TranscapillaryExchange-2023_Student.pptx

Transcapilla ry Exchange Joseph N. Benoit, Ph.D. Professor of Physiology Source Material GGuyton & Hall Textbook of Medical Physiology, 14th edition Chapter 16 The Microcirculation and Lymphatic System: Capillary Fluid Exchange, Interstitial Fluid, and Lymph Flow Session Objectives • Explain how...

Transcapilla ry Exchange Joseph N. Benoit, Ph.D. Professor of Physiology Source Material GGuyton & Hall Textbook of Medical Physiology, 14th edition Chapter 16 The Microcirculation and Lymphatic System: Capillary Fluid Exchange, Interstitial Fluid, and Lymph Flow Session Objectives • Explain how permeability, hydrostatic pressure, and oncotic pressure influence transcapillary exchange of fluid. • Calculate the net filtration pressure at the arterial and venous ends of a capillary and explain how net filtration pressure affects the direction of fluid movement across the capillary. • Explain how transcapillary macromolecular exchange is related to molecular size and capillary permeability. Relate capillary structure to the osmotic reflection coefficient. • Express the factors governing transcapillary exchange in the form of the Starling Relationship. Apply the Starling Relation to different physiological perturbations. • Describe how endogenous compound release can alter capillary permeability. • Explain why normal net capillary filtration does not result in edema. Core Concepts • Nutrient and waste exchange occurs at the level of the microcirculation. • Diffusion governs the process of microvascular exchange. • The capillary wall is a semipermeable membrane. • Capillary structure determines permeability of the membrane. • Exchange across the capillary membrane is a downhill process. • The rate and direction of movement across a capillary wall is determined by the sum of pressures across the capillary wall. Components of the Microcirculation Structure of the Capillary Structure/Function Considerations Exchange of Water & Solute Between the Blood and Interstitial Fluid • Core Concepts: • • • • • • There is a continuous exchange of fluid and solute across the capillary wall. Diffusion across the capillary membrane is proportional to the concentration difference across the membrane. Lipid-soluble substance diffuse directly through the endothelial cell membrane. Water-soluble and non-lipid soluble substances move through fenestrations and intercellular junctions. Interstitial fluid is an ultrafiltrate of plasma. Lymphatic capillaries drain excess fluid from the interstitial compartment. Movement of Molecules Across the Capillary Membrane Pores may be Restricted on the Basis of Molecular Size 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 17,600 0.03 Hemoglobin 68,000 0.01 Albumin 69,000 0.001 Fluid Filtration Across the Capillaries • Determinants of Filtration Rate Capillary Hydrostatic Pressure (PC) Interstitial Fluid Hydrostatic Pressure (PIF) Plasma Colloid Osmotic Pressure (p) Interstitial Fluid Colloid Osmotic Pressure () • Capillary Filtration Coefficient (Kf) • Osmotic Reflection Coefficient (d) • • • • Macromolecu lar Permeability & The Osmotic Reflection Coefficient () Osmotic Reflection Coefficient is probability that molecule will cross the barrier. If sigma is 0, then the membrane is freely permeable to the solute. If sigma is 1, then the molecule is impermeable to the solute. Starling’s Relationship )= [) )] Where: Jv,c is filtration rate Interstitiu m& Interstitial Fluid Questions?