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Semester 2: Physiology > control of blood flow > Flashcards

control of blood flow Flashcards

1
Q

What is TPR?

A

Total peripheral resistance
The force required to maintain blood flow
TPR= BP/CO

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2
Q

What is the purpose of TPR?

A

Increase in TPR = need to increase the pressure to keep the same flow

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3
Q

What 3 things control TPR?

A
  1. Poiseulle’s Law
    1. Myogenic response
    2. Blood viscosity

High viscosity = more resistant to pressure
Low viscosity = less resistant to pressure

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4
Q

What is the formula used to measure blood flow (CO)?

A

CO= BP (pressure gradient)/TPR

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5
Q

Describe how blood pressure affects blood flow in a NORMAL situation

A

(1) Normal blood pressure in artery
(2) Low blood pressure in arterioles
(3) Normal blood flow in capillaries

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6
Q

Describe how low blood pressure can affect blood flow

A

(1) Low blood pressure in artery
(2) Vasodilation occurs = lower TPR
(3) Increases blood flow in capillaries

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7
Q

Describe how high blood pressure can affect blood flow

A

(1) High blood pressure upstream
(2) Vasoconstriction occurs = higher TPR
(3) Decreased blood flow in capillaries downstream

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8
Q

What medical term can be used to describe someone with high blood pressure and why?

A

Hypertension

Over constriction of arterioles = higher arterial BP = less capillary flow = under perfused areas (low in oxygen)

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9
Q

What is the function of the brain stem in terms of blood flow around the body?

A

Brain stem areas control sympathetic nervous activity in various areas of the body depending on their level of demand

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10
Q

Describe the changes in blood flow when a person is sedentary

A

→ Superior mesenteric dilated
Increases blood flow to intestines

→ Common iliac constricted
Decreases blood flow to legs

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11
Q

Describe the changes in blood flow when a person is exercising

A

→ Superior mesenteric constricted
Decreases blood flow to intestines

→ Common iliac dilated
Increased blood flow to legs

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12
Q

What is Poiseuille’s law?

A

Describes parameters that control/determine TPR

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13
Q

What is meant by the R^4 effect?

A

Bigger radius = less resistance = more cardiac output

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14
Q

What is the main vessel involved in the TPR?

A

Arterioles

→ Arterioles have the largest pressure drop

→ Arterioles radius is tightly controlled by sympathetic nerves providing constriction and dilation

  • Arterioles are long vessels
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15
Q

Why is TPR not controlled by capillaries?

A

Even though they have a smaller radius…

○ Less resistance to blood flow = lower pressure drop
Less resistance because bolus flow reduces viscosity

○ No sympathetic innervation OR smooth muscle = cannot alter radius

-Individual capillaries are short

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16
Q

State and explain the difference in resistance between arterioles and capillaries

A

Capillaries are arranged in parallel = low total resistance

caPillaries = Parallel

Arterioles are arranged in series = higher total resistance

17
Q

What are the two types of control mechanisms for the arteriole radius to control local blood flow?

A
  1. Intrinsic
    Factors entirely WITHIN an organ or tissue
  2. Extrinsic
    Factor entirely OUTSIDE the organ or tissue
18
Q

Name the examples of the intrinsic control of the arteriole radius

A
  1. Local hormones
  2. Tissue metabolites
  3. Myogenic properties of muscle
  4. Endothelial factors
19
Q

Name the examples of the extrinsic control of the arteriole radius

A

Hormonal (eg- adrenaline)

Neuronal (eg- sympathetic nervous system)

20
Q

What is blood viscosity and what is it dependent on?

A 
Viscosity is the measure of internal friction opposing the separation of the lamina
Depends on:
1. Velocity of blood 
2. Vessel diameter 
3. Haematocrit
21
Q

What are the effects of high and low blood viscosity and why does this occur?

A

(HIGH) Polycythaemia: high TPR = high BP = low blood flow

LOW) anaemia: low TPR = low BP = high heart rate (baroreceptor reflex

22
Q

What is meant by the Fahraeus-Lindqvist effect?

A

Narrow tube = low blood viscosity = less resistance = high blood flow in micro vessels (eg- capillaries)

23
Q

60% of blood volume at rest is in systemic veins and venules. What is the purpose of this store?

A

Blood reservoir; blood can be diverted in times of need (eg: in haemorrhage or during exercise)

24
Q

What is Bernoulli’s theory?

A

Mechanical energy of flow is determined by pressure, kinetic and potential energies
Energy= pressure (PV) + kinetic (pV^2/2) + potential (pgh) where p= fluid mass

25
Q

Using Bernoulli’s law, explain the blood flow from the feet back to the heart

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). Also, there is greater potential energy at the heart than at the feet (more height).
The greater kinetic/potential energies overcome the pressure gradient to maintain flow.

Semester 2: Physiology (35 decks)

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