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Cardiopulmonary Physiology > Microcirculation (Exam 1) > Flashcards

Microcirculation (Exam 1) Flashcards

1
Q

What is the #1 function of microcirculation?

A

the transport of nutrients to the tissues and the removal of cell excreta

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2
Q

which vessels control blood flow to each tissue

A

small arterioles (local conditions)

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3
Q

True/False: microcirculation is not based on needs

A

False - it is controlled by what the tissue requirements are

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4
Q

What are capillary walls made of?

A

-single-layer, highly permeable endothelial cells
-surrounded by a thin basement membrane

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5
Q

how far is a capillary from any functional cell of the body?

A

no more than 20-30 micrometers
-any further and no diffusion can occur

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6
Q

what are metarterioles?

A

-terminal arterioles
**they do not have tunica media –> replaced w/ single smooth muscle fibers that encircle the vessel at intermittent points

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7
Q

where does pressure drop the most?

A

at the metarterioles

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8
Q

do arterioles have muscle cells?

A

YES, they are highly muscular

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9
Q

what is a precapillary sphincter?

A

a single smooth muscle fiber that usually encircles an entire capillary vessel
-responsible for opening and closing the vessel

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10
Q

What are collateral arteries?

A

extra arteries that are going to the same capillary

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11
Q

How can you grow more collateral arteries?

A

Exercise

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12
Q

what is the general flow of microcirculation?

A

artery –> arteriole –> metarteriole –> capillary –> collecting venule –> small venule

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13
Q

we don’t need to know all the numbers, but roughly how big are the vessels involved in microcirculation?

A

<30 nanometers

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14
Q

what are the two modifications that connect the interior of a capillary with the exterior?

A

-intercellular cleft
-caveola

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15
Q

what is an intercellular cleft?

A

-a thin slitted channel for easy diffusion
-located at the junction b/w adjacent cells
**most water soluble substances diffuse here

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16
Q

what is a caveola?

A

-small membrane invaginations also called plasmalemmal vesicles
-have a role in endocytosis and transcytosis
-transport macromolecules
contain caveolins

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17
Q

what are caveolins?

A

proteins that interact w/ cholesterol and polymerize to form the caveolae

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18
Q

what are the 3 types of normal capillary vessels?

A

-continuous
-fenestrated
-sinusoidal

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19
Q

What makes capillaries in the brain different?

A

they have tight junctions

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20
Q

where do capillary cells have the widest junctions? why is the necessary?

A

-liver, bone marrow, spleen
-so all dissolved substances of the plasma (like proteins) can pass from the blood

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21
Q

what is vasomotion?

A

the intermittent contraction of the metarterioles and precapillary sphincters

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22
Q

Why does vasomotion occur?

A

bc blood usually doesn’t flow continuously through the capillaries
based off of needs

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23
Q

what is the biggest factor in vasomotion?

A

oxygen concentration of the tissues
-increase oxygen usage –> increase time that the capillaries are open (decrease vasomotion)

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24
Q

True/false: when determining rate of flow, pressure, and transfer of substances we use averages

A

TRUE
capillaries are so small so they get grouped by the tissue they are going to

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25
Q

which direction does diffusion occur?

A

both in and out of the capillaries –> creates continual mixing b/w plasma and interstitial fluid

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26
Q

what substances get diffused easily?

A

electrolytes
nutrients
metabolic waste products

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27
Q

where do lipid-soluble substances diffuse (o2 + co2)

A

through the cell membranes

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28
Q

where do water-soluble substances diffuse

A

the intercellular pores

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29
Q

what is the interstitium

A

-spaces between cells
-1/6 total volume of the body
-contains interstitial fluid

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30
Q

what is the interstitial fluid made of?

A

it’s basically just plasma but w/ less proteins
-derived by filtration and diffusion from the capillaries

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31
Q

what are starling forces?

A

the 4 primary forces that determine the direction of fluid movement between the blood and interstitial fluid

32
Q

what are the 4 starling forces?

A

-capillary hydrostatic pressure (Pc)
-interstitial fluid hydrostatic pressure (Pif)
-capillary plasma colloid osmotic pressure (i can’t do greek letters lol but its pi and p)
-interstital fluid colloid osmotic pressure (pi + if)

33
Q

what is capillary hydrostatic pressure (Pc)

A

OUTWARD force of fluid from the capillary to interstitium

34
Q

what is interstitial fluid hydrostatic pressure (Pif)

A

INWARD force of fluid to the capillary from the interstitium

35
Q

what is capillary plasma colloid osmotic pressure (pi, p)

A

increase of proteins in the capillary causes INWARD shift of fluid from the interstitium to the capillary

36
Q

what is insterstitial fluid colloid osmotic pressure (pi, if)

A

increase of proteins in the interstitium cause OUTWARD shift of fluid from the capillary to the interstitium

37
Q

How do you calculate the net filtration pressure (NFP)?

A
38
Q

What does it mean when the NFP is positive

A

there is a net loss of fluid across the capillaries
**under normal conditions the NFP is slightly positive:)

39
Q

what does it mean when the NFP is zero

A

equilibrium
no net movement across the capillaries

40
Q

what does it mean when the NFP is negative

A

there is a net gain of fluid across the capillaries

41
Q

what is the capillary filtration coefficent (Kf)

A

leakiness factor
-size and number of the pores in each capillary and the number of capillaries in which blood is flowing
-measure of the capacity of the capillary to filter water

42
Q

what is the equation for fluid filtration?

A

filtration = Kf * NFP
usually expressed as ml/min pre mmHg

43
Q

what are the 2 ways to estimate the capillary hydrostatic pressure (Pc)

A

-direct micro pipette cannulation of the capillaries –> normal average = 25 mmHg
-indirect functional measurement (looking at the forces) –> normal average = 17 mmHg

44
Q

Initerstitial fluid hydrostatic pressure (Pif) is generally pretty close to zero. what are the 4 places this isn’t true? (#s included)

A

-intrapleural space: -8 mmHg
-Joint synovial spaces: -4 to -6 mmHg
-Epidural space: -4 to -6 mmHg
-brain interstitial fluid: +4 to +6 mmHg

45
Q

which molecules exert osmotic pressure?

A

the molecules/ions that DO NOT pass through the membrane
-ex: plasma proteins

46
Q

what is the % breakdown of pressure from the plasma proteins

A

80% from the albumin
20% from the globulins
almost 0% from fibrinogen

47
Q

what is the average pressure difference between the arterial and venous ends of the capillaries?

A

the arterial ends are 15-25 mmHg higher than the venous ends

48
Q

on average, how much of the plasma is filtered out of the arterial ends? how much is reabsorbed at the venous end?

A

-1/200 is lost
-9/10 is reabsorbed –> remaining 1/10 goes to the lymph vessels

49
Q

The starling equilibrium equations shows a “state of near-equilibrium”. what is the slight imbalance of forces and what does it do

A

-there is a 0.3 mmHg imbalance
-this causes slightly more filtration of fluid into the interstitial spaces than reabsorption

50
Q

where does the net filtration (NFP number) go?

A

the lymphatic system

51
Q

what is the normal rate of net filtration in the entire body - not including the kidneys

A

only about 2 ml/min

52
Q

what would happen if there is a 20 mmHg rise in mean capillary pressure?

A
  1. NFP would go from 0.3 to 20.3 mmHg
  2. 68 times as much fluid would be filtered into the interstitial spaces
  3. this excess fluid would have to go into the lymphatic system to prevent accumulation
    ** OVERALL CAUSES EDEMA**
53
Q

what would happen if there was a decrease in mean capillary pressure?

A
  1. there would be a net re absorption of fluid into the capillaries
  2. blood volume will increase
54
Q

over 24 hours how much fluid does the lymphatic system move?

A

2-3 liters :)

55
Q

what changes the volume of interstitial fluid?

A

-capillary pressure
-interstitial fluid pressure
-oncotic pressure
-proper lymph flow

56
Q

what causes an increased filtration pressure

A

-vasoconstriction
-increased venous pressure (heart failure, incompetent valves, obstructions, increased total ECF volume, etc.)

57
Q

what causes a decreased osmotic pressure gradient across a capillary

A

-decreased plasma proteins level
-accumulation of osmotically active substances in interstitial space

58
Q

what causes an increased capillary permeability

A

-substance p
-histamine and related substances
-kinins

59
Q

how is microcirculation affected in active tissues (working out)

A

-capillary pressure rises –> usually gets higher than oncotic pressure
-**temporarily accumulate interstitial fluid bc it can’t be washed away as rapidly as it is formed
-fluid leaving is increased, fluid reentering is reduced

… after workout swol

60
Q

true/false: there will be more blood flow to tissues that have a metabolic need

A

true :)

61
Q

what are the two phases of local blood flow?

A

-acute
-long-term

62
Q

what is acute control?

A

rapid changes in local vasodilation/vasoconstriction of the arterioles, metarterioles, and precapillary sphincters

63
Q

what is long-term control?

A

slow, controlled changes in flow over a period of days, weeks, or months
–> changes come as a result of an increase or decrease in the physical size and number of blood vessels supplying the tissues
ex: increased long-term blood flow w/ increased exercise/physical activity

64
Q

what is the vasodilator theory?

A

when there is an increased metabolic rate OR a decreased availability of oxygen –> there is a greater rate of formation of vasodilator substance
… body need, vessels get bigger to supply need

65
Q

what are some possible vasodilators? (vasodilator theory)

A

adenosine
-co2
-adenosine phosphate compounds
-histamine
-potassium ions
hydrogen ions

66
Q

which tissue is affected by adenosine?

A

cardiomyocytes!

67
Q

what is the nutrient demand theory?

A

-aka oxygen demand theory
-the number of precapillary sphincters that are open at any given time is roughly proportional to the requirements of the tissue for nutrition.
-when the need is met, the sphincters close

there is a lil flow chart on slide 15:)

68
Q

a lack of glucose in the perfusing blood can cause local tissue ______

A

vasodilation
… same with every other nutrient deficiency

69
Q

what is reactive hyperemia

A

blood supply to a tissue is blocked for 1 sec to 1 hour –> gets unblocked –> *blood flow increases immediately to 4-7 times the normal amount

70
Q

what is active hyperemia?

A

tissue becomes highly active –> rate of blood flow through the tissue increases

71
Q

what is autoregulation

A

-when there is a rapid increase in arterial pressure it causes an immediate rise in blood flow
-preventing massive changes bc of pressure
-even if pressure remains high, the local blood flow remains relatively normal

72
Q

which areas have special regulation

A

-kidney
-brain
-skin

73
Q

what are the 3 endothelial vasoconstrictors
*test q

A

-endothelin
-serotonin (platelets)
-angiotensis

74
Q

what are the 4 endothelial vasodilators
*test q

A

-nitric oxide ****
-prostacyclin/prostaglandin E
-histamine
-cAMP pathway

75
Q

important facts about nitric oxide (NO)

A

-very lipid soluble
-extremely powerful dilator
-released from endothelial cells in response to chemical/physical stimuli
-acts mainly in local tissue bc it has a half life of 6 sec
-NO synthesis is impaired by chronic hypertension and atherosclerosis (causing vasoconstriction)

76
Q

important facts about endothelin

A

-most important vasoconstrictor**
-large 27-amino acid peptide
-it doesn’t take much endothelin to get a huge result
***released when vessels are damaged to prevent extensive bleeding

77
Q

what are the 3 hormonal vasocontrictors

A

-norepinephrine –> both a hormone and a neurotransmitter
-angiotensin 2
-vasopressin/ADH

Cardiopulmonary Physiology (11 decks)

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