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CardioRespiratory Year 1 > Microcirulation and Oedema > Flashcards

Microcirulation and Oedema Flashcards

1
Q

what are the micro vessels in the microcirculation system

A
  • Terminal arterioles
  • Capillary
  • Venules
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2
Q

what is the function of the capillaries

A
  • Site of exchange of nutrients and waste productions between the circulation and interstitial fluid that surrounds the cells
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3
Q

what is another name of a capillary

A

exchange vessels

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4
Q

describe what vessels lead into what vessels in microcirculation

A

arterioles lead into terminal arterioles which lead into capillaries which lead into venues

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5
Q

what is the diameter of arterioles

A

10-200um

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6
Q

what is the diameter of terminal arterioles

A

10-40um

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7
Q

what is the diameter of capillaries

A

5-8um

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8
Q

what is the diameter of venues

A

10-200um

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9
Q

what is the structure of the arterioles

A
  • endothelium
  • muscular walls
  • sympathetic nerves
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10
Q

what is the structure of terminal arterioles

A

smooth muscle

few nerves

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11
Q

what do precapillary sphincters do

A

control blood flow into the capillaries, controls what capillaries have blood in them

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12
Q

what is arteriovenous anastomoses

A
  • This is a connection between two vessels (arteriole and venule)- blood flows through the arteriole into the venule
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13
Q

describe the structure of the capillary

A
  • Composed of endothelial cells that are held together by tight junctions surrounded by a basement membrane upon which the endothelium rests
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14
Q

what is the difference between the capillary and arterioles

A
  • No smooth muscle in the capillary – this differentiates capillaries from arterioles
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15
Q

how many types of capillaries are there

A

3

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16
Q

what are the three types of capillaries

A
  • Continuous capillary
  • Fenestrated capillary
  • Sinusoidal/discontinuous capillary
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17
Q

describe the structure of the continuous capillary

A
  • Least permeable but most widely distributed
  • Have a sealed endothelium and only allow small molecules like water and ions to diffuse through
  • Continuous capillaries have tight junctions and can be further divided into two subtypes
  • The basement membrane is continuous and there are no holes in it
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18
Q

what are the two subtypes fo the continuous capillary

A
  • Those with numerous transport vesicles that are primarily found in skeletal muscles, lungs, gonads and skin
  • Those with few vesicles that are primarily found in the central nervous system
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19
Q

describe the structure of the fenestrated capillary

A
  • Have small circular pores in the endothelial cells (60-80 nm in diameter).
  • usually have a continuous (closed) basal lamina.
  • Pores Permit relatively free passage of salts and water from plasma to the tissues therefore they are more permeable than continuous capillaries
  • Found in tissues that are specialized for bulk fluid exchange.
  • Are primarily located in the exocrine glands, intestines, pancreas, and glomeruli of kidney.
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20
Q

describe the structure of the sinusoidal/discontinous capillary

A
  • Discontinuous capillaries (sinusoidal) have the highest permeability.
  • Contain special fenestrated capillaries that have larger openings (30-40 μm in diameter) in the endothelium to allow red and white blood cells (7.5μm - 25μm diameter) and various serum proteins to pass, a process that is aided by a discontinuous basal lamina.
  • These capillaries lack pinocytotic vesicles and gaps may be present in cell junctions permitting leakage between endothelial cells.
  • Discontinuous capillaries are primarily located in the liver, spleen, bone marrow.
  • Blood cells can pass through and so can large proteins,
  • They are found in places where you want large proteins and cells to go out of the capillaries such as in the liver, spleen and bone marrow
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21
Q

where is the fenestrated capillary found

A

exocrine glands, intestines, pancreas, and glomeruli of kidney.

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22
Q

where is the discontinuous capillary found

A

liver, spleen and bone marrow

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23
Q

what are the 4 main routes for movement across a capillary endothelial cell

A
  1. Diffusion through membrane
  2. Movement through intercellular clefts
  3. Movement through fenestrations
  4. Transport via vesicles or caveolae, these undergo endocytosis
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24
Q

what law determines diffusion

A

Ficks law

25
Q

How do you work out the amount moved by diffusion

A

surface area x concentration gradient x diffusion coefficient

26
Q

what does the surface area and diffusion distance of a capillary depend upon

A

– depends on the density of the capillaries, if the density of the capillaries is higher larger surface area for exchange and a relatively short distance between each capillary

27
Q

what does the concentration gradient of diffusion depend upon

A
  • The net rate of diffusion of a substance through any membrane is proportional to the concentration difference between the two sides of the membrane.
  • Oxygen: concentration in the plasma is greater than that in the interstitial fluid thus causing net movement from blood towards the tissues.
  • Converse true for Carbon Dioxide.
28
Q

what does diffusion depend upon

A
  • surface area
  • concentration radeitn
  • diffusion coefficient
29
Q

describe the diffusion coefficient for small lipid molecules

A
  • Small lipid soluble molecules can diffuse through the lipid bilayer (plasma membrane of the endothelial cells).
  • Higher diffusion coefficient
  • Oxygen, carbon dioxide, anaesthetics.
  • They can therefore cross the entire surface area of the capillary.
30
Q

describe how larger molecules move through the capillary

A
  • via extracellular pathways
  • use paracellular transporter, this is the transfer of substance across an epithelium by passing through the intracellular space between cells
31
Q

describe the diffusion coefficient for lipid insoluble and larger molecules

A
  • Small lipid insoluble ions/molecules and larger molecules cannot easily cross the cell membranes
  • Passage is confined to water filled channels in between the cells (extracellular pathways) and through the pores that are present.
  • Depends on the permeability characteristics of the capillary wall.
  • In continuous endothelia (blood brain barrier) passage of these molecules will be very limited
  • However, tissues that have greater capillary permeability (fenestrations) facilitate movement of larger molecules such as plasma proteins.
32
Q

what is movement across a capillary endothelium determined by

A

determined by hydrostatic pressure and oncotic pressure

33
Q

what are the 4 pressures that determine movement of substance across an endothelium

A

hydrostatic pressure of the capillary,
hydrostatic pressure of the interstitial fluid,
oncotic pressure of the capillary
oncotic pressure of the interstitial fluid

34
Q

describe hydrostatic pressure of the capillary

A
  • pressure reduces as it flows through the capillary bed

- filtration at arterial end and reabsorption at the Venus end

35
Q

what is the hydrostatic pressure of interstitial fluid

A

0 mmHg

36
Q

what is the oncotic pressure in the capillaries generated by

A

plasma proteins

37
Q

what is the value of the capillary colloid oncotic pressure

A

26mmHg

38
Q

what is the value of the oncotic pressure of the interstitial fluid

A

1 mmHg

  • it is called the interstitial fluid colloid omsotic
  • should not get a lot of proteins around in the interstitial fluid
39
Q

How do you work out the net filtration pressure

A

(HPc-HPif)-(OPc-OPif)

40
Q

what happens if the net filtration pressure is positive

A
  • If net filtration pressure is positive like it is at the arterial end water is forced out of the capillary
41
Q

what happens if the net filtration pressure is negative

A
  • If the net filtration is negative like it is at the Venus end water is pulled back into the capillary
42
Q

what happens when you alter the hydrostatic or osmotic pressure

A

• Altering either the hydrostatic or osmotic pressure will disturb the fluid balance across the capillary wall.

43
Q

how much of plasma passes through the capillaries a day

A
  • 4000 L
44
Q

How much of the plasma is filtered

A
  • 0.1-0.2% is filtered
  • this means that 4-8 litres of fluid moves from the capillaries to the interstitial fluid every day
  • Some fluid is reabsorbed but most of it drains into the specialised vessels which is the lymphatic system
45
Q

Describe the structure of the lymphatic system

A
  • Specialised vessels made up of an endothelium with large intercellular gaps surrounded by permeable basement membrane.
  • End as blind sacs within tissues.
  • Also contain one-way valves that ensure lymph travels away from tissues.
46
Q

where does reabsorption of the lymphatic system happen

A
  • the fluid within the lymph enters the subclavian vein or water reabsorption into the lymph nodes
47
Q

what is oedema

A

Increased volume in the interstitial compartment leads to tissue swelling

48
Q

what are the two types of oedema

A

systemic and peripheral

49
Q

where does systemic oedema occur and what is it due to

A

occurs in the lower regions of the body for example the ankles- this is due to the venous pressure in the legs being elevated during prolonged standing

50
Q

How can you distinguish oedema from inflammation

A
  • This can be distinguished by applying firm pressure to the affected area – it does not bounce back immediately, this is pitting oedema and it distinguishes it from inflammation which does bounce back immediately
51
Q

what are the factors causing oedema

A
  1. Increased capillary hydrostatic – forces more fluid out
  2. Decreased plasma oncotic pressure – reduces drawing of water into the capillires
  3. Increased capillary permeability
  4. Lymphatic obstruction
52
Q

what does heart failure need to do

A
  • means heart is unable to pump blood around the body
  • breathlessness after activity or at rest
  • feeling tired most of the time and finding exercise exhausting
  • swollen ankles and legs
53
Q

how does increased capillary hydrostatic pressure cause oedema

A
  • two forces are balanced between driving fluid into the interstitial space and driving fluid into capillary
  • if the venous pressure becomes elevated by gravitational forces in heart failure or with venous obstruction then the capillary hydrostatic pressure will be effected
  • this reduces reabsorption of fluid into the capillaries
54
Q

what is kwashiorkor

A

decreased plasma oncotic pressurepressrue

55
Q

what does kwashiorkor due to

A

due to

  • Severe malnutrition
  • Deficiency in dietary protein
  • Lack of proteins in blood and tissues
  • Reduced OPc
  • pitting edema
  • Water retention in the gut
56
Q

what is the cause of kwashiorkor leading to oedema

A
  • If the plasma oncotic pressure decreases as occurs with hypoproteinaemia during malnutrition or liver disease there is a decrease in the oncotic pressure
  • Reduce reabsorption of fluid into het capillaries
57
Q

how does increased capillary permeability lead to oedema

A
  • Increased capillary permeability - allows water to flow more freely and reduces the oncotic pressure difference by allowing protein to leave the vessel more easily.
  • E.g. Vascular damage (burns, trauma, inflammation)
58
Q

how does lymphatic obstruction cause oedema

A

• Obstruction of lymph drainage
- (e.g. fibrosis or filiariasis – elephantiasis, a worm infestation in lymphatic system)
• Tissue injury
• Inflammation of lymph vessels

59
Q

How do you treat oedema

A
  • Treatment of oedema itself by drugs that promote the loss of sodium and water.
  • Diuretics either osmotic diuretics (increase water excretion) or loop diuretics (increase sodium excretion, natriuresis).

CardioRespiratory Year 1 (28 decks)

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