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Physiology and Neuroscience > Capillary Function > Flashcards

Capillary Function Flashcards

1
Q

What is the distribution of blood circulating in different regions determined by?

A

The output of the left ventricle

Contractile state of the resistance vessels (arterioles)

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2
Q

What is the circulatory system composed of?

A

Conduits (channels) arranged in series and in parallel

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3
Q

What is low pressure in the cardiovascular circuit?

A

25/10mmHg

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4
Q

What is high pressure in the cardiovascular circuit?

A

120/80 mmHg

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5
Q

What causes decreased pressures in CV?

A

Energy being consumed to overcome frictional resistance

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6
Q

Where is pressure highest and lowest in blood vessels?

A

Beginning of small arteries, pressure decreases until it most significantly drops in arterioles

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7
Q

What is the increase in number of vessels from the aorta and capillaries?

A

3-billion fold

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8
Q

Where is blood volume greatest in the systemic circulation?

A

Veins

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9
Q

Where is blood volume greatest in the pulmonary circulation?

A

Equally divided

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10
Q

Where does blood flow velocity become very slow? And why is this useful?

A

In the capillaries. Useful for exchange of diffusable substances

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11
Q

What does resistance to flow depend on?

A

Dimensions of the tube and characteristics of the fluid

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12
Q

What is the caliber of the vessel?

A

Principle determinant of resistance to blood flow through any vessel

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13
Q

What is the organ supplied by? And what is it drained by?

A

Supplied by artery

Drained by vein

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14
Q

What is series resistance?

A

The total resistance of the system is arranged in series is equal to the sum of the individual resistances

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15
Q

What structure is the aorta?

A

Predominantly elastic structure, peripheral arteries become more muscular until at arterioles where musuclar layer predominates

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16
Q

What is microcirculation?

A

Circulation of blood through arterioles, capillaries and venules and neighbouring lymphatic vessels

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17
Q

What are capillaries?

A

Smallest of the body’s blood vessels

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18
Q

How many cells thick are capillaries?

A

One cell thick (endothelium)

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19
Q

What is the capillaries used for?

A

Transfer of oxygen and other nutrients from the bloodstream to the other tissues in the body

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20
Q

How far away are tissue cells from capillaries?

A

60-80 micrometers

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21
Q

How much blood do capillaries contain at any one time?

A

Roughly 250ml

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22
Q

What are the different types of capillaries?

A

Continuous, Fenestrated, Dicontinuous

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23
Q

Describe continuous capillaries

A

Adjacent endothelial cells closely joined together
Muscle, lungs, adipose and CNS
Often have pericytes associated with them

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24
Q

Describe fenestrated capillaries

A

Wide intercellular pores allow rapid fluid movement

Kidney, endocrine glands and intestines

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25
Q

Describe discontinuous capillaries

A

Distance between endothelial cells so great they appear as sinusoids (little cavities) in the organ
Liver, bone marrow and spleen

26
Q

Where is capillary density high?

A

Metabolically active organs

27
Q

What does blood flow in capillaries depend on?

A

Contractile state of arterioles

28
Q

What is the average velocity of blood flow in capillaries?

A

Roughly 1mm/sec

29
Q

How is fluid in extracellular environment of body distributed between blood and tissue compartments?

A

By filtration and osmotic forces acting across capillary walls

30
Q

How much of the blood volume is made up by the intracellular compartment?

A

Two-thirds

31
Q

How much of the blood volume is made up by the extracellular compartment?

A

One third

80% in tissues and 20% in plasma

32
Q

How is the distribution of water in a capillary determined?

A

By balance between opposing forces acting on capillaries

33
Q

In what three ways does transcapillary exchange occur?

A

Diffusion
Filtration
Pinocytosis

34
Q

What is transcapillary exchange?

A

Solvent and solute moving across the capillary endothelial wall

35
Q

Describe diffusion in transcapillary exchange

A

300mL water/ min moves across capillary wall by diffusion

Diffusion of water, 40x greater than rate at which brought to capillaries by blood flow

36
Q

Describe filtration in transcapillary exchange

A

0.06mL water per minute moves across capillary wall as a result of filtration and absorption
2% plasma passing capillaries is filtered

37
Q

How does the exchange of solutes/gases across the capillary wall?

A

Simple diffusion

38
Q

What gases are highly lipid soluble?

A

O2 and CO2

39
Q

What are water soluble substances?

A

Water, ions, glucose and amino acids

40
Q

What does it mean if substances are water-soluble?

A

Cannot cross the endothelial cell membranes. Diffusion is limited to the aqueous clefts between endothelial cells

41
Q

What does concentration of the molecule in blood reach equilbrium with?

A

Concentration in interstitial fluid near origin of capillary from parent arteriole

42
Q

When does the concentration fall to negligible?

A

Near the arterial end of the capillary

43
Q

What are the problems with flow-limited transport?

A

Large molecules can’t pass through, diffusion is rate limiting

44
Q

What is diffusion limited transport?

A

Diffusion of small lipid-insoluble molecules is so rapid that diffusion limits blood-tissue exchange only when distances between capillaries and parenchymal cells are great

45
Q

What is the direction/magnitude of water movement across capillary wall?

A

Sum of hydrostatic and osmotic pressure that exists across a membrane

46
Q

What does an increased concentration of osmotically active particles within vessels favour?

A

Movement of fluid into vessels from interstital space

47
Q

Is hydrostatic pressure in capillaries constant?

A

No

48
Q

What does increased arterial/venous pressure cause?

A

Elevated capillary hydrostatic pressure

49
Q

What does a closure of arteries cause?

A

Reduce in capillary pressure

50
Q

What is the principle force in capillary filtration?

A

Hydrostatic forces

51
Q

What is the capillary hydrostatic pressure in the arterial and venous end?

A

Arterial end- roughly 32 mmHg

Venous end- roughly 15mmHg

52
Q

What is a key factor in restraining fluid loss?

A

Osmotic pressure of plasma proteins

53
Q

What is osmotic pressure also referred to?

A

Colloid osmotic pressure or oncotic pressure

54
Q

What is the total osmotic and oncotic pressure of plasma?

A

Total osmotic pressure- roughly 6000mmHg

Oncotic pressure- roughly 25mmHg

55
Q

What does the oncotic pressure do as a result of osmosis?

A

Favours movement of water into capillaries

56
Q

How much of the capillary filtrate is returned?

A

Roughly 85%

57
Q

What happens to the remaining 15% of capillary filtrate?

A

Returns to lymphatic system

58
Q

What are the three layers that make up blood vessels?

A

The tunica intima, tunica media, and tunica externa

59
Q

What does the tunica intima do?

A

Reduces friction between the vessel walls and the blood

60
Q

What is the role of the tunica media?

A

Controls vasoconstriction an vasodilation of the blood vessels

61
Q

What is the role of the tunica externa?

A

Protects, reinforces, and anchors the vessel to surrounding structures.

Physiology and Neuroscience (40 decks)

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