CAPILLARIES

MICROCIRCULATION AND

LYMPHATIC SYSTEM

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

Functions of Capillaries

*Permit diffusion of:

water

small solutes

Lipid-soluble materials

*Block:

blood cells

plasma proteins

Capillary Function

*it’s the Location of all exchange functions of

cardiovascular system

*Materials diffuse between blood and

interstitial fluid

Capillary Structure

- Endothelial tube, inside thin basal lamina

-- No tunica media

-- No tunica externa

*Diameter is similar to red blood cell

Fig. 10-16b, p. 292

Water-filled pore Interstitial fluid

Endothelial cell

Plasma proteins

generally cannot

cross the capillary

wall

Plasma

membrane

Cytoplasm

Exchangeable

proteins are

moved across

by vesicular

transport

Transport across capillary wall

Small, water-soluble

substances pass

through the pores

Lipid-soluble

substances

pass through the

endothelial cells

Plasma

O2, CO2

Na+, K+, glucose,

amino acids

Exchangeable

proteins

Plasma

proteins

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

Capillary Networks

Figure 21-5

Capillaries Networks

Capillary bed or capillary plexus

Connect 1 arteriole and 1 venule

Collaterals

*Multiple arteries that contribute to 1

capillary bed

*Allow circulation if 1 artery is blocked

Arterial anastomosis:

=> fusion of 2 collateral arteries

Fig. 10-14, p. 291

Blood flow rate

(liters/min)

5

Total cross-sectional

area (cm2)

6,000 4.5

Anatomical

distribution

Velocity of flow

(mm/sec)

500 0.5

Aorta

Arteries

Arterioles

Capillaries

Venules

Veins

Venae

cavae

Fig. 10-17, p. 293

Glucose O2 CO2 Plasma

Interstitial

fluid

Glucose + O2 CO2 + H2O + ATP

Tissue cell

= Carrier-mediated

transport

Fig. 10-19, p. 295

Capillary

pressure

(mm Hg) Transition

point

Fluid

movement

Inward pressure

( pP + PIF)

Outward pressure

(PC + pIF)

Beginning Capillary length End

= Ultrafiltration = Reabsorption

Fig. 10-23, p. 299

Heart

7%

Pulmonary

vessels

9%

Systemic arteries

13%

Systemic arterioles

2%

Systemic capillaries

5%

Systemic veins

64%

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

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

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

0.3=28INWARD-28.3RESULT(OUTWARD

LYMPHATIC CIRCULATION

1-LYMPHATIC STRUCTURE

2-FACTORS DETERMINE LYMPHATIC

FLOW

A.LYMPHATIC PUMP

B.INTERSTIAL FLUID PRESSURE

LYMPHATIC FUNCTION

CONTROLL INTERSTIALFLUID

1. PROTEIN CONCENTRATION

2.VOLUME

3.PRESSURE

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. 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