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sem 2 > Control of blood flow > Flashcards

Control of blood flow Flashcards

1
Q

Define Darcys law?

A

Flow= PA- CVP/ TPR

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2
Q

What controls TPR?

A
  1. Darcy’s and Poiselle’s law
  2. Myogenic response
  3. Blood viscosity
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3
Q

What does total peripheral resistance control?

A
  1. Blood flow

2. Blood pressure

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4
Q

What does an increase in resistance mean?

A

You need to increase pressure to keep the same blood flow

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5
Q

Define conductance?

A

Is how well a vessel conducts blood flow

G= 1/ Total peripheral resistance

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6
Q

What does an increase in resistance mean?

A

An increase in resistancd means you need to increase pressure to keep the same blood flow

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7
Q

what is Conductance ?

A

Is how well a vessel conducts blood flow

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8
Q

What do arteries do?

A

Arteries are bigger than the arterioles. Arteries control blood pressure in the body and can constrict and dialate

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9
Q

What happens during the vasodilatation of arteries?

A

Vasodilation will increase blood flow to the capillaries and decrease total peripheral resistance. There will be decreased blood pressure upstream but greater flow

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10
Q

What happens during the vasoconstriction of arteries?

A

Vasoconstriction will decrease blood flow and increase total periperhal resistance. It will increase blood pressure upstream but less blood flow.

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11
Q

Define Hypertension?

A

Over constriction of arterioles. There is higher arterial blood pressure but less capillary flow so they are under perfusion of the organ.

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12
Q

What do brain stem areas control?

A

Brain stem areas control sympathetic nervous activity to various areas of the body

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13
Q

What happens when an individual is sedentary? (4pts)

A
  1. Superior mesenteric is dilated which supplies the intestines and the GI tract
  2. This increases blood flow to intestine and improves digestion
  3. Common lilac artery is constricted
  4. There is decreased blood flow to the legs
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14
Q

What happens when an individual is exercising? (4pts)

A
  1. The superior mesenteric artery is dilated
  2. There is decreased blood flow to the intestines
  3. The common lilac artery is dilated
  4. There is increased blood flow to the legs
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15
Q

Define Poiseuille’s law?

A

Resistance= 8nL/ nf4

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16
Q

What does higher blood viscosity mean?

A

greater resistance

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17
Q

How does the length of the blood vessel affect resistance?

A

The longer the vessel is the greater the resistance is

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18
Q

Define Darcys law?

A

Flow= Pa- CVP x G

19
Q

Combine Darcy’s and Poiseuille’s law?

A

Flow= Pa- CVP x nr4/ 8nL

20
Q

How does vessel length affect conductance?

A

A vessel with a greater radius has greater conductance

21
Q

What do vasoconstrictor or dilators do?

A

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

22
Q

Define resistance?

A

8NL/ nr4

23
Q

Describe arterioles? (2pts)

A
  1. Arterioles have the largest pressure drop of 40-50 mmHg amongst vessles
  2. Arteriole radius is tightly controlled by sympathetic nerves providing constant tone dilation vs constriction
24
Q

Name 3 main parameters total peripheral resistance is controlled by? (3pts)

A
  1. Radius
  2. Pressure difference across vessels
  3. Length - arterioles are long vessels
25
Q

Describe capillaries? (5pts)

A
  1. In capillaries there is no sympathetic innervation therefore we cannot alter the radius
  2. Individual capillaries are very short
  3. There is less resistance to flow in the capillaries because blood flow reduces viscosity due to its bolus flow
  4. Capillaries are arranged in parallel so they are side by side and the blood flows through them all at the same time. The total resistance is therefore reduced
  5. In contrast arterioles are arranged in series which is one after the other. Resistance is caculated by:

R total= R1 + R2

26
Q

Define intrinsic methods? (2pts)

A

Factors entirely within an organ or tissue ( allows response to local factors)

  1. Local hormones are released in a tissue
  2. Tissue is metabolised
27
Q

Define extrinsic methods?

A

Factors outside the organ or tissue ( nervous and hormonal control of blood vessels)

  1. Signals from the brainstem down the sympathetic nervous system telling the arterioles supplying that tissue to dilate or constrict
  2. Adrenal glands release adrenaline which circulates around the body causing vasodilation.
28
Q

Define Endothelial factors

A

Anything that increases nitric oxide production

  • this causes vasodilation in particular tissues
29
Q

Describe the Bayliss myogenic response? (6pts)

A
  1. At higher pressures when the vessel is stretched it contracts to reduce blood flow
  2. Increased distention of the vessel will make it constrict. Above a certain stretch it will no longer stretch and will just constrict and limit blood flow.
  3. Decreased distention of the blood vessel will make it dilate
  4. There is a linear relationship between blood flow and pressure. As you increase pressure blood flow will increase until a certain point
  5. Stretching of the vessel causes ion channels to open, which then depolarise, leading to smooth muscle contraction. This causes them to constrict
  6. The Bayliss myogenic response maintains blood flow at the same level during changing arterial pressures. It is very important in renal, coronary and cerebral circulation.
30
Q

Describe the Bayliss myogenic response? (6pts)

A
  1. At higher pressures when the vessel is stretched it contracts to reduce blood flow
  2. Increased distention of the vessel will make it constrict. Above a certain stretch it will no longer stretch and will just constrict and limit blood flow.
  3. Decreased distention of the blood vessel will make it dilate
  4. There is a linear relationship between blood flow and pressure. As you increase pressure blood flow will increase until a certain point
  5. Stretching of the vessel causes ion channels to open, which then depolarise, leading to smooth muscle contraction. This causes them to constrict
  6. The Bayliss myogenic response maintains blood flow at the same level during changing arterial pressures. It is very important in renal, coronary and cerebral circulation.
31
Q

Define Viscosity?

A

Is a measure of the internal friction opposing the separation of the lamina

32
Q

How do anaemic patients recover blood pressure?

A

heart rate increases

33
Q

Define the Fahradeus- Lindqvist effect

A

Vessels move to the centre producing a series of concentric vessels to reduce friction. There is very little resistance and increases blood flow

34
Q

What happens in small blood vessels?

A

The red blood cells squeeze and get deformed and pass through very small capillaries leading to a smooth bolus flow where they from a smooth flow

35
Q

What happens in sickle cell anaemia?

A

The red blood cells cannot deform and therefore cannot pass smoothly through the capillaries. This cases the blood to have a higher viscosity

36
Q

Describe what happens in very slow blood flow

A

Increased blood flow due to partial clotting

37
Q

Describe veins? (4pts)

A
  1. Thin walled
  2. Collapsible
  3. Voluminous vessels
  4. Contain 2/3rd of the blood volume
  5. Contractile- they contain smooth muscle which is innervated by sympathetic nerves but thinner than arterial muscle and more compliant so form blood reservoir.
38
Q

What happens when blood is needed in the veins e.g during exercise? (4pts)

A
  1. Veins contract so they send more blood back to the heart and as more blood arrives to the heart it will stretch more
  2. The end diastolic volume of the heart will increase which will cause it to contract harder and send more blood to the lungs
  3. As that blood goes through the lungs it arrives back at the heat and back at the left atrium
  4. It will cause the left ventricle to stretch more and cause heart to contract harder increasing cardiac output
  5. In once heartbeat cardiac output has increased because the smooth muscle in the vein contracted.
39
Q

What happens during the contraction of vessels? (3pts)

A
  1. Contraction of vessels expels blood into the central veins
  2. This increases venous return
  3. This increases stroke volume
40
Q

What happens during the contraction of vessels? (3pts)

A
  1. Contraction of vessels expels blood into the central veins
  2. This increases venous return
  3. This increases stroke volume
41
Q

Describe venous pressure changes?

A
  1. As venous pressure increases blood volume increases till it reaches a certain point. it will then plateau out
  2. At low pressures veins will collapse
  3. At high pressures veins will distend
  4. Venous pressure is high at the feet
  5. When there is very little pressure veins don’t really constrict they will just fold up.
42
Q

What happens during stimulation of sympathetic nerves? (4pts)

A
  1. Stimulation of sympathetic nerves causes vasoconstriction
  2. This will cause the blood to shift centrally
  3. This increases venous return so more blood returns to the heart. This increases central venous pressure and end-diastolic pressure
  4. Increased central venous pressure increases preload and so increases stroke volume.
43
Q

What happens when you are standing up? (6pts)

A
  1. The pressure at your feet is higher than the pressure at your heart
  2. Bernoullis law explains how the heart pumps blood to the feet
  3. The kinetic energy of the blood and the potential energy of gravity which pulls the blood down illustrates how blood flows from the heart to the feet
  4. There is greater potential energy in the heart than at the feet as there is more height
  5. The greater kinetic energy and the potential energy overcomes the pressure gradient to maintain blood flow
  6. In people with compromised blood flow their blood flow to the feet is compromised.

sem 2 (12 decks)

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