Blood II

Question 1

There are […] major forms of fluid transport across the capillary wall: […]

Answer 1

2, filtration and osmotic flow

Question 2

What is bulk flow?

Answer 2

Bulk flow is the flow of molecules subjected to a pressure difference. It is directly proportional to hydrostatic pressure difference.

Question 3

How does bulk flow relate to filtration in the capillaries?

Answer 3

Filtration is bulk flow across a porous membrane (the capillary wall), where large particles will be withheld.

Question 4

Filtration tends to […] fluid in the capillaries because […], while osmotic flow tends to […] fluid in the capillaries because […]

Answer 4

Push out, hydrostatic pressure difference, pull in, of the osmotic pressure exerted by plasma proteins

Question 5

The two […] forces in the capillaries, […] and […], come together to form the […]

Answer 5

Opposing, filtration and osmotic flow, starling forces

Question 6

Explain how blood pressure changes as it travels through the circulatory system.

Answer 6

When the heart contracts, it generates a pressure of around 120 mm Hg. When it relaxes, the pressures comes down to 80 mm Hg. When the blood reaches the capillaries at the arterial end, the pressure drops to 35 mm Hg because the surface area is greater and there is energy loss. When the blood leaves the capillaries at the venous end, the pressure has dropped further to 15 mm Hg.

Question 7

Exchanges between the plasma and the ISF take place in the […]

Answer 7

Capillary bed

Question 8

Why do exchanges between the plasma and the ISF only take place where they do?

Answer 8

They only take place in the capillary bed because the capillaries have thin enough walls for exchanges. Everywhere else, the walls are too thick.

Question 9

The blood pressure in the capillaries at the arterial side is […], while at the venous side it is […]

Answer 9

35 mm Hg, 15 mm Hg

Question 10

The COP is equal to […]

Answer 10

25 m Hg

Question 11

Describe the major forces involved in transcapillary dynamics and where net absorption and net filtration are observed in the capillary bed.

Answer 11

At the arterial end, filtration exerts a pressure 35 mm Hg and COP exerts an opposing pressure of 25 mm Hg, creating a net filtration of 10 mm Hg. At the venous end, filtration exerts a pressure fo 15 mm Hg and COP exerts an opposing pressure of 25 mm Hg, creating a net absorption of 10 mm Hg.

Question 12

Name the 4 substances that exchange through the capillary wall (aside from fluid) and the mode of transport.

Answer 12

Nutrients, O2, CO2, and waste are exchanged via simple diffusion.

Question 13

Starling’s capillary dynamics determine the […] of the […] volume

Answer 13

Distribution, ECF

Question 14

Filtration/absorption takes place […]

Answer 14

Along the whole length of the capillary

Question 15

Describe how filtration/absorption varies across the length of the capillary.

Answer 15

Arterial end: high rate of fluid moving out of the cell, as we move towards the center net filtration decreases, at the middle it’s bidirectional, moving towards the venous end the net absorption increases, at venous end there’s a lot more absorption.

Question 16

[…]% of the fluid that leaves the capillary is reabsorbed. The other [..]% goes into the […]

Answer 16

90%, 10%. lymphatic system

Question 17

The walls of the lymphatic vessels are made up of […] and are permeable to […]

Answer 17

A single layer of endothelial cells, all ISF constituents including proteins that may have leaked from the plasma

Question 18

Explain how the flow of blood remains in balance (include numbers) - draw a diagram to illustrate

Answer 18

Of the 6000 L of blood flow per day, 20 L get filtered through the capillary wall into the interstitial fluid. 17 L get reabsorbed into the capillary and 3 get picked up by the lymphatic system and are returned to the capillary by lymph drainage. [See slide for diagram]

Question 19

Each protein fraction exerts an osmotic pressure, which depends on […]

Answer 19

Its concentration (higher concentration = higher COP), its molecular weight (smaller MW = higher COP)

Question 20

Explain the relationship between plasma protein COP and molecular weight.

Answer 20

It is an inverse relationship. Albumin is the lightest protein but is high in concentration, and is responsible for 20 mm Hg out of 25 total in the plasma. Fibrinogen is the heaviest protein but is low in concentration, and is responsible for <1 mm Hg out of 25. Globulins fall in the middle and exert 5 mm Hg out of 25.

Question 21

Albumin exerts […] mm Hg COP in the plasma out of […]

Answer 21

20 out of 25

Question 22

Globulins exert […] mm Hg COP in the plasma out of […]

Answer 22

5 out of 25

Question 23

Fibrinogens exert […] mm Hg COP in the plasma out of […]

Answer 23

<1 out of 25

Question 24

The main protein that causes the COP to rise is […]

Answer 24

Albumin

Question 25

The key function of albumin is to […]

Answer 25

Control fluid shifts across the capillary wall

Question 26

Name the 4 major factors involved in determining transcapillary dynamics

Answer 26

Hydrostatic pressure, COP, capillary permeability (can vary under certain conditions), and lymphatic drainage

Question 27

What is edema?

Answer 27

The accumulation of excess fluid in interstitial spaces

Question 28

When someone has edema, the proportion of […] increases, while the proportion of […] decreases

Answer 28

ISF, plasma

Question 29

Name the four possible conditions that can lead to edema.

Answer 29

1. Increased hydrostatic pressure
2. Decrease in plasma proteins (decreased COP_
3. Increased capillary permeability
4. Obstruction of lymphatic drainage

Question 30

Explain how hydrostatic pressure affects edema.

Answer 30

If hydrostatic pressure increases enough, it may overwhelm the COP and prevent any net absorption from occurring, even at the venous end - instead you could get no net absorption or just net filtration.

Question 31

Explain how plasma proteins affect edema.

Answer 31

If the prevalent of plasma proteins decreases such that COP decreases, it may overwhelm the hydrostatic pressure and prevent any net absorption

Question 32

Name two possible causes of decreased COP.

Answer 32

Failure to synthesize plasma proteins (e.g. due to liver disease) or severe protein malnutrition (lack of amino acids)

Question 33

Explain how capillary permeability affects edema.

Answer 33

If the capillary wall becomes more permeable, some of the plasma proteins escape into the ISF where they exert an oncotic effect. So this works against the COP and encourages outflow of fluid from the capillaries into the ISF.

Question 34

Explain how lymphatic drainage affects edema.

Answer 34

If the 10% of ISF cannot be absorbed and brought back into the capillaries, the remaining fluid just remains in the interstitial space.

Question 35

Obstructed lymphatic drainage can lead to a condition known as […]

Answer 35

Elephantiasis

Question 36

The cause of elephantiasis is [..]

Answer 36

A parasite (Filaria nematode) that blocks lymphatic drainage.

Question 37

Name the 3 roles of plasma proteins.

Answer 37

1. Controlling transcapillary dynamics
2. Contribution to the viscosity of plasma, maintaining blood pressure
3. Contribution to the buffering power of plasma to maintain it at its normal pH of 7.4

Question 38

Name the specific function(s) of fibrinogen

Answer 38

Clotting

Question 39

Name the specific function(s) of globulins

Answer 39

Clotting, Y globulins provide resistance to infection, some act as carriers for lipids, minerals, and hormones

Question 40

Name the specific function(s) of albumin

Answer 40

Act as carriers for lipids, minerals, and hormones

Question 41

The production of platelets is called […]

Answer 41

Thrombopoiesis

Question 42

The production of white blood cells is called […]

Answer 42

Leukopoiesis