PHSL 232 - LECTURE 8

What happens to vessel diameter and thickness as we move away from the heart

• it decreases

what tissue makes up a large proportion of artery wall

elastic tissue

what tissue makes up a large proportion of arteriole wall

smooth muscle

what function does the high elastic tissue content of artery walls give it

• elastic recoil

what function does the high smooth muscle content of the arteriole give it

• contractile properties

• is able to contract and relax

what are the main functions of arteries

• pressure reservoir

• distribute blood

describe how arteries act as a pressure reservoir, and why this function is necessary

• the ventricles release blood in a pulsatile fashion

• during diastole, there is no blood flow out of them

• but the body needs constant blood flow

• so elastic nature of the arteries, allows them to stretch under the pressure of the blood flow coming out of the ventricles during systole and gain elastic potential energy from it

• and then during diastole, they recoil and push blood into the tissues even though there is no blood flow from the heart

• this maintains arterial flow throughout the cycle

what is compliance

• the change in volume of a vessel with a given pressure

• how much will it stretch

describe what happens to the compliance of arteries as we age and why

• arteries have high compliance to begin with

• as we age, smooth muscle gets replaced with fibrous deposits (collagen)

• this makes arteries more stiff and leads to reduced compliance and dysregulated flow

what are the main blood vessels that contribute to total peripheral reisstance

arterioles

what allows arterioles to control blood flow

• they are able to constrict and dilate due to the smooth muscle in their walls to allow more or less blood to supply different areas of teh body based on demand

• basically decide where blood goes depending on who needs it by rerouting it through constriction and dilation - because blood will always take the path of least resistance

what is it call when the diameter of a vessel decreases/inscreases

vasoconstriction/vasodilation

what is the minimum pressure in the arteries and when does it occur

• diastolic blood pressure

• occurs right before ventricular ejection

what is the maximum pressure in the arteries and when does it occur

• systolic blood pressure

• occurs during ventricular ejection

what is pulse pressure

• the difference between systolic and diastolic pressure

how is blood pressure presented

• systolic/diastolic

what is the formula for contracting mean arterial pressure from diastolic pressure and pulse pressure

MAP=DP + (1/3 x PP)

what is normal blood pressure

• 120/90

what is the formula for mean arterial pressure (phsyiologica factors wise not numerically)

• MAP = CO/Q x TPR

what happens if MAP goes down

• either TPR or CO must go up

• to increase TPR we can do vasoconstriction

• to increase CO we can increase SV or HR

which of the following will decrease MAP: increasing HR, reducing TPR, vasocontriction

reducing TPR

what are the 3 main mechanisms to control vascular diameter

• neural

• hormonal

• local

which of the main mechanisms to control vascular diameter are extrinsic

neural and hormonal

describe sympathetic neural control of blood vessel diameter

• innervates blood vessels and releases noradrenaline

• binds to alpha adrenergic receptors

• causes vasoconstriction

• even at baseline noradrenaline is bound

• so less sympathetic activity can cause vasodilation

are all vessels equally innervated by sympathetic nervous system

• no, different parts have more or less alpha adrenergic receptors

describe sympathetic innervation/alpha adrenergic receptor density of the brain vs GI tract

• few receptors in the brain because we want to maintain constant blood flow and not cause vasoconstriction - that wld be bad

• GI tract on the other hand is not as essential all the time and blood can sometimes be rerouted from there to other places that need it more like the brain and therefore it has a lot of receptors

describe the non adrenergic neural control

• innervation by post ganglionic autonomic nerves

what do post ganglionic autonomic nerves do

• release nitric oxide for vasodilation (relaxes smooth muscle cells)

where do we find post ganglionic autonomic innervation

• Gi system

• penis

• very specialised

what circulating hormone causes vasodilation

adrenaline

what circulating hormone causes vasoconstriction

adrenaline

how does adrenaline cause vasodilation

by binding to b2-adrenergic receptors

how does adrenaline cause vasoconstriction

by binding to alpha 1 adrenergic receptors

describe the ratio of alpha 1 - beta 2 receptors in the skin and say primary function

• more alpha 1 - primary function is vasoconstriction

describe the ratio of alpha 1 to beta 2 receptors in skeletal muscle and say primary function

• more beta 2 - primary function is vasodilation

what hormones do long term regulation of MAP

• antidiuretic (ADH)

• angitensin II

• atrial natriuretic peptide (ANP)

describe the effect of antidiuretic hormone ADH on MAP

• it reduces diuresis and causes more water to enter/ water reabsorption at the kidney

• and that increases blood volume

• which gives a bigger stroke volume

• higher cardiac output

• which increases MAP

describe the effect of angiotensin II on MAP

• stimualtes sodium reabsorption>water will flow

• higher blood volume

• higher stroke volume

• higher cardiac output

• higher MAP

what effect does ADH and angiotensin II have on vessels

• vasocontricts

what effect does atrial natriuretic peptide (ANP) have on MAP

• decreases water reabsorption

• decreases blood volume

• decreases stroke volume

• decreases cardiac ouput

• decreases MAP

what effect does atrial natriuretic peptide (ANP) have on vessels

vasodilation

which hormones increase MAP long term

• antidiuretic hormone ADH

• angiotensin II

which hormones decrease MAP long terms

atrial natriuretic peptide (ANP)

which hormones cause vasocontriction

adrenaline

ADH

angiotensin II

which hormones cause vasodilation

adrenaline

atrial natriuretic peptide (ANP)

describe how local vasodilation occurs (intrinsic control)

• parts of the body that are more metabolically active are going to release more waste products into the blood such as nitric oxide

• nitric oxide triggers vasodilation allowing more blood to flow to those areas

• blood flowing to where it is demanded

what is hyperemia

increased blood flow to an area through vasodilation due to increased metabolic demand

• self regulated (intrinsic control)

what is the flow autoregulation

• if pressure increases

• it stretches the smooth muscle in the arteriole

• the muscle responds by contracting - vasoconstriction

• resistance increases

• flow is maintained

• this is the myogenic response

• the opposite also applies

what is the difference between active and reactive hyperemia

• active: tissue metabolism increases and so waste products increase>vasodilation>increased flow to match demand

• reactive: reduced flow to the organ creates accumulation and waste products increase > vasodilation>increased flow>until blockage removed