1. THE MICROCIRCULATION. MAIN CONCEPTS Guido E. Santacana Ph.D. Professor Dept. of Physiology

2. MICROCIRCULATION  STRUCTURE  LAW OF LAPLACE  TRANSCAPILLARY EXCHANGE  STARLING’S HYPOTHESIS  LYMPHATICS

3. Structure of the Microcirculation Smooth muscle Arteriole Venule Metarteriole Capillary Endothelial cells Precapillary sphincters

4. Ultrastructure of a Capillary Lumen Intracellular channels Endothelial cell 1 Endothelial cell 2 Basement membrane Nucleus Intercellular cleft 5-10  m

5. LAW OF LAPLACE T = P x r/wt Tension = Pressure x Radius / wall thickness Why do the capillaries in our feet don’t just burst from the pressure (about 100mmHg)?

6. How does Laplace Work?

7. Less wall tension with smaller radius?

8. FLOW AND DIFFUSION LIMITED TRANSPORT PARTICLE SIZE AND FLOW CELL FLOW LIMITED PARTICLE SIZE & DISTANCE CELL DIFFUSION LIMITED

9. REFLECTION COEFFICIENT oncotic pressure = o RT (Ci - Co) water=0 albumin=1 RT= gas and temperature constants Ci= concentration inside Co= concentration outside REFLECTION COEFFICIENT = ACTUAL OSMOTIC FLOW/ THEORETICAL

10. CAPILLARY FILTRATION HYDROSTATIC FORCES OSMOTIC FORCES ARTERIAL PRESSURE VENOUS PRESSURE PRE-POST CAPILLARY RES. INTERSTITIAL FLUID PRESSURE ONCOTIC PRESSURE ALBUMIN BALANCE STARLING’S HYPOTHESIS Qf = k (Pc + i) - (Pi + p)

11. Graphic Representation of Capillary Filtration

12. Capillary Filtration in Various Clinical Conditions A B C D

13. What I cannot forget about Microcirculation Four Forces known as Starling Forces Determine Fluid Movement Across the Capillary Membranes. Pc= Capillary Pressure  Tends to move fluid out of the capillary Pi= Interstitial Fluid Pressure  Tends to move fluid into the capillary. Πc = Plasma Colloid Osmotic Pressure  Tends to cause Osmosis of fluid into capillary. Πi = Interstitial fluid colloid osmotic pressure  Tends to cause osmosis of fluid out of the capillary. Net Filtration Pressure = Pnet= ((Pc-Pi) – (Πc- Πi))

14. More things that I cannot forget about the microcirculation EDEMA or excess fluid outflow into the interstitium is commonly caused by : Capillary Pressure ( Pc ; Heart Failure) Plasma Proteins ( Πc ; Nephrotic Syndrome, liver failure) Capillary Permeability ( Kf ; Toxins, infections, burns) Interstitial Fluid Colloid Osmotic Pressure ( Πi; lymphatic blockage) Net Fluid Flow = Pnet (Kf)

15. Pitting Edema of the Feet A Pit forms where the skin is pressured. It may remain there for a few minutes

16. The Lymphatic System

17. Elephantiasis or Lymphatic Filariasis