Microcirculation%20and%20lymphatic%20system

1
Microcirculation and lymphatic system
2
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

3

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

4

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

5

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

6

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

7
Capillaries

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

8

• 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

9

• Specialization
• Brain
• 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

10
Vasomotion

• Capillary flow
• Intermittent rather than continuous
• Vasomotion
• 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)

11
Exchange of solutes and water

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

12

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

13

• 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

14

• Molecular size
• Different permeability
• Tissue capillary-dependent

15

• 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

16
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)

17

• 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

18

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

19
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

20

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

21
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)

22

• 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
23

• Other factors
• Filtration coefficient (Kf)
• Pore size
• Pore number
• Number of capillaries

Filtration Kf X NFP
24
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

25

• 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

26

• Right side of the body
• 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

27

• Structural design of lymphatic capillary
• Anchoring filaments
• Formation of valve

28
(No Transcript)
29
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

30
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

31

• Lymphatic pumps
• 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

32
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