MICROCIRCULATION AND LYMPHATIC SYSTEM CAPILLARIES MICROCIRCULATION AND LYMPHATIC SYSTEM 1

Capillaries *Are smallest vessels with thin wall *Microscopic capillary networks are highly permeable to all water , cell nutrients and cell excreta between the tissues tissues and circulating blood *Chemicals and gases diffuse across walls 2 2

Functions of Capillaries *Permit diffusion of: water small solutes Lipid-soluble materials *Block: blood cells plasma proteins 3 3

Capillary Function *it’s the Location of all exchange functions of cardiovascular system *Materials diffuse between blood and interstitial fluid 4 4

Capillary Structure - Endothelial tube, inside thin basal lamina - No tunica media - No tunica externa *Diameter is similar to red blood cell 5 5

Transport across capillary wall Endothelial cell Interstitial fluid Water-filled pore Plasma proteins generally cannot cross the capillary wall Plasma Plasma proteins Plasma membrane Lipid-soluble substances pass through the endothelial cells O2, CO2 Cytoplasm Exchangeable proteins Na+, K+, glucose, amino acids Exchangeable proteins are moved across by vesicular transport FIGURE 10-16: Exchanges across the capillary wall. (b) As depicted in this schematic representation of a cross section of a capillary wall, small water-soluble substances are exchanged between the plasma and the interstitial fluid by passing through the water-filled pores, whereas lipid-soluble substances are exchanged across the capillary wall by passing through the endothelial cells. Proteins to be moved across are exchanged by vesicular transport. Plasma proteins generally cannot escape from the plasma across the capillary wall. Small, water-soluble substances pass through the pores Fig. 10-16b, p. 292 7

Capillary structure Capillary pores (Intercellular cleft) Plasmalemmal vesicles Vesicular channels

Special types of (pores) in certain organs 1.Brain ,blood brain barriers tight junction 2.Liver very wide 3.GI capillaries, midway in size between muscles and liver 4. Glomerular capillaries of the kidney, Fenestrate ; small oval windows penetrate through middle of endothelial cells 9 9

Capillary Networks Figure 21-5 10 10

Capillaries Networks Capillary bed or capillary plexus Connect 1 arteriole and 1 venule 11 11

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Collaterals *Multiple arteries that contribute to 1 capillary bed *Allow circulation if 1 artery is blocked Arterial anastomosis: => fusion of 2 collateral arteries 13 13

0.5 500 4.5 6,000 5 Velocity of flow (mm/sec) Anatomical distribution Total cross-sectional area (cm2) Blood flow rate (liters/min) 0.5 500 4.5 6,000 5 Aorta Arteries Arterioles Capillaries Venules Veins FIGURE 10-14: Comparison of blood flow rate and velocity of flow in relation to total cross-section area. The blood flow rate (red curve) is identical through all levels of the circulatory system and is equal to the cardiac output (5 liters/min at rest). The velocity of flow (purple curve) varies throughout the vascular tree and is inversely proportional to the total cross-section area (green curve) of all the vessels at a given level. Note that the velocity of flow is slowest in the capillaries, which have the largest total cross-section area. Venae cavae Fig. 10-14, p. 291 14

O2 CO2 Glucose Plasma = Carrier-mediated transport Interstitial fluid FIGURE 10-17: Independent exchange of individual solutes down their own concentration gradients across the capillary wall. Glucose + O2 CO2 + H2O + ATP Tissue cell Fig. 10-17, p. 293 15

Capillary pressure (mm Hg) Transition point Fluid movement Inward pressure ( pP + PIF) Outward pressure (PC + pIF) FIGURE 10-19: Net filtration and net reabsorption along the vessel length. The inward pressure (πP + PIF) remains constant throughout the length of the capillary whereas the outward pressure (PC + πIF) progressively declines throughout the capillary’s length. In the first half of the vessel, where the declining outward pressure still exceeds the constant inward pressure, progressively diminishing quantities of fluid are filtered out (upward red arrows). In the last half of the vessel, progressively increasing quantities of fluid are reabsorbed (downward blue arrows) as the declining outward pressure falls farther below the constant inward pressure. Capillary length Beginning End = Ultrafiltration = Reabsorption Fig. 10-19, p. 295 16

Pulmonary Systemic arteries vessels 13% 9% Systemic arterioles 2% Heart 7% Systemic capillaries 5% Systemic veins 64% FIGURE 10-23: Percentage of total blood volume in different parts of the circulatory system. Fig. 10-23, p. 299 17

PLASMA COLLOID OSMOTIC P=28 SUMMATION OF FORCES ARTERIAL END OF CAP FORCES OUTWARD CAP P 30+NEG IFFP 3 +IFCOP8=41 FORCES INWARD PLASMA COLLOID OSMOTIC P=28 SUMMATION OF FORCES OUTWAR 41-INWARD 28=13mmhg 19

PLASMA COLLOID OSMOTIC P=28 SUMMATION OF FORCES VENOU END OF CAP FORCES OUTWARD CAP P 10+NEG IFFP 3 +IFCOP8=21 FORCES INWARD PLASMA COLLOID OSMOTIC P=28 SUMMATION OF FORCES INWAR 28-OUTWARD 21=7mmhg 20

STARLING EQUILIBRIUM FOR CAPILLARY PRESSURE OUTWAD FORCES MEAN CAP P=17.3 NEG IFFP=3 IFCOP=8 TOTAL=28.3mmhg INWARD FORCES PLASMA COLL OSM PRES=28mmhg RESULT(OUTWARD28.3-INWARD28=0.3 21

LYMPHATIC CIRCULATION 1-LYMPHATIC STRUCTURE 2-FACTORS DETERMINE LYMPHATIC FLOW A.LYMPHATIC PUMP B.INTERSTIAL FLUID PRESSURE 22

LYMPHATIC FUNCTION CONTROLL INTERSTIALFLUID 1. PROTEIN CONCENTRATION 2.VOLUME 3.PRESSURE 25

Lymph flow 1.Interstial fluid pressure A. Elevate capillary pressure B. Increase interstitial fluid colloid osmotic pressure C. Decrease plasma colloid osmotic pressure D. Increase permeability of capillaries

2. Lymph pump and valves 3. External compression A 2. Lymph pump and valves 3.External compression A. Surrounding skeletal muscles B. Movements of parts of the body C. Pulsation of arteries D. Compression of the tissues by objects outside the body

4. Lymphatic capillary pump