Blood pressure Flashcards
Semester 1 year 1
Describe the arteries
-under high pressure
-blood in arteries is known as ‘stressed volume’
-arteries have lower compliance and capacitance compared to veins
Describe arterioles
-tonically active vascular smooth muscle (VSM)
-highest resistance to blood flow
In arterioles, resistance to blood flow can change in response to what?
-sympathetic nerves - alpha 1 adrenergic receptors decrease arteriole diameter + increase resistance, beta 2 adrenergic receptors in heart arterioles dilate + relax
-circulating catecholamines (e.g adrenaline)
-other vasoactive substances
What pressure is in the capillaries?
Low pressure
Describe venules and veins
-low pressure
-large capacitance
-contain largest percentage of blood in CV system - ‘unstressed volume’
-increased activity via alpha 1 adrenergic receptors, causing contraction to reduce capacitance, decreasing the ‘unstressed volume’
What is the relationship between velocity and total cross sectional area?
Inverse relationship
In a blood vessel, as tee cross-sectional area decreases through bifurcation (branching), what happens to the velocity of the blood?
Velocity goes down as the cumulative cross-sectional area of the blood vessel is greater
How do you calculate velocity of blood flow in cm/s?
V = Q (flow-mL/s)/A (cross-sectional area-cm^2)
What is blood flow determined by?
-pressure difference between 2 points in a vessel
-resistance
What is the significance of the relationship between blood flow, resistance and pressure?
- blood pressure regulation:
-vasoconstriction increases resistance, increasing BP
-vasodilation decreases resistance, decreasing BP - blood flow distribution
What is total peripheral resistance (TPR)?
Resistance of the entire systemic vasculature
How can resistance of a single organ be calculated?
By substituting flow for e.g renal flow
How do you calculate blood volume per unit of time in mL/s?
Q (blood vol-mL/s) = delta P (pressure difference-mmHg)/R (resistance-mmHg/mL per min)
What is resistance to flow proportional to?
-directly proportional to vessel length and blood viscosity (haematocrit)
-inversely proportional to 4th power of the radius
Describe series resistance (within an organ)
-total resistance = sum of individual resistances
-pressure decreases through each sequential component
-largest decrease in pressure in arterioles = largest resistance: delta P = RxQ
Describe parallel resistance
-less than any of the individual resistances
-no loss of pressure
How does blood pressure vary throughout the cardiovascular system?
-decreases with blood flow as energy lost overcoming frictional resistance
-aorta - pressure high + low compliance
-arteries - pressure high + elastic recoil
-arterioles - low pressure due to high resistance
-capillaries - low pressure due to frictional resistance to flow + filtration
-venules + veins - low pressure + high capacitance
Describe arterial pressure (Pa)
-systemic circulation
-oscillations reflect pulsatile heart activity
-diastolic pressure - lowest Pa during ventricular relaxation
-systolic pressure - highest Pa after ventricular blood ejection during contraction
Describe venous pressure (Pv)
-systemic circulation
-pressure less than 10mmHg in venules + veins
-result of decreased resistance at each level
Is the pressure of pulmonary vasculature lower than systemic?
Vasculature pressure much lower than systemic due to much lower resistance
How do you calculate pulse pressure?
Pulse pressure = systolic - diastolic pressure
How do you calculate mean arterial pressure?
Mean arterial pressure = diastolic pressure + 1/3 pulse pressure
-average pressure in complete cardiac cycle
What are baroreceptors?
-pressure receptors
-found in carotid + aortic sinuses
What does the hormonal system regulate (RAAS)?
-blood volume
-electrolyte balance
-systemic vascular resistance
In kidneys, what does decreased arterial pressure lead to?
-decreased renal perfusion detected by kidney afferent arteriole mechanoreceptors (prorenin)
-renin released into blood
-helps convert angiotensinogen, then angiotensin I, then angiotensin II
What are the effects of angiotensin II?
-increased aldosterone, leads to sodium reabsorption, increasing ECF
-stimulates sodium reabsorption, increasing ECF
-hypothalamus - increased thirst + ADH secretion, leading to increased water reabsorption in collecting ducts
-vasoconstriction of arterioles
What are other regulatory mechanisms in BP homeostasis?
-chemoreceptors
-ADH (AVP) secretion from pituitary
What can a small increase in BP lead to for someone with hypertension?
Increased risk of morbidity + mortality
What are treatments of hypertension?
-lifestyle changes
-diuretics
-angiotensin-converting enzyme (ACE) inhibitors
-angiotensin II receptor blockers (ARBs)
-renin inhibitors
-calcium channel blockers
-beta blockers
