L14 Blood Pressure Flashcards
Which blood vessel is under the most blood pressure?
The arteries
What does compliance/ capacitance mean?
The ability of blood vessels to expand and hold a larger volume of blood without a significant increase in blood pressure
Do arteries have a low or a high compliance/capacitance?
They have a lower compliance
Which blood vessel has the highest resistance to blood flow?
Arterioles
What type of muscles does arterioles have?
Tonically active vascular smooth muscles.
Give me examples of alpha 1 adrenergic receptors
The skin, mucous membrane, splanchnic arterioles
What happens when alpha 1 adrenergic receptors contract in the VSM?
The diameter of arterioles decreases
The resistance to blood flow increases
What does VSM stand for ?
Vascular smooth muscle
Where are beta 2 adrenergic receptors?
Skeletal muscle and heart arterioles
What 3 things increases resistance to blood flow in the arterioles?
- Sympathetic nerves
- Circulating catecholamines e.g. adrenaline
- Other vasoactive substances (NO)
What does balance of alpha and beta receptor do?
Balance of α1 + β2 receptor activation plays a crucial role in regulating blood flow to different organs and tissues in changing conditions.
How is the blood flow within the capillaries controlled?
Controlled by dilation/ constriction of arterioles.
What is the pressure like in capillaries and why?
Capillaries have low pressure and slow flow because this would facilitate the diffusion of nutrients and oxygen
What is the blood pressure like in the venules and veins?
They have low blood pressure
The walls contain much less elastic tissue than arteries
Do veins/venules have a small or large capacitance?
They have a large capacitance
How do venules and veins increase activity via α1- adrenergic receptors?
Contraction to reduce capacitance - decrease in ‘unstressed volume’ .
Unstressed volume - no pressure exerting on the vessel walls. Vessels = relaxed and not stretched
How do you calculate the velocity of blood flow?
V = Q/A
V - Velocity of blood flow (cm/s)
Q - flow (mL/s)
A - cross-sectional area (cm^2)
What happens to the velocity when you increase the cross sectional area of a blood vessel?
Velocity decreases as cross sectional area increases
Inverse relationship between velocity and cross sectional area (total)
How would you calculate the blood volume per unit of time?
Q = DeltaP/R
- Q - blood vol per unit of time
- Delta P - Pressure difference
- R = Resistance
What two factors affect blood flow (Q)?
Pressure difference between two points in a vessel
Resistance - vessel opposition to blood flow
What is the significance of the relationship between blood flow, resistance and pressure? (Check)
Q = 🔼P/R
What does NB mean?
Fran says it means important
What does TPR mean?
Total peripheral resistance
(Resistance of entire systemic vasculature)
How do you calculate the resistance of a single organ?
Can be calculated by substituting flow eg. renal flow.
What is Poiseuille’s Law?
Posieuille’s law is resistance to blood flow.
What 4 things about blood vessels (+ blood) affects resistance?
- Blood vessel diameter
- Vessel length
- Series/parallel arrangement (see slide 10)
- Blood viscosity
Resistance to flow - directly proportional to vessel length and blood viscosity
Inversely proportional to fourth power of the radius
What happens to resistance and pressure in the series resistance?
Series resistance - pressure decreases through each component and largest decrease in pressure in arterioles = largest resistance (ΔP=R x Q)
Total resistance = sum of individual resistances
What happens to individual resistance/pressire in the parallel resistance?
Parallel resistance - less than any of the individual resistances which results in no loss of pressure eg. Aorta.
Why does blood pressure increase and decrease in the aorta ,arteries, arterioles, capillaries and veins/venules?
(Break this up into multiple flashcards)
- Blood pressure increases in the aorta due to large cardiac output and low compliance (ability of blood vessels to expand and contract).
- Pressure remains high in arteries due to elastic recoil.
- Pressure is low in arterioles due to high resistance to flow.
- Capillaries produce frictional resistance due to flow and filtration.
- Veins have low pressure due to high capacitance.
What does capacitance mean?
The ability of a blood vessel to contract and expand.
What does CO mean?
Cardiac output
Why does pressure decrease with blood flow?
Pressure decreases with blood flow because energy is lost overcoming frictional resistance
What are arterial pressure and venous pressure?
Blood pressure exerted on the blood vessel wall by the arteries for arterial pressure and veins for venous pressure.
Why is the pulmonary vasculature pressure much lower than the systemic? (Gemini the question)
- Lower resistance because of thinner walls and vasodilation
- Lower bloood volume
- Compliance meaning it can easily stretch and accomodate changes in blood volume.
Out of pulmonary and systemic circulation, which one has less pressure?
Pulmonary circulation has lower pressure therefore less resistance
How do you calculate pulse pressure?
Pulse pressure = systolic - diastolic pressure
How do you calculate mean arterial pressure?
Diastolic pressure + 1/3 pulse pressure
(Average pressure in a complete cardiac cycle)
Is blood pressure lower or higher during the day?
Higher in the day so lower bp in the night because at night you’re asleep and bp needs to be regulated to meet body needs + activity levels during the day
What receptor regulates the blood pressure?
Baroreceptors
What does baro refer to?
Refers to pressure
Where are Baroreceptors found?
Carotid and aortic sinuses
What happens to the Baroreceptors if there’s an increase in blood pressure?
There’s an increased stretch of the baroreceptor which increases the afferent nerve firing
What does the solitary nucleus have to do with the Baroreceptors?
Solitary nucleus (SN) receives input from the Baroreceptors and redirects signals to the SNS + PNS changes via medullary CV centres
What does RAAS stand for?
Renin - angiotensin - aldosterone system
How does Angiotensin II form?
Renin cleaved onto angiotensinogen which forms angiotensin I
Angiotensin I is then converted to angiotensin II by angiotensin - converting enzyme (ACE)
What are the downstream effects of Angiotensin II?
1) Increase aldosterone which increases Na+ absorption so increases ECF
2) Hypothalamus increases thirst + ADH secretion so increased water reabsorption in collecting ducts (CD)
3) Vasoconstriction of arterioles increases TPR
What are chemoreceptors?
Chemoreceptors are specialized sensory receptors which send signals to the brain when there is a change in the chemical composition of the blood.
Where is ADH (AVP) secreted from? And when is it secreted?
Secreted from posterior pituitary gland.
Secreted when low BP or high blood osmolarity
What is hypertension?
Hypertension is a long term elevation of blood pressure leading to pathologies, drugs can act to block pathways
What risks emerge from small increases in BP?
Increased risk of morbidity + mortality
What does ACE stand for?
Angiotensin- converting enzyme
What lifestyle changes can act as hypertension treatments?
Increase salt intake
Increase exercise
Decrease alcohol and stress
Weight management
What does ARBs stand for?
Angiotensin II receptor blockers
How does the parasympathetic control bp?
PNS outflow via vagus nerve to SAN which decreases heart rate and blood pressure
How does the sympathetic nervous system control BP?
SNS control to elevate BP:
1) SAN increases heart rate
2) Increase cardiac muscle contraction and increased stroke volume
3) Arterioles vasoconstriction so increased total peripheral resistance
4) Vein vasoconstriction leads to decreased unstressed volume
What is TPR?
Total peripheral resistance
Refers to the overall resistance that blood encounters as it flows through the blood vessels of the systemic circulation
What does persistent high BP increase the chances of getting?
Increases risk of:
- Heart disease
- Heart attacks
- Strokes
- Heart failure
- Aortic aneurysms
- Peripheral arterial disease
- Kidney disease
- Vascular dementia
What drug treatments can help with hypertension? (6)
Diuretics - decrease ECF by increase urine production
Angiotensin-converting enzyme (ACE) inhibitors
Angiotensin II receptor blockers (ARBs)
Renin inhibitors
Calcium channel blockers - decreases contractility and increase vessel relaxation
Beta blockers - decreases HR + heart contractility
