Lesson 26: Topic 22 - Capillary Filtration and Reabsorption

Question 1

what is capillary filtration?

Answer 1

fluid exiting the capillary into the interstitial fluid

Question 2

what is capillary absorption?

Answer 2

fluid entering the capillary from the interstitial fluid

Question 3

what is the primary function of capillary filtration/absorption?

Answer 3

regulate/dictating the distribution of extracellular fluid between the plasma and interstitial fluid
- also plays an important regulatory role in moving solutes (not gases) in and out of the capillary

Question 4

why is capillary filtration and absorption not playing a role in moving gases in and out of the capillary?

Answer 4

because gases can readily diffuse across. they do not need the help of filtration/absorption to do so

Question 5

whether a substance is filtrated of absorbed is predominantly dictated by?

Answer 5

hydrostatic pressure and osmotic pressure

Question 6

what is hydrostatic pressure?

Answer 6

refers to the pressure being induced by the fluid within a confined space
ex1. in a capillary, we have blood in a confined space and that is going to be exerting a certain pressure on the capillary that will drive the liquid into a certain direction
ex2. we have fluid inside the interstitial fluid and that is going to generate a pressure.

Question 7

what is osmotic pressures?

Answer 7

the pressure dictated by solutes (dissolved substances that are inside a substance and fluid
ex. if two balloons were able to diffuse, water will move into salty water to dilute salty water (think grade 12)

Question 8

what are the two places we can have hydrostatic and osmotic pressures?

Answer 8

• capillary (capillary hydrostatic pressure Pc and Osmotic force (PiC - Plasma proteins)
• interstitital fluid (interstitial fluid hydrostatic pressure Pif and Osmotic force (interstitial fluid proteins PiIF)

Question 9

the osmotic forces that are going to be dictated by the movement of fluid is going to do with the osmotic forces insider the capillary due to?

Answer 9

plasma proteins (albumin)

Question 10

why do we want something like albumin to not be able to leave the capillary?

Answer 10

because they play an important role in driving liquid back into the capillary

Question 11

any plasma proteins that are inside the interstitial fluid can help draw liquid into?

Answer 11

the interstitial space

Question 12

how can net filtration pressure be calculated?

Answer 12

with adding the forces that dictate capillary filtration(PC and PiIF) and subtracting the forces that dictate capillary absorption (PIF and PiC)

Question 13

what dictates capillary filtration (the movement of fluid over of the capillary)?

Answer 13

• capillary hydrostatic pressure
• osmotic force (interstitial fluid proteins)

Question 14

if net filtration pressure is positive, what does that dictate?

Answer 14

an outward movement of fluid from the capillary into the interstitial space (filtration)

Question 15

if net filtration pressure is negative, what does that dictate?

Answer 15

an inward movement of fluid from the interstitial space into the capillary (absorption)

Question 16

blood pressure in a capillary =

Answer 16

capillary pressure

Question 17

what is the capillary hydrostatic pressure on the arterial end of a capillary?

Answer 17

37mmHg

Question 18

what is the capillary hydrostatic pressure on the venous end of a capillary?

Answer 18

17mmHg

Question 19

what is the osmotic force of the capillary(albumin) at the arterial and venous end of a capillary?

Answer 19

25 - ALWAYS - albumin does not go anywhere EVER. when we are exercising it still does not leave the capillary

Question 20

what is the hydrostatic pressure in the interstitial fluid?

Answer 20

1

Question 21

what is the osmotic force in the interstitial fluid?

Answer 21

always 0

Question 22

on which end of a capillary do we have net filtration and on which end do we have net absorption?

Answer 22

arterial end: net filtration
venous end: net absorption

Question 23

Equation for calculating net filtration.

Answer 23

NF = Pc + PiIF (0) - PIF (1) - PiC(25)

Question 24

which end of a capillary is favouring absorption?

Answer 24

venous end (think of it like CO2 is going (absorbing) into the veins to leave the body)

Question 25

if we have a raised capillary pressure (upstream arterioles vasodilate), what happens?

Answer 25

for majority of the length of the capillary, it is going to favour filtration

Question 26

why would we want to raise capillary pressure and favour filtration?

Answer 26

because we want to deliver electrolytes - the movement of certain ions of maintain essentially the ability for skeletal muscle to depolarize properly - we want to deliver nutrients to skeletal muscle during exercise because it requires it

Question 27

when we have a lowered capillary pressure, (upstream arterioles vasoconstrict), what happens?

Answer 27

for majority of the length of the capillary, it is going to favour absorption

Question 28

in what organs are we going to have a lowered capillary pressure?

Answer 28

bones, kidneys and digestive tract

Question 29

why does a vasoconstriction of arterioles make a capillary pressure drop?

Answer 29

Vasoconstriction of arterioles increases resistance, which reduces the blood flow into capillaries, leading to a lower capillary pressure.

Question 30

why would we want our kidneys, digestive tract and bones to favour absorption during exercise?

Answer 30

this way, if the arterioles constrict (which is what causes the drop in capillary pressure in order to favour absorption), causing vasoconstriction towards bone, we can essentially make sure that glucose is efficiently delivered to skeletal muscle and not to tissue that does not need it

Question 31

if we dehydrate, is our cardiac output reduced?

Answer 31

yes

Question 32

why does our cardiac output reduce when we are dehydrated?

Answer 32

because our total plasma volume drops

Question 33

when we are dehydrated, our total plasma volume decreases so our MAP drops so our cardiac output drops. what happens to capillary pressure?

Answer 33

it also drops

Question 34

why would we want capillary pressure to drop if we are dehydrated?

Answer 34

so that we favor reabsorption and this way it is going to help to draw fluid from our organs back into our plasma volume in order to restore plasma volume

Question 35

what is the osmotic pressure of albumin (PiC)?

Answer 35

25mmHg

Question 36

what is the net filtration pressure on the arterial side of the capillary?

Answer 36

11mmHg (favoring filtration)

Question 37

what is the net filtration pressure on the venous side of the capillary?

Answer 37

9 mmHg (favoring reabsorption)

Question 38

during the resting state, is filtration or absorption favoured?

Answer 38

filtration (11mmHg vs 9mmHg) - this means that we have an accumulation of fluid inside our interstitial fluid all the time

Question 39

the accumulation of fluid inside our interstitial fluid due to capillary filtration goes where?

Answer 39

into the lymphatic system via the initial lymphatics (lymph capillaries)

Question 40

what is edema?

Answer 40

excess fluid accumulation in the extracellular/interstitial space

Question 41

what does the lymphatic system connect to?

Answer 41

both the blood capillaries in your lungs in your pulmonary circulation and also to the capillaries in your systemic circulation - lymphatic system is present in both your pulmonary circulation and your systemic circulation

Question 42

where is the lymphatic system?

Answer 42

it is parallel to the venous circulation - it does not connect to the arterial side, only the venous side

Question 43

is the lymphatic system an open or closed circulation?

Answer 43

open circulation

Question 44

why is the lymphatic system an open circulation?

Answer 44

because where the lymph vessel drains into the venous system, it does not connect back to where the lymph system is essentially getting the fluid from. so the lymph system is essentially dumping fluid into a pool (your circulatory system) but it does not meet up with the start of the lymphatic system

Question 45

what ensures a one-way flow of the lymphatic system?

Answer 45

the one way valves in the lymph vessels

Question 46

what allows the lymph vessels to move the fluid in one direction?

Answer 46

smooth muscle is situated in the lymph vessels to help move the fluid in the one direction

Question 47

is there smooth muscle in the lymph capillaries?

Answer 47

no, it is a capillary. it only has endothelial cells

Question 48

what are the important functions of the lymphatic system

Answer 48

- fluid balance - immune surveillance - movement of immune cells

Question 49

when we get sick, our lymph nodes swell up. this is because it detects an infection in our body. how does it detect an infection?

Answer 49

it detects it because of the little bit of interstitial fluid that is accumulating in the tissues that is then being drained into the lymphatic system that is then undergoing detection by the immune system in the lymph nodes.

Question 50

if you have an infection, your lymph nodes will detect this and then what happens?

Answer 50

immune cells are going to be released from the lymph nodes (T and B cells) which will drain into the immune system to start fighting off an infection in the circulatory system

Question 51

about 20L per day of fluid is undergoing capillary filtration, of this, how much L/day is going to be reabsorbed back into the capillary?

Answer 51

17L/day

Question 52

20L per day of fluid is undergoing capillary filtration and of that, 17L/day is getting reabsorbed. what happens to the 3L/day?

Answer 52

it gets filtered by the lymphatic system

Question 53

what happens if we block the lymphatic system? ex. in the leg.

Answer 53

our leg will swell up

Question 54

what is the difference in structure between blood and lymph capillaries?

Answer 54

blood capillaries: the endothelial cells are adjacent to another (beside) lymph capillaries: the endothelial cells are overlapping slightly

Question 55

what is important about the slight overlapping of the endothelial cells in lymph capillaries?

Answer 55

by ensuring the ends of the endothelial cells are closed and form a closed structure

Question 56

assuming there is sufficient pressure being accumulated by the interstitial fluid, how does the overlapping of the endothelial cells in the lymph capillaries affect the movement of fluid?

Answer 56

it is going to force the movement of fluid into the lymph capillary. the interstitial fluid will move into the lymph capillary between endothelial cells

Question 57

is smooth muscle present in the lymph vessels?

Answer 57

yes

Question 58

what does the smooth muscle in the lymph vessels do?

Answer 58

it is going to help to contract and create rhythmic contractions that move the lymph fluid, through a one way direction back into the veins

Question 59

true or false regarding the lymphatic system: interstitial fluid enters into the lymph vessel through the endothelial cells

Answer 59

false. enters into the lymph capillary from in between the endothelial cells

Question 60

true or false regarding the lymphatic system: lymph capillaries have smooth muscle

Answer 60

false

Question 61

true or false regarding the lymphatic system: the lymphatic system is a "closed" circulation

Answer 61

false

Question 62

true or false regarding the lymphatic system: the lymphatic system is situated in the pulmonary circulation

Answer 62

true