Pressure and flow in arteries and veins Flashcards
(30 cards)
How is arterial pressure measured?
Auscultation of korotkoff sounds (turbulent blood flow) using a sphygmomanometer(device used to measure blood pressure) and sethescope.
What are the disadvantages of measuring the blood manually ?
Discontinous
accuracy
needs care and skill
What are the advantages of measuring blood manually?
- Non invasive
- Cheap
How is the aortic valve closed and how does blood keep flowing when it is closed??
Aorta is an elastic artery. When left ventricle contracts during systole, blood is injected into the aorta. The walls of the aorta will strech and act as a pressure resvoir. During ventrical relaxation or diastole, there is elastic recoil from the walls of the aorta that pushes on the column of blood. This closes the aortic valve and keeps the blood flowing even during the relaxation phase
What effects the pressure wave>
- Stroke volume
- Velocity of ejection
- Elasticity of arteries
- Total peripheral resistance
How does the stroke volume affect the pressure wave?
If contractility increases because of increased sympathetic tone and you’re pumping the blood out with more force, then the rising phase is going to rise more rapidly and there will be a larger systolic pressure.
How does velocity of ejection effect the pressure wave?
This influences more than the stroke volume. Blood will be pumped out quicker, therefore rising phase will be a lot steeper which results in a greater systolic pressure. This is because if blood is pumped into the aorta quicker then aorta walls have less time to stretch. Diastolic pressure will be lower
How does elasticity of the arteries effect the pressure wave?
As age we lose elasticity and the effect of this is, is it will cause the systolic pressure to rise. The aorta will be less able to act as the pressure resvoir. The diastolic pressure will also fall as there is less of elastic recoil.
How does total peripheral resitance effect the pressure wave?
This is mostly affecting the falling phase after the aortic valve has closed. This is because blood is being pushed from arteries into arterioles. If arterioles are contricted then the total peripheral resistance will be higher, therefore it will be harder to push blood from the arteries into the arterioles. The diastolic pressure will be higher.
Explain the systemic filling pressure when blood comes from left ventricle into the arteries?
When blood comes from the left ventricles into the arteries, it is 95mmHg. As it moves through the arteries there is small dropped to 90 mm Hg. This is because arteries can be though of as low resistance coduits. These vessels have a very wide lumen to make it as easy as possible for blood to flow through them.
Explain the systemic filling pressure when blood flows from the arteries into the arterioles?
When blood flows into arterioles there is a much larger drop. It goes from 90-40 mmHg. Arterioles as we know are resistanced vessels. There is a very narrow lumen and a thick muscular wall. This muscle wall can be contracted which constricts the arterioles, increasing the total peripheral resistance
Explain the systemic filling pressure when blood goes from arterioles to the capillaries?
When the blood gets to capillaries the pressure is already low (40 mmHg). This is good because the capillaries walls are very thin already and they cannot handle high pressures.
Explain the systemic filling pressure when blood goes from capillaries to the veins and venules
When blood reaches the vein and venules, it’s going to be 20 mmHg and then dropping down to 5 mmHg when it reaches the atrium.
Explain how the velocity differentiates throughout the vascular tree
Velocity is high in the aorta and decreases as it moves through the arteries and arterioles. It is the lowest in capillaries and then when it reaches veins and venules it begins to increased. It is fairly high in the vena cavae.
Why does velocity differentiate throughout the vascular tree
Velosity is related to the total cross section area. Total cross section of the aorta is very small. Capillaries have a very low cross sectional area but since there is a lot of these they add up to a very large total cross sectional area.
Explain the pressure flow in veins
Pressure flow in veins is low. Veins and venules have very thin walls, this means they are distensible, so the walls can expand and they are also collapsable. Due to this, they are very susceptible to external influences and that affects flow.
How does gravity effect vessels ?
As a person is stood up the pressure in the veins will be increased due to gravity causing the veins to distend and so they expand and blood will be pulled. If there is more blood pooling the legs, less blood will return to the heart.
explain orthostatic pressure
Due to a decreased return of blood to the heart and blood pooling in legs, this will result in decreased end-diastolic volume, followed by decreased preload and then a decreased stroke volume. Less blood pumped by the left side of the aorta hence a lower cardiac output and fall in mean arterial pressure. This is known as orthostatic hypotension. Standing up for too long will cause a person to feel light headed and faint.
How does the skeletal muscle pump effect the pressure in the veins>
Veins and venules in the leg are surrounded by skeletal muscle when the contract it shortens and becomes fatter. This causes a squeeze on the veins and venules which causes blood to be pushed in both directions, the blood will be pushed to the heart and also down to the feet. The back flow of blood is limted by the valves within your veins and venules.
How does the respiratory pump effect the pressure in veins?
Similarly to skeletal muscled this increases venous return and increase in diastolic volume. When you inspire your diaphragm moves down and that causes a negative pressure within the thorax and positive pressure below. This positive pressure below gets transmitted to vessels causing a large pressure gradient, pushing blood to the heart and increasing venous return. Faster and harder breathing increases how blood is pushed back to the heart.
How does the venomotor tone effect the pressure in veins and venules?
Venomotor tone is the state of contraction of the smooth muscle surrounding the veins and venules which mobilises capacitance and increases end diastolic volume.
How does systemic fillinf pressure effect the pressure in the veins?
Systemic filling pressure can change, for example, when you are doing exercise. During exercise there is also increased sympathetic tone and increased contractility so increase in the strength of contraction in the heart. Mean arterial pressure will then increase. Pressure created by ventricles and transmitted through the vascular tree to the veins.
What does clotting involve?
Clotting involves formation of platelet plug and formation of fibrin clot
How is platelet plug developed?
Platelets do not do anything unless blood vessels are damaged. If they are damaged and platlets have access to collagen in that basement membrane the platlets become activated and they stick to the collagen, they send local chemical signals to other platlets and therefore there is formation of platelet plug. The platelet plug is weak and therefore the next step in clotting is the formation of sturdier fibrin clot.
