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1 Morphology of the Intestinal Mucosa..- A. Introduction.- I. General Considerations.- II. Heterogeneity of Intestinal Epithelium.- B. Morphological Techniques.- C. The Mucosal Interface.- I. Surface Morphology of Small Intestine.- II. Surface Morphology of Large Intestine.- D. The Enterocyte.- I. The Striated Border.- II. The Apical Cell Coat and Cell Membrane.- III. The Cores of Microvilli and the Terminal Web.- IV. Other Enterocyte Surfaces.- V. The Enterocyte Cytoplasm.- VI. The Precursor Cells of the Crypt and Epithelial Dynamics.- VII. Special Features of Large Bowel Enterocytes.- E. Other Cell Types of Intestinal Mucosa.- I. Goblet Cells.- II. Intestinal Endocrine Cells.- III. Paneth Cells.- IV. Tuft Cells.- V. M Cells.- VI. Intraepithelial Lymphocytes.- VII. Globule Leukocytes.- F. Deeper Layers of the Intestine.- I. Lamina Propria.- II. Muscle Layers and Their Autonomic Innervation.- III. The Serosa.- G. Conclusion.- References.- 2 Intestinal Permeation and Permeability: an Overview..- A. Introduction.- B. Diffusion Processes.- C. The Intestine.- D. Passage of Substances Across Biologic Membranes.- I. Simple Diffusion.- II. Specific Transport Mechanisms.- III. Persorption.- E. Intestinal Permeation.- References.- 3 Permeability and Related Phenomena: Basic Concepts.- A. Introduction.- B. Passive Transport of Nonelectrolytes in Solution.- I. Nonequilibria Determining a Passive Net Flux.- II. Kinetics of Polar Solute Passage Driven by a Concentration Difference.- III. Kinetics of Nonpolar Solute Passage Driven by a Concentration Difference.- IV. Calculation of the Relative Values of the Permeability Coefficients of a Substance Across Two Membranes in Series.- C. Passive Transport of Univalent Electrolytes.- I. Kinetics of the Passive Net Transport off Univalent Electrolytes Across a Porous Membrane.- II. Transmembrane Potentials.- III. Transepithelial Potentials.- D. Transport Across Biological Membranes.- I. Passive Transport of Polar Nonelectrolytes Through Biological Membranes.- II. Passive Transport of Polar Electrolytes Through Biological Membranes.- E. Passive Transport by Carrier Facilitation.- I. Kinetics of Carrier-facilitated Transport.- II. Calculation of the Apparent Affinity Constant.- III. Saturation Kinetics.- IV. Substrate Competition.- V. Countertransport.- F. Passive Transport of Water.- I. Driving Forces.- II. The Hydrophilic Pores and Their Radius.- III. The Reflection Coefficient of Staverman.- IV. Solvent Drag.- G. Active Transport.- I. Identification.- II. Dependence of Water Transport on Metabolism.- III. Countercurrent Exchange.- IV. Thermodynamic Efficiency.- References.- 4 Methods for Investigation of Intestinal Permeability.- A. Introduction.- B. In Vivo Techniques.- I. In Conscious Animals.- II. In Anesthetized Animals.- C. In Vitro Techniques.- I. Isolated Loops.- D. Modifications of the Permeant.- I. Artificial Sugar Compounds.- II. Artificial Amino Acid Analogs.- III. Radioisotopes.- References.- 5 Vascular Perfusion of Rat Small Intestine for Permeation and Metabolism Studies.- A. Introduction.- B. Isolated Intestine with Lymph Collection.- I. Historical Aspects.- II. Development of Procedure.- III. Description of Procedure.- IV. Evidence for Sustained Viability.- V. Perfusate Composition During Recirculation.- VI. Applications.- C. Autoperfused Intestinal Segment In Vivo.- I. Description of Basic Procedure.- II. Specialized Techniques and Adaptations.- III. Applications.- D. Concluding Remarks.- I. Advantages of the Isolated Intestinal Preparation.- II. Advantages of the Autoperfused Intestinal Preparation.- References.- 6 The Use of Isolated Membrane Vesicles in the Study of Intestinal Permeation.- A. Introduction.- B. Methods for Membrane Isolation.- I. Brush Border Membranes.- II. Basolateral Plasma Membranes.- III. Enzyme and Polypeptide Content of Isolated Brush Border and Basolateral Membranes.- IV. Morphology and Orientation of Isolated Brush Border and Basolateral Membranes.- C. Methods for Analysing Transport Properties of Isolated Membrane Vesicles.- D. Transport Studies ..- I. Systems Involved in Primary Active Transport.- II. Systems Involved in Secondary Active Transport.- E. Energetics and Kinetics.- F. Studies with Isolated Membrane Vesicles on the Physiological Regulation of Transepithelial Transport.- G. Conclusions.- References.- 7 The Transport Carrier Principle.- A. The Carrier Concept in Relation to Intestinal Transport.- I. Early Development of the Carrier Concept.- B. The Kinetic Approach to Membrane Carriers.- I. The Simple Pore and Simple Carrier.- II. Coupled Transport Systems.- III. Chemiosmotic Coupling.- C. The Thermodynamics and Energetics of Membrane Carrier Systems.- I. Carrier Asymmetry.- II. Energetics of Countertransport Systems.- III. Energetics of Cotransport.- References.- 8 Energetics of Intestinal Absorption.- A. Introduction.- B. Special Fuels as Sources of Energy.- C. Membrane Transport and Oxidative Phosphorylation.- D. General Features of Energy Utilization.- E. Basal Energy Requirements of Tissues.- F. The Energetics of Absorption Are the Energetics of Movement Along a Multistep Pathway.- G. Variable Patterns of Fuels Available to the Small Intestine.- H. Intestinal Metabolism of Nutrients During Absorption.- I. Energetics of Brush Border Transport Processes.- K. Influence off Circulation of Epithelial Transport: General Principles.- I. Convective Transport.- II. Cellular Transport: Influence of Vascular Flow on Power Requirements.- III. A Simple Model.- L. Effects of Circulation on Epithelial Transport in the Steady State.- M. Influence of Circulation on Wash-out from Epithelium.- N. Influence of Circulation on Sodium Fluxes Across Vascularly Perfused Intestine.- I. Na Fluxes Across the Small Intestine.- II. Na Fluxes Across the Colon.- III. Factors Affecting Na Fluxes Across Frog Intestine.- O. Effects of Vascular Flow on Size of Tissue Fluid Compartments.- I. Measurement of Extracellular and Interstitial Space.- II. Influence of Vascular Flow on Permeability of the Pathway Between Epithelium and Blood.- P. Conclusions.- References.- 9 Polarity of Intestinal Epithelial Cells: Permeability of the Brush Border and Basolateral Membranes.- A. Introduction.- B. Functionally Polarized and Unpolarized Cells.- C. The Epithelial Layer as a Selective Barrier.- D. Brush Border Membrane: Morphology, Chemical Composition, and Biochemical Characteristics.- I. Morphology.- II. Chemical Composition.- III. The Brush Border as a Selective Membrane.- E. Basolateral Membrane: Chemical and Biochemical Organization.- I. Chemical Composition.- II. Enzyme Content.- F. Permeability of Brush Border and Basolateral Membranes.- G. Factors Affecting Membrane Permeability.- H. Concluding Remarks.- References.- 10 Electrical Phenomena and Ion Transport in the Small Intestine.- A. Introduction.- B. Transepithelial Electrical Parameters and Ionic Fluxes in the Small Intestine.- I. Ionic Conductance and its Structural and Functional Correlates . 316 II. Ionic Fluxes.- C. Pathways of Ion Transport in the Small Intestine.- I. The Cellular Pathway.- II. The Paracellular Pathway.- D. Analysis of Intestinal Electrical Parameters in Terms of Electrical Equivalent Circuits.- E. Na+-Coupled Transport of Organic Solutes by the Small Intestine.- I. Transepithelial Effects: The Na+ Gradient Hypothesis.- II. Intracellular Effects: The Electrical Potential Profile of the Absorptive Cell.- III. Equivalent Circuit Analysis: Is the Na+/K+ Exchange Pump Rheogenic?.- IV. Transapical Sugar Transport: Energetics and Stoichiometry.- F. The Regulation of Ion Transport in the Small Intestine.- I. Cyclic Nucleotides and Intestinal Transport: Secretion.- G. Conclusion.- References.- 11 Intestinal Permeation of Water.- A. Introduction.- B. Historical Concepts of Intestinal Fluid Absorption.- C. Formal Description of Water Transfer.- I. General Principles.- II. Diffusion.- III. Filtration.- IV. Osmosis.- V.…