Blood pressure is generated by ventricular contraction and measured in mmHg. It has two components: systolic (maximum pressure) and diastolic (minimum pressure). Blood pressure is regulated through both rapid nervous mechanisms like baroreceptor and chemoreceptor reflexes, and longer-term mechanisms involving blood volume control. Baroreceptors detect changes in blood pressure and stimulate the vasomotor center to increase or decrease sympathetic outflow and heart rate. Chemoreceptors detect chemical changes in blood and stimulate respiratory and cardiovascular responses during hypoxia or hemorrhage.

1. Blood Pressure

2. Blood Pressure
 Pressure is force on an area
 If there is a fluid in a container
we measure the pressure
on the surface area of the container.
 That pressure is related to
the number of particles that crash into
that surface area per unit time

3. Blood Pressure
 Pressure in the reservoir is easy
 Since there is no net flow, the force on all sides of the
reservoir is equal. Thus, measuring pressure anywhere
measures pressure.

4. Blood Pressure
 Pressure in a pipe is hard
 Since there is net flow, there are fewer particles hitting the
inflow area than the wall and more particles hitting the
outflow area than the wall.

5. Blood Pressure
 There are two types of pressure:
 Static Pressure
 Pressure from the blood distending the vessel against the
vascular smooth muscle
 LaPlace: T=Pr (tension, pressure, radius)

6. Blood Pressure
 There are two types of pressure
 Dynamic Pressure
 Pressure from the movement of particles along the blood
stream
 Pitot: P=ρv2
/2 (density, velocity)

7. Blood Pressure
in a tube or a blood vessel the total energy—the sum of the kinetic energy of flow and the
potential energy—is constant (Bernoulli's principle).
According to the principle, the greater the velocity of flow in a vessel, the lower the lateral
pressure distending its walls. When a vessel is narrowed, the velocity of flow in the narrowed
portion increases and in the distending pressure decreases. Therefore, when a vessel is
narrowed by a pathologic process such as an atherosclerotic plaque, the lateral pressure at the
constriction is decreased and the narrowing tends to maintain itself.

8. Bernoulli Pressure Lowering
The linear drop in fluid pressure is according to Poiseuille's law, but the constriction
produces an extra drop in pressure according to the BernoulliPrinciple
The liquid column height is a measure of the fluid pressure at that point in the flow
tube. The vertical tubes act as manometers. The manometers show that the pressure
is lowered at the constriction relative to what it would have been in a uniform tube.
The pressure that drives the fluid through the tube is the static fluid pressure at the
bottom of the reservoir. The resistance to flow represented by the tube causes a drop
in pressure as you proceed along the tube.

9. Blood Pressure
 The Total Pressure is the sum of the static and
dynamic pressures.
 This is much like Total Energy is the sum of the
kinetic and potential energies.

10. Blood Pressure
 From a practical standpoint…
 THE blood pressure is what we measure if we stick a
catheter into the lumen of a vessel and measure the
outflow pressure.

11. If a cannula is inserted into an artery, the arterial pressure can be measured
directly with a mercury manometer

12. Arterial Blood Pressure (BP)
= The lateral pressure force generated by the pumping
action of the heart on the wall of aorta & arterial blood
vessels per unit area.
■ Measured in (mmHg), & sometimes in (cmH2O), where
1 mmHg = 1.36 cmH2O.
■ Of 2 components:
 systolic … (= max press reached) = 110-130 mmHg.
 diastolic … (= min press reached) = 70-90 mmHg.
In normal adult ≈ 120/80 mmHg.

13. Arterial Blood Pressure (continued)
■ Diastolic pressure is more important, because diastolic
period is longer than the systolic period in the cardiac
cycle.
■ Pulse pressure = Systolic BP – Diastolic BP.
■ Mean arterial pressure = Diastolic BP + 1/3 Pulse
press.
In normal adult ≈ 120/80 mmHg.

15. Blood Pressure:Blood Pressure:
Generated by Ventricular ContractionGenerated by Ventricular Contraction

16. Formation of the blood
pressure:
 （ 4 ） Elasticity of Windkessel vessel
 ① diastolic blood pressure
 ② continuous blood flow in diastole
 ③ buffering blood pressure

19. Blood Pressure (BP): Measurements
Figure 15-7: Measurement of arterial blood pressure

20. Factors Controlling MAP :
The Driving Pressure for Blood Flow
Figure 15-10: Factors that influence mean arterial pressure

21. Factors affecting ABP:
■ Sex … M > F …due to hormones/ equal at menopause.
■ Age … Elderly > children …due to atherosclerosis.
■ Emotions …↑ due to secretion of adrenaline &
noradrenaline.
■ Exercise …↑ due to ↑ venous return.
■ Hormones …↑ (e.g. Adrenaline, noradrenaline, thyroid H).
■ Gravity … ↑ Lower limbs > upper limbs.
■ Race … Orientals > Westerns … ? dietry factors, or
weather.
■ Sleep … ↓ due to ↓ venous return.
■ Pregnancy …↑ due to ↑ metabolism.

23. Effects of gravity on arterial and venous pressures.
Each cm of distance produces a 0.77 mmHg change.
Sphincters protect
capillaries
VENOUS PUMP keeps PV < 25 mm Hg
Veins Arteries
190 mm Hg
100 mm Hg0

24. Factors determining ABP:
Blood Pressure = Cardiac Output X Peripheral
Resistance
(BP) (CO)
Flow
(PR)
Diameter of
arterioles
■ BP depends on:
1. Cardiac output ⇒ CO = SV X HR.
2. Peripheral resistance.
3. Blood volume.

29. Regulation of Arterial Blood Pressure

30. Regulation of ABP:
■ Maintaining B.P. is important to ensure a steady blood
flow (perfusion) to tissues.
■ B.P. is regulated neurally through centers in
medulla
oblongata:
1. Vasomotor Center (V.M.C.), or (pressor area):
⇒ Sympathetic fibers.
2. Cardiac Inhibitory Center (C.I.C.), or (depressor area):
⇒ Parasympathetic fibers
(vagus).

31. Regulation of ABP (continued)
cardiac control centers in medulla
oblongata
1. Cardiacaccelerator
center
(V.M.C)
2. Cardiacinhibitory
center
(C.I.C)
Sympathetic n. fibers Parasympathetic n. fibers
 Regulatory mechanisms depend on:
a. Fast acting reflexes:
Concerned by controlling CO (SV, HR), & PR.
b. Long-term mechanism:
Concerned mainly by regulating the blood volume.

32. Regulation of Blood Pressure
Mechanisms for controlling MAP ―
(a) Rapid/Short term BP Control/Nervous
Mechanisms
(b) Intermediate Bp Control Mechanisms
(c) Long Term BP Control mechanisms

33. Rapid / Short term / Nervous
Mechanisms for controlling BP
Charactristics -
 Act rapidly - within secs. to few mts.
 Lasts for - few hrs. to few days
 Prevents - sudden rise or fall in BP
 Operates through -
(a) Baroreceptors
(b) Chemoreceptors
(c) CNS Ischemic Response

34. Baroreceptors
 Def. - Stretch receptors,mechanoreceptor
 Present in - walls of heart & large blood vesels
 Structure - highly branched myelinated, knobby nerve
endings
 Stimulated by – stretching of art. wall
High BP stretching discharge freq.→ → ↑

36. Types of Baroreceptors
1. High Pressure baroreceptors –
Located at - carotid sinus Imp.
- aortic arch baroreceptors
- wall of LV
- root of Rt. Subclavian A.
2. Low Pressure baroreceptors –
Located at - RA, LA,
- Entrance of SVC,IVC,
- Pulm. trunk, pulm.A. & Veins

37. 1. Baroreceptors reflex:
■ Baroreceptors are receptors found in carotid sinus
&
aortic arch.
■ Are stimulated by changes in BP.↑
BP
+ Baroreceptors
= V.M.C ++ C.I.C
= Sympathetic
Vasodilatation & ↓ TPR
+ Parasympathetic
Slowing of SA node (↓ HR)
& ↓ CO

38. Baroreceptor Reflex
 Normally – Baroreceptors discharge at low rate
 Discharge rate - at high BP & at low BP↑ ↓
 Below 60 mm Hg – no discharge at all
 Above 160 mm Hg – no further rise in discharge
 i.e. baroreceptors are sensitive in the range of 60 -
160 mm Hg.
 Maximally sensitive at MAP 95 mm Hg.
 Respond more to rapidly changing BP than to a
stationary high or low levels of BP.

40. Baroreceptor Reflex
 Baroreceptor resetting – Baroreceptors reset
themselves in 1-2 days, to whatever they are
exposed.
 So they have no role in long term regulation of BP
(only in short term control)
 Applied – Carotid sinus massage to reduce HR in
PAT (vagally mediated slowing of HR)

43. Baroreceptor Reflex
Atrial stretch receptors & pulm. Baroreceptors
 Present in – atria, pulm trunk & its divisions
 Imp. Role in reducing arterial pr. Changes due to
changes in blood vol.
all receptors art. Baroreceptors all receptors
intact denervated, denervated
atrial receptors intact
↑ BV BP BP BP→ ↑ ↑↑ ↑↑↑
atrial receptors make total reflex system much more potent for control
of MAP.

44. Baroreceptor Reflex
Atrial stretch receptors & pulm. Baroreceptors
mechanism
↑BV venous return discharge from atrial― ↑ ― ↑
receptors
↓ BP

45. MOTOR CORTEX
HYPOTHALAMUS
VASOMOTOR CENTER
PRESSOR AREA
DEPRESSOR AREA
CARDIOINHIBITORY AREA
Vagus
HEART
Arterioles
Veins
Adrenal
Medulla
Baroreceptors
Carotid Sinus
Aortic Arch
Chemoreceptors
Carotid Bodies
Aortic Bodies
Bainbridge Reflex (↑ Heart Rate)
Atrial Receptors Volume Reflex (↑ Urinary OUTPUT)
a. ↓ Vascular Sympathetic Tone
b. ↓ ADH Secretion
c. ↓ Aldosterone Secretion
Chemosensitive Area
Glossopharyngeal
Nerve
Sympathetic
Nervous
System

46. Chemoreceptor Reflex
 Respond to - ↓ Po2, ↑ Pco2 ,↑ H+ conc.
 Present in – Carotid and Aortic Bodies.
 N. Supply – Sinus & Aortic N.
 Concerned mainly withResp.Regulation
 Discharge at low freq.in Normal person.
 No role in BP regulation if >60 mm.Hg.

47. Role of Chemoreceptors
 In Hypoxia & Hypotension(Hemorrhage)
Chemoreceptors stimulated (if BP <60mm.Hg.)
Hyper ventillation VMC +
↑ Force of contr. SV & SBP PR DBP→ ↑ ↑ → ↑

48. 2. Chemoreceptors reflex:
■ Chemoreceptors are receptors found in carotid &
aortic bodies.
■ Are stimulated by chemical changes in blood mainly
hypoxia (↓ O2), hypercapnia (↑ CO2), & pH changes.
↓
BP
+ Chemoreceptors
++ V.M.C = C.I.C
+ Sympathetic
Vasoconstrictio
n
& ↑ TPR
= Parasympathetic
↑ HR
Haemorrhage
Hypoxia
+ Adrenal
medulla

49. CNS Ischemic Response
Seen if BP falls <60mm.Hg. –max. at 15-20 mm. Hg.
↓ Blood flow to VMC Ischemia of VMC→
VMC Stimulated Accumulation of CO2
& Lactic acid
vasoconstriction
& Inotropic action
BP
It is an Emergency art. Pressure control system.
Irreversible neuronal damage in 3-10 mts.

50. Intermdiate BP Control Mechanisms
CHARACERSTICS
 Becomes active after several minutes
 Remain active for few days to few
weeks
 By altering Blood Volume they control
BP

51. Stress Relaxation
ReverseStress
Relaxation
↑ Fluid load BP BP→ ↑ ↓
Stretching of vessels
↑ tone of smooth m. tone of smooth m.↓
Reflex in tone Reflex in tone↓ ↑
↓ BP BP↑

52. Capillary Fluid Shift
Mechanism
↑ BP BP↓
↑ mean cap. Pressure mean cap. Pressure↓
Fluid enter into IS Comp. Fluid enter into vessels
↓ BV BV↑
↓ BP BP↑
2 times more effective than barorecepters but slow.

53. Regulation of Blood Volume:
■ A long-term regulatory mechanism.
■ Mainly renal:
1. Renin-Angiotensin System.
2. Anti-diuretic hormone (ADH), or
vasopressin.
3. Low-pressure volume receptors.

54. 1. Renin-Angiotensin System:
■ Most important mechanism for Na+
retention in
order to maintain the blood volume.
■ Any drop of renal blood flow &/or ↓ Na+
, will
stimulate volume receptors found in juxtaglomerular
apparatus of the kidneys to secrete Renin which
will
act on the Angiotensin System leading to
production
of aldosterone.

55. Renin – Angiotensin Vasoconstrictor
Mechanism
 Main function –
(i) Control of BP
(ii)Regulation of ECF Volume
Renin – Secreted from – JG Cells
Stimulus – Low BP
Function – convert ATG to AT-I
ACE
AT-I → AT-II (in lungs endo cells)

56. Renin
Aldosterone
Adrenal
cortex
Corticosterone
Angiotensinogen
(Lungs)
↓ renal blood flow &/or ↓ Na+
++ Juxtaglomerular apparatus of kidneys
(considered volume receptors)
Angiotensin I
Converting
enzymes
Angiotensin II
(powerful
vasoconstrictor)
Angiotensin III
(powerful
vasoconstrictor)
• Renin-Angiotensin System:
N.B. Aldosterone is the main regulator of Na+
retention.

58. Functions of Angiotensin-II
 Vasoconstriction BP→ ↑
 Na+ & Water retention by Kidney BP→ ↑
 Stimulate thirst BV BP→ ↑ → ↑

59. Functions of Angiotensin-II

66. 2. Anti-diuretic hormone (ADH), or
vasopressin:
■ Hypovolemia & dehydration will stimulate the
osmoreceptors in the hypothalamus, which will lead
to release of ADH from posterior pituitary gland.
■ ADH will cause water reabsorption at kidney
tubules.

68. 3. Low-pressure volume receptors:
■ Atrial natriuritic peptide (ANP) hormone, is secreted
from the wall of right atrium to regulate Na+
excretion
in order to maintain blood volume.

70. 3. Other Vasomotor Reflexes:
1. Atrial stretch receptor reflex:
↑ Venous Return ⇒ ++ atrial stretch receptors ⇒
reflex vasodilatation & ↓ BP.
2. Thermoreceptors: (in skin/or hypothalamus)
 Exposure to heat ⇒ vasodilatation.
 Exposure to cold ⇒ vasoconstriction.
3. Pulmonary receptors:
Lung inflation ⇒ vasoconstriction.