regulation of ABP

1. REGULATION OF ARTERIAL
BLOOD PRESSURE

2. 1-Medulla Centers
1. Vasomotor Center (V.M.C.), or (pressor area):
 Sympathetic fibers.
2. Cardiac Inhibitory Center (C.I.C.), or (depressor area):
 Parasympathetic fibers (vagus).
2- Hypothalamic control
1- Anterior hypothalamus N.---
Hypotension and bardycardia
2- Posterior hypothalamus
Hypertension and tachycardia
3- ADH secreted also affects BP
3- Cortical control
Frontal cortex – sympathetic vasodilator
Motor & Pre motor- increase BP
B.P. is controlled neurally

3.  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.

4. A. Rapid blood pressure control
mechanism,
B. Intermediate blood pressure
control mechanisms and
C. Long-term blood pressure control
mechanisms.

5. 1- Rapid / Short term / Nervous Mechanisms
a - Characteristics -
 Act rapidly - within secs. to few mts.
 Lasts for - few hrs. to few days
 Prevents - sudden rise or fall in BP
b - Operates through -
(a) Baroreceptors
(b) Chemoreceptors
(c) CNS Ischemic Response
c- Mediated through
1. Baroreceptor reflexes
2. Chemo receptor reflexes
3. Cerebral ischaemic response (Cushing Reflex)

7. a) Baroreceptors Reflex Mechanism- life
saving reflex (Sino-aortic reflex)
Baroreceptors-
Stretch receptors / mechanoreceptor that
detect change in pressure.
Structure - highly branched myelinated, knobby nerve
endings
Present in - walls of heart & large blood vessels

8. 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

9. Baroreceptors - properties
 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.

10. 1- Location of receptors for Baroreceptor reflex

11. 2- Afferent Pathways Baroreceptor reflex
3-Centre for Baroreceptor reflex
Vasomotor Centre & Cardiac Inhibitory Centre
4- Efferent's are
sympathetic fibers and vagus n. From NTS

13. Baroreceptors Reflex

14. 5- Response-
Response Depends on –
1- Nature of change of blood
pressure
2- Degree & rate of change of
blood pressure

16. Net effect
 Peripheral resistance
 Myocardial contractility
 Heart rate (Bradycardia)
 Fall in BP
Vasodilatation &  TPR
Slowing of SA
node ( HR)
&  CO

17. BP BARO RECEPTOR REFLEXES

Stimulation of baroreceptors
(carotid sinus and aortic arch)

Tractus solitarius stimulation
Inhibition of VMC Stimulation of CIC
(nucleus ambiguous)
SNS Vagus
 Symp tone Vagal tone 
Blood Vessels Heart Rate Decreased
- Vasodilatation
- Venodilatation Bradycardia
BP
MAREY’S REFLEXES

18. Short-term Regulation Of Falling Blood Pressure
Baroreceptors inhibited
Decreased impulses to the brain
Decrease stimulation of NTS
Decreased parasympathetic activity,
increased sympathetic activity
Effects
Heart
increased heart rate and
increased contractility
Vessels
increased vasoconstriction
Adrenal gland
release of epinephrine and
norepinephrine which enhance heart
rate
Contractility and vasoconstriction
Increased blood pressure

22. Pressure Buffer Mechanism ,Nerves are buffer N.
•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)

23. Atrial stretch receptors & pulm. Baroreceptors
 Present in – atria, pulmonary trunk & its divisions
 Imp. Role in reducing arterial pressure
 Changes due to changes in blood volume
Atrial stretch Reflex
Venous Return
Increase atrial filling
Stimulated type-B receptors
Inhibition Sympathetic stimulation
Renal Vasodilatation, Decrease BP ( Vasopressin & ANP)
but Increase HR
pulmonary stretch Reflex
Stimulated
Pulmo. Arterial pressure
Bardycardia & Hypotension

24. 2. Chemoreceptor Reflex Mechanism
Chemoreceptor are receptors found in carotid & aortic
bodies.
■ Are stimulated by chemical changes in blood mainly
hypoxia ( O2), hypercapnia ( CO2), & pH changes.
 N. Supply – Sinus & Aortic N.
 Concerned mainly with
Resp.Regulation
 Discharge at low freq. in Normal
person.
 BP regulation if 40 to 70 mmHg.

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

26. pO2 and
pH 
pCO2 
Stimulation of
vasomotor
center
CO  HR vasoconstriction
BP (speeding return of
blood to the heart and
lungs)

29. - Special type of CNS Ischemic Response
Increased pressure of cerebrospinal fluid (cranial vault)
Increase intracranial tension
Compress whole brain & arteries in the brain
Cuts off blood supply to brain
CNS Ischemic Response initiated & arterial pressure rises
Relieve brain ischemia

30. Severe decrease blood flow to brain (Brain Tumors)
Cerebral hypoxia
Vasomotor center stimulated – causes powerful
vasoconstriction
( INCREASE SYMPATHETIC DISCHARGE – Norepinephrine)
Increase blood pressure & blood flow(Cushing’s reflex)
 BP with reflex
bradycardia

31. CAPILLARY FLUID SHIFT MECHANISM
STRESS RELAXATION
REVERSE STRESS RELAXATION

33. 4/15/2018
Delayed or Intermediate Mechanism
Capillary fluid shift phenomenon:
Whenever there is an increase in blood pressure
more fluid is filtered through the capillary wall into
the interstitial space.
Blood volume decreases
and so BP itself decreases.
Reverse changes take
place when BP falls.

34. 4/15/2018
Stress Relaxation Phenomenon:
BP
Blood vessels are stretched
Stress relaxation
Increased capacity
Decreased effective
blood volume
BP decreased
relaxation
BP

35. STRESS RELAXATION
MECHANISM
 B.P in blood storage organs
B.P vasodialatation
REVERSE STRESS
RELAXATION
B.P vasoconstriction perfusion .

36. 4/15/2018
Long term Regulatory Mechanisms:
All the mechanisms
that tend to alter the
blood volume
participate in
Long term regulatory
mechanisms

37. RENAL MECHANISM FOR
REGULATION OF BLOOD PRESSURE
 Long term regulation of Arterial B.P
 Renal Mechanism works even when nervous
mechanism adapts to the new pressure.
 Two ways of regulation of B.P
1. By regulation of ECF volume (ANP &ADH)
2. Through reninangiotensin mechanism.

38. 1. By regulation of ECF volume
Increase
in B.P
Atrial
Pressure
excretion of water
(pressure diuresis)
excretion of salts (sodium)
(Pressure Natriuresis)
decrease in ECF
Volume
decrease in blood
volume
Blood pressure
restored
Role of ANP

39. Decrease in Water reabsorption Increase in ECF
B.P from & Blood
renal-tubules volumes
Blood pressure Increase in cardiac
Restored output
Role of ADH

40. „2- THROUGH RENIN-ANGIOTENSIN
MECHANISM
Renin along with Angiotensin forms Renin-
Angiotensin system, which is a hormone
system that plays an important role in the
maintenance of blood pressure

41. Renin –Angiotensin System
B.P blood flow to the kidney.
This results is ischaemic kidney.
Renin is released from J.G. cells
Renin-J.G Cells of Kidney
Angiotensinogen -Liver Cells
ACE -Lungs

42. Renin
Angiotensinogen Angiotensin I
ACE
Angiotensin I Angiotensin II
ACE - Angiotensin Converting Enzyme
( Present in the lungs)

43. 4/15/2018
ACTION OF ANGIOTENSIN - II
1. Vasoconstriction
2. Aldosterone secretion
3. Stimulation of the
thirst centre
4. Increased absorption
of Na+ from PCT by
direct effect. As a result
B.V  C.O  BP 