1. REGULATION OF BP
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Regulation of BP

2. Systemic Arterial Pressure
Normal range is about 120/80 mmHg
Varies with age:
17 – 40  140/90mmHg
41 – 60  150/90
>  160/90
Higher systolic pressure with age
reflects in part diminishing arterial compliance
Pulse pressure = SBP –DBP
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Regulation of BP

3. Physiological changes in BP
Mean Arterial pressure (MAP)
Average of all the pressures
measured mSec. By mSec.
Over a period of time.
MAP = DBP + 1/3 pulse pressure
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Regulation of BP

4. Physiological changes in BP
MAP is determined by CO and systemic vascular resistance
MAP =CO x TPR
CO and TPR determine average volume
of blood in systemic arteries over time.
It is this blood that causes pressure.
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Regulation of BP

5. Physiological changes in BP
It is total arteriolar resistance
that influence systemic arterial pressure
Clinical methods for measuring BP
Korotkoff sounds
Arterial pressure determine Blood flow
Decreased BP → Hypoperfusion
Increased BP →
i.e need for control
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Regulation of BP

6. Regulation of BP Autoregulation Homornal regulation Nervous system
Renal
Note
Short term vs long term regulation
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Regulation of BP

7. Regulation of local blood flow
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Regulation of BP

8. Blood flow to different organs and tissues under basal conditions.
% ml/min ml/min/100gm
Brain
heart
Brounchi
Kidney
Liver
Muscle
(inactive state)
bones
Myroid gland
Adrenal gland
Skin (cool)
Other tissues
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Regulation of BP

9. Regulation of local blood flow
Autoregulation
ability of tissue to regulate its own blood flow
↑ tissue metabolism
Or ↓ O2 availability
→↑local blood flow
How
Vasodilator/metabolic theory
O2 demand/myogenic theory
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Regulation of BP

10. Regulation of local blood flow
In any tissue of the body
acute increase in arterial pressure
will cause an immediate rise in blood flow,
the blood flow in most tissues return most of the way back towards the normal level
How
Metabolic theory
Myogenic theory
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Regulation of BP

11. Regulation of local blood flow
dilatation of large arteries when microvascular blood flow is increased.
EDRF
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Regulation of BP

12. Regulation of local blood flow
Chronic changes in local blood flow leads to
Change in tissue vascularity
Neovascularization/Angiogenesis
Angiogenic factor released by
Ischaemic tissues
Rapidly growing tissues
Tissues with excessively high met
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Regulation of BP

13. Systemic regulation of BP by hormones
vasoconstrictors
Vasopressin
Norepinephrine & Epinephrine
Angiotensin II
vasodilators
Bradykinins
formed during active secretions in sweat glands salivary glands & pancrease.
ANP
Secreted by the heart
antagonizes the action of various vasoconstrictors and lowers BP.
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Regulation of BP

14. Regulation of BP by the NS
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Regulation of BP

15. Regulation of BP by the NS
Nervous control of BP is by far the most rapid
of all mechanisms for pressure control.
The means by which the NS controls BP is almost entirely through the Autonomic NS.
The most important part of ANS for regulation of BP is SNS.
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Regulation of BP

16. Regulation of BP by the NS
All vessels except capillaries, precapillary sphincters and most of metarterioles are innervated by SNS .
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17. In the medulla and lower third of pons.
Vasomotor Center:
In the medulla and lower third of pons.
The center transmits parasympathetic impulses
through the vagus nerves to the heart,
and sympathetic impulses through the cord and peripheral nerves to blood vessels.
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Regulation of BP

18. Vasomotor center
Sympathetic chain
heart
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Regulation of BP

19. Vasoconstrictor area (C1 Vasodilator area (A1)
Vasomotor Center
Vasoconstrictor area (C1
Nerves secrete Noradrenaline.
Vasodilator area (A1)
whose fibers project to the C1 and inhibit vasoconstrictor activity of C1
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Regulation of BP

20. Vasomotor Center Sensory area (A2)
Located in the NTS
Neurons of this area receive sensory nerve signals mainly from X and 1X
the output signals from this area control the activities of both C1 and A1
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Regulation of BP

21. IX NTS C1 Carotid sinus X Aortic arch Adrenal medulla heart Vessel
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Regulation of BP

22. Vasomotor Center
Under normal conditions the C1 of the vasomotor center
transmits signals continuously to the sympathetic vasoconstrictor nerve fibers over the entire body
causing slow firing of these fibers. “Sympathetic vasoconstrictor tone”.
These impulses maintain a partial state of contraction in the blood vessels called vasomotor tone.
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Regulation of BP

23. BP is adjusted by variation in the rate of this tonic discharge.
Vasomotor Center
BP is adjusted by variation in the rate of this tonic discharge.
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Regulation of BP

24. Vasomotor Center    
Lateral portion of vasomotor center transmit excitatory impulses
through the sympathetic nerve fibers to the heart.
Medial portions transmit impulses through the vagus nerves to the heart.
Sympathetic impulses are transmitted to the adrenal medullae at the same time they are transmitted to the blood vessels.
Nerve endings of vasoconstrictor nerve secrete noradrenaline
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Regulation of BP

25. Vasomotor Center
Vasomotor center is controlled by higher nervous centers.
Reticular substances of the pons, mesencephalon, diencephalons can excite or inhibit the vasomotor center
Cerebral cortex, hypothalamus
When vasoconstrictor tone is increased, there is arteriolar constriction and increase in BP.
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Regulation of BP

26. Vasomotor Center
Venoconstriction leads to decrease stores of blood in venous reservoirs
usually accompany these changes
HR and stoke volume increase because of sympathetic activity, and CO is increased.
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27. Afferents to the vasomotor center.
Fibers from baroreceptor
Other parts of the NS
Carotid and aortic chemoreceptors.
Some stimuli act directly on the center, eg CO2, hypoxia.
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Regulation of BP

28. Baroreceptors: Abundant in the carotid Sirius and arch of the aorta.
Signals from the carotid Sinus
are transmitted though Hering’s nerve
To 1X and then to NTS in the medullary area.
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29.  Baroreceptor 
From arch of the aorta to X also into the same area of the medulla.
Carotid Sinus baroreceptors are stimulated by pressure more than 60mmHg,
reach a maximum stimulation at 180mmHg
Baroreceptors respond extremely rapidly to changes in arterial pressure.
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Regulation of BP

30. Baroreceptor Signals from baroreceptors are carried by 1X/X to NTS
Then to Sensory area (A2)
And eventually inhibit vasoconstrictor center of the medulla and excite vagal center
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Regulation of BP

31. Baroreceptor Excitation of baroreceptors reflexly lowers BP
Low pressure has opposite effect
Baroreceptors opposes either rise or fall n BP, thus called Pressure buffer.
Baroreceptors rest in 1 – 2 days to whatever pressure level they are exposed.
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32. Baroreceptor
Atrial and Pulmonary Arteries stretch receptors(Low pressure receptors)
Detect BP caused by volume.
Atrial reflexes to the kidney:
Stretch of atrial causes reflex dilatation of afferent arteries to the kidney
Leading to decreased secretion of vasopressin
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Regulation of BP

33. Chemoreceptors
Carotid bodies in the bifurcation of each common carotid artery
And Aortic bodies adjusent to the aorta.
Stimulated when arterial pressure falls below 80mmHg.
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34. CNS ischaemic response.
Stimulated when arterial pressure falls below 60mmHg
Greatest degree of stimulation at 15 – 20 mmHg.
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35. Long term regulation of BP
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36. Long term regulation of BP
When the arterial pressure changes slowly over hrs Or days,
the nervous mechanisms gradually lose all or almost all of their ability to oppose the changes.
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37. Long term regulation of BP
Renal-body fluid system
Renin Angiotensin system
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Regulation of BP

38. Renal – body fluid system
↑ ECF →↑arterial pressure
Rising pressure in turn has a direct effect
to cause the kidneys to excrete the excess ECF, i.e. returning pressure to normal
This is the basis for long term arterial pressure control.
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39. 9 -- 8 -- 7 -- 6 -- 5 -- Urinary volume output 4 -- 3 -- 2 -- 1 --
( X normal)
Arterial pressure (mmHg)
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Regulation of BP

40. Renal – body fluid system
Determinants of long term Arteriolar pressure are:
Renal output of salt and water
Salt and water intake
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Regulation of BP

41. How increase in ECF vol. raise BP
Increase in ECF volume increases blood volume
Increasing Mean Systemic Filling pressure
Increase venous return
Increase CO
Autoregulation causes increase in TPR
Raising arterial pressure
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42. Note that: Hypertension is often caused by
excessive ECF volume
ECF volume  CO  Autoregulation
Autoregulation (TPR)  BP
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43. Renin-Angiotensin System
Apart from capability of control of arterial pressure through changes in ECF Vol.
The kidneys have another powerful mech.
Renin is small protein enzyme released by the kidney
When arterial pressure falls too low.
Or reduced ECF Vol.
Synthesized and stored in inactive form in JG cell
which are modified smooth muscle cells in the afferent arterioles
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44. Angiotensinogen  Angiotensin I (plasma protein)
Arterial pressure 
Renin
Angiotensinogen  Angiotensin I
(plasma protein)
ACE (lungs)
Angiotensin II
Angiotensinase
Inactivated
Renal retention of salt&water
vasoconstriction BP 
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45. Effects of Angiostensin II
Vasoconstriction
occurs rapidly
Intensely in arterioles
Less extent in veins
Max. effect after 20 – 30 min
Act on the kidney to reduce salt and water excretion.
This slowly increases ECF Volume
which then raises arterial pressure over hrs – days.
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46. Effects of Angiostensin II
Acts directly on kidneys
Or to the Adrenal cortex to secrete Aldosterone
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47. In the kidneys Constrict renal blood vessels,
diminishing blood flow i.e. less fluid filters through the glomeruli into the tubules
Slows blood flow in peritubular capillaries
Reducing their pressure which allows rapidly osmotic reabsoption of fluid from the tubules.
Effect on tubular cells themselves to increase tubular rabsorption of salt and water.
Aldosterone causes marked increase in Na+ and water reabsoption by renal tubules.
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Regulation of BP

48. Effects of Angiostensin II
Acts on brain to increase
water intake
Secretion of ADH
Facilitate release of Naradrenaline by direct action on postanganglionic sympathetic nerves
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49. Renin Angiotensin System
Increase in ECF Vol.
Raises BP
Resulting in decreased Renin release( i.e decreased Angiotensin II)
Therefore less renal reabsorption of salt and water
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Regulation of BP