Block 3 - Bsf: Microcirculation And Lymphatics

Front 1

Where does microcirculation occur?

Back 1

Extends from 1st order arteriole to 1st order venule with a network of true capillaries in between them

Front 2

How can the flow through capillaries be altered?

Back 2

By contraction or relaxation of small arteries, arterioles and metarterioles.

Front 3

What type of movement across the capillary promotes exchange of gases, substrates and waste?

Back 3

Diffusion

Front 4

What type of movement across the capillary has net transfer of fluid achieved by this and absorption.

Back 4

Filtration

Front 5

T/F

Capillary permeability is the same across different tissues.

Back 5

False!

Capillary permeability varies in different tissues.

Also, the venous end of a capillary is more permeable than the arterial end.

Front 6

What is the most common type of capillary?

Back 6

Continuous capillary

Front 7

Which type of capillary has inter-endothelial junctions 10-15 nm wide?

Back 7

Continuous capillary

Front 8

A special exception in the continuous capillary is what?

Back 8

The blood brain barrier.

Clefts are absent - instead capillaries have tight junctions

Front 9

What type of capillary has thin endothelial cells and perforations?

Back 9

Fenestrated capillary

Front 10

What type of capillary is found in surrounding epithelia of the small intestine, exocrine glands and glomerular tufts of kidney?

Back 10

Fenestrated capillary

Front 11

Which type of capillary has large gaps, in addition to fenestrae.

Back 11

Sinusoidal (discontinuous) capillaries

Front 12

Where are sinusoidal (discontinuous) capillaries primarily found?

Back 12

Found primarily in the sinusoids of the liver

Front 13

Fick’s law as it relates to the vasculature
J = S Px([C]o – [C]i)

What does each variable represent?

Back 13

J: flux of substance per unit time
S: capillary surface area
Px: capillary permeability to X
([C]o – [C]i): Difference between concentration in capillary and concentration outside capillary

Front 14

Fick's law of diffusion (diffusion of water-soluble, non-liquids)

J = -DA (dc/dx)

What does each variable represent?

Back 14

J: flux of substance per unit time
D: diffusion coefficient of molecule
A: cross sectional area
Dc/dt: concentration gradient

Front 15

T/F

Diffusion depends largely on molecular size and concentration difference.

Back 15

True!

Front 16

T/F

Relative permeability is fairly constant amongst capillary beds.

Back 16

False!

Relative permeability (Px) varies in different capillary beds.

Front 17

Molecules move across the capillary membrane at a rate that is (directly/inversely) proportional to their size until MW ~ 60,000.

Beyond this size, what happens?

Back 17

Inversely

Beyond this size molecules do not pass through the membrane.

Front 18

How do lipid insoluble molecules diffuse from the capillaries?

Back 18

Through pores of the capillaries

Front 19

Capillaries have little restriction to diffusion (small reflection coefficient), and diffusion is rapid, when the molecules are what?

Back 19

Small molecules

Front 20

What is it called when, for small molecules, the only limit to net movement is the rate of blood flow?

Back 20

Flow limited

Front 21

What is it called when, for large molecules, capillary permeability to the large molecules limits its transport across the capillary wall?

Back 21

Diffusion limited

Front 22

How do lipid soluble molecules diffuse from the capillaries?

Back 22

Pass readily through endothelial cells.

Front 23

Water can travel through what 2 pathways?

Back 23

Transcellular and paracellular pathways

Front 24

What is the principle trans-cellular pathway?

Back 24

Aquaporins (AQP1)

Front 25

T/F

Water moves via convection.

Back 25

True!

Front 26

According to Starling, what are the 2 driving forces for movement of water

Back 26

1) trans-capillary hydrostatic pressure difference (blood pressure).

2) effective osmotic pressure difference (colloid osmotic pressure or oncotic pressure).

Front 27

What is the principal force in capillary filtration?

Back 27

Hydrostatic pressure

Front 28

Fluid leaves the capillaries if Pc is (less/greater) than Pif.

Back 28

Greater

Front 29

T/F

Hydrostatic pressure promotes filtration.

Back 29

True!

Front 30

What are 5 factors affecting capillary pressure?

Back 30

Resistance, changes in upstream and downstream pressure, location, time and gravity.

Front 31

Decreasing pre-capillary resistance or increasing post-capillary resistance causes a)(decrease/increase) in hydrostatic pressure in capillary. Therefore, b)(less/more) fluid leaks out.

Back 31

a) Increase
b) More

Front 32

Increasing pre-capillary resistance or decreasing post-capillary resistance causes a)(decrease/increase) in hydrostatic pressure in capillary. Therefore, b)(less/more) fluid leaks out.

Back 32

a) Decrease
b) Less

Front 33

Increasing pre-capillary pressure or increasing post-capillary pressure causes (decrease/increase) in capillary pressure.

Back 33

Increase

Front 34

What are 3 examples of location affecting capillary pressure?

Back 34

Kidney - very high Pc of near 50mmHg required for ultrafiltration

Retinal capillaries - bathe vitreous humor ~20mmHg

Pulmonary capillaries - very low between 5-15mmHg to avoid edema in alveolar air spaces

Front 35

Why does capillary pressure vary over time at any given site?

Back 35

Primarily due to factors that influence arteriolar diameter and pre-capillary sphincter.

Front 36

What are 2 solid structures in the interstitium and interstitial fluid?

Back 36

Collagen fiber bundles: strong and provide tensile strength of the tissues

Proteoglycan filaments: forms fine reticular filaments

Front 37

What part of the interstitial fluid is similar to plasma but has a lower concentration of protein?

Back 37

Gel

Front 38

What fluid is trapped in the proteoglycan filaments?

Back 38

Gel

Front 39

T/F

Interstitial fluid flows through the gel.

Back 39

False!

Fluid does not flow through the gel but moves via diffusion, one molecule at a time. This occurs 95-99% as rapidly as through free fluid.

Front 40

How much "free" fluid (not trapped in the gel) is there normally in interstitial fluid?

What about in edema?

Back 40

Usually less than 1%.

During edema the free fluid pockets expand so that over half the fluid is free of the proteoglycan filaments

Front 41

Interstitial fluid pressure (Pif) is usually (negative/positive) in loose tissues, due to fluid removal by the lymphatic system.

Back 41

Negative

In general, Pif is close to zero or slightly negative.

Front 42

When may Pif be positive?

Back 42

In rigid compartments like bone marrow or brain or in encapsulated organs like kidney.

Front 43

The difference in colloid osmotic pressure between plasma proteins and interstitial fluid proteins and protoglycans is called what?

Back 43

Oncotic pressure

Front 44

Molecules with MW greater than 30,000 are called what?

Back 44

Colloids

Front 45

T/F

All molecules present in the capillary contribute to oncotic pressure.

Back 45

False!

Only those molecules that do not move across the capillary wall contribute to the oncotic pressure.

Front 46

What is the key factor that retains fluid loss from capillaries?

Back 46

Plasma proteins

Front 47

When π c (capillary oncotic pressure) is greater than π if (interstitial fluid oncotic pressure), what happens?

Back 47

This promotes absorption and fluid wants to enter the capillary.

Front 48

What is the principle force in capillary absorption?

Back 48

Oncotic pressure

Front 49

A factor that affects capillary oncotic pressure is composition of what?

Back 49

Plasma proteins

Front 50

T/F

Capillary oncotic pressure stays relatively constant.

Back 50

False!

Due to diff molecular wgts π c can vary considerably (mmol amount of each is what matters)

Front 51

What is the average capillary oncotic pressure?

Back 51

Average πc ~25 mmHg

Front 52

What is the equation for Net Filtration Pressure (NFP)?

Back 52

NFP = (Pc – Pif) – (πc –πif)

For arterial side:
(35-0) – (26-1) =
35 – 25 = +10 mmHg

For venous side:
(17–0) – (26-1) =
17 - 25 = - 8 mmHg

Front 53

In the intestinal mucosa, which is lower, capillary pressure or capillary oncotic pressure?

Back 53

Pc always much lower than πc so that re-absorption occurs continually.

Front 54

In the kidney, which is lower, capillary pressure or capillary oncotic pressure?

Back 54

Glomerular capillary Pc exceeds πc so that filtration occurs almost continuously.

Front 55

What are the 2 semi-indepedendent parts of the lymphatic system?

Back 55

A meandering network of lymphatic vessels

Lymphoid tissues and organs scattered throughout the body

Front 56

When is interstitial fluid called lymph?

Back 56

Once it has entered lymphatic vessels

Front 57

What are the general functions of the lymphatic system?

Back 57

Maintaining fluid balance, purification and defense, and nutrition.

Front 58

How does the lymphatic system maintain fluid balance?

Back 58

Transports interstitial fluid back to circulation
Transports protein back to circulation

Front 59

How is the lymphatic system involved in purification and defense?

Back 59

Clears extra-cellular space of particulate matter, exudates and bacteria
Brings immune cells in contact with invaders

Front 60

How is the lymphatic system involved in nutrition?

Back 60

Absorbs fats from the small intestine

Front 61

T/F

The lymphatic system has an organ which acts as a pump.

Back 61

False!

The lymphatic system lacks an organ that acts as a pump.

Front 62

Lymphatic vessels are (low/high)-pressure conduits.

Back 62

Low

Front 63

a) The lymphatic vessels propel lymph using the same methods as what other vessels?

b) What methods are these?

Back 63

a) Veins

b) Pulsations of nearby arteries
Contractions of smooth muscle in the walls of the lymphatics

Front 64

Filtration at arteriolar end is (less than/greater than) reabsorption at venular end of capillaires.
What does this result in?

Back 64

Greater than

Net loss of fluid from plasma

Front 65

What lymphatics are open to the liquid phase of the interstitium?

Back 65

Terminal lymphatics

Front 66

Where are lymphatics absent or reduced?

Back 66

Myocardium and brain

Front 67

Where are lymphatics prevalent?

Back 67

Skin, respiratory, urogenital and gastrointestinal regions.

Front 68

What are 5 factors that influence interstitial pressure?

Back 68

Capillary hydrostatic pressure
Plasma protein
Interstitial protein
Capillary permeability
Interstitial hydrostatic pressure

Front 69

What factors affect lymph flow?

Back 69

Factors influencing interstitial pressure
Lymphatic pumping (Intrinsic pumping by smooth muscle and extrinsic pumping)

Front 70

What is the amount of fluid (in liters) related to each loop of the circulation of extra-cellular fluid?

Back 70

1) cardiovascular loop
5 l/min = 7200 l/day

2) trans-vascular loop
Filter 20 l at arteriolar end
Re-absorb 16-18 l at venule end

3) lymphatic loop
Returns 2-4 l back to venous system

Front 71

Where is the primary site for delivery of glucose to tissues?

Is any glucose absorbed?

Back 71

Diffusion at capillaries

No, none is absorbed

Front 72

A (small/large) amount of proteins is filtered, while a (small/large) amount is absorbed.

Back 72

Large, small

Front 73

T/F

Most proteins are returned to the blood stream via lymphatics.

Back 73

True!

Front 74

a) Why does edema occur in most cases?

b) Why else can it occur?

Back 74

a) As a result of increased fluid accumulation in the interstitial space.

b) As a result of increased fluid inside of cells.

Front 75

What are the extracellular effects of edema?

Back 75

A disruption in the balance of Starling forces
An increase in capillary permeability

Front 76

What are the intracellular effects of edema?

Back 76

↓ activity of Na+-K+ ATPase (due to ↓ O2) can result in an increase in sodium inside the cell, which draws water into cell