3. Peripheral resistance
• Resistance is the impediment to the blood flow
in a vessel.
• TPR (Total peripheral resistance )- resistance of
entire circulation.
• Unit is PRU (peripheral resistance unit)
• In CGS unit =dyne-sec/cm5
4. Laws related to blood flow and
resistence
1.Poiseuille Hagen formula:
2.Ohm’s law:
F=∆P/R
.Resistance is inversely related to radius
𝜋
5. Peripheral resistance depends on
• Luminal diameter of vessel
• Elasticity of arterial wall
• Velocity of blood
• Viscosity of blood
6. Viscosity is the internal friction to flow
of a fluid
• Whole blood 3-4 times viscous as water
• Plasma 1.8 times viscous
Viscosity depends on
• Hematocrit
• Composition of plasma
• Temp
• Velocity of fluid
7. Elastance
• Blood in the artery stretch the wall of blood vessel
which then recoil and generate pressure, this
recoil force is termed as elastance.
• Elastance=1/distensibility
• Systolic BP related to elasticity
• Diastolic BP is related to peripheral resistance
8. Blood pressure
• It is the lateral pressure exerted by blood on
the vessel wall while flowing through it.
4 types-
1. Systolic pressure
2. Diastolic pressure
3. Pulse pressure
4. Mean pressure
9. Blood pressure contd.
Lateral pressure: It is pressure when force is exerted at
right angles to the direction of fluid(blood) flow at any
point within a tube(blood vessels).
10. Blood pressure contd.
• Systolic pressure: It is the maximam pressure
during systole.
❑ Importance: Systolic pressure indicates-
➢ The extent of work done by heart.
➢ The force with which the heart is working.
➢ It is the index of cardiac output.
11. Blood pressure contd.
• Diastolic pressure: It is the minimum pressure
during diastole.
• Importance: Distolic pressure indicates-
➢ The constant load against which the heart works.
➢ It is the index of peripheral resistance.
12. Blood pressure contd.
• Pulse pressure: It is the difference between systolic
and diastolic pressure.
➢Importance: It is related with stroke volume &
vascular resistance.
• Mean pressure: It is the average pressure persist in
the circulation. It is calculated by=
diastolic pressure +1/3rd of pulse pressure
➢Importance: It forces the fluid to move
forward to get tissue perfusion.
13. Blood pressure
Cardiac output Peripheral resistance
Stroke volume Heart rate
End diastolic volume End systolic volume
14. Mean pressure is nearer to diastolic pressure.
Why?
Q. If systolic BP 120 mm/hg, diastolic BP 90
mm/hg. Calculate the mean pressure of the
subject.
15. Methods of measuring BP
• 1.Palpatory method – only systolic
pressure can be measured
• 2.Auscultatory method- both systolic &
diastolic pressure can be measured.
• Measured by sphygmomenometer.
16. 1. A stethoscope is placed over ante-cubital artery
2. A blood pressure cuff is inflated around the upper
arm.
3. The pressure in the cuff is elevated above systolic
pressure. So brachial artery collaps. No sound is
heard.
4. Gradual decrease of pressure in cuff, so blood
begin to slip through narrow artery, turbulance
flow in vessel. Produce Korotkoff sound
17. • 5. As the pressure falls in the artery the
korotkoff sound changes its quality
• 6.when the pressure is near to diastolic
pressure the sound become muffled.
18. Korotkoff sound
• The jetting of blood through a squeezed artery
produce a sound called so.
• Phases:
1. Phase I:Systolic pressure
2. phase II
3. Phase III
4. Phase IV:Diastolic pressure
19. Vasomotor tone
• a partial state of contraction in the blood
vessels called vasomotor tone
• Under normal condition the vasoconstrictor
area causing continuous & slow & sustained
sympathetic firing .
20. Vasomotor Center in the Brain
• Location: medulla and of the lower
third of the pons
• Vasomotor center transmits
--------- parasympathetic impulses through
the vagus to the heart.
---------sympathetic impulses through
peripheral sympathetic nerves to
virtually all arteries, arterioles, and
veins of the body.
21. Control of arterial pressure
A. Rapid control of arterial pressure(nervous
regulation):Within seconds
1. Baroreceptor reflexes/ baroreceptor
feedback mechanism
2. Chemoreceptor reflexes
3. Atrial & pulmonary artery reflexes
4. Central nervous system ischemic
response
22. B.Intermediate time period pressure
control mechanism (30 min – several hrs)
1.Renin angiotensin II vasoconstrictor mechanism
2. Stress relaxation of vasculature
3. Capillary fluid shift mechanism
23. c.Long term regulation (several days)
1. Renal body fluid mechanism
2. Renin-Angiotensin-Aldosterone
mechanism
24. Physiologic anatomy of baroreceptor
• Baroreceptors are spray-type nerve endings.
Location:
1. Wall of internal carotid artery above the
carotid bifurcation (carotid sinus)
2. Wall of the aortic arch.
• signals are transmitted from carotid sinus by
glossopharyngeal nerves
• "aortic baroreceptors" by vagus nerves to the
tractus solitarius in the medula
25.
26. Working of baroreceptor in high pressure
Stimulous Increased arterial blood
pressure(>60mmHg-180mmHg)
Receptor Baroreceptor:carotid sinus,aortic sinus
Afferent
nerve
Hering nerve & depressor nerve
Center Vasomotor center—nucleus tractus
solitarius
Efferent
nerve
Vagus
Sympathetic
Effector organ Heart & blood vessel
27. effect
(1) vasodilation of the veins and arterioles:
(↓ peripheral resistance & ↓ BP)
(2) decreased heart rate and strength of heart
contraction. (↓ CO & ↓ BP)
28. Role of the baroreceptors in low pressure
• In low pressure the baroreceptors become inactive
• lose inhibitory effect on vasomotor center.
• The vasomotor center then becomes much more
active
• causing the aortic arterial pressure to rise.
29. Function of the baroreceptors during
changes in body posture.
• Immediately on standing, the arterial pressure
in the head and upper part of body tends to
fall and could cause loss of consciousness.
• falling pressure at the baroreceptors elicits an
immediate reflex, resulting in strong
sympathetic discharge & increase pressure.
30. Chemoreceptor reflexes
• Stimulous: O2 lack, CO2 excess, and [H+]
excess
• Chemoreceptors : chemosensitive cells of
------carotid bodies in bifurcation of common
carotid artery)
---- aortic bodies adjacent to aorta.
• Afferent nerve: Hering's nerves and the vagus
nerves
• Center: vasomotor center
• Whenever the arterial pressure falls below a
critical level (80 mm Hg)
• Effect: elevates the arterial pressure.
31. Atrial & pulmonary artery reflexes
• Stimulous: Response to changes in blood volume
(They detect increased pressure )
• Receptors: low-pressure receptors(Atria and the
pulmonary arteries ).
32. Stretch of the atria
release of atrial
natriuretic
peptide (ANP)
reflex dilation of the afferent
arterioles of kidneys
decrease the
reabsorption of water
from renal tubules
Signals to
hypothalamus
glomerular
capillary pressure
rise
decrease
secretion of ADH
increase
filtration of
fluid
increase excretion
of Na+ & fluid in
the urine
Blood pressure become normal
33. Central nervous system ischemic
response
• Stimulous: low blood flow (60 mm Hg and
below). CO2 increases greatly and & stimulates
Vasoconstrictor area.
Vasoconstrictor area respond directly and become
strongly excited
systemic arterial pressure rises highly (upto 250 mm Hg)
34. Central nervous system ischemic response
• This arterial pressure elevation in response
to cerebral ischemia is known as the CNS
ischemic response.
• CNS ischemic response is one of the most
powerful activators of the sympathetic
vasoconstrictor system.
35. Importance of the CNS Ischemic Response
• It is an emergency pressure control system
that acts rapidly and very powerfully when
blood flow to the brain decreases to the lethal
level.
• It is also called the "last ditch stand" pressure
control mechanism.
36. Cushing reaction
A special type of CNS ischemic response that
results from increased pressure of the CSF .
• The Cushing reaction helps to protect vital
centers of the brain when CSF pressure rises
high enough to compress the cerebral
arteries.
37. Increased pressure of the cerebrospinal fluid around
the brain.
it compresses whole brain & the arteries & cuts off the
blood supply to brain
initiates a CNS ischemic response that causes the
arterial pressure to rise.
38. the arterial pressure has risen to a level higher
than CSF pressure,
blood will flow once again into the vessels of brain
& relieve the brain ischemia
40. 1.Renin angiotensin II vasoconstrictor
mechanism
• Renin is a protein enzyme
• Released by the juxtaglomerular (JG) cells of the
kidneys( afferent arteriole
• When the arterial pressure falls too low
• renin raises the arterial pressure
41.
42. Effects of angiotensin II :
1. Vasoconstriction in many areas of the body
2. Decrease excretion of both salt and water by
the kidneys →increase ECF volume →
increase arterial pressure
43. 2.Stress relaxation of vasculature
When blood pressure increases
Blood vessel stretched
the pressure in the vessels falls toward
normal.
45. 3.Capillary fluid shift mechanism
Capillary pressure falls too low
Fluid is absorbed through the capillary
membranes from the tissues to circulation
↑blood volume
↑blood pressure
47. 1.Renal-body fluid mechanism
When body contains too much extracellular
fluid, the blood volume and arterial pressure
rise. The rising pressure cause kidneys to
excrete excess extracellular fluid, thus
returning pressure back normal.
48. 1.Renal-body fluid mechanism
• Pressure diuresis & pressure natriuresis is a
renal mechanism for decreasing arterial
pressure.
• Pressure diuresis :an increase in arterial
pressure can ↑ renal output of water.
• Pressure natriuresis : ↑ the output of salt
49.
50. 2.Renin-angiotensin-aldosterone
mechanism
• Angiotensin II retain salt and water in two
major ways:
I. Acts on the kidneys: decrease excretion
of salt and water .
I. Acts on adrenal glands to secrete
aldosterone: increases salt and water
reabsorption by the kidney tubules.
51. Decrease arterial pressure
Renin secretion from kidney
Renin act on angiotensinogen
Formation of angiotensin I
angiotensin II
Angiotensin converting
enzyme
52. Cont…….
Angiotensin II
Constrict renal arteriol
Decrease renal blood
flow
Stimulate aldosteron
secretion
Increase Na
reabsorption
Decrease pressure in
peritubular capillary Increase ECF
Increase BP
Rapid reabsorption of fluid from
tubule.
53. Hypertension
• Persistence high blood pressure.
• Mean arterial pressure greater than 110
mm Hg (normal 90) is considered to be
hypertensive.
• This diastolic blood pressure> 90 and
systolic pressure>135 mm Hg.
54. Two types:
i.Primary (Essential) Hypertension:
• (90 to 95%) or hypertension of unknown
origin.
• There is a strong hereditary tendency
ii.Secondary Hypertension :
Hypertension due to known causes such as renal
artery stenosis, Adrenal medullary tumor etc.
