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بسم الله الرحمن الرحيم

بسم الله الرحمن الرحيم. ﴿و ما أوتيتم من العلم إلا قليلا﴾. صدق الله العظيم الاسراء اية 58. Capillary Circulation. By Dr. Abdel Aziz M. Hussein Lecturer of Medical Physiology Member of American Society of Physiology. Vascular System. Vascular System. Functional Morphology of Capillary.

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بسم الله الرحمن الرحيم

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  1. بسم الله الرحمن الرحيم ﴿و ما أوتيتم من العلم إلا قليلا﴾ صدق الله العظيم الاسراء اية 58 dr abdelaziz Hussein, Mansoura Faculty of Medicine

  2. Capillary Circulation By Dr. Abdel Aziz M. Hussein Lecturer of Medical Physiology Member of American Society of Physiology dr abdelaziz Hussein, Mansoura Faculty of Medicine

  3. Vascular System dr abdelaziz Hussein, Mansoura Faculty of Medicine

  4. Vascular System dr abdelaziz Hussein, Mansoura Faculty of Medicine

  5. Functional Morphology of Capillary • They are extremely thin vessels to allow exchange of nutrients and cellular excreta ( ) the tissues and the circulating blood occur No • About 10 billion capillaries Surface area • Total surface area is about 500 to 700 m2. dr abdelaziz Hussein, Mansoura Faculty of Medicine

  6. Types of Capillaries dr abdelaziz Hussein, Mansoura Faculty of Medicine

  7. Types of Capillaries dr abdelaziz Hussein, Mansoura Faculty of Medicine

  8. Structure of Capillary Wall Thickness 0.5 um Endothelial cell Diameter 4-9 um Basement membrane dr abdelaziz Hussein, Mansoura Faculty of Medicine

  9. Capillary Blood Flow (Vasomotion) dr abdelaziz Hussein, Mansoura Faculty of Medicine

  10. Capillary Blood Flow • Blood in capillary is not continuous, but it is intermittent Cause: • It is due to intermittent contraction of the metarterioles and precapillary sphincters ( Vasomotion) • There is a cycle of constriction and relaxation for 5 to 10 timesper min, so only about 10-20% of the capillaries are opened at a time. dr abdelaziz Hussein, Mansoura Faculty of Medicine

  11. Capillary Blood Flow Regulation of capillary Vasomotion: • Vasomotion is controlled by the O2 concentration in the tissues. • When the O2 concentration is very low→ the intermittent periods of blood flow occur more often and the duration of each period of flow lasts for a long time, thereby allowing the blood to carry ↑ed quantities of O2 to the tissues. dr abdelaziz Hussein, Mansoura Faculty of Medicine

  12. Capillary Blood Flow Regulation of capillary Vasomotion: Low O2 tension dr abdelaziz Hussein, Mansoura Faculty of Medicine

  13. Capillary Blood Flow Regulation of capillary Vasomotion: High O2 tension dr abdelaziz Hussein, Mansoura Faculty of Medicine

  14. Capillary Blood Velocity • It is about 0.5-1 mm/second→ slow blood flow→ suitable for exchange of materials between the plasma and interstitial fluid. dr abdelaziz Hussein, Mansoura Faculty of Medicine

  15. Capillary Blood Pressure Value: • At the arterial end, it is about 30-35 mmHg. • At the venous end, it is about 10-15 mmHg. • The mean capillary blood pressure is 25 mmHg. Arterial End Mean Cap. P. Venous End 30-35 mmHg 25 mmHg 10-15 mmHg dr abdelaziz Hussein, Mansoura Faculty of Medicine

  16. Factors affecting Capillary B.P. and B. Flow dr abdelaziz Hussein, Mansoura Faculty of Medicine

  17. Passive Extracapillary Factors • a. Diameter of arterioles: • Arteriolar VD →↑es the capillary blood flow and the capillary pressure. • VC of the arterioles has the reverse effect. • b. Venous pressure: • -↑ed venous pressure → ↑capillary BP and ↓capillary blood flow. • -↑ed venous pressure occurs in; • Congestive heart failure. • Local obstruction of the vein by thrombosis or tumour. • c. Gravity: • It ↑es the capillary blood pressure in parts below the level of the heart by antagonizing the VR. • It ↓es the capillary BP in parts above the level of the heart. dr abdelaziz Hussein, Mansoura Faculty of Medicine

  18. Effect of Arteriolar Diameter Arteriolar dilatation ↑ capillary B.P. ↓ capillary B.P. Arteriolar Constriction dr abdelaziz Hussein, Mansoura Faculty of Medicine

  19. Effect of Venous Pressure ↑ capillary B.P. ↑ venous B.P. ↓ capillary B.P. ↓ Venous B.P. dr abdelaziz Hussein, Mansoura Faculty of Medicine

  20. Effect of Gravity dr abdelaziz Hussein, Mansoura Faculty of Medicine

  21. Active capillary Contraction dr abdelaziz Hussein, Mansoura Faculty of Medicine

  22. Active capillary Contraction Swelling of endothelial cells Contraction of metarterioles Contraction of precapillary sphincter dr abdelaziz Hussein, Mansoura Faculty of Medicine

  23. Chemical Factors 1. Vasoconstrictor substances • Adrenaline: • VC of cutaneous and splanchnic capillaries. • Noradrenaline →VC of all the capillaries except the coronaries. • ADH → generalized VC of the capillaries • Angiotensin II → generalized VC of the capillaries. dr abdelaziz Hussein, Mansoura Faculty of Medicine

  24. Chemical Factors 2. Vasodilator substances • Adrenaline: • VD of Sk. Ms and coronary capillaries. • Acetyl choline →VD of all the capillaries including coronaries • Histamine → generalized VD of the capillaries • Gases → CO2 excess, ↑ed H and O2 lack produce capillary dilatation. dr abdelaziz Hussein, Mansoura Faculty of Medicine

  25. Nervous Factors • True capillaries receive no nerve supply, so it is not affected by nervous factors. • Capillary dilatation or constriction is dependent on the tone of the precapillary sphincter which is influenced by the local regulatory mechanisms. dr abdelaziz Hussein, Mansoura Faculty of Medicine

  26. Physical Factors • Warming causes capillary VD because heat relaxes the smooth ms fibers of the precapillary sphincter. • Coolingof the skin for a short time produces VC, while prolonged cooling causes VD due to accumulation of metabolites. Skin colour and temperature • The colour of the skin depends on the state of capillaries • The temperature of the skin depends on the state of the arterioles dr abdelaziz Hussein, Mansoura Faculty of Medicine

  27. Capillary Fragility • ◊Def, • It is the liability of the capillary wall to rupture on raising the capillary pressure. • The capillaries do not rupture easily under normal conditions because of their very small diameter→ according to the law of Laplace. Law of Laplace • This law states that the tension developed in the wall of a hollow organ (T) is equal to the distending pressure (P) x the radius (r) of the organ T = P x r dr abdelaziz Hussein, Mansoura Faculty of Medicine

  28. Capillary Fragility Law of Laplace • As the pressure in the aorta is 4 times the pressure in the capillary and its radius is 4000 times as much as the radius of the capillary, so the tension in the aortic wall is 16000 times the tension in the capillary wall. • This very low tension in the capillary wall (1/16000 that in the aortic wall) explains the little liability of the capillary wall to rupture. ◊Causes of ↑ed capillary fragility: Defects in their wall (e.g. vitamin C deficiency, certain toxins, allergic conditions, old age). Defect in blood (e.g. thrombocytopenic purpura). dr abdelaziz Hussein, Mansoura Faculty of Medicine

  29. Capillary fragility test dr abdelaziz Hussein, Mansoura Faculty of Medicine

  30. THANKS dr abdelaziz Hussein, Mansoura Faculty of Medicine

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