Regulation of blood pressure Flashcards
What is blood vessel capacitance?
blood volume held at a given pressure (related to distensibility)
What type of muscle is present in arterioles?
active vascular smooth muscle (VSM)
What 3 reasons change the resistance to blood flow?
- sympathetic nerves - decreased diameter of arteriole/increased resistance to blood flow
- circulating catecholamines (e.g. adrenaline)
- other vascular substances
What are capillaries?
site of exchange - but not all perfumed with blood
What controls capillaries?
dilation/ constriction of arterioles (pre-capillary sphincters in mesentery & brain)
What regulates capillaries?
sympathetic innervation of vascular smooth muscle & vasoactive metabolites produced in the tissue
Describe how much elastin is found in veins vs arteries?
more elastic tissue in arteries
What blood vessel contains the largest % of blood in the cardiovascular system?
veins
What can increase the activity of veins?
alpha-adrenergic receptors
What is the equation for the velocity of blood?
v = Q/A
velocity = flow/cross-sectional area
What is blood flow determined by?
- pressure difference between vessel inlet & outlet
- resistance of vessel to blood flow
What is the blood flow equation?
Q = change P/R
flow = difference in pressure/resistance
What is the TPR (total peripheral resistance)?
resistance of entire systemic vasculature
Who’s law can be used to figure out the resistance to blood flow?
Poiseullie’s law
What is Poiseuille’s law?
R = 8nl/pieR^4
resistance = 8 x viscosity of blood x length of blood vessel/ pie x radius of blood vessel (^4)
describe the relationship between resistance to flow & vessel length & blood viscosity
RESISTANCE TO FLOW DIRECTLY proportional to vessel length and blood viscosity
describe the relationship between resistance to blood flow & the radius
resistance to flow is INVERSELY PROPORTIONAL to 4th power of the radius
Where is series resistance seen in blood vessels?
series resistance can be seen within an organ
What is the total resistance?
sum of individual resistances
What is the benefit of parallel resistance?
no loss of pressure
Why does pressure decrease with blood flow?
energy lost overcoming frictional resistance
What level of compliance (elasticity) does the aorta have?
low
What level of cardiac output is in the arteries?
remain high
Why is there a decrease in pressure in the arterioles?
high resistance of flow
What is the compliance + pressure in veins?
high compliance + low pressure
What is systolic pressure?
pressure when heart is contracting
What is diastolic pressure?
pressure when the heart is relaxing
What is the arterial pressure like during systolic pressure?
highest following ventricular blood ejection during contraction
What is the arterial pressure like during diastolic pressure?
lowest during ventricular relaxation
What is the pressure in veins?
<10mmHg
Why is pressure so low in veins?
result of decreased resistance of each level of vasculature
What is pulse pressure?
- reflects blood volume ejected from the left ventricle (stroke volume)
pulse pressure = systolic - diastolic pressure
What is mean arterial pressure?
- average pressure in one complete cardiac cycle
mean arterial pressure = diastolic pressure + 1/3 pulse pressure
Why is only 1/3 pulse pressure included to work out mean arterial pressure?
as the heart spends a longer time in diastole than in systole
Throughout the day, what happens to the systolic & diastolic pressure?
reduces during sleep & increases in the morning
What regulates blood pressure?
baroreceptors (mechanoreceptors) - carotid & aortic sinuses
Describe how baroreceptors respond to an increase in pressure
increase in pressure = increased stretch = increased afferent nerve firing
Describe how baroreceptors respond to an decrease in pressure
decrease in pressure = decreased stretch = decreased afferent nerve firing
What nucleus receives input regarding blood pressure from the baroreceptors and directs the SNS + PNS changes via medullary CV centres?
Solitary Nucleus
How does the peripheral nervous system cause a decrease in heart rate + blood pressure?
via vagus nerve
How does SAN lead to increased heart rate?
increased cardiac muscle contractility = increased stroke volume
What hormonal system can control arterial pressure?
medium/long term control of arterial pressure (Pa) can be controlled Renin angiotensin-aldosterone system (RAAS)
Renin angiotensin-aldosterone system (RAAS)
regulates blood volume, electrolyte balance + systemic vascular resistance
How does kidneys decrease arterial pressure (Pa)?
decrease perfusion pressure detected by kidney afferent arteriole mechanoreceptors, prorenin - renin released into blood
Angiotensinogen - angiotensin I - angiotensin II
What are the effects of angiotensin II?
- increase in sodium reabsorption
- stimulates Na+-H+ exchange with kidney
= hypothalamus - increases thirst & ADH secretion - increase water reabsorption in collecting ducts
How do chemoreceptors in carotid & aortic bodies that detects O2 regulate blood pressure?
arteriole vasoconstriction
How can Atrial natriuretic peptide regulate blood pressure?
V1Rec = vasoconstriction
V2Rec = water retention
What is chronic hypertension ?
elevated blood pressure
What are the effects of chronic hypertension?
leads to desensitisation of baroreceptors
What are the effects of hypertension?
- small increase in blood pressure - increased risk of morbidity + mortality.
- if BP is too high - extra strain on blood vessels + other organs
What does persistent high BP lead to increased risk of?
- heart disease
- heart attacks
- strokes
- heart failure
- aortic aneurysms
- peripheral arterial disease
- kidney disease
- vascular dementia
What are 3 hypertension treatments?
- angiotensin-converting enzyme (ACE) inhibitors
- angiotensin II receptor blockers (ARBs)
- Renin inhibitors
What is the effect of diuretics (Thiazide) as a hypertension treatment?
decreases extracellular fluid
What is the effect of beta-blockers as a treatment for hypertension?
decreased heart rate + contractility
What is the effect of calcium channel blockers as a treatment for hypertension?
decreased contractility + increased vessel relation
What is the effect of alpha-blockers as a treatment for hypertension?
inhibit alpha adrenoreceptors - decreased vasoconstriction