Microcirculation and lymphatic system

Microcirculation Most purposeful function of circulation Nutrient transport Cell excreta removal Regulation of blood flow Small arterioles Local conditions within the tissue Diameter of arterioles

Structural organization Organ-specific Meet its demands Nutrient artery Braches 6 to 8 times Arterioles

Structural organization Arterioles Highly muscular Changes in diameter Metarterioles (terminal arterioles) Smooth muscles No muscle sheath

Structural organization True capillary Smooth muscle fibers Precapillary sphincter Venules Larger than capillary Weak musculature

Metarterioles and precapillary shincter Close contact with tissue Regulation of blood flow Local condition of tissues

Capillaries Capillary wall Diameter Extremely thin 4 to 9 micrometer Highly permeable Single endothelial cell layer Basement membrane Diameter 4 to 9 micrometer Barely large enough passage for RBC and other cells

Movement of solute and water Intercellular cleft Thin slit, curving channels Large amount of transport activity Plasmalemmal vesicles Endocytosis Picnocytosis Vesicular channels Little of important

Specialization Brain Liver GI capillary membrane Blood-brain barrier (tight junctions) Only small molecules can pass Liver Larger pores and slits GI capillary membrane Intermediate in size Glomerular tufts of kidney Fenestrae (oval window) Large amount of small molecules and ions

Vasomotion Capillary flow Intermittent rather than continuous Intermittent contraction of metarterioles and precapillary sphincter Regulated by oxygen concentrations Decrease in oxygen concentration (greater tissue demand), increase in vasomotion (increased frequency with longer duration)

Exchange of solutes and water Diffusion Most important method of transfer Results from thermal motion of the water molecules and solutes in the fluid

Movement of lipid-soluble substances Direct diffusion No pores required Oxygen Carbon dioxide Faster than lipid-insoluble materials Require facilitation

Water-soluble materials Intercellular cleft Extremely efficient Cleft occupy 1/1000 of the entire capillary surface area Diffusion of water is 80X faster than flow of plasma itself

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 Insulin 5000 0.2 Myoglobin 17,600 0.03 Hemoglobin 69,000 0.01 Albumin 69,000 .0001 Molecular size Different permeability Tissue capillary-dependent

Concentration gradient Greater the difference in concentrations between inside and outside, faster the rate of diffusion Rates of diffusion of most nutrients Much greater than other materials Require small concentration differences

Interstitium and interstitial fluid Space between the cells Structures Collagen fiber bundles Tensional strength Proteoglycan filaments Thin, coiled/twisted molecule (98 % hyaluronic acid, 2 % protein) Forms brush pile (reticular filaments)

Interstitial fluid Filtrate and diffusion of plasma components Same constituents but lower concentrations of proteins Entrapped in minute space along proteoglycan filaments Formation of tissue gel Diffusion of fluid and molecules Very rapid

Interstitial fluid Free fluid Edema Very small amount (less than 1 %) Expansion of fluid stored in the interstitium until 50 % of fluid becomes free of proteoglycan Rivulets Pockets

Fluid filtration across capillary Pressures Hydrostatic Physical pressure that forces fluid and solutes out of capillary via pores Osmotic Concentration gradient of plasma proteins Movement of fluid out of interstitial space Regulates amount of fluid being moved out of blood

Role of lymphatic system Return of excess fluid and proteins to blood Leakage into interstitial space

Hydrostatic and colloid osmotic forces Determination of fluid movement through capillary Four forces Capillary pressure (outward movement of fluid) Interstitial fluid pressure (inward movement of fluid) Capillary colloid plasma osmotic pressure (inward movement of fluid) Interstitial fluid colloid osmotic pressure (outward movement of fluid)

Net filtration pressure Sum of these forces Fluid filtration to the interstitium if positive Fluid absorption to the blood if negative NFP = Pc-Pif-p+ if

Other factors Filtration coefficient (Kf) Filtration = Kf X NFP Pore size Pore number Number of capillaries Filtration = Kf X NFP

Lymphatic system Accessory route Flow of fluid from interstitium to the blood Movement of proteins and large particles away from tissue to the blood Extremely critical Lethal if no movement Drainage Channels Not present on skin, the CNS, endomysium, and bones Prelymphatics

Thoracic duct Common drainage of lymphatic ducts in the lower body and left side of head, left arm, and chest Drains into left internal jugular and subclavian vein

Right side of the body 10 % of arterial blood Right lymph duct Empty into right internal jugular and subclavian vein 10 % of arterial blood Enters lymphatic capillaries Returns through lymphatic system Removal of proteins

Structural design of lymphatic capillary Anchoring filaments Formation of valve

Lymph formation Derived from interstitial fluid Same composition Differences in protein concentrations Average 2g/dl (most tissues) As high as 6g/dl in lymphs from the liver 3-4g/dl in lymphs from the intestine Used for nutrient absorption Lipids Infectious agents Destroyed

Rate of lymph flow 100 ml per hour through thoracic duct 20 ml per hour through other channels 120 ml per hour 2-3L per day Increased interstitial fluid pressure, increased lymph flow Changes in balance of fluid exchange

Lymphatic pumps Rate of lymph flow Contraction of smooth muscles surrounding lymphatic and large lymph ducts Compression of lymphatics Rate of lymph flow Interstitial fluid pressure X activity of lymphatic pumps

Regulation of interstitial fluid Protein level Accumulation of plasma proteins in the interstitium Small but continuous leakage from the capillary Alters colloid osmotic pressure Alters fluid filtration rate and cause fluid accumulation Alters interstitial fluid pressure and volume Increased flow of lymph Removal of proteins