3. Regulation of Blood pressure
Dr Farzana Salman

4. Regulation of blood pressure
1. Short-term –Rapidly acting Mechanisms -----Neural control
Counteract fluctuations in blood pressure by altering Total peripheral resistance
2.Intermediate mechanisms----- Hormonal mechanisms
Conunteract fluctuations by altering blood Volume and Peripheral Resistance
3.Long-term Renal regulation
Counteracts fluctuations in blood pressure by altering blood volume through kidneys

5. Short-Term Regulation of Blood Pressure
1. Baroreceptor reflex
Mainly sensitive to sudden change in blood pressure
2. Chemoreceptor reflex
Sensory receptors sensitive to oxygen, carbon dioxide, and pH levels of blood
3. Central Nervous System Ischemic Response
Sensitive to Ischemia of Nervous system due to reduced Mean Arterial pressure
4. Cushing Reaction
Occurs when there is Brain Ischemia due to Increased Intracranial Pressure e.g. due to tumor or increased CSF Pressure

6. Baroreceptor System

9. Baroreceptors
Stretch receptors ,Volume Receptors, Pressure receptors.
Spray type free nerve ending present in the wall of almost all the large blood vessels in chest and neck region
Most abundant in
Carotid sinuses (bifurcation of common carotid artery)
Aortic arch (Arch of aorta)
Baroreceptors project to the vasomotor centre (Nucleus of tractus solitarius)
Vagus and Gloosopharyngeal

10. Nucleus of Tractus solitaries
Inhibition of Vasoconstrictor area
Stimulation of parasympathetic center

11. Response of Baroreceptor to Pressure
No impulses at 0 – 50 mm Hg
Rapid response up to about mm Hg
Baroreceptors respond more to changing pressure than to stationary pressure

12. Baroreceptor Reflex

13. Functions of Baroreceptor-Initiated Reflexes
Baroreceptors taking part in the carotid sinus reflex protect the blood supply to the brain
Baroreceptors taking part in the aortic reflex help maintain adequate blood pressure in the systemic circuit

14. Baroreceptor Reflexes
Baroreceptors protect against short term changes in BP – e.g., standing up too quickly.
Baroreceptors are ineffective in protecting against sustained BP changes as they tend to reset at a new “normal” value.
Baroreceptors are the pressure buffer system

15. Chemoreceptors

16. Chemoreceptor Chemosensitive cells located mainly in:
Carotid bodies
Aortic bodies
Cells sensitive to Hypoxia, CO2 & H+
Small nutrient arteries supply each of these
↓BP→ ↓blood flow → ↓O2 + ↑CO2 + ↑ H+
Excitation →VMC stimulation → ↑BP
Operational at BP below 80 mm Hg

17. Low pressure receptors
In atria and pulmonary artery
Stretch receptors like baroreceptors
Function at much lower pressures
More responsive to volume changes

18. Bainbridge reflex Prevent the damming of blood in atria & veins
↑blood volume → ↑ Venous Return → ↑stretch of atria → ↑ Heart rate
Stretch of SA node → ↑ firing rate SA → ↑heart rate (15 % increase)
Bainbridge reflex (30-40 % increase)
Receptor stretch receptors in atrial wall
Afferent :Vagus nerve - → VMC
Efferent nerves Sympathetic nerves and vagus nerve
↑ Heart Rate
Prevent the damming of blood in atria & veins

20. Cushing Reaction

21. Blood pressure control
Intermediate Mechanisms of
Blood pressure control

22. These include mostly hormonal. mechanisms and takes minutes to
These include mostly hormonal mechanisms and takes minutes to hours for their action to control BP.
Vasopressin (ADH) mechanism
Atrial natriuretic Peptide (ANP)
Stress-relaxation Phenomenon
Capillary Fluid shift mechanism
Abdominal compression reflex
Adrenal Medullary hormone

23. Vasopressin mechanism
ADH is released from the posterior pituitary in response to:
1. Decrease in blood pressure
2. Decreased blood volume
3. Decreased stretch of atria
Increased production of ADH (Vasopressin) causes
-vasoconstriction
-increased reabsorption of water from the kidney tubules

24. ATRIAL NATRIURETIC PEPTIDE
Released from right atria
Atrial volume/ Pressure increases
Decreases reabsorption of sodium in renal tubules
Increases urine output
Decreases blood volume BP decreases

25. Stress-relaxation response
Adjustment of smooth muscles of blood vessels in response to change in blood volume.
Ability of vascular tree to adjust its capacity on available volume of blood.
↑ volume of blood → stress relaxation of the blood vessels→ ↓ B.P
↓ blood volume → reverse stress relaxation (contraction) of the blood vessels → ↑ B.P.

26. Capillary fluid shift mechanism
Movement of fluid from the interstitial spaces into the capillaries in response to a decrease in blood pressure to increase the blood volume and pressure.
Movement of fluid into the interstitial spaces from the capillaries in response to a increase in blood pressure to reduce the blood volume and blood pressure.

27. Abdominal Compression Reflex
Baroreceptor/Chemoreceptor
Nerve signals are transmitted through skeletal nerves to skeletal muscles of the body abdominal muscles.
Muscle contraction compresses all the venous reservoirs of the abdomen
Blood is translocated towards the heart.
Increased quantities of blood is made available for the heart to pump.

28. Nicotine causes intense vasoconstriction.
Adrenal medullary hormones
Stress → causes the release of NE and Epi. NE causes vaso-constriction while both NE and Epinephrine increase HR and SV.
Nicotine causes intense vasoconstriction.
Smoking  nicotine →↑vasoconsriction→↑peripheral resistance →Hypertension  Quick Death