This document outlines a lecture on microcirculation. It begins by stating the objectives of understanding microcirculation functions and control. The content includes the structure of capillaries and microcirculation, factors that influence permeability, exchange of fluids between blood and tissues, Starling forces, and abnormalities in capillary pressure. Examples are given of typical capillary beds and how structures vary between tissues. The key concepts of vasomotion, Starling equilibrium, and net filtration pressure are also explained.

1. Microcirculation
Prof. Dr. Rashid Mahmood

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

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
Filtration Coefficient
•Describe forces across capillary wall
•Calculate Net Filtration Pressure
31-May-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
Vascular
distensibility &
Functions of
Arterial and
Venous System |
51-May-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 |
131-May-18

14. • Intermittent contraction and relaxation of muscles
in the metarterioles and precapillary sphincters
• Main regulator: Concentration of O2 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 |
161-May-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 |
171-May-18

18. Exchange between blood and interstitial fluid
Microcirculation | © Prof. Dr. Rashid Mahmood 18
Mainly 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 0.001Microcirculation | © 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 |
221-May-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 H2O = mmol / liter x n, where n =
A. Molecular weight or atomic weight of the
substance
B. No. of discrete particles into which solute
dissociates
C. No. of equivalents produced
D. No. of mmoles dissolved
E. 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 |
251-May-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 = Pc – Pif – πC + πif
Starling Forces

29. Activity No: 2(B)
• Pc at venous ends of tissue capillaries is ________ Pc at
arterial end
A. Equal to
B. Less than
C. 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 (πif)
8 8 8
Interstitial fluid hydrostatic
pressure (Pif) (normal value : -
3 mmHg) (due to lymphatics)
3 3 3
Plasma colloid osmotic
pressure (πC)
-28 -28 -28
Net filtration Pressure 13 -7 0.3 30Microcirculation | © Prof. Dr. Rashid Mahmood

31. Activity 3
• Calculate NFP, if
• Mean Pc= 20 mmHg
•πif= 8 mmHg
•Pif= -5 mmHg
•πC= 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 |
321-May-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 |
351-May-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
1. Interstitial fluid
2. Lymphatic System
1-May-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
381-May-18

39. Take Home Points (Slide 1/2)
•A typical tissue capillary is made up of single layer
of endothelial 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 391-May-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 drained40

41. Thank You
Vascular distensibility & Functions of Arterial and Venous System | ©
Prof. Dr. Rashid Mahmood
1-May-18 41
Questions ?
Comments ?
drrashid62@gmail.com
rashid.mahmood@rmi.edu.pk
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