Cardiovascular Physiology

1. Cardiovascular Physiology Qiang XIA (夏强), PhD Department of Physiology Room C518, Block C, Research Building, School of Medicine Tel: 88208252 Email: xiaqiang@zju.edu.cn

2. Regulation of Cardiovascular Activities • Lecture Outline • Nervous Regulation • Humoral Regulation • Autoregulation

3. Nervous Regulation

4. Innervation of cardiovascular system

5. Nervous regulation of the circulation

6. Cardiac mechanisms of norepinephrine

7. Mechanisms of norepinephrine —increase Na+ & Ca2+ permeability • If , phase 4 spontaneous depolarization, autorhythmicity  • Ca2+ influx , phase 0 amplitude & velocity , conductivity  • Ca2+ influx , Ca2+ release , [Ca2+ ]i , contractility 

8. Asymmetrical innervation of sympathetic nerve

9. Cardiac mechanisms of acetylcholine

10. Mechanisms of acetylcholine • —increase K+ & decrease Ca2+ permeability • K+ outward , |MRP|, phase 4 spontaneous depolarization , autorhythmicity  • Inhibition of Ca2+ channel, phase 0 amplitude & velocity , conductivity  • Ca2+ influx , [Ca2+ ]i , contractility 

11. Cardiac effect of parasympathetic stimulation

12. Interaction of sympathetic and parasympathetic nerves

13. Predominance of autonomic nerves

14. Cardiovascular Center A collection of functionally similar neurons that help to regulate HR, SV, and blood vessel tone

15. Vasomotor center Located bilaterally mainly in the reticular substance of the medulla and of the lower third of the pons • Vasoconstrictor area • Vasodilator area • Cardioinhibitor area – dorsal nuclei of the vagus nerves and ambiguous nucleus • Sensory area – tractus solitarius

16. Vasomotor center

17. Higher cardiovascular centers • Reticular substance of the pons • Mesencephalon • Diencephalon • Hypothalamus • Cerebral cortex • Cerebellum

18. Baroreceptor Reflexes • Arterial baroreceptors • Carotid sinus receptor • Aortic arch receptor • Afferent nerves (Buffer nerves) • Cardiovascular center: medulla • Efferent nerves: cardiac sympathetic nerve, sympathetic constrictor nerve, vagus nerve • Effector: heart & blood vessels

19. Baroreceptor neurons function as sensors in the homeostatic maintenance of MAP by constantly monitoring pressure in the aortic arch and carotid sinuses.

21. Characteristics of baroreceptors: • Sensitive to stretching of the vessel walls • Proportional firing rate to increased stretching • Responding to pressures ranging from 60-180 mmHg • Receptors within the aortic arch are less sensitive than the carotid sinus receptors

23. The action potential frequency in baroreceptor neurons is represented here as being directly proportional to MAP.

24. i.e., MAP is above homeostatic set point i.e., reduce cardiac output Baroreceptor neurons deliver MAP information to the medulla oblongata’s cardiovascular control center (CVCC); the CVCC determines autonomic output to the heart.

25. Reflex pathway

26. Click here to play the Baroreceptor Reflex Control of Blood Pressure Flash Animation

27. Typical carotid sinus reflex

28. Physiological Significance Maintaining relatively constant arterial pressure, reducing the variation in arterial pressure

29. Other Cardiovascular Reflexes Click here to play the Chemoreceptor Reflex Control of Blood Pressure Flash Animation

30. Humoral Regulation • Vasoconstrictor agents • Vasodilator agents

31. Renin-angiotensin system

32. Juxtaglomerular cell Renin

33. Physiological effects of angiotensin II • Constricts resistance vessels • Acts upon the adrenal cortex to release aldosterone • Stimulates the release of vasopressin • Facilitates norepinephrine release from sympathetic nerve endings • Stimulates thirst centers within the brain

34. Epinephrine & Norepinephrine • Sources Epinephrine---- adrenal medulla Norepinephrine---- adrenal medulla sympathetic nerves

35. Catecholamines Norepinephrine Epinephrine

36. Effects Epinephrine Norepinephrine Receptor a-adrenoceptor ++ +++ b-adrenoceptor ++ + Heart heart rate + + (in vitro)－ (in vivo) cardiac output +++ ± Vessels constriction (skin, visceral) + +++ relaxation (SM, liver) － +++ total peripheral resistance ± +++ Blood pressure systolic +++ +++ diastolic ± ++ MAP + ++ Clinical application positive inotropic pressor agent agent

38. Vasopressin (antidiuretic hormone, ADH)

40. Endothelium-derived vasoactive substances • Vasodilator factors • PGI2--prostacyclin • EDRF, NO--endothelium-derived relaxing factor, nitric oxide • EDHF--endothelium-dependent hyperpolarizing factor • Vasoconstrictor factors • Endothelin

41. Atrial natriuretic peptide (ANP) • Produces natriuresis and diuresis • Decreases renin release • Reduces total peripheral resistance via vasodilatation • Decreases heart rate, cardiac output

42. Autoregulation Definition: Intrinsic ability of an organ to maintain a constant blood flow despite changes in perfusion pressure, independent of any neural or humoral influences

45. The End.