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Lec61 Lec61 Presentation Transcript

  • Coronary Capillary System The outer surface epicardial coronary arteries Smaller intramuscular arteries Subendocardial arteries
    Subendocardial Arterial Plexus
  • Control of Coronary Blood Flow Local Muscle Metabolism is the Primary Controller of Coronary Flow
    Blood flow through the coronary system is regulated by local arteriolar vasodilation in response to cardiac muscle need for nutrition
    Whenever the vigor of cardiac contraction is increased, the rate of coronary blood flow also increases
  • Oxygen Demand as a Major Factor in Local Coronary Blood Flow Regulation
    About 70 % of the oxygen in the coronary arterial blood is removed as the blood flows through the heart muscle
    Coronary sinus blood has lower oxygen content than any other place in the cardiovascular system
    The coronary blood flow does increase almost in direct proportion to any additional metabolic consumption of oxygen by the heart.
    View slide
  • Adenosine released from myocardial muscle cells in response to increased metabolic rate may be an important local coronary metabolic vasodilator influence
    View slide
  • Nervous Control of Coronary Blood Flow
    The direct stimulation result from action of the acetylcholine from the vagus nerves and norepinephrine and epinephrine from the sympathetic nerves on the coronary vessels themselves
    The indirect stimulation result from secondary changes in coronary blood flow caused by increased or decreased activity of the heart.
    The indirect effects play a far more important role in normal control of coronary blood flow
  • Ischemic Heart Disease
    Results from insufficient coronary blood flow
    The most frequent cause of diminished coronary blood flow is atherosclerosis
    Large quantities of cholesterol deposited beneath the endothelium at many points in arteries throughout the body
    The net result is the development of atherosclerotic plaquesthat actually protrude into the vessel lumens
  • Mechanism of Atherosclerosis
  • Mechanism of Atherosclerosis
  • Mechanism of Atherosclerosis
    LDL build up
     Flow
    Blocked flow
    Tissue death
  • Basal Coronary Requirements
    Coronary muscle gets about 8 ml/min/100 g of tissue.
    To stay alive it needs about 1.3 ml/min/100 g.
    The heart can remain alive at ~20% of its normal flow.
    Subendothelium is usually the first to go because of high compression.
  • Myocardial Infarction (Heart Attack)
    Atheroscelrosis (Athere: “Gruel”; Sclerosis: “Hardening”)
    Thrombosis: Sudden occlusion or embolus.
    Local spasm
    Slowly progressing disease allows collaterals to be developed.
    The area of muscle that has either zero flow or little flow that it can not sustain cardiac muscle function is said to be infarcted
    The overall process called myocardial infarction
  • Causes of Death by Heart Attack
    Decreased cardiac output – shock.
    Failure of kidneys to excrete enough urine.
    Ventricular fibrillation (post-event):
    Rapid depletion of potassium
    Injury current (muscle cannot repolarize)
    Sympathetic reflex stimulation
    Abnormal conduction.
  • Cerebral blood flow
    Normal blood flow through the brain of adult person averages 50 – 65 ml/100 gm/min or 15% of resting cardiac output
  • Three metabolic factors control cerebral blood flow
    Carbon dioxide concentration
    Hydrogen ion concentration
    Oxygen concentration
  • Increase of cerebral blood flow in response to excess CO2 and H ion concentration
    Cerebral blood flow increase whenever (PCO2) is raised above normal in the arterial blood
    Increases the acidity in the brain tissue and therefore increases hydrogen ion concentration will increase cerebral blood flow
    Higher than normal arterial blood PO2 produces little decrease in cerebral blood flow
  • Autoregulation of cerebral blood flow when arterial pressure changes
    Cerebral blood flow regulated by local mechanism
    Flow through the cerebrum is autoregulated strongly and little affected by changes in arterial pressure unless it increased as high as 140 mmHg or falls below 60 mm Hg
  • Role of sympathetic nervous system in controlling cerebral blood flow
    The cerebral vessels receive both sympathetic vasoconstrictor and parasympathetic vasodilator fiber innervation
    Cerebral blood flow is influenced very little by changes in the activity of either because the blood flow autoregulation mechanism
    Sympathetic vasoconstrictor responses could be important in protecting cerebral vessels from excessive distention following high arterial pressure
  • Cutaneous blood flow
    The metabolic activity of body cells produces heat that must be lost in order for the body temperature remain constant
    The skin is the primary site of exchange of body heat with the external environment
    Cutaneous blood flow, which is about 6% of the resting cardiac output can be decreased when heat is to be retained and increases when heat is to be lost