Systemic Circulation Flashcards
What is pulse pressure?
It is the difference between the systolic and diastolic pressures.
What happens to the pulse pressure in vessels further from the heart?
It widens. (the gap increases)
What happens to the mean arterial pressure as you go further out from the heart?
The mean arterial pressure continuously declines.
What is the mean arterial pressure?
Diastolic Pressure + (1/3)*Pulse Pressure
Where does the greatest decrease in arterial pressure occur?
Arterioles
What happens to the compliance of the arteries as you go further from the heart?
It decreases
What is the BP difference between the right arm and the left arm? Why is this the case?
The right arm will have higher systolic and lower diastolic pressures. This is because the right brachial artery is further from the heart than the left and so the compliance is lower.
Describe pulse pressure profile of the atria.
The pulse pressure of the atria is low as it does not fluctuate much.
Describe pulse pressure profile of the ventricles.
It starts at low pressure and increases to around 120 mmHg before it decreases again for filling. The peaks are sharp as the pressure change is rapid.
Describe pulse pressure profile of the aorta.
The pressure starts around 80 mmHg and increases to 120 before decreasing. There is a dichotic notch due to the elasticity of the aorta.
Describe pulse pressure profile of the arteries.
They have an increased pressure compared to the aorta over 120 mmHg due to their lower compliance. They also have a notch due to elasticity.
Describe pulse pressure profile of the arterioles.
The arterioles show similar profiles to the arteries at lower pressure. Going across the arterioles though, the greatest decrease in arterial pressure occurs.
Describe pulse pressure profile of the veins and capillaries.
They do not have pulse pressure.
Where is elastin found and what function does it serve structurally?
It is found in the tunica intima and media as the Internal Elastic Lamina and External Elastic Lamina respectively. It is not found in veins.
It allows the arteries to flex with increased blood pressures.
Where is smooth muscle found in the vessels and what function does it serve structurally?
It is found in the tunica media of arteries and veins, but the smooth muscle is much more developed in arteries.
Where is collagen found in the vessels and what function does it serve structurally?
Collagen is found in the tunica adventitia of arteries and veins, but it is more developed in veins. Collagen limits the compliance of veins once they reach a certain pressure.
What are the vasa vasorum and where are they found?
They are in the tunica adventitia. They are a network of small blood vessels that supply the walls of large blood vessels, such as elastic arteries (aorta and large veins (vena cava).
How does vessel wall compliance affect the arterial pressure?
Arteries have low compliance due to smooth muscle so they have higher pressures. However, elastin has high compliance, which allows arteries to stretch initially before rebounding due to the smooth muscle and collagen layers. It allows for the maintenance of the diastolic pressure.
Explain the hydraulic filtering properties of the aorta.
The aorta is stretched as blood is pumped into it and is distended. The aortic wall recoils after systole and acts as a secondary pump.
What happens the pressure pulse as it goes further away from the heart?
It increases in velocity
What is the pressure pulse?
It is the wave that travels down the aorta and can be felt as a radial pulse.
What are the physiological factors that determine the mean arterial pulse?
Cardiac Output
Peripheral Resistance
What are the physical factors that determine the mean arterial pulse?
Blood Volume
Arterial Compliance
What is the primary determinant of the systolic pressure?
Cardiac Output
What is the primary determinant of the diastolic pressure?
Peripheral Resistance
How does arterial compliance affect the systolic and diastolic pressures?
The arterial compliance determines the amount of systolic pressure that is absorbed into kinetic energy and the amount of diastolic pressure that is propagated.
What are the factors that determine peripheral arterial resistance?
Arteriolar Radius - controlled by local and global control mechanisms from the autonomic system
Viscosity - determined by the hematocrit of the blood
How is mean arterial pressure regulated by the autonomic system?
The sympathetic system controls changes in the heart, veins and arterioles in order to control the mean arterial pressure.
Which part of the autonomic system is the main determinant of the mean arterial pressure?
Sympathetic
What changes are done in the heart in order to control the Pma?
- Heart rate can be increased to increase cardiac output, which increases the arterial pressure
- Contractility can be increased which increases stroke volume, thereby increasing the cardiac output and the arterial pressure
What changes are done in the veins in order to control the Pma?
Venoconstriction will increase the venous return which will increase the preload and increase the stroke volume, which increases cardiac output and raises the arterial pressure.
What changes are done in the arterioles in order to control the Pma?
The arterioles can undergo vasoconstriction which will increase the peripheral resistance sand increase the blood pressure.
How does exercise affect the heart?
- Increased HR
- Increased contractility
- Increases cardiac output
How does exercise affect the arteries?
- Vasoconstriction -> resistance increases
- Blood diverted away from skin, kidneys and splanchnic region to the pulmonary, cardiac, muscle and cerebral regions.
How does exercise affect capillaries?
-Active muscle capillaries are all opened for maximum blood flow
How does exercise affect venous return?
-Venoconstriction increases the venous return to the heart
How does exercise affect the arterial pressure?
- Stroke volume increases so the systolic pressure increases
- Diastolic pressure can increase, decrease or remain unchanged, as it is determined by peripheral resistance
What happens to the pulse pressure during exercise?
-The pulse pressure widens
What is the transmural pressure?
Pressure tending to distend or collapse a vessel
What is the baroreceptor reflex?
Acts via the autonomics and it affects both cardiac output and peripheral resistance.
What is the structure of continuous capillaries?
Have no holes and are continuous with endothelial cells
What is the structure of fenestrated capillaries?
Continuous with endothelial cells and have holes in walls
What is the structure of discontinuous capillaries?
Discontinuous with endothelial cells and are separated from them by wide spaces.
Where are continuous capillaries found?
Muscle and connective tissue.
Where are fenestrated capillaries found?
Kidney and intestines for absorption
Where are discontinuous capillaries found?
Liver, bone marrow and spleen for the export of large molecules like cells and proteins.
What happens to the arterial pressure as the compliance increases?
Pulse pressure narrows. Systolic pressure decreases and the diastolic pressure increases.
What happens to the arterial pressure as the peripheral resistance increases?
Both the systolic and diastolic pressures increase.
What is the global cardiovascular response usually controlled by?
Hormones
What is the local cardiovascular response usually controlled by?
Metabolism
Where are α-receptors not present and why is this important?
No α-receptors in pulmonary/cerebral/cardiac tissues so they do not respond to vasoconstriction
What opens capillaries during exercise?
They open in response due to increased blood flow.
Can the heart increase O2 extraction?
No
