Blood vessel function & determinants of flow

Question 1

What is the main function of blood vessels?

Answer 1

• ‘Vascular highways’ that transport blood around the body to meet demands:
– Oxygen delivery
– Nutrient delivery
– Waste removal
– Chemical messenger delivery (e.g. hormones) – Maintain body temperature

Question 2

Arteries, arterioles, capillaries, venules, veins what’s the difference?

Answer 2

• Arteries transport blood out of the heart
• Arterioles regulate the flow of blood into tissues
• Capillaries exchange substances in blood (nutrients, gases, hormones) with tissues - site of exchange
• Venules carry away the waste from tissues
• Veins transport blood into the heart

Question 3

Systemic vs pulmonary circulation

- oxygenated blood

Answer 3

Oxygenated blood from left side of heart goes to systemic arterial circulation > supplies various tissues > deoxygenated blood returns via systemic veins to right side of heart

Question 4

Systemic vs pulmonary circulation

- deoxygenated blood

Answer 4

Deoxygenated blood from right side of heart goes to pulmonary arterial circula4on > gas exchange in lungs > oxygenated blood returns via pulmonary veins to le] side of heart

Question 5

Systemic vs pulmonary circulation

arteries and veins

Answer 5

systemic:
arteries and veins = oxygenated
pulmonary : arteries and veins = deoxygenated

Question 6

Distribution of blood around the body

Answer 6

• Parallel arrangement of vessels from the aorta ensures fresh blood to all organs
• More blood goes to organs that are responsible for ‘reconditioning’ blood (replenishing the blood)
• Other organs receive just enough blood to meet needs & therefore ‘less tolerant’ of reductions in blood flow e.g. the brain

Question 7

Blood flow

Answer 7

• Blood flow to each organ can be changed independently

Flow rate (volume per unit of time) is directly proportional to pressure gradient & inversely propositional to vessel resistance:

Question 8

blood flow

ΔP = pressure gradient

Answer 8

ΔP = pressure gradient

• Difference between the start & end of a vessel
• Blood flows down a pressure gradient, from high to low
• Contrac4on of heart is the main driving force for blood flow

Question 9

blood flow

R = resistance

Answer 9

• Opposition to blood flow caused by friction between blood flow & vascular walls

Question 10

How is blood flow affected by ΔP?

Answer 10

• The greater the ΔP, the greater the flow

- Pressure is lower at the end of a vessel because of frictional loss (resistance) along vessel length

Question 11

Is blood flow the same between these vessels?

Answer 11

Flow is determined by the pressure difference between the start & end of a vessel - not the absolute pressures!

Question 12

How is blood flow affected by R?

Answer 12

• The greater the R, the lower the flow
• Resistance is directly proportional to viscosity of blood & length of vessel, & inversely proportional to radius of vessel which has the greatest impact

Question 13

Determinants of R & ultimately flow

Answer 13

blood viscosity: the thicker a liquid, the greater the viscosity
inc. viscosity =inc. R = dec. F

L / r4, surface area: the longer a vessel & smaller a radius, the greater the surface contact with blood
dec.r (inc.surface area) =inc.R = dec.F

Question 14

The radius (r) has a major effect on R & ultimately flow

Answer 14

A slight change in r causes a considerable change, i.e. R 1/r4

Question 15

Upon arterial stenosis (thus increased resistance), how does ΔP increase to maintain adequate flow?

Answer 15

HEART MUST WORK HARDER - INCRS. HR, INSCR. STRENGTH OF CONTRACTION