oedema

Question 1

how does interstitial fluid act as a go-between blood and body cells

Answer 1

> is essentially has the same constituents as plasma (Much less protein)
is a tissue gel, and because of the large number of proteoglycan filaments its difficult for fluid to flow easily
so it moves molecule by molecule from one place to another
hydrostatic pressure in the capillaries force fluid and its dissolved substances through the capillary walls and into the interstitial spaces
osmotic pressure caused by plasma proteins cause fluid movement via osmosis from interstitial spaces into the blood

Question 2

starling forces - in governing fluid movement across the capillary wall

Answer 2

forcing favouring filtration: when blood moves from arterioles to capillary bed
>within the capillary there is the capillary hydrostatic pressure (arises due to blood pressure) (ie in the lumen - Pc)
-35mmHg ie higher pressure at arteriolar end than venular end
-tends to move water from capillary to interstitium
>pi1 denotes interstitial osmotic pressure

forces opposing filtration:
>pic - denotes oncotic/ capillary osmotic pressure
(due to presence of plasma proteins in the capillaries ie they stay in the capillaries)
-25mmHg
-remains a constant pressure due to plasma proteins
-tends to move water from interstitium back to lumen of capillary
>interstitial fluid hydrostatic pressure (Pc) drops from arterioles to venules
forces
-17mmHg
-less pressure at the venular end

Question 3

what is oedema

Answer 3

accumulation of fluid in the interstitial spaces

Question 4

how can heart failure cause pulmonary and systemic oedema

Answer 4

left ventricular failure - right ventricular failure
both of these can cause a back flow in pressure which hinders the Pc / pi c forces favouring reabsorption/filtration which can cause oedema if there is too much fluid in interstitial space

Question 5

what pressure stays constant and why

Answer 5

capillary osmotic pressure
(the symbol of pi followed by a lower case c)
because plasma proteins are large molecules that cannot enter or leave the lumen of the capillary generally and so the pressure remains the same
(about 25mmHg)

Question 6

what pressure drops and why

Answer 6

Pc - capillary hydrostatic pressure
from about 35mmHg to 17mmHg
dropping from arteriolar to venular end (hydrostatic pressure of blood ie arteries carry under high and veins under low)

Question 7

when is reabsorption favoured/filtration favoured

Answer 7

> filtration is favoured when Pc is above pi c
(ie >25mmHg)
reabsorption is favoured when Pc is below pi c (ie below 25mmHg)
** when water is pretty central in the capillary (ie not at either end) there is a balance

Question 8

when is NFP higher

Answer 8

net filtration pressure is higher at the arteriolar end
ie filtration exceeds reabsorption by 2-4 litres a day
and so the excess fluid (the stuff that needs reabsorbed) is returned to the circulation via lymphatic system as lymph

Question 9

starling forces -pulmonary circulation (4)

Answer 9

• resistance is only about 10% of that of systemic circulation
• pulmonary Pc is low (8-11mmHg)
• capillary osmotic pressure is about 25mmHg
• efficient lymphatic drainage remove any filtered fluids this preventing accumulation of interstitial fluid

Question 10

what is oedema

Answer 10

accumulation of fluid in the interstitial space

Question 11

what can happen with oedema

Answer 11

diffusion distance increases and so gas exchange is compromised as a result

Question 12

causes of pulmonary oedema (1)

Answer 12

raised capillary hydrostatic pressure
>this is due to:
arteriolar dilation and raised venous pressure ie hindering the normal process of filtration and reabsorption
» this can happen when there is

Question 13

causes of pulmonary oedema (1)

Answer 13

raised capillary hydrostatic pressure
>this is due to:
arteriolar dilation and raised venous pressure ie hindering the normal process of filtration and reabsorption
» this can happen when there is left ventricular failure (pulmonary oedema)
»right ventricular failure (peripheral oedema ie ankle/sacrum)
»prolonged standing (swollen ankles

Question 14

when is NFP higher

Answer 14

net filtration pressure is higher at the arteriolar end
ie filtration exceeds reabsorption by 2-4 litres a day
and so the excess fluid (ie excess protein and fluid that leak from the blood) is returned to the circulation via lymphatic system as lymph

Question 15

left ventricular failure

Answer 15

causes ..
pulmonary oedema is the accumulation of fluid in the interstitial and idntraalveolar spaces 
>SOB 
>crackles /crepitations 
>haziness in the perihilar region

Question 16

right ventricular failure

Answer 16

pitting oedema /peripheral
ie in the ankles and in the sacrum
»caused by increased Pc but the lymphatic system is still working well - causing the pitting effect

Question 17

heart failure

Answer 17

a clinical syndrome 
>breathlessness
>ankle swelling
>fatigue 
>>elevated JVP
>>pulmonary crackles
>>peripheral oedema
- caused by a structural and or functional cardiac abnormality resulting in reduced cardiac output and/or elevated intracardiac pressures at rest of during stress

Question 18

causes of oedema (2)

Answer 18

reduced plasma osmotic pressure (a major force that moves water back into capillary)
>normal is 65-80 g/l
oedema if there is 30g/l or less (ie the force isn’t high enough to move water from interstitium into capillary)
»caused by malnutrition
»protein malabsorption
»excessive renal excretion of protein
»hepatic failure

Question 19

causes of oedema (3)

Answer 19

lymphatic insufficiency
»caused by lymph node damage
ie filariasis - elephantiasis
»> the fluid will accumulate in the interstitium if not carried away as lymph

Question 20

causes of oedema (4)

Answer 20

changes in capillary permeability
»caused by inflammation
»histamine increases leakage of protein

Question 21

check animation ! cardio week 4 !!

Answer 21

just fucking watch it you stupid bitch

Question 22

how does vasodilation cause oedema

Answer 22

more blood/fluid in the capillary bed ie more of it will b pumped into the capillary bed – the hydrostatic capillary pressure is increased

Question 23

what is interstitial fluid

Answer 23

context = abou 1/6 of body’s total volume consists of spaces between cells
»the fluid that occupies these spaces is the interstitial fluid

Question 24

Pc

Answer 24

capillary hydrostatic pressure (forces fluid outward from capillaries)

Question 25

P if / Pi

Answer 25

interstitial fluid hydrostatic pressure (forces fluid inward when Pi is + but outward when negative)

Question 26

pi p

Answer 26

capillary osmotic pressure (causes osmosis of fluid inward through the capillary membrane)

Question 27

pi if / i

Answer 27

interstitial fluid osmotic pressure (osmosis of fluid outward through capillary membranes)

Question 28

NFP =

Answer 28

(Pc + Pi) - (pi c + pi i)