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Physiology 1 : cardiovascular > Control of blood flow > Flashcards

Control of blood flow Flashcards

1
Q

What three things mainly control TPR?

A

→Poiseulle’s Law
→ myogenic response
→blood viscosity

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2
Q

What does an increase in resistance mean?

A

→ Pressure must be increased to maintain the same flow

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3
Q

What is the equation for blood flow? (CO)

A

→ Pressure gradient / TPR

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4
Q

What is hypertension?

A

→ over constriction of arterioles

→ Higher arterial BP but less capillary flow - under perfusion

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5
Q

What are the changes in blood flow when sedentary?

A

→ Superior mesenteric dilated
increased flow to intestines

→ Common Iliac constricted
decreased flow to legs

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6
Q

What are the changes in blood flow when exercising?

A

→Superior mesenteric constricted
decreased flow to intestines

→ Common iliac dilated
increased flow to legs

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7
Q

What does Poiseuille’s Law describe?

A

→ Parameters that govern TPR

→Illustrates why the radius of a vessel is such an important determinant in changing blood flow.

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8
Q

What is the state of the BP and blood flow in arteries and arterioles in a normal situation?

A

→In a normal situation, the arteries have a greater BP than the arterioles.
→The pressure drop between the arteries and arterioles causes blood flow.

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9
Q

What is the state of BP and blood flow when the arterioles are dilated?

A

→With the arterioles dilated, there is a decrease in TPR. →These leads to decreased BP upstream, but greater blood flow.

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10
Q

What is the state of BP and blood flow when the arterioles are constricted?

A

→With the arterioles constricted, there is an increase in TPR.
→ This leads to increased BP upstream, but less blood flow.

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11
Q

What is the equation for conductance ?

A

Conductance (G) = (πr^4)/(8ηL)

r: radius of vessel
η: blood viscosity
L: vessel length

(blood vessel radius to the power of 4 controls TPR)

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12
Q

What is Poiseuille’s and Darcy’s Law combined?

A

→CO = Pa - CVP x (πr^4)/(8ηL)

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13
Q

What is the r^4 effect ?

A

→Double the radius of vessel 2 compared to vessel 1
→ The change in r^4 is 16 x
→ 16x greater flow in vessel 2 as flow is proportional to r^4

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14
Q

How do vasoconstrictors or dilators have large effects on blood flow?

A

→ Vasoconstrictors or dilators produce small changes in the vessel radius by affecting smooth muscle
→ these have large effects on blood flow

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15
Q

What is the pressure in arterioles?

A

→40-50 mmHg amongst vessels

→ largest pressure drop

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16
Q

What is the arteriole radius controlled by?

A

→ Tightly controlled by sympathetic nerves providing constant tone
→dilate and constrict

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17
Q

What parameters is TPR controlled by?

A

→ Radius r^4
→ Pressure difference across vessels (P1-P2)
→ Length (L)

18
Q

Why do arterioles control TPR and not capillaries?

A

→ Capillaries are arranged in parallel so they have a low total resistance
→ R total = 1/R1 + 1/R2
→ arterioles are in series so total resistance is greater
→ R total = R1+R2

19
Q

How is local blood flow through individual organs/ tissues controlled?

A

→ Controlled by changes in radius of arterioles supplying a given organ/ tissue

20
Q

What are the control mechanisms for the arteriole radius?

A

→Intrinsic
factors are within the organs or tissues

→Extrinsic
factors are outside the organ or tissue

21
Q

What is Baylis’s myogenic response?

A

→ Increased distension of a vessel makes it constrict

→ Decreased distension of a vessel makes it dilate

22
Q

What is the function of Baylis’s myogenic response?

A

→ It maintains blood flow at the same level during changing arterial pressure

23
Q

In what circulations is Baylis’s myogenic response important?

A

→renal, coronary and cerebral circulation

24
Q

What happens when the muscle is stretched to make it contract ?

A

→ Ion channels open which depolarize leading to muscle contraction

25
Q

What is blood viscosity?

A

→Viscosity is the measure of internal friction opposing the separation of the lamina.

26
Q

What does blood flow depend on?

A

→ Viscosity
→ Vessel diameter
→ Haematocrit

27
Q

How much of the blood volume is at rest in systemic veins and venules?

A

60%

28
Q

What do veins function as?

A

→ reservoir

→ blood can be diverted from it in times of need

29
Q

What are properties of veins?

A

→ they are thin walled and collapsible, voluminous vessels

30
Q

How much of the blood volume do veins contain?

A

→2/3rds of blood volume

31
Q

What are veins innervated by?

A

→ smooth muscle which is innervated by sympathetic nerves

32
Q

what is the difference between arterial muscle and vein muscle?

A

→ Vein muscle is thinner and more compliant so forms a reservoir

33
Q

What does contraction of venous vessels do?

A

→ Expels blood into central veins
→Increases venous return/CVP/ End-diastolic volume
→ Increases SV

34
Q

What are the venous pressures in the limb veins at heart level?

A

→ 5-10 mmHg

35
Q

What is the central venous pressure?

A

→ 0-7mmHg

36
Q

What is the venous pressure in the foot vein while standing?

A

→ 90mmHg

37
Q

Why is the venous pressure high at the feet?

A

→ so high pressure is generated for return to the heart

38
Q

What is venous pressure helped by in the feet?

A

→ thoracic pump and skeletal muscle contraction

39
Q

what does stimulation of sympathetic nerves causing venoconstriction cause?

A

→ Shifts blood centrally
→ Increase in venous return, CVP and end diastolic pressure
→ Increased CVP increases preload and so increases SV

40
Q

What is the Bernoulli theory?

A

→ Mechanical energy of flow is determined by pressure, kinetic + potential energies

41
Q

How does blood flow from the heart to the feet in terms of kinetic energy, potential energy + pressure?

A

→There is a -90 mmHg pressure gradient against the flow from the feet back to the heart.
→The ejected blood has greater kinetic energy at the heart than the feet (more velocity).
→greater potential energy at the heart than at the feet (more height).
→The greater kinetic/potential energies overcome the pressure gradient to maintain flow.

Physiology 1 : cardiovascular (18 decks)

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