Phys - Capillary Dynamics

Question 1

Primary function of the cardiovascular system

Answer 1

1.) Delivery of O2 and metabolic substrates 2.) Removal of waste products

Question 2

What two steps are involed in vascular transport of substrates and waste products

Answer 2

1.) Convective blood flow to the capillaries 2.) Exchange of fluids and solutes between the capillaries and parenchyma (diffusion and osmosis)

Question 3

Importance of the lymphatic system

Answer 3

very important for removing excess fluid and plasma protains that have filtered from the mircocirculation into the interstitial space = MAINTAINING INTERSTITIAL HOMEOSTASIS

Question 4

What is the Interstitial space

Answer 4

Gel matrix composed of large mucopolysaccharides (primarily hyularonic acid) that hold everything together (tightly coiled and packed into a meshwork)

Question 5

Functions of the interstitial gel matrix

Answer 5

1.) Fills the interstitial space around the tissue and parencyma (provides a pathway for diffusion) 2.) Fluid Trapping - prevents free flow of fluid throughout the body) 3.) Immobilization of trapped particulate matter and bacteria (minimizes the stread of infection)

Question 6

Describe the characteristics of arterioles in microcirculation

Answer 6

1.) Greatest Resistance 2.) Greatest change in pressure (biggest drop)

Question 7

what are exchange vessels

Answer 7

capillaries and small venules

Question 8

Describe the characteristics of exchange vessels in microcirculation

Answer 8

1.) Largest cross sectional area 2.) large surface area 3.) Low pressure 4.) Low velocity

Question 9

What makes microcirculation well suited for exchange of substrates and oxygen

Answer 9

Combination of low pressures, low flow velocity and large surface area

Question 10

Describe the microcirculatory arcade

Answer 10

Tree like branching pattern. Terminal arterioles (metarterioles) to capillaries to small venules and ultimately to larger venules and veins.

Question 11

How does change in arterial size change resistance

Answer 11

small changes result in BIG changes in resistance (1/r^4)

Question 12

Composition of the capillary wall

Answer 12

single layer of thin endothelial cells overlying a basement membrane (basal lamina)

Question 13

Intercellular clefts

Answer 13

endothelial cells in the capillary overlap and are attached through junctional complexes to form intercellular clefts - restrict the movement of larger solutes

Question 14

what lines the capillary endothelium on the luminal side

Answer 14

glycolax “fuzzy coat”

Question 15

List three ways solutes move across the capillary wall

Answer 15

1.) Diffusion 2.) Bulk Flow 3.) Vesicular transport

Question 16

What is the most important means of soulute exchange

Answer 16

Diffusion (can occur in both directions)

Question 17

What dictates capillary diffusion

Answer 17

Flicks law of diffusion

Question 18

Flicks law of diffusion

Answer 18

smaller things have a smaller diffusion coefficient - Inversely proportional to the thickness of the barrier

Question 19

What is bulk flow

Answer 19

When water moves out it washes solutes with it (solutes move with water out of the capillaries) through intercellular clefts

Question 20

Where is bulk flow important

Answer 20

glomerular capillaries

Question 21

What is vesicular transport

Answer 21

Movement of large macromolecules through pinocytotic channels. Occurs on both the luminal and abluminal surfaces and occurs in both directions.

Question 22

How does water move across an exchange vessel

Answer 22

1.) Osmosis (both directions) 2.) Bulk flow (OUTWARD ONLY)

Question 23

How does water move across the capillaries

Answer 23

1.) Transcellular route 2.) Paracellular route

Question 24

Water: Transcellular route

Answer 24

through endothelical cells via water channels (eg: aquaporin 1 on the luminal membrae) High surface area

Question 25

Water: Paracellular route

Answer 25

through intercellular clefts between the endothelial cells. LOW surface area

Question 26

What is filtration

Answer 26

movement of water OUT of the capillaries

Question 27

What is reabsorption

Answer 27

movement of water INTO the capillaries

Question 28

Filtration vs Reabsorbtion… Which exceeds the other

Answer 28

Filtration exceeds reabsortion resulting in NET FILTRATION (goes into the lymph)

Question 29

What are the driving forces for fluid movement

Answer 29

1.) Hydrostatic Pressures 2.) Oncotic Pressures

Question 30

List the types of hydrostatic pressures

Answer 30

1.) Capillary pressure (Pc) 2.) Interstitial hydrostatic pressure (Pi)

Question 31

List the types of oncotoc pressures

Answer 31

1.) Plasma oncotic pressure 2.) Interstitial fluid oncotic pressure

Question 32

What determines the direction of fluid movement

Answer 32

the BALANCE between Hydrostatic and oncotic pressures

Question 33

Capillary hydrostatic pressure (Pc) moves water in what direction

Answer 33

pushes water OUT of the capillary

Question 34

Interstitial Hydrostatic pressure (Pi) moves water in what direction

Answer 34

Pulls water OUT of the capillary

Question 35

Plama oncotic pressure moves water in what direction

Answer 35

pulls water INTO the cappillary

Question 36

Interstitial fluid oncotic pressure moves water in what direction

Answer 36

pulls water OUT of the capillary

Question 37

direction of water movement when hydrostatic pressure is greater than oncotic pressure

Answer 37

water moves out

Question 38

direction of water movement when hydrostatic pressure is less than oncotic pressure

Answer 38

water moves in

Question 39

Describe the change in pressure across the capillary tube

Answer 39

Pressure falls along the tube - 25-35 mmHg at the arteriolar end and 7-10 mmHg at the venular end

Question 40

Changes in capillary hydrostatic pressure with increases in arterial pressure and increases in venous pressure

Answer 40

increas in arterial pressure with cause an increase in capillary pressure but not directly/by as much because it is blunted (multiplied by 0.3) however, changes in venous pressure directly increase the capillary pressure (85% of venous pressure reaches the capillaries)

Question 41

Determinants of Pc

Answer 41

1.) Ratio of postcapillary and precapillary vascular resistance (~0.3) 2.) Arterial pressure (small effect due to 0.3) 3.) Venous pressure (greater effect)

Question 42

How are capillaries protected from sudden changes in arterial pressure

Answer 42

myogenic vasoconstriction

Question 43

What is Pc the measure of

Answer 43

the fluid pressure in the capillaries

Question 44

what is Pi a measure of

Answer 44

the fluid pressure in the interstitial space

Question 45

Interstitial hydrostatic pressure

Answer 45

Slightly atmospheric (averages between 0 and -6 mmHg) Due to normally "dry" interstitail space (maintained by lymphatics)

Question 46

Capillary Filtration Coefficient

Answer 46

Kf : Describes the conductance (1/resistance) of the vessel wall to water

Question 47

Capillary flow equation

Answer 47

Flow = (Pc-Pi)xKf

Question 48

In terms of pressures when does water move out of the capillary

Answer 48

when capillary pressure is greater than interstitial pressure

Question 49

Define osmotic pressure

Answer 49

Hydrostatoc pressure required to oppose the movement of water acorss a semipermeable membrane in response to a differnece in solute concentrations

Question 50

What is the most important determinant of osmotic force

Answer 50

the number of osmotically active molecules in the solution

Question 51

osmotic forces in the vascular bed are due to the presence of what

Answer 51

plasma proteins - large molecular size greater than that of the intercellular clefts. Capillaries are relatively impermeable to plasma proteins

Question 52

what is oncotoc pressure

Answer 52

the osmotic pressure exerted by the plasma proteins

Question 53

Majority of oncotic pressure is due to the presence of what

Answer 53

albumin (78%)

Question 54

Donnan Effect

Answer 54

Since plasma proteins are negatively charged they attract cations (particularly Na) to balance the negative charge. The presence of Na increases the number of particles in solution contributing to the effective osmotic pressure

Question 55

Reflection Coefficient

Answer 55

descrives the relative permeability of the exchange vessels to the plasma proteins 0-1 (1 is impermeable)

Question 56

Net direction of oncotic forces (movement of water)

Answer 56

pulls water in

Question 57

Conditions that increase capillary permeability (ex: allergic reactions or burns) will

Answer 57

disrupt the balance of forces across the capillary wall and will increase both the loss of plasma porteins and fluid filtration

Question 58

Net Oncotic forces (movement of water)

Answer 58

pulls water in

Question 59

Starling Landis Equation

Answer 59

Jv \>0 there is net fluid FILTRATION Jv \<0 there is net fluid REABSORPTION

Question 60

average net fluid filtration in a 70 kg person? What is the fate of this fluid?

Answer 60

3 L/day or 2 ml/min - becomes lymph and is returned to central circulation