Ch 16 Circulation PDF

Chapter 16: The Microcirculation and the Lymphatic System: Capillary Fluid Exchange, Interstitial Fluid and Lymph Flow. One of the most important functions of the circulation, to deliver nutrients and remove wastes, occurs in the microcirculation. Microcirculation - small arterioles, (diagram in fol...

Chapter 16: The Microcirculation and the Lymphatic System: Capillary Fluid Exchange, Interstitial Fluid and Lymph Flow. One of the most important functions of the circulation, to deliver nutrients and remove wastes, occurs in the microcirculation. Microcirculation - small arterioles, (diagram in following slide). capillaries, small venules Small arterioles control blood flow to each tissue area, and local conditions within the tissue control arteriolar diameter (and thus flow). So, generally speaking, each tissue controls its own flow based on tissue needs/demands. Slide 37 The Microcirculation VSMC coating Components Arteriole Metarteriole Capillary Venule Figure 16-1 Metarteriole Capillaries Terminal arteriole. Muscular. Discontinuous muscle coating. Last smooth muscle coating is usually site of pre-capillary SITE OF SOLUTE AND WATER TRANSFER. Suitable characteristics for the job: High surface area. Thin, single cell layer. sphincter (controls flow into capillaries – recruit more capillaries if have increased demand). Site for occlusion when nutrient delivery not needed (endothelial cell, no smooth muscle!!) Highly permeable. Slide 38 Venules Larger than arterioles. Weaker muscular coat. Capillary Morphology Relative Permeability lumen Molecular size can limit permeability (very thin) Substance Water NaCl Urea Glucose Hemoglobin Albumin MW 18 59 60 180 68,000 69,000 P 1.0 .96 .8 .6 .01 .001 Features of the capillaries Capillaries are permeable Capillary diameter = 4 - 5 µm to small water soluble Wall thickness = 0.5 µm Single endothelial cell layer NO vascular smooth muscle cells!!! Slide 39 substances and lipid soluble substances. Capillary Morphology 1. 2. 3. Pathways for diffusion – concentration dependent Directly through membrane - lipid soluble, gases (CO2, O2). Intercellular Cleft - water soluble substances, glucose, small amino acids - Molecules < 7 nm (Na+, Cl-) Plasmalemmal vesicles - may be important in transport of larger proteins. May coalesce to form vesicular channels. Capillaries are permeable to small water soluble substances and lipid soluble substances. Slide 40 Endothelial Cell Arrangement and Permeability “Pores” in capillaries have particular characteristics to meet the particular needs of certain organs. 1. Continuous - nonfenestrated low permeability, no protein leakage. skin, skeletal muscle, heart, lung The brain has tight junctions that form the blood brain barrier. 2. Fenestrated medium permeability, no protein leakage. visceral organs (kidney), endocrine glands 3. Discontinuous extremely permeable (protein leakage: even proteins can pass freely) liver, spleen, bone marrow Slide 41 The Interstitium Interstitium: Space between the cells. Interstitial Fluid: Fluid in the spaces. Free fluid not bound in gel. (1%) Interstitial fluid: - composition similar to plasma except for proteins. Figure 16-4 2 major structures -Derived from filtration and diffusion from capillaries. -mainly entrapped in the minute spaces among proteoglycan filaments. Figure 16-4: Major types of structures comprising interstitium. Collagen/proteoglycan trap water molecules and form “gel”. Water diffuses, molecule by molecule, thru interstitium. Slide 42 Fluid Filtration Across Capillaries determined by hydrostatic and colloid osmotic pressures, and capillary filtration coefficient (Kf). Dr. Ernest Starling, 1896 Figure 16-5 Slide 43 Forces Favoring Filtration (pushes fluid out of capillary) capillary pressure (Pc) interstitial colloid pressure (πif) “Starling Forces” Forces Favoring Reabsorption (draws fluid into capillary) plasma colloid pressure (πp) **interstitial fluid pressure (Pif)** function of protein Colloid osmotic pressure is a concentration (albumin). Fluid Filtration Across Capillaries determined by hydrostatic and colloid osmotic pressures, and capillary filtration coefficient (Kf). Figure 16-5 Starling’s Law of the Capillary NFP = net filtration pressure Kf = capillary filtration coefficient (+) ¢ filtration (fluid pushed out of capillary) (-) ¢ reabsorption (fluid drawn into capillary Slide 44 Arterial EXAMPLE: Calculate the net movement of fluid from the arterial end of a capillary into the interstitial space. ↓ Pc Venous 10 30 mmHg ↑ Πp 28 ↑ Pif -3 ↓ Π if 8 -3 mm Hg Exchange of fluid volume through the capillary membrane Arterial End of Capillary Forces tending to move fluid out Pc = 30 mm Hg Πif = 8 Pif = - (-3) NFP = 30 - (-3) - 28 + 8 = 13 Sum Out = 41 Forces tending to move fluid in Πp = 28 FILTRATION FAVORED AT ARTERIAL END Sum in = 28 Slide 45 Net Movement = 41 - 28 = 13 out Arterial EXAMPLE: Calculate the net movement of fluid from the venous end of a capillary into the interstitial space. ↓ Pc 10 30 mmHg ↑ Πp 28 ↑ Pif -3 ↓ Π if 8 Venous End of Capillary Forces tending to move fluid out Pc = 10 Pif = - (-3) Πif = 8 Sum Out = Venous -3 mm Hg NFP = 10 - (-3) - 28 + 8 = - 7 21 Forces tending to move fluid in Πp = 28 REABSORPTION FAVORED AT VENOUS END Sum in = 28 Slide 46 Exchange of fluid volume through the capillary membrane Net movement = 21 - 28 = -7 in Lymphatic System Lymphatic System - collects fluid and protein from interstitial spaces and returns to the venous circulation (blood). 2 - 3 L/ day 100 g protein/day 1/10 of that filtered is not reabsorbed, thus remains in the lymphatic system. fluid Lymphatic capillary Lymphatic Capillary can collect proteins attach to connective tissue Figure 16-8 Slide 47 Overlap between endothelial cells form valves to prevent backflow and allows easy entry of HMW substances and proteins. Lymphatic System Lymphatic System - collects fluid and protein from interstitial spaces and returns to the venous circulation (blood). 1-2 mm Hg > than atmospheric P Lymph flow is function of: (1) interstitial fluid (IF) pressure (2) activity of lymphatic pump. Flow increases (1) >IF Press >Lymph flow. What causes IF press to >? Low lymph flow Normal ISFP Figure 16-9 Slide 48 Lymphatic Pump: (Stretch Lymph Vessel / VSMC contraction) Compression by surrounding tissue (skeletal muscle) Pulsation of surrounding arteries Lymphatic valves in lymph channels Lymphatic System 1-2 mm Hg > than atmospheric P >IF Press >Lymph flow. What causes IF press to increase? Flow increases Why does this curve plateau? Low lymph flow Normal ISFP Figure 16-9 Lymph flow is function of: (1) interstitial fluid (IF) pressure (2) activity of lymphatic pump. Kf = capillary filtration coefficient Slide 49 Factors Affecting Lymph Flow When capillary filtration > lymphatic drainage: EXTRACELLULAR EDEMA Factors that increase flow or favor edema: • Elevated capillary pressure (fluid retention) • Decreased plasma colloid pressure (protein loss through urine or low protein production-liver disease) • Increased interstitial colloid pressure • Increased capillary permeability (allergic response) ∆ Kf • Lymphatic obstruction (tumor, infection, obesity) Slide 50 The lymphatic system is important for immune barrier function and for tissue fluid balance. Swollen gums can occur for many reasons, including poor dental hygiene, gingivitis and periodontal disease. Clinical Correlation