8/12/2019 Lecture 7 - Regulation of Blood Pressure
1/30
The extrinsic regulation of blood
pressure and cardiac output
Lecture 7
Chapter 22 B&BAll but pages 550-554
8/12/2019 Lecture 7 - Regulation of Blood Pressure
2/30
Arterial Blood Pressure
Flow Pressures
Aortic arch
Thoracic aorta
Abdominal aorta
Femoral artery
~120 systolic/80 diastolic
Flow changes b/c
-resistance
-compliance
-inertia
8/12/2019 Lecture 7 - Regulation of Blood Pressure
3/30
Mean Arterial Blood Pressure (MAP)
MAP = DP + 1/3 (SP-DP)
average arterial blood pressure
during a cardiac cycle
Perfusion pressure
A MAP of ~ 60 mmHg is
sufficient for end organ
perfusion.
For a BP of 120/80, MAP is
~ 93.5 mmHg
8/12/2019 Lecture 7 - Regulation of Blood Pressure
4/30
stretch
Baroreceptor Feedback Loop for the Regulation of
Mean Arterial Blood Pressure
mechanoreceptors
8/12/2019 Lecture 7 - Regulation of Blood Pressure
5/30
High pressure baroreceptors respond to stretch in
the aortic arch and carotid sinus.
sinus nerve
depressor nerve
8/12/2019 Lecture 7 - Regulation of Blood Pressure
6/30
Fig 22-2
Carotid and Aortic Baroreceptors
8/12/2019 Lecture 7 - Regulation of Blood Pressure
7/30
Aortic sinus
Carotid nerve fires above and belownormal pressures.
Aortic nerves are activated abovenormal pressures.
The aortic receptors help reinforce the carotid activation above normal
pressures.
MAP ~ 93.5 mmHg
8/12/2019 Lecture 7 - Regulation of Blood Pressure
8/30
MAP
Increased firing ofBaroreceptors
by stretch
Medulla Oblongata
Sympathetic and
Parasympathetic
EFFERENTS
Vagal/glossopharyngeal
AFFERENTS
TARGET ORGANS
-heart
-blood vessels
-adrenal medulla
-glands (skin/sweat)
NTS
Cardio-inhibitory area
Vasomotor area
8/12/2019 Lecture 7 - Regulation of Blood Pressure
9/30
Medullary
Cardiovascular Center
Nucleus
of the Tractus
Solitarius (NTS)
Vasomotor area
Receives
afferents from CN IX and X
interneurons
Dorsal motor nucleus of X
Nucleus ambiguous of
X and IX
Cardio-inhibitory
Area
+
+
-
Increased MAP
8/12/2019 Lecture 7 - Regulation of Blood Pressure
10/30
Vasomotor area
Dorsal motor nucleus of X
Nucleus ambiguous of
X and IX
Cardio-inhibitoryArea
To spinal cord
Sympathetic activation of:
-Blood vessels
-Heart
-Adrenal medulla
To heart
Parasympathetic activation
bradycardia
(tonic vasoconstriction)
Coordination of Medullary Cardiovascular Inputs
8/12/2019 Lecture 7 - Regulation of Blood Pressure
11/30
afferents efferents
Fig. 22-4
8/12/2019 Lecture 7 - Regulation of Blood Pressure
12/30
8/12/2019 Lecture 7 - Regulation of Blood Pressure
13/30
Low Pressure Cardiac Baroreceptors
Respond to fullness or volume
Located in Low pressure sites
Control the effective circulating volume Indirect lyregulate MAP
Unlike activation of the high-pressure
baroreceptors, activation of the A and
B fibers will INCREASEheart rate.(and also cause renal vasodilation).
Bainbridge Reflex
8/12/2019 Lecture 7 - Regulation of Blood Pressure
14/30
The dependence of cardiac output on effective
circulating volume is the result of the complex
Interplay among three factors :
1) Bainbridge reflex
2) Baroreceptor reflex
3) Starlings Law
8/12/2019 Lecture 7 - Regulation of Blood Pressure
15/30
Cardiac Output
Stroke Volume
Heart rate
BainbridgeBaroreceptor
In volume loading
conditionsBainbridge
response prevails
In volume depletion
conditionsBaroreceptor
response prevails
Bainbridge responseonly HRis affected
Baroreceptor -Increased stretch on high
pressure decreases stroke
volumeflattening the Starling response.
Heart rateincreases under
volume depletion and
loading
8/12/2019 Lecture 7 - Regulation of Blood Pressure
16/30
Sympathetic input - HEART
ACTIONS
Nerve fibers release
NE
SA, atria, andventricles
HR and contractility
R side SA node L side contractility
MECHANISM
1 receptors
pacemaker activity
1 myocardium
contraction
8/12/2019 Lecture 7 - Regulation of Blood Pressure
17/30
Parasympathetic input - HEART
ACTIONS
Vagus nerve releases
ACH
SA and myocardium
HR and conduction
velocity
R side SA node (HR) L side contractility
(slight)
MECHANISM
Muscarinic receptors
(M2)
subunit (HR) Nitric oxide (weak
inotropic effect)
8/12/2019 Lecture 7 - Regulation of Blood Pressure
18/30
Sympathetic inputBlood vessels
ACTIONS
Activated -
Vasoconstriction
throughout body Skin/kidney BVs
most abundant
De-activated
Vasodilation
MECHANISM
Norepinephrine
>
Epinephrine >
Vasoconstriction1Vasodilation2
8/12/2019 Lecture 7 - Regulation of Blood Pressure
19/30
Parasympathetic inputBlood vessels
ACTIONS
Vasodilation of BVs
Less common than the
sympathetic activity Salivary glands, g.i.
glands, reproductive
tissues
MECHANISM
ACH increases
vasodilation indirectly
through other secondmessengers.
8/12/2019 Lecture 7 - Regulation of Blood Pressure
20/30
Sympathetic activation of skeletal muscle
Causes vasodi lat ion
Release of ACH
Action is on pre-capillary sphincters
Vasoconstriction in all vascular beds except skeletal
muscle
Increased HR and contractility
Control center is not medulla but rather cerebral cortex
-fight or flight response
-Anticipatory response to exercise
8/12/2019 Lecture 7 - Regulation of Blood Pressure
21/30
Adrenal medulla
Sympathetic release of epinephrine and
norepinephrine
Global effects on increasing arterial blood
pressure.
8/12/2019 Lecture 7 - Regulation of Blood Pressure
22/30
Chemoreceptors
Exert a positive drive on vasomotorarea
Exert a positive drive on cardio-inhibitoryarea
Respond to a PaO2, PaCO2, fall in pH
Normal O2changes not significant stimulus
Severe hypoxia is potent stimulus Coordination of inputs to cardiovascular
centers and respiratory centers.
Vasoconstriction and Bradycardia
8/12/2019 Lecture 7 - Regulation of Blood Pressure
23/30
Chemoreceptors
Peripheral (ventilation)
Sense low O2
Carotid and aortic (glomus cell)
Synapse with IX and X, respectively
Central (medulla/CNS)
Sense low pH primarily
8/12/2019 Lecture 7 - Regulation of Blood Pressure
24/30
Net result of Chemoreceptor stimulus is an integration
of central and peripheral chemoreceptors
Stretch of pulmonary receptors
cancel peripheral stimulus on cardio-inhibitory areacausing tachycardia
8/12/2019 Lecture 7 - Regulation of Blood Pressure
25/30
Fight or Flight Reaction
(Sudden Sympathetic Drive)
1. Skeletal muscle blood flowsympathetic cholinergic stimulation -
vasodilation.
2. Cutaneous blood flowsympathetic cholinergic responsesweat
glands.
3. Adrenal medullasympathetic stimulation release epinephrine
causes vasodilation in muscleand vasoconstriction in kidney/splanchnicVessels.
4. Veinsvasoconstriction (sympathetic)
5. HeartIncreased sympathetic stimulusincreased HR and contractility
6. MAPOverall output is an increase in blood pressure.
8/12/2019 Lecture 7 - Regulation of Blood Pressure
26/30
Fight or Flight
Response
Fig. 24-4
vasodilation
sweat
epinephrine
vasoconstriction
Heart rate
contractility
8/12/2019 Lecture 7 - Regulation of Blood Pressure
27/30
FAINTING
(Massive Parasympathetic Response)
vasovagal syncope
1. Massive vasodilation occursremoval of sympathetic tone causes
a rapid fall in blood pressure.
2. Decreased Cardiac outputIncreased vagal output to heart causes
bradycardia and decreased stroke volume
3. Decreased arterial blood pressuresecondary to vasodilation and CO.
4. Cerebral blood flowreduced (> 10 seconds)fainting occurs
8/12/2019 Lecture 7 - Regulation of Blood Pressure
28/30
vasodilationBradycardia
Decreased MAP
AVP release
Reduce cerebral blood flow
Emotional stress
FAINTING
(Massive Parasympathetic Response)
8/12/2019 Lecture 7 - Regulation of Blood Pressure
29/30
Integrated Response to Massive Hemorrhage
1. Baroreceptorshigh pressuredecreased firingresult is enhanced
Sympathetic output and less vagal output tachycardia, contractility, vasoconstrictionre-establish MAP
2. Baroreceptorslow pressurereduced VOLUMEless activity of LPBs.
Increased sympathetic outputvasoconstriction particularly of kidney BVs
Increased release of Anti-diuretic hormone/Arginine Vasopressin/Vasopressin
3. Peripheral Chemoreceptorslow MAP reduces perfusion of carotid/aortic bodies
Local hypoxiaincreased firing of chemoreceptorsvasoconstrictionand
changes in ventilation.
4. Central Chemoreceptorsfall in blood pH (acidosis)increased sympatheticOutputvasoconstriction
5. Adrenal medullaas a result of sympathetic stimulationincreased
Medullary secretion of epinephrine(a BP drop to 40 mmHg - 50 fold increase in Epi)
8/12/2019 Lecture 7 - Regulation of Blood Pressure
30/30
Hemorrhage
Venous return blood volume
MAP
SV and CO Atrial volume
LP Baroreceptors
HP BaroreceptorsCentral
Chemoreceptors
Peripheral
Chemoreceptors
Medullary
Cardiovascular
Control CenterSYMPATHETIC RESPONSE
Heart rate
Contractility
Vasoconstriction
(arteriole/venous)
Hormonal response
-Angiotensin/Renin
-ADH release
-ANP (decreased)
Top Related