1. Department of Physiology
Special Circulation
XIA Qiang (夏强), PhD
Department of Physiology
School of Medicine
Tel: ,

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. 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.
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
Relaxing or contracting VSMCs

4. Sophisticated feedback,
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. Coronary circulation
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: ml/100g/min
Exercise: ml/100g/min
O2 consumption 7-9 ml/100g/min is about % of O2 extraction
Adenosine activates purinoceptors to induce vasodilation by lowing [Ca2+]i

12. Local metabolic changes that cause vasodilation in the systemic circulation
MECHANISM
↓ PO2
↓ [ATP]i, adenosine release
↑ PCO2
↓ pHo
↓ pH
↑ [K+]o
Depolarization → opens voltage-gated Ca2+ channels
↑ [lactic acid]o
Probably ↓ pHo
↓ [ATP]i
Opens KATP channels
↑ [ATP]o
Activates purinergic receptors
↑ [ADP]o
↑ [Adenosine]o

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.