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Physiology and Neuroscience > Capillary Function > Flashcards

Flashcards in Capillary Function Deck (61):
1

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

The output of the left ventricle
Contractile state of the resistance vessels (arterioles)

2

What is the circulatory system composed of?

Conduits (channels) arranged in series and in parallel

3

What is low pressure in the cardiovascular circuit?

25/10mmHg

4

What is high pressure in the cardiovascular circuit?

120/80 mmHg

5

What causes decreased pressures in CV?

Energy being consumed to overcome frictional resistance

6

Where is pressure highest and lowest in blood vessels?

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

7

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

3-billion fold

8

Where is blood volume greatest in the systemic circulation?

Veins

9

Where is blood volume greatest in the pulmonary circulation?

Equally divided

10

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

In the capillaries. Useful for exchange of diffusable substances

11

What does resistance to flow depend on?

Dimensions of the tube and characteristics of the fluid

12

What is the caliber of the vessel?

Principle determinant of resistance to blood flow through any vessel

13

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

Supplied by artery
Drained by vein

14

What is series resistance?

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

15

What structure is the aorta?

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

16

What is microcirculation?

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

17

What are capillaries?

Smallest of the body's blood vessels

18

How many cells thick are capillaries?

One cell thick (endothelium)

19

What is the capillaries used for?

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

20

How far away are tissue cells from capillaries?

60-80 micrometers

21

How much blood do capillaries contain at any one time?

Roughly 250ml

22

What are the different types of capillaries?

Continuous, Fenestrated, Dicontinuous

23

Describe continuous capillaries

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

24

Describe fenestrated capillaries

Wide intercellular pores allow rapid fluid movement
Kidney, endocrine glands and intestines

25

Describe discontinuous capillaries

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

26

Where is capillary density high?

Metabolically active organs

27

What does blood flow in capillaries depend on?

Contractile state of arterioles

28

What is the average velocity of blood flow in capillaries?

Roughly 1mm/sec

29

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

By filtration and osmotic forces acting across capillary walls

30

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

Two-thirds

31

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

One third
80% in tissues and 20% in plasma

32

How is the distribution of water in a capillary determined?

By balance between opposing forces acting on capillaries

33

In what three ways does transcapillary exchange occur?

Diffusion
Filtration
Pinocytosis

34

What is transcapillary exchange?

Solvent and solute moving across the capillary endothelial wall

35

Describe diffusion in transcapillary exchange

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

Describe filtration in transcapillary exchange

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

37

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

Simple diffusion

38

What gases are highly lipid soluble?

O2 and CO2

39

What are water soluble substances?

Water, ions, glucose and amino acids

40

What does it mean if substances are water-soluble?

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

41

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

Concentration in interstitial fluid near origin of capillary from parent arteriole

42

When does the concentration fall to negligible?

Near the arterial end of the capillary

43

What are the problems with flow-limited transport?

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

44

What is diffusion limited transport?

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

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

Sum of hydrostatic and osmotic pressure that exists across a membrane

46

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

Movement of fluid into vessels from interstital space

47

Is hydrostatic pressure in capillaries constant?

No

48

What does increased arterial/venous pressure cause?

Elevated capillary hydrostatic pressure

49

What does a closure of arteries cause?

Reduce in capillary pressure

50

What is the principle force in capillary filtration?

Hydrostatic forces

51

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

Arterial end- roughly 32 mmHg
Venous end- roughly 15mmHg

52

What is a key factor in restraining fluid loss?

Osmotic pressure of plasma proteins

53

What is osmotic pressure also referred to?

Colloid osmotic pressure or oncotic pressure

54

What is the total osmotic and oncotic pressure of plasma?

Total osmotic pressure- roughly 6000mmHg
Oncotic pressure- roughly 25mmHg

55

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

Favours movement of water into capillaries

56

How much of the capillary filtrate is returned?

Roughly 85%

57

What happens to the remaining 15% of capillary filtrate?

Returns to lymphatic system

58

What are the three layers that make up blood vessels?

The tunica intima, tunica media, and tunica externa

59

What does the tunica intima do?

Reduces friction between the vessel walls and the blood

60

What is the role of the tunica media?

Controls vasoconstriction an vasodilation of the blood vessels

61

What is the role of the tunica externa?

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