Control of Blood Flow

Created by

Jessica Jardine

Cards (43)

Define diastolic pressure.
Lowest arterial pressure measured during a cardiac cycle
Pressure in the arteries during ventricular relaxation when no blood is being ejected from left ventricle
Define systolic pressure.
Highest arterial pressure measured during a cardiac cycle
Pressure in arteries after blood has been ejected from the left ventricle during systole
'blip' in arterial pressure curve (in image) or dicrotic notch - produced when aortic valve closes -> produces brief period of retrograde flow
Define pulse pressure.
Difference between systolic & diastolic pressure
Define mean arterial pressure.
The average pressure over a complete cardiac cycle
What is the calculation for mean arterial pressure?
Pa = DP + 1/3 pulse pressire
Pa = mean arterial pressure
DP = diastolic pressure
What is the normal range of mean arterial pressure?
70 - 100 mmHg
What is the distribution of the blood?
85% in systemic circulation
10% in pulmonary
5% in cardiac chanbers at end of diastole
What does velocity depend on?
flow
cross sectional area (of vessels)
What is the relevance of this image?
The cross sectional area of vessel type (collectively) increases from aorta -> arteries -> capillaries
This decreases the velocity, and vice versa
What does flow depend on?
Pressure difference (between 2 ends of vessel)
Resistance of vessel
What is the equation for blood flow?
Q = ΔP/R
Q = flow
ΔP = pressure difference
R = resistance
Define total peripheral resistance.
Resistance of the entire systemic vasculature (TPR) or the systemic vascular resistance (SVR)
Where is series resistance seen in the body?
Arrangement of blood vessels within a given organ
Where is parallel resistance seen in the body?
Distribution of blood flow among various major arteries branching off aorta
What is Poiseuille's Law?
Resistance is directly proportional to 1/r^4
-> if you halve the radius, resistance increases 16 fold
This means that small changes in the radius of the lumen of blood vessels can have significant effects on the resistance of the vessels
What is the flow in the CVS?
Laminar
Describe laminar flow.
Velocity of blood flow is highest in the centre of the vessel & lowest towards vessel walls
Smooth parabolic (shape)
Describe turbulent flow.
Irregularity occurs in blood vessel -> laminar stream is disrupted & blood flow may become turbulent
Laminar flow is silent, turbulent flow is audible
What are the major influences on Reynolds number?
Changes in blood viscosity
Changes in velocity of blood flow
What is the clinical significance of Reynolds number?
If Reynolds number (NR) is less than 2000, blood flow will be laminar
If NR is more than 3000, blood flow will be turbulent
What are the different vascular controls?
Local (metabolic or myogenic)
Central (neural)
Hormonal
Endothelial
What is the local metabolic control of blood flow?
Intrinsic factors (high K+, adenosine, lactate, H+, CO2)
Increased metabolic activity -> increased release of metabolic byproducts -> increase resistance -> vasodilation -> increase blood flow -> increase supply of O2 & nutrients
CHECK
What is the local myogenic control of blood flow?
Vessels constrict reflexively when intraluminal pressure increases
mediated by stretch activated Ca+2 channels in smooth muscles
protects capillaries from surges in arterial pressure
What are hormones that can control blood flow?
ADH
Angiotensin II
ANP
Adrenaline
How does ADH impact blood flow?
Released from posterior pituitary
Binds to V1a receptors
Cause vasoconstriction
How does ang II impact blood flow?
Acts on AT1 receptors
Causes vasoconstriction
How does ANP impact blood flow?
From atrial myocytes
Binds to NPR1 receptor
Causes vasodilation
How does adrenaline impact blood flow?
Released from adrenal medulla
Binds to…
a1 adrenergic receptors -> vasoconstriction
b2 adrenergic receptors -> vasodilation
What is blood flow to tissues driven by?
Difference in pressure between the arterial & venous sides of the circulation
What is the central control of blood flow?
Sympathetic adrengeric nerve fibres
a1 adrenergic receptors (noradrenaline acts) -> vasoconstriction -> decreases diameter of arteriole -> increases resistance to blood flow
b2 adrenergic receptors (adrenaline) -> vasodilation -> increases diameter -> decreases resistance to blood flow
What is active hyperaemia?
Normal vasodilatory response to increased tissue activity & rising metabolic levels
What is post-exercise hyperaemia?
A period of increased blood flow that persists even after activity has ceased
What is reactive hyperaemia?
Period of increased blood flow that follows transient ischaemia
What are the physiologic consequences of local control of blood flow?
Autoregulation (intrinsic ability of an organ to maintain stable blood flow in changing perfusion pressures)
Hyperaemia (increased blood flow)
What is the process of active hyperaemia?
Increased tissue metabolism -> increased release of metabolic vasodilators into ECF -> vasodilation -> decrease resistance -> increase blood flow -> O2 & nutrient supply to tissue (as long as metabolism is increased)
What is the process of reactive hyperaemia?
Decreased tissue blood flow due to occlusion -> metabolic vasodilators accumulate in ECF -> dilation of arterioles but occlusion prevents blood flow
Remove occlusion -> decreased resistance -> increase blood flow
As vasodilators wash away, arterioles constrict & blood flow returns to normal
Fill in the blanks
A) Tyrosine
B) L-dopa
C) Dopamine
D) Noradrenaline
E) Adrenaline
What molecules cause contraction/constriction of blood vessels by acting on endothelium?
Endothelin
PGF
Thromboxane
What molecules cause relaxation/dilation of blood vessels by acting on endothelium?
PGI2
PGE
Trauma
NO
Toxins from bacteria & stress
Where is the vasoconstrictpr centre (C1)?
Upper medulla, lower pons