1. Cardiovascular system- L6
Faisal I. Mohammed, MD, PhD
Yanal A. Shafagoj MD, PhD
University of Jordan

2. The peripheral resistance:
It is the resistance to blood flow through a vessel caused by friction between the moving fluid and the vascular wall.
Most of the peripheral resistance to blood flow occurs in arterioles ( 50%) and capillaries ( 25%)

3. Velocity of Blood Flow is Greatest in the Aorta
Velocity of Blood Flow = Blood Flow
Cross sectional area
Aorta >Arterioles > Small veins >Capillaries 3

4. Hemodynamic laws Ohm’s law: F =∆P/R F = Flow, ∆P = Change in Pressure,
R = Resistance
CO = cardiac output, MAP = mean arterial pressure, TPR = total peripheral resistance. Since Rt. Atrial pressure = 0 then

5. Hemodynamic laws… cont
Poiseuille’s law
F =  ∆Pr4/ 8L
F = flow,
∆P = change in pressure
r = radius of the vessel
(eta) = viscosity
L = length of the vessel
Then Resistance, R = 8L / r4

6. Effect of Vessel Diameter on Blood Flow
P= 100
mm Hg 6 6

7. How Would a Decrease in Vascular Resistance Affect Blood Flow?
FLOW = P
RESISTANCE
Conversely,
FLOW = P
RESISTANCE 7

8. Poiseuille’s law …cont

9. Poiseuille’s law …cont

10. Blood Pressure Regulation10

11. Sphygmomanometer 11

12. Measurement of Systolic and Diastolic Pressures
Auscultatory method is the most commonly used method for measuring systolic and diastolic pressures.
When cuff pressure reaches systolic pressure, one begins to hear tapping sounds in the antecubital artery; as the cuff pressure reaches diastolic pressure, one hears muffled sounds and then Korotkoff sounds disappear.
Mean arterial pressure can be estimated by adding 40% of systolic pressure to 60% of diastolic pressure. 12 12

13. Blood Pressure Regulation
What regulation means…narrow fluctuations
What are your tools? …HR & SV& radius of art& blood volume
Mean Arterial Pressure (MAP) = 1/3 systolic pressure + 2/3 diastolic pressure
MAP= Diastolic Pressure+1/3 Pulse Pressure
Why we need to keep ABP within narrow range.
What do we man by ABP regulation
What are the tools we are going to use to bring ABP back to normal 13

14. Mean Arterial Pressure
Mean ABP is closer to Pd rather than to Ps…..WHY? 14 14

15. Short term regulation of BP
Baroreceptors or pressoreceptos (High pressure)
Carotid and Aortic Baroreceptors…very fast response 15

16. Short term regulation of BP cont…
1. Baroreceptors or pressoreceptos (stretch receptors) 16

17. The Vasomotor Center (VMC)
The VMC transmits impulses downward through the cord to almost all blood vessels.
VMC is located bilaterally in the reticular substance of the medulla and the lower third of the pons.
The VMC is composed of a vasoconstrictor area, vasodilator area, and sensory area. 17

18. Arterial Baroreceptor Reflex
Important in short term regulation of arterial pressure.
Reflex is initiated by stretch receptors called baroreceptors or pressoreceptors located in the walls of the large systemic arteries.
A rise in pressure stretches baroreceptors and causes them to transmit signals to the vasomotor center (VMC) and feedback signals are sent via the automonic nervous system to the circulation to reduce arterial blood pressure back to normal.
Blood
Pressure
Arterial
Baroreceptors
Vasomotor
Center 18

19. Baroreceptor mechanism19

20. 20

21. Effect of Parasympathetic and Sympathetic Nervous Systems on Factors that Influence the Mean Arterial Pressure 21

22. Short term regulation of BP cont…
Chemoreceptors 22

23. Carotid and Aortic Chemoreceptors
Chemoreceptors are chemosensitive cells sensitive to oxygen lack, CO2 excess, or H ion excess.
Chemoreceptors are located in carotid bodies near the carotid bifurcation and on the arch of the aorta.
Activation of chemosensitive receptors results in excitation of the vasomotor center. O2
CO2 pH
Chemoreceptors
VMC
Sympathetic
activity BP 23

24. Nervous Control of the Heart24

25. Intermediate / Long term Regulation of BP
1. Epinephrine – Adrenal medulla system
works as intermediate term needs  10 min to work…. causes vasoconstriction
2. ADH (vasopressin) system needs  30 min to work causes vasoconstriction and water retension 25

26. Long term Regulation of BP…cont
3. Renin-Angiotensin-Aldosterone system  1 hour to be effective
Angiotensinogen (14 a.a peptide) converted into Angiotensin I (10 a.a peptide) by Renin that come from afferent arteriolar cell, the angiotensin I is converted into angiotensin II (8 a.a peptide) by Angiotensin converting enzyme mainly in the lungs.
Angiotensin II (A II) is very potent vasoconstrictor. AII also stimulates aldosterone synthesis and secretion from the adrenal coretx (Zona glomerulosa), aldosterone increases Na+ reabsorption from the renal nephrone and so water.
AII is also a positive inotropic agent 26

27. Juxtaglomerular Apparatus

28. Renin-Angiotensin System
Renin is synthesized and stored in modified smooth muscle cells in afferent arterioles of the kidney.
Renin is released in response to a fall in pressure.
Renin acts on a substance called angiotensinogen to form a peptide called angiotensin I.
AI is converted to AII by a converting enzyme located in the endothelial cells in the pulmonary circulation. 28

29. Long term Regulation of BP …cont
4. Atrail Natriuretic peptide (ANP): An 28 a.a peptide released mainly from the Rt. Atrium in response to stretch. It causes increase in GFR and thus, increase Na+ and water excretion . Its concentration decreases when BP is low and its concentration increases if BP is high, mainly due volume overload 29

30. University of Jordan 30 30 30