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Lec61

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

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