Capillary Permeability

Question 1

what percent of total circulating blood is in the capillaries at any given time?

Answer 1

• 5%

- this amount is the most important part of the blood volume

Question 2

what is the capillary wall made up of?

Answer 2

-a semipermeable membrane composed of a single layer of endothelial cells to promote efficient exchange

Question 3

what components are exchanged between blood and cells during capillary exchange?

Answer 3

• all nutrients
• gases
• metabolites
• water

Question 4

why are capillaries efficient sites for gas and nutrient exchange?

Answer 4

• blood velocity is low, allowing time for exchange

- huge surface area (over 10 mil capillaries in the human body)

Question 5

what are the 3 main exchange mechanisms between capillaries and interstitial space?

Answer 5

• diffusion
• bulk flow
• vesicular transport

Question 6

describe the diffusion exchange mechanism

Answer 6

• passive movements of nutrients, O2, CO2 and lipid soluble substances
• driven by osmotic gradients
• critical point - plasma proteins cannot cross capillary wall

Question 7

describe the bulk flow exchange mechanism

Answer 7

• ultrafiltration
• movement of water soluble substances and extracellular fluid
• occurs through water-filled pores or intercellular clefts

Question 8

describe the vesicular transport exchange mechanism

Answer 8

-larger, exchangeable macromolecules cross capillary endothelium via vesicular trancytosis

Question 9

name 4 factors that affect the rate of diffusion

Answer 9

1) faster at higher temps (due to Brownian movement)
2) faster with higher concentration gradient
3) faster for smaller solutes
4) slower in more viscous solutions

Question 10

T or F:

diffusion can only occur if membrane is permeable to the solute

Answer 10

true

Question 11

T or F:

lipid solubles materials do not pass through the plasma membrane of endothelial cells

Answer 11

false

they pass directly through the plasma membrane

Question 12

how can water molecules cross the plasma membrane?

Answer 12

-pass through spaces/pores between endothelial cells via bulk flow or vesicular transport

Question 13

how can exchangeable proteins cross the plasma membrane?

Answer 13

vesicular transport

Question 14

what are hydrostatic and oncotic pressures?

Answer 14

• different net pressures that operate at capillary beds to cause most of the plasma’s fluid to be filtered out at the arteriolar end
• the fluid is then mostly reabsorbed at the venous end
• the small amount of fluid that remains in the interstitial space becomes part of the interstitial fluid compartment

Question 15

what do lymphatic vessels do?

Answer 15

• collect excess interstitial fluid and return it to the venous bloodstream
• fluid is called lymph once it enters the lymphatic vessels

Question 16

T or F:

lymphatic vessels form a one-way system in which lymph only flows back toward the heart

Answer 16

true

Question 17

what 3 pressures make up starling forces?

Answer 17

• crystalline osmotic pressure
• oncotic pressure
• hydrostatic pressure

Question 18

what is crystalline osmotic pressure?

Answer 18

• oncotic pressure due to small molecules in plasma
• small molecules are water-soluble, so concentrations are equivalent on either side of capillary wall, so there is no effect on water flow

Question 19

what is oncotic pressure?

Answer 19

• osmotic pressure exerted by impermeable plasma proteins in a blood vessel’s plasma that pull water into the circulatory system from interstitial fluid
• albumin is main plasma protein
• increases the length of the capillary

Question 20

what is hydrostatic pressure?

Answer 20

-force that is directed out of the capillary by a fluid pushing against the capillary wall

Question 21

What is Starling’s Law?

Answer 21

-fluid leaves (via filtration) or re-enters (via reabsorption) the capillary depending on how the opposing pressures in the capillary and in the interstitial spaces relate to one another (hydrostatic and oncotic mainly)

Question 22

what is the equation of Starling’s Law?

Answer 22

NFP = (net forces pushing out) - (net forces pushing in)

NFP = (HPc + OPif) - (HPif + OPc)

NFP = net filtration pressure
HPc = capillary hydrostatic pressure
HPif = interstitial fluid hydrostatic pressure
OPc = oncotic pressure due to protein concentration
OPif = osmotic pressure due to interstitial fluid protein concentration

Question 23

describe velocity of blood flow in the aorta and capillaries

Answer 23

• speed of blood flow changes as it passes through systemic circulation
• fastest in aorta
• slowest in capillaries
• remember, reduced velocity facilitates exchange

Question 24

what is hydrostatic pressure?

Answer 24

• force per unit area exerted on the wall of a blood vessel by the blood
• this pressure gradient provides the driving force that keeps blood moving from higher to lower pressure areas

Question 25

how is capillary microcirculation regulated?

Answer 25

• capillary beds
• vascular shunts
• precapillary sphincter

Question 26

T or F:
fluid moves through the interstitial space at the arterial level, and fluid and lymphatics are reabsorbed at the venule level

Answer 26

true

Question 27

T or F:

pinocytosis and trancytosis are used in the diffusion exchange mechanism

Answer 27

false

they are used in the vesicular transport exchange mechanism

Question 28

what determines the bulk flow of protein-free plasma and interstitial fluid?

Answer 28

the relative hydrostatic and oncotic pressures on either side of the capillary wall (starling forces)

Question 29

describe 5 characteristics of lymphatic capillaries

Answer 29

1) blind-ended sacs in interstitial space
2) relatively low pressure
3) absorb fluids from interstitial space only; unidirectional toward the heart
4) wider than blood capillaries
5) colorless

Question 30

describe 5 characteristics of blood capillaries

Answer 30

1) join to arterioles on one end and venules on the other end
2) higher pressure than lymphatic capillaries
3) filter and then reabsorb most of the fluids by bulk flow into interstitial space
4) narrower than lymphatic capillaries
5) reddish and easy to observe

Question 31

what 4 events can potentially cause edema?

Answer 31

• increased capillary blood pressure
• decreased plasma colloid osmotic (oncotic) pressure
• increased capillary permeability
• obstruction/disruption of lymphatics (lymphedema)