Regulation of arterial pressure-I

Regulation of arterial pressure-I (Physiology of Blood Pressure)

1. Regulation of Arterial
Pressure-I
Prof. Dr. Rashid Mahmood

2. Regulation of Arterial Pressure
1.Nervous regulation
2.Hormonal regulation
Prof. Dr. Rashid Mahmood 2

3. Three Mechanisms for Regulation of
Arterial Pressure
1.Rapid acting mechanisms
Act within seconds or minutes
1.Intermediately acting mechanisms
Act after many minutes
1.Long term acting mechanisms
Act after many minutes or hours
(sometimes days)
Prof. Dr. Rashid Mahmood 3

4. Rapid acting mechanisms
A.Baroreceptor Reflex
B.Chemoreceptor Reflex
C.CNS Ischemic Response
Prof. Dr. Rashid Mahmood 4

5. Nervous regulation
1.Vasomotor Center
2.Baroreceptor Reflex
3.Chemoreceptor Reflex
4.CNS Ischemic Response
Including Cushing reaction
1.Other reflexes
1.Bainbridge Reflex
2.Atrial and Pulmonary Reflex (Low pressure
receptors)
3.Arterial Reflexes to Kidneys (Volume reflex)
4.Abdominal compression reflex
Prof. Dr. Rashid Mahmood 5

6. Nervous regulation
of
Circulation
Prof. Dr. Rashid Mahmood 6

7. Vasomotor Center (VMC)
•Located in Medulla and
Pons
•Three important areas
Prof. Dr. Rashid Mahmood 7

8. Vasomotor centre
Consists of
¨Vasoconstrictor area, bilateral Area C
1
–upper medulla
¨Vasodilator area bilateral AreaA
1
–lower medulla
–Inhibits area C
1
¨Sensory area - Area A
2

–medulla & pons
–Receives signals from Vagus &
glossopharyngeal nerves
–Controls C
1
& A
1

¨Cardioinhibitory area
•Medial portion of VM area
Prof. Dr. Rashid Mahmood 8

9. Afferent and Efferent Connections of
VMC
Baroreceptors
Chemoreceptors
Other areas of nervous system
Heart
Blood vessels
Prof. Dr. Rashid Mahmood 9

10. Brain areas affecting VM activity
Prof. Dr. Rashid Mahmood 10

11. Q.1
¨Name any rapidly acting blood pressure
control mechanism
Prof. Dr. Rashid Mahmood 11

12. Nervous Regulation of
Blood Vessels
Prof. Dr. Rashid Mahmood 12

13. Sympathetic
nervous system
Prof. Dr. Rashid Mahmood 13

14. Sympathetic innervations of blood
vessels
Prof. Dr. Rashid Mahmood 14

15. Roll of nervous system in BP control
¨Very rapid BP homeostasis
¨Rapid increase in BP
–Sympathetic stimulation
–Reciprocal inhibition of parasympathetic nervous
system
Prof. Dr. Rashid Mahmood 15

16. Maintenance of Blood Pressure
¨The main factors influencing BP
–COP
–Peripheral resistance
–Blood volume.
¨BP = COP x PR
Prof. Dr. Rashid Mahmood 16

17. Q.2
¨Calculate the peripheral resistance if cardiac
output = 4000 ml/min, and arterial pressure
is 100 mm of Hg
Prof. Dr. Rashid Mahmood 17

18. Determinants of
Blood Pressure
Prof. Dr. Rashid Mahmood 18

19. Blood
pressure
control
systems
Prof. Dr. Rashid Mahmood 19

20. Baroreceptors
¨Stretch receptors
¨in almost all the large blood vessels in chest and neck
region
¨Most abundant in
•Carotid sinuses
•Aortic arch.
Prof. Dr. Rashid Mahmood 20

21. Baroreceptor system
Prof. Dr. Rashid Mahmood 21

22. Baroreceptor system
Prof. Dr. Rashid Mahmood 22

23. Figure 21.15
B
a
r
o
r
e
c
e
p
t
o
r

R
e
f
l
e
x
e
s
Prof. Dr. Rashid Mahmood 23
1
2
3a
3b
3c
4a
4b 5
6
7
8
9a
9b
9c
10a
10b
11
12

24. Chemoreceptor
¨Chemosensitive cells
•Carotid bodies
•Aortic bodies
¨Cells sensitive to Hypoxia, CO
2
& H
+
¨Operational at BP below 80 mm Hg
Prof. Dr. Rashid Mahmood 24

25. Prof. Dr. Rashid Mahmood 25
1
2
3a
3b
3c
3d
4a
4b
4c 5
6

26. Q.3
¨Where are baroreceptors located?
Prof. Dr. Rashid Mahmood 26

27. Low pressure receptors
¨In atria and pulmonary artery
¨Stretch receptors like baroreceptors
¨Function at much lower pressures
¨More responsive to volume changes
¨↑volume → ↑stretch → stimulation of low
pressure receptors
Prof. Dr. Rashid Mahmood 27

28. Arterial Reflexes to Kidneys
¨↑blood volume → ↑stretch of atria →
•↑ renal afferent arteriolar dilatation → ↑GFR
•↓ADH → ↓ reabsorption of H
2
O
•Atrial Natriuretic Peptide.
•All → ↑loss of water in urine
¨All these will reduce the volume of blood
¨Volume reflex
Prof. Dr. Rashid Mahmood 28

29. Prof. Dr. Rashid Mahmood 29
1
2
3
4a 4b 4c 4d
5a
5b
5c
6

30. Bainbridge Reflex
Increased VR
Atrial stretch
Stretch of SA
Feedback to
medullary
cardiac
centers via
CN IX & X
Increased
sympathetic
output to the
heart
Increased HR
Increased
Blood Volume
-Ve
Prevents the
damming of blood
in atria & veins
Prof. Dr. Rashid Mahmood 30

31. ¨↓Blood pressure to very low level
¨↓blood flow to VMC (ischemia)

¨Strong excitation of VMC
CNS ischemic response
Prof. Dr. Rashid Mahmood 31

32. Cushing reaction
¨Special type of CNS ischemic response
¨Ischemia due to ↑CSF pressure
¨Occlusion of cerebral blood vessels
Prof. Dr. Rashid Mahmood 32

33. © 2005 Elsevier
Cushing reaction
Prof. Dr. Rashid Mahmood 33

34. Skeletal muscle contraction
¨Abdominal compression reflex
•Baroreceptor stimulation and chemoreceptor
stimulation
•Stimulation of somatic nerves to abdominal muscles
Prof. Dr. Rashid Mahmood 34

35. ¨Blood pressure is control by nervous
and hormonal signals
¨Rapidly acting mechanism act within
seconds or minutes, and include
A.Baroreceptor Reflex
B.Chemoreceptor Reflex
C.CNS Ischemic Response
¨Nervous regulation is by Vasomotor center in
lower brain and by autonomic (mainly
sympathetic) nervous system
Take Home Points (1/3)
Prof. Dr. Rashid Mahmood 35

36. ¨Blood pressure = cardiac output × peripheral
resistance
¨Baroreceptors are stretch receptors located in
aorta and carotid arteries. They are stimulated by
high blood pressure
¨Chemoreceptors are located in brain, aortic
bodies and carotid bodies. They are stimulated
by ↓ O
2
, ↑ CO
2
and ↑ H
+
¨CNS Ischemic response is a powerful mechanism
and responds to very low blood pressure
¨Low pressure receptors in atria and pulmonary
artery are stretch receptors responsive to volume
changes
Take Home Points (2/3)
Prof. Dr. Rashid Mahmood 36

37. ¨Stretch of atria sends signals to kidney to
decrease salt reabsorption through ANP. This is
also called volume reflex
¨Stretch of SA Node due to increased pressure in
atria results in increased heart rate. This is called
Bainbridge Reflex
¨Cushing reaction is a special type of CNS
Ischemic response due to ↑CSF pressure
¨Stimulation of somatic nerves to abdominal
muscles to cause their contraction results in ↑ in
venous return. This is called abdominal
compression reflex
Take Home Points (3/3)
Prof. Dr. Rashid Mahmood 37

38. Q.4
¨List the functions of Atrial Natriuretic
Peptide.
Prof. Dr. Rashid Mahmood 38

39. Questions ?
?
Prof. Dr. Rashid Mahmood 39