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Special Circulation

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  1. Special Circulation XIA Qiang (夏强), PhD Department of Physiology School of Medicine Tel: 88206861 Email: xiaqiang@zju.edu.cn

  2. System Overview • The blood flow to organs depends on • ⒈ The difference between aortic pressure and • central venous pressure • ⒉ The diastolic and systolic state of blood vessel • in this organ • The blood flow to individual organs must vary to meet the needs of the particular organ, as well as of the whole body

  3. Blood pressure Cardiac output Local blood flow Autoregulation in the vessels of heart, brain, skeletal muscle, and kidneys Local control in the vessels of heart, brain, skeletal muscle during exercise System Overview Neural, myogenic, metabolic, and endothelial mechanisms control regional blood flow • Neural mechanism: • Autonomic nervous system • (sympathetic division) • Myogenic mechanism: • Metabolic mechanism: PO2, pH, etc. • Endothelial mechanism: NO, EDHF, PGI2, ET, EDCF, etc. Relaxing or contracting VSMCs

  4. System Overview Sophisticated feedback, Mechanical forces, etc. • Neural mechanism: • Autonomic nervous system • (sympathetic division) • Myogenic mechanism: • Metabolic mechanism: PO2, pH, etc. • Endothelial mechanism: NO, EDHF, PGI2, ET, EDCF, etc. Local circulation Resting vasomotor tone Vasomotor control Electrical and chemical signalling VSMCs ECs Gap junction

  5. Coronary circulation冠脉循环

  6. Coronary circulation Heart: view from front

  7. Coronary circulation Heart: view from diaphragm

  8. Coronarycirculation • Coronary circulation receives 5%of the resting cardiac output from the left heart, and mostly returns it to the right heart • Heart muscle consumes as much O2 as does equal mass of SM during vigorous exercise • Heart tissue extracts maximal amount of O2 at rest • The only way to increase of energy is by increasing blood flow • Autoregulation: relative stable flow between 70 and more than 150mmHg

  9. Diagram of the epicardial, intramuscular, and subendocardial coronary vasculature • The branches of left and right coronary artery often penetrate myocardium in direction perpendicular to cardiac surface • Myocardial capillary distribution is extremely abundance • Collateral coincidence between coronary is less

  10. Extravascular compression impairs coronary blood flow during systole Isovolumic contraction phase ↓↓→ rapid ejection phase ↑→reduced ejection phase ↓→ diastolic phase ↑ (isovolumic relaxation phase↑↑)

  11. Myocardial blood flow parallels myocardial metabolism • Metabolic signals are the principal determinants of O2 delivery to myocardium • Resting: 60-80 ml/100g/min • Exercise: 300-400 ml/100g/min • O2 consumption 7-9 ml/100g/min is about 65-70% of O2 extraction • Adenosine activates purinoceptors to induce vasodilation by lowing [Ca2+]i

  12. Local metabolic changes that cause vasodilation in the systemic circulation

  13. Notes • Although sympathetic stimulation directly constricts coronary vessels, accompanying metabolic effects predominate, producing an overall vasodilation • Collateral vessel growth can provide blood flow to ischemic regions • Vasodilator drugs may comprise myocardial flow through “coronary steal”

  14. Collateral vessel

  15. Coronary steal

  16. Cerebral circulation The major arteries of the brain. (A) Ventral view, Lateral (B) and (C) midsagittal views, (D) Idealized frontal section circle of Willis

  17. Cerebral circulation Blood supply of the three subdivisions of the brainstem. (A) Diagram of major supply. (B) Sections through different levels of the brainstem indicating the territory supplied by each of the major brainstem arteries

  18. Cerebral circulation • Brain weight: 2% of body weight • Blood flow: 15% of cardiac output at rest • Brain is the least tolerant of ischemia • Arteries: internal carotid arteries, vertebral arteries • Brain lacks lymphatic vessels

  19. 1. 脑循环特点 Changes in regional blood flow • SENS 1: Low-intensity electrical stimulation of hand • SENS 2:High-intensity electrical stimulation of hand

  20. Cerebral Blood Flow • Neural control: • Sympathetic nerve • Parasympathetic nerve • Sensory nerve: “axon reflex” • Metabolic control: • PO2 • PCO2 • pH • Myogenic control

  21. Autoregulation • Nearly constant blood flow: perfusion pressure from 70 to 150 mmHg

  22. Cushing Reflex • Cushing reflex is a physiological nervous system response to increased intracranial pressure (ICP) • Cushing's triad: • Hypertension • Bradycardia • irregular respiration • It was first described in detail by American neurosurgeon Harvey Cushing in 1902.

  23. The End.