Special Circulation

Qiang XIA (夏强 ), PhD

Department of Physiology

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

Tel: 88208252

Email: xiaqiang@zju.edu.cn

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

Neural, myogenic, metabolic, and endothelialmechanisms control regional blood flowNeural mechanism: Autonomic nervous system (sympathetic division)

Myogenic mechanism:

Metabolic mechanism: PO2, pH, etc.

Endothelial mechanism:NO, EDHF, PGI2, ET, EDCF, etc.

System Overview

Autoregulation in the vessels of heart, brain, skeletal muscle, and kidneys

Blood pressureCardiac outputLocal blood flow

Local control in the vessels of heart, brain, skeletal muscle during exercise

Relaxing or contracting VSMCs

Neural mechanism: Autonomic nervous system (sympathetic division)

Myogenic mechanism:

Metabolic mechanism: PO2, pH, etc.

Endothelial mechanism:NO, EDHF, PGI2, ET, EDCF, etc.

System Overview

Resting vasomotor tone

ECs

VSMCs

Gap junction

Electrical and chemical signalling

Vasomotor control

Sophisticated feedback,Mechanical forces, etc.

Local circulation

Coronary circulation冠脉循环

Coronary circulation

Heart: view from front

Coronary circulation

Heart: view from diaphragm

Coronary circulation• 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

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

Isovolumic contraction phase ↓↓→

rapid ejection phase ↑→reduced

ejection phase ↓→ diastolic phase ↑

(isovolumic relaxation phase↑↑)

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

CHANGE MECHANISM

↓ PO2 ↓ [ATP]i, adenosine release

↑ PCO2 ↓ pHo

↓ pH ↓ pHo

↑ [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 Activates purinergic receptors

↑ [Adenosine]o Activates purinergic receptors

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”

Collateral vessel

Coronary steal

• 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

• 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

Cerebral circulation

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

circle of Willis

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

• 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

1. 脑循环特点

SENS 1: Low-intensity electrical stimulation of hand

SENS 2:High-intensity electrical stimulation of hand

Changes in

regional

blood flow

Cerebral Blood Flow

• Neural control:– Sympathetic nerve– Parasympathetic nerve– Sensory nerve: “axon reflex”

• Metabolic control:– PO2

– PCO2

– pH• Myogenic control

Autoregulation

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

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.

• 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

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

A Skin

B Brain

C Heart

D Skeletal Muscle

• 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.