Coronary 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
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
System Overview
Neural, myogenic, metabolic, and endothelial
mechanisms control regional blood flow
Neural mechanism:
Autonomic nervous system
(sympathetic division)
Blood pressure
Cardiac output
Local blood flow
Myogenic mechanism:
Autoregulation in the vessels of heart,
brain, skeletal muscle, and kidneys
Metabolic mechanism:
Local control in the vessels of heart,
brain, skeletal muscle during exercise
PO2, pH, etc.
Endothelial mechanism:
NO, EDHF, PGI2, ET, EDCF, etc.
Relaxing or contracting VSMCs
System Overview
Neural mechanism:
Autonomic nervous system
(sympathetic division)
Myogenic mechanism:
Metabolic mechanism:
Sophisticated feedback,
Mechanical forces, etc.
Local circulation
Resting vasomotor tone
Vasomotor control
Electrical and chemical signalling
PO2, pH, etc.
Endothelial mechanism:
NO, EDHF, PGI2, ET, EDCF, etc.
VSMCs
ECs
Gap junction
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
circle
of
Willis
The major arteries
of the brain.
(A) Ventral view,
Lateral (B) and (C)
midsagittal views,
(D) Idealized frontal
section
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
Changes in
regional
blood flow
 SENS 1: Lowintensity
electrical
stimulation of
hand
 SENS 2:Highintensity
electrical
stimulation of
hand
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.
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