Factors controlling BP.pdfBlood pressure is lateral pressure exerted on the walls of vessels

Blood pressure is lateral pressure exerted on the walls of vessels

1. Number of factors controlling the BP
1. Baroreceptors
2. Chemoreceptors
3. CNS ischemic response
Rapidly acting
4. Stress relaxation changes in the vasculature
5. Renin-angiotensin vasoconstrictor mechanism
6. Capillay fluid shift
7. Renal blood volume pressure control
mechanism-slow acting
8. Aldosterone

2. Sensors: Aortic & Carotid
Sinus baroreceptors
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Sensitivity
Carotld sinus baroreceptors have response
threshold of MAP 5OmmHg, & saturate
at 200mmHg
Response is more & more above
60mmHg till maximum
pressure160mmHg
Aortic barorecoptors-respond at 110
200mmHg
Baroreceptors respond very fast-no. of
impulses Increase during systole &
decrease during diastole
Respond to rapidly changing pressure
(pulsatle) than static pressure
Not effective for long term regulatlon of
BP, due to adaptatlon

3. 1. Nervous mechanism-Arterial
Baroreceptor Reflex
Stretching of baroreceptors
Slgnal to CV centre in medulla
Inhibition of sympathetic tone
Dilatation of blood vessels
W8P

4. Baroreceptor
Reflex mechanism
"Baroreceptor nerves
terminate In the NTS
and ralezso glutamate.
NTS neurons project to
the CVLM and nucleus
ambiguus and ralease
glutamate.
CVLM neurons project
to RVLM and reloase
GABA.
" Thís leads to a
reduction in
sympathetic actlvity
and an Increaso in
vagal activity.
-Cadon
-Pesolo
>Bood
Vagis
-Har
Bood

5. Cardiopulmonary Receptors: Volume
Receptors
" Provide information to CNS about fullness of
vascular system
" Modulate renal function
" Atria contain 2 types of baroreceptors
Areceptors respond to atrial wall tension during
atrial systole
Breceptors sensitive to atrial wall stretching
during atrial filling
" Raise HR when CVP is high-Bainbridge reflex

6. 300ml Blood Transfusion in dog
" Causes increased arterial pressure
" Detected by low pressure areas in circulation
" Reflex decrease in BP

7. Atrial reflexes activate Kidney: Volume
reflex
" Stretch of atria causes
1.Reflex dilation of afferent arterioles in kidney
2. Signal sent to hypothalamus to decrease
secretion of ADH
" Resultant increase in glomerular filtration &
decreased reabsorption of water & increased
water loss
" 3. Release of ANP-excretion of water in urine
" & return of blood volume to normal

8. "
Pulmonary Arteries receptors
Low pressure receptors
" Respond to increase pressure in pulmonary
arteries due to increased blood volume
" Potentiate the action of arterial baroreceptors

9. 3. CNS Ischemic
response
Ischemia
Excitatlon of VMC
MBP
" Reduced blood supply to brain
tissue cause nutritional deficiency
Operational when BP falls <
60mmHg
Greatest degree of stimulus at 15
to 20 mmHg
" Not a mechanism for mild to
moderate changes in BP
" Acts only in emergency
" Hence called last ditch stand
Magnitude of response is
tremendous
" MAP Can be elevated as long as
10min
" up to 250mmHg

10. Mechanism
Vasoconstrictor & cardio-acceleratory neurons
in vasomotor centre respond to ischemia
" Arterial pressure rises due to sympathetic
vasoconstriction

11. Cushing's Reaction to increased
Pressure Around the Brain
" Special type of CNS ischemic response
" Resulting from increased pressure of CSF
" Compress the whole brain & its arteries
" Initiates CNS ischemic response
" Blood pressure increases slightly above the
intracranial pressure allowing blood flow

12. Vasomotor
waves or
Mayer's
Pressure (mm Hg) wave
200
160
120
80
40
Oscillation of pressure reflex control system
caused by respiration
" 10-40mmHg
" Duration of cycle 26 sec to 7-10 sec in
anesthetized dog
" 7-10 sec in un-anesthetized human
Cyclical rise & fall in arterial pressure
A
100
60 WwW
B
A: Vasomotor waves caused by B: Vasomotor waves caused by
CNS 0schemic response Baroreceptor reflex oscillation

13. Increase in Arterial Pressure During Muscle
Exercise and Other Types of Stress
Require greatly increased blood flow
" Mechanism: RAS of the brain stem is activated
Stimulation of the vaso constrictor and
cardio-acceleratory areas of the VMC
2. At the same time that the motor areas of the
brain become activated
" 3. Local vasodilation of the muscle vasculature
caused by increased metabolites
" These increase the arterial pressure

14. Long Term Regulation of Arterial
Pressure
1. Renal-body fluid mechanism: Pressure
Diuresis
2. Renin-Angiotensin-Aldosterone System

15. 7. Renal-Body Fluid System
|Arterial pressure
| Glomerular filtration of
water-pressure diuresis
1 Excretion of salt -
pressure natriuresis
|T Loss of ECF & salt
B Blood volume
Blood pressure

16. Conversely
I Arterial pressure
IFlltration of water & salt
JECF & salt
‘ Blood volume
1 Arterial pressure

17. At arterial pressure 50mmHg, renal output is
zero
At 100mmHg-normal
200mmHg-6-8 times normal
" Also increases sodium output called pressure
natriuresis

18. Mechanism of
Arterial
pressure
Regulation in
Salt & water
intake
Increased sall intake
Increased extracellular volume
Increased arterial pressure
Decreased renin and angiotensin
Decreased renal retention of salt and water
Retun of extracellular volume almost to nomal
Return of arterial pressure almost to normal

19. Equating Salt & water intake with
renal output
" Equilibrium point
" the level at which
the arterial
pressure will be
regulated
" MAP wll readjust
to 100mmHg
Intake
or
output
(x
normal)
8
0
Equlibrium point
50
Renal output of
water and salt
100 150
Water and
salt intake
Arterial pressure (mm Hg)
200

20. Two Determinants of Long Term
Arterial Pressure
1. The degree of pressure shift of the renal
output curve for water and salt
2. The level of the water and salt intake

21. Long term effect of salt &
water intake
FiB A. SOme abnormality of kidney
" Causes renal output to shift
50mmHg higher than normal
" Therefore arterial pressure will
follow a new set point within a few
days
Fig. B-change in water & salt intake can
change arterlal pressure
" Intake level Increased 4fold
" Equilibrium polnt shifted to a new
pressure level 160mmHg, ie
60mmHg >
B
Intake
or
output
(x
normal)
6
2
4
2
0
0 0+
0
50
50
Normal
100
Nomal
-
150
Bevated
pressure
Elevated
100
Arterial pressure (mm Hg)
pressure
200 250
-
150 200 250

22. 2. Long term regulation of BP: Renin
Angiotensin mechanism:
Vasoconstriction
1
&PR
MAP
MAP
Secretlon of angiotensin ll
Acts directly on
kidneys
Retention of salt & water
1 Blood volume
‘ BP
Secretlon of aldosterone
from adrenal cortex
Retention of salt & water
Thirst

23. Decroasod
artorlal pressuro
Ronin (kidnoy)
Renin substrato
(angiotensinogon)
Angiotonsin I
Het Guyton
CopyngRt
Converting
onzymo
(lung)
Angiotonsin
Angiotensinase
(Inactivated)
Renal rotention Vasaconstriction
of salt and walor
Inoroasod artorial prossuro
d Hl Tetbock of Madical Physotsgy, 1Zth Cdtion
201I bSaunders, en mprnt of Elevie, Inc AI ights reseened