Unit 2 - Blood Flow & Blood Pressure PART F

Question 1

Movement of material across the capillary wall.

Answer 1

1. Protein channels (intracellular channels) in endothelial cell membranes and intercellular pores between adjacent cells (paracellular pathway)
2. Serves two purposes
3. Starling forces
4. Net Filtration Pressure
5. Net colloid osmotic pressure

Question 2

Movement of material across the capillary wall.
1. Protein channels (INTRACELLULAR CHANNELS) in endothelial cell membranes and intercellular pores between adjacent cells (PARACELLULAR PATHWAY) are:

Answer 2

a. EXCHANGE SITES FOR H2O, Na+, K+, GLUCOSE, AMINO ACIDS

b. mostly impermeable to macromolecules:
i. E.g. PLASMA PROTEINS (e.g. ALBUMIN) are so large they remain in capillary
ii. Any larger proteins that can be exchanged do so using transcytosis

Question 3

Transcytosis

Answer 3

= endocytosis into endothelial cell from plasma/ISF, transport across cell, ending with exocytosis from cell into the ISF/plasma.

Question 4

Tissues with a ↑ metabolic rate req. more O2 & nutrients. Therefore,

Answer 4

have MORE capillaries per unit area

• subcutaneous tissue & cartilage have the LOWEST capillary density
• muscles & glands have the HIGHEST

Question 5

Movement of material across the capillary wall.
2. Serves two purposes

What are they?

Answer 5

a. Exchange of material between the blood and the cells.

b. Maintain fluid balance between plasma and interstitial fluid.

Question 6

Movement of material across the capillary wall.

2. Serves two purposes
   a. Exchange of material between the blood and the cells.

Answer 6

• Rapid DIFFUSION of small solutes across capillary walls –> i.e. down PARTIAL PRESSURE, electrochemical, and concentration gradients
• Certain proteins are selectively transported across endothelial cells by a slow, energy-requiring process (TRANSCYTOSIS)

Question 7

Movement of material across the capillary wall.

2. Serves two purposes
   b. Maintain fluid balance between plasma and interstitial fluid.

Answer 7

• Distribution of ECF between plasma and ISF in a state of dynamic equilibrium due to FILTRATION and ABSORPTION of fluid by capillaries
• Via the BULK FLOW of protein-free plasma through channels and pores driven by HYDROSTATIC and COLLOID OSMOTIC PRESSURE gradients (termed ‘STARLING FORCES’) that augment diffusion processes

Question 8

Filtration

Answer 8

the fluid movement, if the direction of flow is OUT of the capillaries
- caused by hydrostatic pressure that forces fluid out of the capillary through leaky cell junctions

ANALOGY: think of garden “soaker” hoses whose perforated walls allow water to ooze out

Question 9

Absorption

Answer 9

the fluid movement, if the direction of bulk flow is INTO the capillaries

Question 10

Bulk Flow

Answer 10

mass movement of fluid as the result of hydrostatic or osmotic pressure gradients

Question 11

Hydrostatic Pressure

Answer 11

lateral pressure component of BF that pushes fluid out through the capillary pores

Question 12

Colloid Osmotic Pressure

Answer 12

a measure of the osmotic pressure created by proteins

• higher in the plasma (πcap = 25 mm Hg) than in the interstitial fluid (πIF - mm Hg)
• therefore, the osmotic gradient favours water movement by osmosis from the interstitial fluid into the plasma
• constant along the length of the capillary, π = 25 mm Hg

Question 13

Osmotic pressure

Answer 13

is determined by solute concentration of a compartment

• the main solute diff. b/t plasma & interstitial fluid is due to proteins
• the osmotic pressure created by the presence of these proteins is known as colloid osmotic pressure (π)

Question 14

Most capillaries show a transition from net _____ at the arterial end to net ______ at the venous end

Answer 14

filtration

absorption

Question 15

Movement of material across the capillary wall.

3. Starling forces

Answer 15

a. PC = capillary hydrostatic pressure (HP)
b. PI = interstitial fluid hydrostatic pressure
c. πC = plasma colloid-osmotic pressure
d. πI = colloid-osmotic pressure of interstitial fluid

Question 16

PC = capillary hydrostatic pressure (HP)

Answer 16

• HP inside capillary favouring FILTRATION of plasma
• declines as blood moves from arteriole (~37 mm Hg) to venule side (~17 mm Hg) of capillary (as energy is lost to friction)

Question 17

PI = interstitial fluid hydrostatic pressure

Answer 17

• HP outside capillary favouring ABSORPTION of ISF

- ~1 mm Hg

Question 18

πC = plasma colloid-osmotic pressure

Answer 18

• osmotic pressure within capillary due to NONPENETRATING solutes that favours ABSORPTION of interstitial fluid
• ~25 mm Hg

Question 19

πI = colloid-osmotic pressure of interstitial fluid

Answer 19

• osmotic pressure due to nonpenetrating solutes within the
  ISF that favours plasma filtration
• ~0 mm Hg –> means that water movement due to hydrostatic pressure is directed out of the capillary, with the pressure gradient decreasing from the arterial end to the venous end

Question 20

Movement of material across the capillary wall.

4. Net Filtration Pressure

Answer 20

a. PC - PI = AT ANY GIVEN POINT ALONG THE CAPILLARY.
- Force favouring plasma FILTRATION along entire length of
capillary
- = 37 – 1 = 36 mmHg

Question 21

Movement of material across the capillary wall.

5. Net colloid osmotic pressure

Answer 21

a. πC – πI.
- force favouring ABSORPTION of ISF along entire length of capillary
- = 25 – 0 = 25 mmHg

Question 22

Net fluid movement at any given point in capillary:

Answer 22

= Net P – Net π
= 36 mmHg – 25 mmHg = +11 mmHg (filtration)
= 16 mmHg – 25 mmHg = -9 mmHg (absorption)

Question 23

Positive values indicate _______, negative values indicate ________

Answer 23

FILTRATION

ABSORPTION

Question 24

If the point at which filtration =’s absorption occurred in the middle of the capillary, there would be…

Answer 24

NO net movement of fluid

• all volume that was filtered at the arterial end would be absorbed at the venous end
• however, filtration is usually greater than absorption, resulting in bulk flow of fluid out of the capillary into the interstitial space

Question 25

If filtered fluid couldn’t be returned to the plasma, the blood would turn into…

Answer 25

a sludge of blood cells & plasma