Cardiovascular Physiology 4- Relationship between blood pressure and blood flow Flashcards Preview

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Flashcards in Cardiovascular Physiology 4- Relationship between blood pressure and blood flow Deck (19):

What are the 4 different blood vessels which make up the cardiovascular system?

1) Arteries
2) Arterioles
3) Capillaries
4) Veins


What are the arteries and what are their properties?

Arteries: Blood vessels that carry blood away from the heart
1) Large diameter
2) Elastic + fibrous tissue= Can withstand high pressure
3) Stiff + Flexible
4) Pressure reservoirs= Low resistance to blood flow
5) Low compliance= Measure of how stretchy they are=Cannot stretch


How do arteries act as pressure reservoirs?

When heart is in systole= Blood flows into aorta= Greater volume of blood flows into arteries from the heart than leaves them to flow into arterioles

Causes artery wall to expand= Pressure energy in stretched walls

Diastole= Stretched walls passively recoil= Exerting pressure on blood= Pushes blood into downstream vessels to ensure flow, Keeps blood pumping through the cardiovascular system


What do arterioles do? What are their properties?

Arterioles= Primary resistance vessels, determine the distribution of cardiac output

They are the smallest arteries

1) Little elastic connective tissue
2) Thick layer of smooth muscle on walls= Can contract and relax as they are chemical sensitive
3) Small radii
4) Can selectively stretch and relax depending on the tissue= Variable resistance


How do arterioles act as major resistance vessels?

Radius is very small= Offers resistance to flow= Since it is so small, blood does not have to have as much pressure in order to push it through

Blood flow is opposed by resistance of the system

Drop in arterial pressure when it reaches arterioles= Decrease in pressure is due to energy lost as a result of the resistance to flow offered by the vessels

Stimulation of sympathetic nervous system= Can constrict or widen the rings

Smooth muscle contraction= Vasoconstriction= Increased resistance and decreased flow through the vessel
Smooth muscle relaxation= Vasodilation


What do capillaries do? What are their properties?

Capillaries: Exchange materials between blood and tissue cells, branch extensively to bring blood within the reach of essentially every cell

Once blood reaches capillaries, the plasma and the cells can exchange material across the thin walls

1) Thin wall
2) Narrow diameter
3) Extensive network
4) Continuos Endothelial cells are joined to one another with leaky junctions
5) Can also have fenestrated capillaries (pores): Have large pores that allow high volumes of fluid to pass rapidly between the plasma and interstitial fluid= Intestines, kidneys
6) Can also have discontinuous ones: Gaps between the cells, wide= blood cells and plasma proteins need to cross the endothelium to enter the blood e.g. liver. Need free exchange


What happens to the speed of blood flow in capillaries?

Flow rate of fluid is constant as it is equal to cardiac output BUT speed can change:

Velocity of flow changes as it is inversely proportional to total cross sectional area of all the vessels in a given area= It is fast when there is a small cross section

A single capillary has small diameter but when put together= Very large total cross sectional area= Very slow speed= Gives time for material to be exchanged


What are veins and what are their properties?

Veins: Carry blood towards the heart

1) Thinner walls compared to arteries
2) High compliance= Stretchy
3) Larger radii

Blood reservoir
Small change in pressure= Large degree stretch due to volume


What is blood pressure?

The pressure exerted by blood on the walls of the blood vessels

Depends upon volume of blood within the vessel and the compliance of the vessel


What is the main driving force for blood flow?

Mean Arterial pressure


What is diastolic pressure?

DP= Lowest pressure in the circulatory system, associated with the relaxation of the ventricles

Ventricles: falls only to a few mm Hg as the ventricles relaxes

Arteries: High as the vessels are able to capture and store energy in their walls


What is systolic pressure?

The highest pressure in the circulatory system that reflect the pressures created by contraction of the ventricles


What is the formula for MAP?

MAP= DP + 1/3 (SP-DP)
It is closer to diastolic pressure than to systolic pressure as diastole lasts twice as long as systole


What is flow rate and how is it related to pressure gradient?

Flow rate through a vessel= Volume of blood passing through per unit time

Blood flows if a pressure gradient is present= blood flows from areas of high pressure to low pressure

Directly proportional to the pressure gradient= As PG increase, flow rate increases


How is flow related to resistance?

Blood flow is inversely proportional to vascular resistance

Resistance in vessels= Pressure drops as blood flows through the vessels

High resistance= Narrow diameter= Reduce blood flow


What is the equation for blood flow?

Flow= Change in pressure / Resistance


What are the other factors which can be related to resistance to blood flow?

Resistance to blood flow is directly proportional to the viscosity of the blood= The thicker the blood, the more resistant to blood flow

Resistance to blood flow is directly proportional to vessel length= The longer the vessel, the more resistant the blood flow= STRAW

Resistance to blood flow is inversely proportional to vessel radius= The smaller the radius, the more resistance there is to blood flow


What is total peripheral resistance? How does it affect MAP?

Combined resistance in all organs including blood vessels

Determining mean arterial pressure: Balance between blood flow into and out of the arteries
Blood flow into aorta= Determined by cardiac output the left ventricle
Blood flow out of aorta= Peripheral resistance
If cardiac output increases, the heart pumps more blood into arteries per unit time, and if resistance stays the same, flow into arteries is greater than flow out= Blood volume increases= MAP increases


How does fluid flow across capillaries?

Bulk flow= Difference in hydrostatic and colloid osmotic pressures (Created by presence of proteins) between plasma and interstinal fluid

High blood pressure on one end, low on the other

A positive value for net pressure= Indicates net filtration
A negative value for net pressure= Indicates net absorption

At the artery end= Positive= Net filatration= Water does out

At the venous end= Negative= Net reabsorption

Filtration is usually greater than absorption= Bulk flow of fluid out of the capillary into the interstitial space