Regulation of blood pressure Flashcards
What is ‘stressed volume’?
The volume of blood in the arteries
Blood under high pressure
Where do arteries receive blood from?
Directly from the heart
Describe the structure of an artery
Thick muscular ring
Folded parts enable stretching
Name 3 things which can change the rate of blood flow in arterioles
- SNS causing contraction of vsm
- Circulating catecholamines (adrenaline)
- Vasoactive substances (NO)
Define tonically active
Constant muscle tone
Structure of arterioles
Smaller blood vessels
Round with vascular smooth muscle
What are capillaries controlled by?
Pre capillary sphincters
Dilation/constriction of arterioles
Which blood vessel has more elastic tissue in their walls?
Venules and veins
Which blood vessel has the largest percentage of blood in the cv system?
Venules and veins
How do alpha 1 adrenergic receptors interact with veins and venules?
Vasoconstriction due to reduced capacitance leading to a decrease in ‘unstressed volume’
What is the equation for velocity of blood flow?
V = Q/A
V = velocity of blood flow (cm/s)
Q = flow (ml/s)
A = cross sectional area (cm2)
What is the relationship between velocity and cross-sectional area in identical flow?
An inverse relationship
What is the equation for the relationship between blood flow, resistance and pressure?
Q = DeltaP/R
Q= flow (ml/s)
DeltaP = Pressure difference (mmHg)
R = Resistance (mmHg/ml per min)
What is total peripheral resistance?
Resistance of an entire systemic vasculature
What is the equation for Poiseille’s law?
R = 8nl/(Pi)r4
R= resistance
n = blood viscosity
l = length of blood vessel
(pi) r4 = radius of the blood vessel (to the power of 4)
What factors contribute to blood flow resistance?
Blood vessel diameter
Vessel length
Parallel/series arrangement
Blood viscosity
What is the relationship between resistance to flow, vessel length and blood viscosity?
Resistance to flow is directly proportional to vessel length and blood viscosity
What is haemocrit?
% of rbc in a sample
How to calculate the total resistance in a series vessel arrangement?
Sum of all the individual resistances
What happens to pressure as you move through a series arrangement?
Pressure decreases through each sequential component
How to calculate total resistance in a parallel vessel arrangement
1/Rx
x= sequential components
What is an advantage of a parallel series?
No loss of pressure so blood can perfuse sufficiently
What happens to the pressure as the blood flows? Why?
Pressure decreases
- energy is lost due to frictional resistance
How does the pressure in the aorta change with age?
High proportion of elastin decreases with age therefore, compliance decreases
What is a dicrotic notch? What can it cause?
The closure of the aortic valve between systole and diastole
Can cause slight backflow
When is arterial pressure at its lowest? (diastolic pressure)
Ventricular relaxation
When is arterial pressure at its highest? (systolic pressure)
Ventricular ejection during contraction
What is the equation for pulse pressure?
Pulse pressure = systolic - diastolic pressure
What does pulse pressure show?
Blood volume ejected from the left ventricle (stroke volume)
What is the equation for mean arterial pressure?
Mean arterial pressure = diastolic pressure + 1/3 pulse pressure
What does mean arterial pressure show?
Average pressure in a cardiac cycle
How does blood pressure change throughout the day?
Systolic bp is always higher than diastolic
Day > Night
Highest in the hours when just waking up
What are the 2 baroreceptors?
Carotid sinus
Aortic sinus
Describe the rapid regulation of blood pressure.
Solitary nucleus receives input from cranial nerve IX (carotid) and X (aortic) ->
PNS outflow via vagus nerve to SAN causes decresae in HR and BP
OR
SNS to SAN causes
1. An increase in hr
2. Increase in cardiac muscle contractility&sv
3. Arteriole vasoconstriction = increase in TPR
4. Vein vasoconstriction = decrease in unstressed volume
Where is the solitary nucleus located?
Medulla
What is renin?
A factor which converts angiotensinogen to angiotensin 1
Describe medium/long term control of arterial p
RAAS (renin, angiotensin, aldosterone) system regulates blood volume ->
A decrease in arterial pressure = decrease in renal prefusion (prorenin to renin) ->
Renin converts angiotensinogen to angiotensin 1 ->
Angiotensinogen converting enzyme converts angiotensin 1 to angiotensin 2
What are the effects of angiotensin 2 in the adrenal cortex?
Causes aldosterone synthesis and secretion causing an increase in Na+ reabsorption ->
Stimulates Na+ - H+ exchange within the kidney and Na+ + HCO3 reabsorption
What are the effects of angiotensin 2 iin the hypothalamus?
Increase in thirst and ADH secretion leading to an increase in water reabsorption in collecting ducts
Vasoconstriction of arterioles leading to an increase in TPR
What is the effect of O2 and CO2 detection in the carotid and aortic sinus chemoreceptors?
Arteriole vasoconstriction
What do V1 receptors control?
Vascular smooth muscle cells -> vasoconstriction
What do V2 receptors control?
CD -> water retention
What does Atrial natriuretic peptide do?
Powerful vasodilator
Increases diuresis
Decreases circulating volume
What carries info from carotid sinus to brain stem?
Cranial nerve IX
What carries info from aortic sinus to brain stem?
Cranial nerve X
What happens to baroreceptors in hypertension?
Baroreceptors reset therefore hypertension isn’t corrected but maintained
Name 5 risks of persistent high bp
Heart attacks
Strokes
Aortic aneurysms
Kidney disease
Vascular dementia
Name 5 hypertension treatments
ACE inhibitors
Angiotensin II receptor blockers
Diuretics
Beta-blockers
Renin inhibitors
