Capillaries II Flashcards

1
Q

What is the importance of fluid exchange?

A

• Fluid exchange is important for normal physiological function, we need H2O for chemical reactions.

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2
Q

Give a simple reason as to why we have fluid re-absorption?

A

• Fluid re-absorption from tissues to blood can maintain circulation during haemorrhage.

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3
Q

If fluid filtration is damage what are the consequences?

A

• Abnormalities in fluid exchange can lead to oedema/tissue swelling. This is in the interstitial (between the basement membrane) space.

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4
Q

Describe the structures that surround the capillary in a body cell

A

On image

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5
Q

How does fluid move out of the capillaries and where does it move to?

A
  • Capillary wall is a semi-permeable membrane.

* Fluid moves across membrane into interstitial space due to blood flow which exerts a hydraulic pressure.

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6
Q

What do large molecules create?

A

• Large molecules (eg. plasma proteins) cannot pass through membrane so they exert an osmotic pressure termed oncotic pressure which creates suction force to move fluid into capillary.

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7
Q

What does fluid movement across capillaries depend on?

A

• Fluid movement across capillary walls depends on the balance between hydraulic and oncotic pressures across the capillary wall.

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8
Q

Define oncotic and hydraulic/ hydrostatic pressure and why is one greater than the other?

A

Oncotic = reabsorption
Hydrostatic or Hydraulic = filtration
Hydrostatic pressure > oncotic pressure gradient – the essence of starlings law of capillary exchange

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9
Q

What four pressures determine filtration rate?

A

On image

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10
Q

Describe Starlings law for fluid exchange

A

On image

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11
Q

Starlings forces normally favour filtration

What factors promote filtration?

What factors promote reabsorption?

A

Capillary blood pressure and interstitial proteins

Plasma proteins

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12
Q

What develops if filtration is found in excess?

A

Oedema

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13
Q

How is excess fluid returned to the circulation?

A

• Excess fluid is returned to the circulation via lymphatic system.

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14
Q

Describe the pressure from the arteriole end to the venous end

A

• This diagram shows at the arteriole end there is a pressure of around 35mmHg. Continuing along the capillary pressure is lost. We have a declining gradient of hydrostatic pressure.

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15
Q

Does the osmotic pressure change?

A

• The osmotic pressure does not change and would give a horizontal line

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16
Q

Describe the structure of lymph vessels?

A

• Lymph vessels have valves and smooth muscle

17
Q

What is the purpose of contractions of the lymph vessels

A
  • Spontaneous contractions of the smooth muscle contribute to lymph flow.
  • Surrounding skeletal muscle contractions/relaxation also contributes to lymph flow.
18
Q

Overall control of extracellular fluid balance depends on:

A
  • Capillary filtration
  • Capillary reabsorption
  • Lymphatic system
19
Q

Starling’s factors determine changes in fluid balance:

A
  • Circulation
  • Interstitial fluid
  • Lymphatic system
20
Q

What is low capillary pressure called?

A

Hypovolemia

21
Q

Describe the premise of hypovolemia (6)

A
  • This is what happens when we lose blood. You lose a large amount of blood.
  • The blood volume decreases and venous return decreases.
  • There is less preload due to less blood returning the heart. So cardiac output drops.
  • Therefore, the pressure at the arteriole end is going to be much lower to start with and dropping to a much lower pressure.
  • In terms of the osmotic pressure, there is no change as the concentration of cells in the blood remains the same.
  • Therefore, the net balance of forces is now in favour of reabsorption. This is good as we need to maintain blood volume, so we withdraw fluid from tissue, to compensate for blood loss.
22
Q

What is oedema?

A
  • Excess of fluid within the interstitial space.

* Imbalance between filtration, reabsorption, lymph function.

23
Q

What are the causes of oedema?

A
  • Increased capillary pressure (Pc)
  • Decreased plasma protein oncotic pressure (πP)
  • Inflammatory response
  • Lymphatic problems
24
Q

Give some scenarios of increased capillary pressure

A
  • Dependent (gravitational) oedema – standing up for long periods
  • Deep venous thrombosis
  • Cardiac failure
  • eg. Deep vein thrombosis (DVT) prevention of venous return
  • Increases venous pressure causes ‘back-up’ of pressure leading to…
  • Increased PC across capillaries and increased filtration
25
Q

Describe a decrease in plasma protein oncotic pressure

A

Low protein oedema…

Malnutrition: Low protein intake to produce plasma proteins

Nephrotic syndrome: urinary protein loss - replaced by liver function

Liver disease: not enough endogenous albumin produced

Reduced plasma protein concentration = reduced plasma oncotic pressure - the greater influence of Pc and Pie I = fluid efflux from capillaries into interstitial fluid = oedema.

26
Q

Describe inflammatory mediated oedema

A

Swelling is triggered by a rise in local chemical mediators of inflammation

The large increase in capillary permeability

Rate of bulk movement increases, protein permeability increases, decrease in reflection coefficient

e.g chemicals, insect bite, nettles, infection, autoimmune disease.