Microcirculation

Physiology of Microcirculation. Blood Flow through small Blood Vessels and Capillaries

1. Microcirculation Prof. Dr. Rashid Mahmood

2. Microcirculation | © Prof. Dr. Rashid Mahmood 2 Microcirculation

3. Objectives Goal /Aim By the end of this session students should be able to understand the functions & control of Microcirculation . Specific objectives By the end of this lecture student should be able to : Describe Structure of Microcirculation and Capillary System List the factors effecting Capillary Permeability Differentiate between Net Filtration Pressure and Fi ltration Coefficient Describe forces across capillary wall Calculate Net Filtration Pressure 3 19-Mar-18

4. Lesson contents Structure of Microcirculation and Capillary System Vasomotion Exchange between blood and interstitial fluid Factors affecting Permeability BODY FLUIDS Starling Forces Starling Equilibrium Abnormalities of capillary pressure

5. Lesson contents Structure of Microcirculation and Capillary System Vasomotion Exchange between blood and interstitial fluid Factors affecting Permeability BODY FLUIDS Starling Forces Starling Equilibrium Abnormalities of capillary pressure Vascular distensibility & Functions of Arterial and Venous System | © Prof. Dr. Rashid Mahmood 5 19-Mar-18

6. Typical Capillary bed Microcirculation | © Prof. Dr. Rashid Mahmood 6

7. Typical Capillary beds Microcirculation | © Prof. Dr. Rashid Mahmood 7

8. Typical Capillary beds Microcirculation | © Prof. Dr. Rashid Mahmood 8

9. 9 Structure of the capillary Very tight in brain cells – Blood brain barrier Very wide in liver cells –even proteins can pass More developed in glomerular capillaries Vesicular transport Fenestrations

10. Structure of the capillary Microcirculation | © Prof. Dr. Rashid Mahmood 10

11. Structure of the capillary Microcirculation | © Prof. Dr. Rashid Mahmood 11

12. Typical Capillary bed Microcirculation | © Prof. Dr. Rashid Mahmood 12

13. Lesson contents Structure of Microcirculation and Capillary System Vasomotion Exchange between blood and interstitial fluid Factors affecting Permeability BODY FLUIDS Starling Forces Starling Equilibrium Abnormalities of capillary pressure Vascular distensibility & Functions of Arterial and Venous System | © Prof. Dr. Rashid Mahmood 13 19-Mar-18

14. Intermittent contraction and relaxation of muscles in the metarterioles and precapillary sphincters Main regulator: Concentration of O 2 in the tissues regulates vasomotion Vasomotion Microcirculation | © Prof. Dr. Rashid Mahmood 14

15. Vasomotion Microcirculation | © Prof. Dr. Rashid Mahmood 15

16. Lesson contents Structure of Microcirculation and Capillary System Vasomotion Exchange between blood and interstitial fluid Factors affecting Permeability BODY FLUIDS Starling Forces Starling Equilibrium Abnormalities of capillary pressure Vascular distensibility & Functions of Arterial and Venous System | © Prof. Dr. Rashid Mahmood 16 19-Mar-18

17. Lesson contents Structure of Microcirculation and Capillary System Vasomotion Exchange between blood and interstitial fluid Factors affecting Permeability BODY FLUIDS Starling Forces Starling Equilibrium Abnormalities of capillary pressure Vascular distensibility & Functions of Arterial and Venous System | © Prof. Dr. Rashid Mahmood 17 19-Mar-18

18. Exchange between blood and interstitial fluid Microcirculation | © Prof. Dr. Rashid Mahmood 18 M ainly by Diffusion Interstitial fluid

19. Microcirculation | © Prof. Dr. Rashid Mahmood 19 1 2 3 4 5 6 Figure Focus: Activity No. 1: What are constant factors affecting Permeability ? (Not related to substance to be diffused) Factors affecting Permeability

20. Microcirculation | © Prof. Dr. Rashid Mahmood 20 Surface Area × Permeability = Filtration Coefficient (Permeability depends on cell membrane composition & thickness ) Capillary Filtration coefficient: 6.67 ml/min/mm Hg (for whole body) 0.021 ml/min/mm Hg (per 100 gm of tissue) varies drastically in different tissues (Kidney:12.51 ml/min/mm Hg (per 100 gm of tissue )

21. Effect of molecular size on diffusion Substance Molecular weight Permeability Water 18 1.00 NaCl 58.5 0.96 Urea 60 0.8 Glucose 180 0.6 Sucrose 342 0.4 Inulin 5000 0.2 Myoglobin 17600 0.03 Hemoglobin 68000 0.01 Albumin 69000 0.001 Microcirculation | © Prof. Dr. Rashid Mahmood 21

22. Lesson contents Structure of Microcirculation and Capillary System Vasomotion Exchange between blood and interstitial fluid Factors affecting Permeability BODY FLUIDS Starling Forces Starling Equilibrium Abnormalities of capillary pressure Vascular distensibility & Functions of Arterial and Venous System | © Prof. Dr. Rashid Mahmood 22 19-Mar-18

23. 23 20% 40 % BODY FLUIDS Intracellular fluid Interstitial Fluid Plasma Microcirculation | © Prof. Dr. Rashid Mahmood Extracellular fluid

24. Activity: 2(A) mOsmol / Kg H 2 O = mmol / liter x n, where n = Molecular weight or atomic weight of the substance No. of discrete particles into which solute dissociates No. of equivalents produced No. of mmoles dissolved Total valency of all the particles Microcirculation | © Prof. Dr. Rashid Mahmood 24 B

25. Lesson contents Structure of Microcirculation and Capillary System Vasomotion Exchange between blood and interstitial fluid Factors affecting Permeability BODY FLUIDS Starling Forces Starling Equilibrium Abnormalities of capillary pressure Vascular distensibility & Functions of Arterial and Venous System | © Prof. Dr. Rashid Mahmood 25 19-Mar-18

26. Forces acting across capillary wall Microcirculation | © Prof. Dr. Rashid Mahmood 26 Starling Forces

27. Forces acting across capillary wall Microcirculation | © Prof. Dr. Rashid Mahmood 27 1 2 3 4 Interstitial fluid Capillary fluid

28. Forces acting across capillary wall Microcirculation | © Prof. Dr. Rashid Mahmood 28 Net Filtration Pressure NFP = P c – P if – π C + π if Starling Forces

29. Activity No: 2(B) Pc at venous ends of tissue capillaries is ________ Pc at arterial end Equal to Less than Greater than Why? Microcirculation | © Prof. Dr. Rashid Mahmood 29 B

30. Pressures ( in mmHg) at arterial & venous ends of the capillaries Forces moving the fluid out Arterial end Venous end Mean forces Capillary hydrostatic pressure (Pc) 30 10 17.3 Interstitial colloid osmotic pressure ( π if) 8 8 8 Interstitial fluid hydrostatic pressure ( P if ) (normal value : -3 mmHg) (due to lymphatics ) 3 3 3 Plasma colloid osmotic pressure ( π C) -28 -28 -28 Net filtration Pressure 13 -7 0.3 30 Microcirculation | © Prof. Dr. Rashid Mahmood

31. Activity 3 Calculate NFP, if Mean Pc= 20 mmHg π if = 8 mmHg P if = -5 mmHg π C = 32 mmHg Microcirculation | © Prof. Dr. Rashid Mahmood 31 1 mmHg

32. Lesson contents Structure of Microcirculation and Capillary System Vasomotion Exchange between blood and interstitial fluid Factors affecting Permeability BODY FLUIDS Starling Forces Starling Equilibrium Abnormalities of capillary pressure Vascular distensibility & Functions of Arterial and Venous System | © Prof. Dr. Rashid Mahmood 32 19-Mar-18

33. Microcirculation | © Prof. Dr. Rashid Mahmood 33 0.5% (1/200) plasma filters at Arterial end Starling Equilibrium: Net filtration Pressure of 0.3 mmHg results in net filtration of 2ml/min Fluid not reabsorbed is absorbed by Lymphatics

34. Activity 4 Will Net filtration Pressure of 0.3 mmHg result in equal amount of net fluid filtered per 100 gram of all tissues? Why? Microcirculation | © Prof. Dr. Rashid Mahmood 34 Different Filtration-Coefficient in different tissues

35. Lesson contents Structure of Microcirculation and Capillary System Vasomotion Exchange between blood and interstitial fluid Factors affecting Permeability BODY FLUIDS Starling Forces Starling Equilibrium Abnormalities of capillary pressure Vascular distensibility & Functions of Arterial and Venous System | © Prof. Dr. Rashid Mahmood 35 19-Mar-18

36. Abnormalities of capillary pressure Microcirculation | © Prof. Dr. Rashid Mahmood 36 ↑mean capillary pressure: ↑ Arterial Pressure Venous stasis ↓ Plasma colloid osmotic pressure Hypoproteinemia Nephritic syndrome

37. More topics Interstitial fluid Lymphatic System 19-Mar-18 Vascular distensibility & Functions of Arterial and Venous System | © Prof. Dr. Rashid Mahmood 37

38. Learning Resources Guyton and Hall (Text book of physiology), 13th Edition Berne & Levy Principles of Physiology ( Koeppen BM), 6th Edition Human Physiology, Silverthorn Human Physiology : from cells to system, Lauralee Sherwood, 9th edition 38 19-Mar-18

39. Take Home Points (Slide 1/2) A typical tissue capillary is made up of single layer of e ndothelial cells lying on a basement membrane , separated by intercellular clefts Blood supply to capillaries is controlled by intermittent contraction and relaxation of muscles in metarterioles and precapillary sphincters . This process is called vasomotion Amount of fluid filtered by capillaries depends upon net filtration pressure (NFP) and filtration coefficient 39 19-Mar-18

40. Take Home Points (Slide 2/2) Filtration coefficient is product of permeability and surface area NFP depends on Starling forces Starling forces include capillary hydrostatic pressure interstitial hydrostatic pressure, plasma colloid osmotic pressure, and interstitial fluid colloid osmotic pressure At Starling Equilibrium there is net filtration of fluid at the rate of 2ml/min in entire body. The fluid not reabsorbed by venous end of capillaries is drained by Lymphatics 40

41. Thank You Vascular distensibility & Functions of Arterial and Venous System | © Prof. Dr. Rashid Mahmood 19-Mar-18 41 Questions ? Comments ? [email protected] [email protected] ppt also available at https://www.slideshare.net