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CardioRenal II > Phys- Local control of Blood flow > Flashcards

Phys- Local control of Blood flow Flashcards

1
Q

most potent vasoconstrictors known

A

Endothelin

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2
Q

Myogenic Theory/ response

A

increasing pressure in a vessel causes vasocontriction (inreased resistance)

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3
Q

Law of La Place

A

T=P x r. (tension = transural pressure x radius) ——– Increase pressure and keep T (flow) contant by decreasing the radius ( = myogenic response)

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4
Q

Purpose of the myogenic response

A

protecting the capillaries from sudden increases in blood pressure

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5
Q

Intrinsic neurons (local control)

A

located within the walls of arterioles- may be involved in rapid, conducted vasicdilation and/or vasoconstriction (communication within the vascular tree)

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6
Q

Autocoids

A

locally produced vasoactive substances - generally potent vasodilators

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7
Q

resistance equation

A

1/r^4

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8
Q

Resting tone

A

tonic sympathetic activity (extrinsic) creates a level of vasconstriction

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9
Q

Reactive Hyperemia

A

after a period of ischemia, blood flwo increases above control level ( the magnitude and duration of reactive hyperemia correlates with the duration of the ischemic period)

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10
Q

what determines the distribution of the cardiac output

A

local control

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11
Q

Give examples of disorders of local control

A

1.) Diabetes 2.) Anaphylactic Shock 3.) Septic Shock (complete breakdown of local control)

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12
Q

Autoregulatory zone

A

80-150 mmHg - flow remains relatively constant in this area

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13
Q

Passive Vasodilation

A

due to decrease in active vasoconstriction. Decreases vascular resistance

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14
Q

Principle functions of blood flow to the tissues

A

1.) Delivery of metabolic substances to capillaries 2.) Removal of metabolic biproducts from the tissues (waste products, carbon dioxide, ions, urea, heat )

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15
Q

importance of autoregulation

A

1.) Maintains tissue flow at low perfusion pressures 2.) Protects the tissue from over perfusion and possible damage at high perfusion pressure

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16
Q

Metabolic Vasodilation

A

an increase in tissue metabolism causes the release of substances in the tissue that relax vascular smooth muslce and produce metabolic vasodilation (vasoregulation)

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17
Q

what conditions set us up for suitable exchange in the capillaries

A

1.) low pressure (due to resistance in arterioles) 2.) increased cross sectional area from arterioles to capillaries - results in a marked fall in flow velocity - suitable for exchange

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18
Q

Vasomotion (definition)

A

describes the normal pattern of rhythmic changes in flow within a capollary bed

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19
Q

Passive Vasoconstriction

A

due to the removal of dilatory influence. Increases vascular resistance

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20
Q

Extrinsic control

A

Systemic - mediates outside the tissues (ANS and humoural) IRRESPECTIVE OF METABOLISM

21
Q

**Autoregulation (define) **

A

intrinsic tendency of an organ or tissue to alter local vascular resistance to maintain constant blood flow despite changes in perfusion pressure

22
Q

Vasoconstrictors

A

very few of our local metabolic factors (most are vasodilators)

23
Q

what causes vasomotion

A

spontaneous changes in the pre-capillary resistance in response to the changes in tissue environment (subtle chanes in the local concentration of vasoactive substances in the interstitium)

24
Q

Temperature (local control)

A

Increases in temperature causes vasodilation - Decreases in temperature cause vasoconstriction

25
Q

When do Mygenic Factors dominate

A

predominate when MAP IS INCREASED suddenly- prevent increases in pressure from reaching the capillaries

26
Q

Intrinsic control

A

Local control - originates from WITHIN the tissues. Involves changes in vascular resistance at the tissue level. CLOSELY COUPLED TO METABOLIC DEMAND

27
Q

Name an example of vasomotion

A

Reactive hyperemia

28
Q

Endogenic vasoregulation

A

sheer stress of the endothelium causes release of nitric oxide (NO ) - vasodilator

29
Q

Indirectly acting vasodilators

A

endothelium dependent - substances that trigger nitric oxide production/release (increased shear stress etc)

30
Q

where do we see the greatest drop in arterial pressure

A

greatest drop in pressure corresponds to the vascular resistance in the arterioles

31
Q

Examples of indirectlt acting vasoconstrictors

A

1.) Endothelial-derived contracting factor (ECF) 2.) Endothelin

32
Q

purpose of metabolic vasodilation

A

increase tissue blood flow and the delivery of exygen and substrates as well as the removal of metabolic waste products in proportion to tissue metabolism

33
Q

When do Metabolic Factors dominate

A

repdominate when MAP IS DECREASED and flow is low or when tissue metabolism is elevated relative to flow

34
Q

Active Hyperemia vs sympathetic input

A

active hyperemia (activity of the muscles) tends to override the sympathetic vasoconsrtiction

35
Q

Mechanical Muscle Pump (local control)

A

Rhythmic contractions in skeletal muscle contribute to blood flow through the muscle pump. During contraction the increase in untramuscular pressure compresses veins. During relaxation the surrounding pressure on both the arterial and venous side is lower which enhances blood flow and perfusion

36
Q

most local metabolic factors act as

A

vasodilators

37
Q

Active Vasoconstriction

A

due to neural or humeral influence. Increases vascular resistance (above resting tone)

38
Q

Gap junctions (local control)

A

between endothelial cells - involved in rapid cell to cell conduction of both constrictor and dilatory signals along vessel segments

39
Q

Relationship between local control of blood flow and metabolic capacity

A

the degree of local contrl of blood flow exhibited by a tissue tends to be proportional to its metabolic capacity (ex: heart has high metabolic activity - high local control) - makes sense: flow can be maintained at a level adequate to support the metabolic demands of the tissue while not imposing excessive demands on the cardiovascular system.

40
Q

Endothelial-derived contracting factor (ECF)

A

may be superoxide ion produced by endothelial cells in response to oxidative stess - VASOCONSTRICTOR

41
Q

Vasoregulation

A

ability of the tissues to control blood flow to meet the metabolic needs and waste disposal of the tissue while not over-perfusing it

42
Q

Active vasodilation

A

due to a “dilatory influence” - Vascular resistance falls below resting and/or basal tone

43
Q

Resting tone is (greater/less than) basal tone

A

Resting tone is greater than basal tone

44
Q

What is the driving force for blood flow

A

Mean arterial pressure (MAP)

45
Q

Active Hyperemia

A

during increased tissue metabolic activity the rate of substrate utilization and waste production increases. There is a coincident and proprotional increase in tissue blood flow due to vasodilation

46
Q

Vasodilators

A

Products of cellular metabolism or locally released vasoactive substances (autocoids) - NOT INVOLED IN THE SYSTMEIC REGULATION OF BLOOD PRESSURE

47
Q

Basal tone

A

exhibited in blood vessels (even when they arent innervated). Blood vessels possess an INTRINSIC myogenic tone. INDEPENDENT of extrinsic influences (sympathetic influence, humeral effects, drugs)

48
Q

Discuss perfuion of capillary beds

A

In resting state not all capillaries within a capillary bed are uniformly perfused (some have high flow while adjacent have no or sluggish flow)

49
Q

what determines the magnitude and duration of reactive hyperemia? Why?

A

duration of the ischemic period - presumably due to the accumulation of metabolic byproducts during the ischemic period

CardioRenal II (12 decks)

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