1. Coronary blood flow is regulated locally by the heart muscle in response to metabolic demand and oxygen needs. When the heart works harder, blood flow increases to supply more oxygen and nutrients. 2. Atherosclerosis occurs when cholesterol builds up in artery walls, forming plaques that block coronary blood flow. This reduced flow can cause myocardial infarction (heart attack) if the flow is cut off to part of the heart muscle. 3. Cerebral blood flow is tightly regulated to maintain adequate oxygen and remove waste. It increases with higher carbon dioxide and hydrogen ion levels but is relatively unaffected by oxygen levels within normal ranges. Blood flow autoregulation keeps flow stable during changes in blood pressure.

1. Coronary Capillary System The outer surface epicardial coronary arteries Smaller intramuscular arteries Subendocardial arteriesEpicardialSubendocardial Arterial PlexusPressure

2. 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

3. Oxygen Demand as a Major Factor in Local Coronary Blood Flow RegulationAbout 70 % of the oxygen in the coronary arterial blood is removed as the blood flows through the heart muscleCoronary sinus blood has lower oxygen content than any other place in the cardiovascular systemThe coronary blood flow does increase almost in direct proportion to any additional metabolic consumption of oxygen by the heart.

4. Adenosine released from myocardial muscle cells in response to increased metabolic rate may be an important local coronary metabolic vasodilator influence

5. Nervous Control of Coronary Blood FlowThe direct stimulation result from action of the acetylcholine from the vagus nerves and norepinephrine and epinephrine from the sympathetic nerves on the coronary vessels themselvesThe 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

6. Ischemic Heart DiseaseResults from insufficient coronary blood flowThe most frequent cause of diminished coronary blood flow is atherosclerosisLarge quantities of cholesterol deposited beneath the endothelium at many points in arteries throughout the bodyThe net result is the development of atherosclerotic plaquesthat actually protrude into the vessel lumens

7. Mechanism of Atherosclerosis

8. Mechanism of Atherosclerosis

9. Mechanism of AtherosclerosisLDL build upPlaque FlowRuptureClotBlocked flowTissue death

10. Basal Coronary RequirementsCoronary 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.

11. Myocardial Infarction (Heart Attack)Atheroscelrosis (Athere: “Gruel”; Sclerosis: “Hardening”)Thrombosis: Sudden occlusion or embolus.Local spasmSlowly 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 infarctedThe overall process called myocardial infarction

12. Causes of Death by Heart AttackDecreased cardiac output – shock.Failure of kidneys to excrete enough urine.Ventricular fibrillation (post-event):Rapid depletion of potassiumInjury current (muscle cannot repolarize)Sympathetic reflex stimulationAbnormal conduction.

13. Cerebral blood flowNormal blood flow through the brain of adult person averages 50 – 65 ml/100 gm/min or 15% of resting cardiac output

14. Three metabolic factors control cerebral blood flowCarbon dioxide concentrationHydrogen ion concentration Oxygen concentration

15. Increase of cerebral blood flow in response to excess CO2 and H ion concentrationCerebral 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 flowHigher than normal arterial blood PO2 produces little decrease in cerebral blood flow

16. Autoregulation of cerebral blood flow when arterial pressure changesCerebral blood flow regulated by local mechanismFlow 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

17. Role of sympathetic nervous system in controlling cerebral blood flowThe cerebral vessels receive both sympathetic vasoconstrictor and parasympathetic vasodilator fiber innervationCerebral blood flow is influenced very little by changes in the activity of either because the blood flow autoregulation mechanismSympathetic vasoconstrictor responses could be important in protecting cerebral vessels from excessive distention following high arterial pressure

18. Cutaneous blood flowThe metabolic activity of body cells produces heat that must be lost in order for the body temperature remain constantThe skin is the primary site of exchange of body heat with the external environmentCutaneous 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