P: Arterial blood pressure Flashcards
How is mean arterial pressure (MAP) (Pa) calculated?
Pa = Pd + (Ps - Pd)/3
Ps = Systolic pressure
Pd = Diastolic pressure
What is the normal Pa?
Pa = 93 mmHg (120/80) –> rounded up to 100 mmHg
What is the main physical determinant + physiological determinants of MAP?
- Physical determinant = arterial blood volume (Va)
- Physiological determinants = rate of inflow of blood (Qh) + rate of outflow (Qr)
What happens to MAP if:
- Qh = Qr
- Qh > Qr
- Qh < Qr
- Qh = Qr –> MAP stays constant
- Qh > Qr –> MAP increases
- Qh < Qr –> MAP decreases
- Constriction causes pressure to ___ in the arterioles and downstream vessels.
- Constriction causes pressure to ___ upstream in the arterial system.
- Increase in total peripheral resistance (TPR) (vasoconstriction of arterioles) causes blood pressure to ____.
- fall
- increase
- increase
Long term increases in either ___ or ___ will result in long term effects on Pa.
- CO
- TPR
MAP = ____ x ____
and
MAP = ___ x ___ x ___
- CO x TPR
- SV x HR x TPR (CO = SV x HR)
What determines the rate of change of Pa?
Compliance of the arteries
- Rigid arteries attain higher Pa level rapidly
- Elastic arteries: increases in Pa occur at slower rate (pressure absorbed by wall)
What are 2 determinants of pulse pressure?
- SV (major determinant)
- Compliance
What is the tool used to measure systolic and diastolic pressure and how?
- Sphygmomanometer and inflatable cuff
- Cuff placed around upper arm over brachial artery –> inflated cuff = pressure on artery
- Cuff pressure > systolic pressure (120 mmHg) –> artery closed, blood flow stops
- Cuff pressure slowly dropped: cuff pressure < systolic pressure –> partially opens artery –> blood flow restarts in a turbulent fashion
- Causes Korotkoff sounds (thumping noise), detected with stethoscope on artery
- Cuff pressure < diastolic pressure (80 mmHg) –> artery completely open –> sounds stop
Regulation of smooth muscle contraction/relaxation in arterioles controls ____
TPR
- Contraction closes lumen of blood –> reduces blood flow
- Relaxation increases lumen diameter (dilation) –> increases blood flow
What is the equivalent of troponin C from skeletal/cardiac muscle in skeletal muscle?
Calmodulin: Ca2+ sensor
- Ca2+/calmodulin complex binds and activates MLCK
Myogenic regulation of vascular smooth muscle (VSM):
- ____ in blood pressure induces reflex contraction of arterioles
- ____ in blood pressure induces reflex dilation of vessels
- ____ is maintained (autoregulation of blood flow)
- Rapid increase in blood pressure induces reflex contraction of arterioles
- Rapid reduction in blood pressure induces reflex dilation of vessels
- Constant blood flow is maintained (autoregulation of blood flow)
Where is resistance to blood flow the greatest?
In arterioles and capillaries due to narrow diameter
How does stroke volume determine pulse pressure?
- During ventricular ejection, arterial blood volume increases to V2
- Blood pressure increases to P2
- During diastole, peripheral runoff reduces volume to V1 and pressure to P1.
(V2- V1) proportional to (P2-P1) = pulse pressure
Explain endothelial-mediated regulation
- Increased blood flow causes shear stress to endothelium and induces release of nitric oxide (NO) (synthesised from L-arginine)
- NO diffuses to VSM cells and activates guanylyl cyclase –> increases [cGMP]i –> decreases [Ca2+]i in VSM –> dilation of blood vessels
How can metabolic activity of a tissue regulate capillary blood flow? What is the name given to rise in blood flow caused by increased tissue activity?
- If O2 levels are inadequate, metabolites with vasodilator activity are produced –> diffuse to VSM –> relaxation –> increases capillary blood flow
- Active hyperemia = rise in blood flow caused by increased tissue activity
Explain extrinsic control of peripheral blood flow
- Post-ganglionic sympathetic nerves innervate VSM of arterioles and veins
- Noradrenaline binds to alpha1-adrenergic receptors on VSM cells = vasoconstriction (activate phospholipase C –> produces 2nd messengers –> increase [Ca2+]i)
- Adrenaline binds to B2-adrenergic receptors on VSM cells in skeletal blood vessels = vasodilation (activate adenylate cyclase –> increase [cAMP]i –> inhibits MLCK)
- NA binds to alpha 1 = activate PLC = 2nd messengers = increase in Ca2+ = vasoconstriction
- Adrenaline binds to Beta2 in skeletal blood vessels = activate adenylyl cyclase = increase cAMP = inhibit MLCK = vasodilation
In arterioles:
- At rest, SNs constantly release ___ inducing a degree of ___ (tonically active or ___ tone)
- noradrenaline
- vasoconstriction
- vasoconstrictor tone
Sympathetic nerve stimulation:
- Reduces ____ into tissues by ____ of arterioles
- Decreases tissue ____ by ____ of venules
- Reduces capillary ____ pressure –> absorption of ____ into capillaries increases
- blood flow, constriction
- blood volume, constriction
- hydrostatic, interstitial fluid
Vasoconstriction mobilizes blood from ____ and returns it to ___. During exercise:
- Increased ____
- Increased ____
- Increased ____
- Increased ____
- capacitance vessels, heart
- venous return
- EDV
- SV
- CO
Regulation of peripheral resistance is mediated by ____
sympathetic nerves
What’s another word for cardiovascular control centre in the brain and where is it located?
- Vasomotor Centre: in reticular substance of medulla + lower third of Pons
The Vasomotor Centre transmits impulses via ____ to the heart, sympathetic impulses via ____ and peripheral ____ nerves to the heart and arteries, arterioles and veins.
- vagus nerves
- spinal cord
- sympathetic
Stimulation of rostral ventrolateral medulla (RVLM) increases ___ and ___
BP and HR (very important in maintaining normal BP –> vasoconstrictor area)
Caudal ventrolateral medulla (CVLM) function
Inhibit RVLM activity –> vasodilation
What is the origin of vagal projection to the heart?
Nucleus ambiguus (NA, AMB) and dorsal motor nucleus of vagus (DMV)
- Nucleus of the tractus solitarius (NTS) receives sensory nerve signals from circulatory system mainly through ____ and ____ nerves.
- These nerves are stimulated by ____ and ____.
- NTS sends the output to the ____ and ____.
- Stimulation of NTS reduces ____ and increases ____.
- Vagus and glossopharyngeal
- Baroreceptors and cardiopulmonary receptors
- NA and CVLM
- Sympathetic outflow, vagal outflow
NTS in the medulla receives sensory impulses from:
- Baroreceptors
- Cardiopulmonary receptors
- Chemoreceptors
- Other brain regions
How are sudden changes in blood pressure detected?
Stretch-sensitive mechanoreceptors (baroreceptors) in walls of carotid artery (carotid sinus) and aortic arch become more active in response to stretched walls from raise in BP
What are the afferent pathways of arterial baroreceptors?
- Carotid sinus nerve, glossopharyngeal nerve, NTS
- Vagus nerve, NTS
BP > ___ mmHg –> rapid inhibition of sympathetic nerve activity + increase in vagal activity (and vice versa)
100 mmHg
Firing of baroreceptor terminals is enhanced by increases in ____ and diminished by reductions in ____
Arterial pressure for both
Which baroreceptors are quantitatively more important for regulating arterial blood pressure?
Carotid sinus baroreceptors (aortic are less sensitive)
What is responsible for short term vs long term changes in arterial pressure?
- Short term = baroreceptors
- Long term = kidney
Consequences of sudden reduction in blood pressure
Increased sympathetic nerve activity will:
- Increase ____ by increasing ___ and ___
- Contract ____ muscle promoting ____
- Stimulate contraction of ____ muscle to increase ____
- ____ in kidney arterioles also minimizes urine formation
Reduction in ____ nerve –> diminish inhibitory effect on HR
Increased sympathetic nerve activity will
- Increase CO by increasing HR and SV
- Contract venous smooth muscle promoting venous return
- Stimulate contraction of arterial smooth muscle to increase peripheral resistance
- Vasoconstriction in kidney arterioles also minimises urine formation
Reduction in vagus nerve –> diminish inhibitory effect on HR
Consequences of sudden elevation blood pressure
- Stimulation off vagus nerve activity will reduce CO by slowing HR
- Inhibition of sympathetic nerve activity will: reduce CO by slowing HR and SV + cause relaxation of arterial smooth muscle (vasodilation) –> decrease peripheral resistance
- Kidneys are stimulated –> excrete more water as urine –> reducing total blood volume (long term control)
Where are cardiopulmonary receptors located and what is their function?
- Atria, ventricles and pulmonary vessels
- Reflex that lowers arterial BP in response to changes in blood volume
- Acts mainly on kidneys to reduce blood volume by increasing urine output
What’s the Bainbridge Reflex?
- Increased blood volume increases atrial pressure –> rapid increase in HR
- Mediated by atrial stretch receptors that transmit afferent signals via vagus nerves to the NTS
- Efferent signals are transmitted back through vagal and sympathetic nerves to increase HR and contractility
- Bainbridge and baroreceptor reflexes are ____.
- Higher blood volume –> ____ predominates
- antagonistic
- Bainbridge reflex
Where are chemoreceptors located and what do they do?
- Medulla, carotid sinus and aortic arch
- Respond to changes in arterial PO2, PCO2 and pH
- Set appropriate rate and depth of ventilation (breathing)
- Chemoreceptor reflex: increase BP and HR (secondary effect of increase in ventilation)
Anterior hypothalamus function
decreases BP and HR
Posterior and lateral hypothalamus function:
- Alerting reaction
- Increased BP + HR, vasodilation in skeletal muscle
- Vasoconstriction in skin and splanchnic organs
Cerebral cortex functions:
- Involved in ___ functions
- Cause ____ of skin, splanchnic and renal vessels
- ____ in skeletal muscles
- Involved in motor functions
- Cause vasoconstriction of skin, splanchnic and renal vessels
- Vasodilation in skeletal muscles
Equation of pulse pressure
Pulse pressure = Systolic (Ps) - Diastolic pressure (Pd) = 40 mmHg at rest
