vascular control

Question 1

what does blood vessel radius depend on?

Answer 1

• smooth muscle contraction
• how much elastic + collagen present
• blood pressure inside the vessel

Question 2

what is the law of Laplace about distending pressure?

Answer 2

distending pressure=wall tension/radius.

Question 3

how do you maintain the blood vessel calibre?

Answer 3

there is a balance between the distending pressure and the wall tension

Question 4

what happens to the wall tension if there is an increase in the wall radius of a vessel?

Answer 4

if the wall radius increases then the wall tension increases.
the balance between distending pressure & the wall tension is offset
so the calibre of the blood vessel is no longer maintained.
if the distending pressure gets too high the vessel can rupture but normally the elastin can develop more tension in response to the increase in distending pressure.

Question 5

what is the capillary sphincters?

Answer 5

a band of smooth muscle around the start and end of a capillary that adjusts the flow of blood into or out of the capillary.

Question 6

why is the active control of the vessel calibre (lumen diameter) important?

Answer 6

it allows the directed redistribution of the blood flow.
it control the pre and post capillary sphincters.
the regulation of blood pressure.

Question 7

what is active and passive tension ?

Answer 7

passive tension is when the muscle fibres are stretched out beyond their resting length.
active tension requires energy and is created by contractions.

Question 8

what happens to active/passive tension during vasoconstriction

Answer 8

vasoconstriction- increased active tension and decreased passive tension

Question 9

what happens to active/passive tension during vasodilation?

Answer 9

vasodilation- decreased active tension and increased passive tension.

Question 10

what are the intrinsic (local) mechanisms for vasodilation?

Answer 10

release of PGI2 (prostacyclin) and nitric oxide and EDHF (endothelium derived hyperpolarizing factor)

Question 11

where do the sympathetic nerves sit on the blood vessels?

Answer 11

on the tunica adventitia/media border

Question 12

where are the SNS neurotransmitters kept in the blood vessels?

Answer 12

in the SNS varicosities on the tunica adventitia/media border

Question 13

what’s the most important neurotransmitter released by SNS on blood vessel and what’s its function?

Answer 13

releases noradrenaline which acts on mostly alpha1 adrenoceptors and some alpha2adrenoceptors and causes vasodilation.
they can also sometimes activate beta2adrenoceptors on skeletal muscle to cause vasoconstriction. but mostly vasodilation.

Question 14

what 3 other hormones affect smooth muscle constriction/dilation?

Answer 14

-angiotensin to constrict, -bradykinin to dilate

and -vasopressin to constrict.

Question 15

what does metabolically active tissues do to the blood pressure?

Answer 15

increase in lactate produced
decrease pH (more acidic),
cells release more K+ and the breakdown of ADP releases adenosine and these all cause vasodilation.
Blood vessels get bigger to encourage more blood to flow there.

Question 16

how does oxygen and carbon dioxide levels affect blood vessel constriction in the systematic system?

Answer 16

i high oxygen levels and low carbon dioxide levels = that area does not need a lot of blood as it is doing fine, so vasoconstriction to direct blood elsewhere.
oxygen levels are low and the carbon dioxide levels are high there is vasodilation so blood can be directed here as it needs more oxygen and to take away carbon dioxide.

Question 17

how does oxygen levels and carbon dioxide levels cause vasoconstriction in the pulmonary system?

Answer 17

in the PS (in the lungs)
if alveoli have low Oxygen and high Co2 then vasoconstriction of pulmonary blood vessels happens to direct blood away from here as it would give inefficient gas exchange.
if the alveoli has highO2 and low CO2 then there is vasodilation to allow more blood flow here to take advantage of the efficient gas exchange

Question 18

why is is important to have constant steady blood pressure to the Brain?

Answer 18

very important to have autoregulation of blood to stop bursting blood vessels in the brain.
too low blood supply=faint
too high=burst vessels

Question 19

how does the brain’s blood vessels auto regulate blood pressure in their vessels?

Answer 19

is the blood pressure is too high, the walls of the brain’s blood vessels stretch.
this stretch is detected and causes the vessel to vasoconstrict. this reduces the blood pressure through that blood vessel.

Question 20

how much blood does the brain need to receive?

Answer 20

the brain need 14% of the cardiac output