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Hypertensiona > Oedema > Flashcards

Oedema Flashcards

1
Q

Another name for capillary beds

A

microcirculation

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2
Q

What is the input into capillaries?

A

arteriole blood

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3
Q

What kind of blood flow is travelling through the arterioles?

A

smooth flow

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4
Q

How is the blood flow controlled to go to specific capillaries from the arterioles?

A

arterioles have pre-capillary sphincter

smooth muscle which can be contracted and relaxed, which opens or closes the capillary beds

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5
Q

How do venules control where blood goes from the capillaries?

A

post-capillary sphincter

smooth muscle which can be contracted and relaxed, makes it harder or easier for blood to travel through that venule

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6
Q

Function of capillaries

A

sites of exchange

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7
Q

Can capillaries control where the blood flows to?

A

no - have no smooth muscle in their walls

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8
Q

What is the blood flow velocity in capillaries like?

And what does it depend on?

A

not constant - can vary from 0 to 8mm/s

depends on contractile state of the arterioles/pre-capillary vessels

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9
Q

What is the solute/solvent movement across capillaries like?

And what does it depend on?

A

not constant

depends on the permeability which can vary between tissues, at different times and along the capillary bed

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10
Q

What is solute/solvent movement across capillaries dricen by?

A

diffusion - largely
filtration - fluid, find space
pinocytosis - larger molecules, lipid insoluble packed into vesicles

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11
Q

What are the prime determinants for diffusion?

A

Capillary permeability of substance and surface area

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12
Q

What is the law associated with the rate of diffusion?

A

Fick’s Law

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13
Q

What type of substances readily pass through endothelial cells?

A

lipid soluble substances

eg. O2 and CO2

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14
Q

How does fluid move?

A

filtration and reabsorption

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15
Q

What is filtration and reabsorption?

A

bulk flow

movement of a volume of protein-free fluid out of the capillary (filtration) and back (reabsorption)

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16
Q

Why is bulk flow important?

A

helps to determine distribution of ECF

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17
Q

Driving forces for filtration

A

capillary hydrostatic pressure (Pc)

interstitial fluid colloid osmotic pressure (πi)

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18
Q

Driving forces for reabsorption

A

capillary (plasma) colloid osmotic pressure (πc)

interstitial fluid hydrostatic pressure (Pi)

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19
Q

What is capillary hydrostatic pressure (Pc) a major determinant of?

A

fluid movement

20
Q

What does capillary hydrostatic pressure depend on?

and give an example

A

pre/post capillary resistances due to:
venous pressure
(arterial pressure)

21
Q

If arteriole constricts, how does Pc change?

A

increased pressure upstream
decreased pressure downstream
therefore increased resistance and precapillary constriction reduces Pc

22
Q

If venule constricts, how does Pc change?

A

increased pressure upstream
decreased pressure downstream , less flow
postcapillary constriction increases Pc

23
Q

How important is interstitial fluid colloid osmotic pressure on fluid movement?

A

minor determinant

24
Q

What does interstitial fluid colloid osmotic pressure depend on ?

A

presence of protein in interstitium, therefore the capillary premeability to protein which is normally very low

25
Q

How important is capillary colloid osmotic pressure on fluid movement?
and why?

A

major determinant

lots of protein in the blood

26
Q

What does capillary colloid osmotic pressure depend on ?

A

synthesis/breakdown of protein - liver
capillary permeability to protein
abnormal protein loss - kidney damage

27
Q

Symptoms of end-stage liver failure

A

lose fluid to tissues and abdomen
hear water sloshing in abdominal cavity
lost protein in blood, decreased colloid osmotic pressure

28
Q

How important is interstitial fluid hydrostatic pressure on fluid movement?

A

minor determinant

29
Q

What does interstitial fluid hydrostatic pressure depend on?

A

interstitial fluid volume
compliance of organ
effective drainage

30
Q

What provides drainage for the cappilaries?

A

lymphatic system

31
Q

Characteristics of lymphatic system which allows for drainage

A

valved and highly permeable to protein

32
Q

What is the purpose of the lymphatic system?

A

returns excess filtered fluid and 95% of protein lost from vascular system back into circulation close to jugular vein

33
Q

What occurs if the lymphatic system does not function?

A

build up of fluid in tissues

swelling

34
Q

Equation for fluid movement

A

fluid movement ∝ filtration forces - reabsorption forces

Q ∝ (Pc + πi) - (πc + Pi)
Q = Kf [(Pc + πi) - (πc + Pi)]
where Kf (filtration coefficient) is a constant that depends on permeability and surface area available
35
Q

What does capillary fluid transfer depend on and why?

A

capillary hydrostatic pressure
plasma colloid osmotic pressure

πi and Pi are normally negligble

36
Q

If capillary hydrostatic pressure is increased, how does this affect fluid movement?

A

increased filtration

37
Q

If plasma colloid osmotic pressure is increased, how does this affect fluid movement?

A

increased reabsorption

38
Q

If Pc > πc, what occurs?

A

net filtration

39
Q

If Pc < πc, what occurs?

A

net reabsorption

40
Q

How does Pc and πc present in a typical capillary?

A

higher Pc pressure on arteriolar side
same pressures mid-capillary
higher πc pressure on venular side

41
Q

How does Pc and πc change moving from arteriole to venules? and what does this mean for the net movement of fluid?

A

Pc decreases
πc remains constant

net filtration until Pc = πc, then no movement
net reabsorption once Pc < πc

42
Q

How would Pc and πc be affected by pre-capillary vasoconstriction?
and therefore movement of fluid?
give an example of where this occurs

A

reduced Pc, no change in πc
therefore less time for filtration and therefore increased reabsorption
eg. lungs - not driving fluid into alveoli and do not interfere with gas exchange

43
Q

How would Pc and πc be affected by pre-capillary vasoconstriction?
and therefore movement of fluid?
why might this occur?

A

increase Pc due to increased venous pressure
no change in πc
increased filtration
RHS heart failure - swollen ankles
LHS - breathlessness due to increased hydrostatic pressure in pulmonary veins

44
Q

How would Pc and πc be affected by hypoproteinaemia?

Examples of when this would occur

A

πc reduced, no change in Pc
reduction in net reabsorption, increased filtration,
liver failure - comprimised capacity for protein synthesis
renal failure - lose protein in urine

45
Q

Causes of oedema

A

lymphatic obstruction - reduced drainage
increased venous pressure - congestion (HF)
hypoproteinaemia - renal damage
hypervolaemia inflammation - vasodilation and increased permeability

Hypertensiona (8 decks)

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