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Module 6: Section 512
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Module 6: Section 613
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Module 6: Section 743
