Special circulation
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Special Circulation. Qiang XIA ( 夏强 ), PhD Department of Physiology Room C518, Block C, Research Building, School of Medicine Tel: 88208252 Email: [email protected] System Overview. The blood flow to organs depends on ⒈ The difference between aortic pressure and

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Special Circulation

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Special circulation

Special Circulation

Qiang XIA (夏强), PhD

Department of Physiology

Room C518, Block C, Research Building, School of Medicine

Tel: 88208252

Email: [email protected]


Special circulation

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


Special circulation

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


Special circulation

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


Coronary circulation

Coronary circulation冠脉循环


Special circulation

Coronary circulation

Heart: view from front


Special circulation

Coronary circulation

Heart: view from diaphragm


C oronary circulation

Coronarycirculation

  • Coronary circulation receives 5%of the resting cardiac output form 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


Special circulation

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


Extravascular compression impairs coronary blood flow during systole

Extravascular compression impairs coronary blood flow during systole

Isovolumic contraction phase ↓↓→ rapid ejection phase ↑→reduced ejection phase ↓→ diastolic phase ↑ (isovolumic relaxation phase↑↑)


Myocardial blood flow parallels myocardial metabolism

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


Local metabolic changes that cause vasodilation in the systemic circulation

Local metabolic changes that cause vasodilation in the systemic circulation


Notes

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”


Special circulation

Collateral vessel


Special circulation

Coronary steal


Special circulation

  • Which of the following is the most common cause of an increased coronary blood flow?

    A A decreased coronary perfusion pressure

    B An increased ventricular diastolic pressure

    C An increased stimulation of α-adrenergic receptors in the heart

    D An increased stimulation of β-1 adrenergic receptors in the heart

    E An increased stimulation of β-2 adrenergic receptors in the heart


Special circulation

  • Coronary blood flow

    A Is greatest during diastole in the left ventricle

    B May increase twelve-fold at maximal myocardial work levels

    C Is dependent upon the difference between aortic pressure and coronary sinus pressure

    D Is not affected by heart rate or myocardial contractile state

    E Is increased by incomplete ventricular relaxation


Special circulation

Cerebral circulation

The major arteries of the brain.

(A) Ventral view, Lateral (B) and (C) midsagittal views, (D) Idealized frontal section

circle of Willis


Special circulation

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


Cerebral circulation

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


Special circulation

  • 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


Cerebral blood flow

Cerebral Blood Flow

  • Neural control:

    • Sympathetic nerve

    • Parasympathetic nerve

    • Sensory nerve: “axon reflex”

  • Metabolic control:

    • PO2

    • PCO2

    • pH

  • Myogenic control


Autoregulation

Autoregulation

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


Cushing reflex

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.


Special circulation

  • Which of the following would be expected to DECREASE cerebral blood flow?

    A Hyperventilation

    B Hypoventilation

    C Activity of sympathetic adrenergic nerves

    D Activity of parasympathetic cholinergic nerves

    E Moderate exercise


Special circulation

  • The circulation through all of the following tissues is almost exclusively locally controlled, EXCEPT

    A Skin

    B Brain

    C Heart

    D Skeletal Muscle


Special circulation

  • A 16-year-old male presents to your emergency room with a gun shot wound to his abdomen. The bullet entered the upper left quadrant, perforating the spleen and removing the splenic flexure of the large intestine. His heart rate is rapid, and he is bleeding profusely. He is unconscious, and his blood pressure is low, but his pupils still respond to light. Under normal circumstances what percent of cardiac output goes to the brain?

    A 6%

    B 10%

    C 14%

    D 18%

    E 22%


The end

The End.


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