Lecture 19 - Peripheral Vascular Resistance Flashcards
How is blood pressure measured
A sphygmomanometer
What are the Kortkoff sounds produced by
Intermittent and turbulent flow through the artery
How are the Kortkoff audible
Through a stethoscope
When do Kortkoff sounds begin
When the cuff pressure is just below systolic pressure
When do the Kortkoff sounds begin to fade
When the cuff pressure is close to diastolic pressure
What is the normal systolic pressure at rest for a 20 year old
100-140 mmHg
What is the normal diastolic pressure for a 20 year old at rest
50-90 mmHg
How is mean arterial blood pressure calculated
By the cardiac output multiplied by the total peripheral resistance
What mainly affects systolic pressure
The stroke volume and particularly the ejection velocity
What is diastolic pressure mainly affected by
Total peripheral resistance and the time allowed for blood to flow out of the arteries
What are the functions of the peripheral vascular system
To convey blood from the heart to the capillaries and then back to the heart, the regulation of arterial tone and peripheral vascular resistance, the regulation of blood flow to muscles and other tissues, to respond to traumatic injury with vasoconstriction and haemostasis, and the response to sustained increase in intraluminal pressure which occurs through growth and hypertrophy
What vessels are the main site of resistance
Arterioles
Where is the biggest drop in pressure
Between the conduit arteries and the arterial end of the capillaries
What controls local blood flow
Local arteriole radius
What does doubling the radius of a blood vessel cause
A 16-fold increase in the flow
What controls TPR and therefore MABP
The arteriole radius
What causes hypertension
The narrowing of the resistance vessels
What is the internal radius of arteries
2.5cm to 1mm
What is the internal radius of arterioles
0.01-0.2 mm
What size of effect does small changes in the radius of the resistance vessels locally cause on blood flow
A relatively large effect
What is Raynauld’s disease
Vasoconstriction of the resistance vessels in the hand causing the reduction of blood flow to the point of damage
What is causes if all the blood vessels become a little narrower
Hypertension
What type of control alters arteriolar radius
Intrinsic or extrinsic
What are the intrinsic (local) control mechanisms to alter arteriolar radius
Stretching, production of metabolites and local release of chemicals
What are the extrinsic control mechanisms to alter arteriolar radius
Hormones and the autonomic nervous system (mainly sympathetic)
What do many organs and tissues have which is caused by sympathetic activity
A resting vasomotor tone
What does increased sympathetic activity to arterioles cause
Vasoconstriction
What does decreased sympathetic activity to arterioles cause
Vasodilation
What is the sympathetic nervous system neurotransmitter
Noradrenaline
What receptors does the sympathetic neurotransmitter act on
Alpha 1-adrenoceptors of vascular smooth muscle
What are veins stimulated by
Sympathetic venoconstrictor nerves
What do the sympathetic venoconstrictor nerves cause
They shift the blood centrally which supports the central venous pressure
What causes the sigmoidal shape of the pressure-volume curve in veins
The thin-walled nature of veins
If there is less blood on the central veins what happens
The central venous pressure drops causing the stroke volume to decrease
What do peripheral veins have in the tunic media
Smooth muscle
What do veins serve as
Blood reservoirs
Within vascular smooth muscle vasoconstriction occurs through the release of
Adrenaline
What activates the alpha 1 vascular receptors
Angiotensin II and endothelin
What does the release of angiotensin II and endothelin cause
Vasoconstriction within the endothelium and the opening of calcium channels through depolarisation
Within vascular smooth muscle how does vasodilation occur
Through the release of cholinergic and adrenergic molecules
What activates the beta 2 vascular receptors
Adenosine and prostacyclin
What happens in response to the release of adenosine
The opening of ATP-dependent K+ channels
What is the endothelium derived releasing factor
Nitric oxide
Why is nitric oxide usually relased
Due to shear stress
What does the release of nitric oxide cause
Increased blood velocity and vessel dilation
