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CAM201 Physiology > CO and blood flow > Flashcards

CO and blood flow Flashcards

1
Q

What organs ALWAYS receive blood even at the expense of other organs/

A

Brain and heart

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2
Q

Name the various mechanisms that exist to match blood flow to demand

A
  • special receptors
  • metabolic controls
  • oxygen deficiency
  • nitric oxide
  • long term control mechanisms
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3
Q

How do special receptors work to match blood flow to demand?

A

Skeletal muscle arterioles dilate in response to moderate levels of adrenaline

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4
Q

How does metabolic control contribute to blood flow?

A

Diffusion of metabolic products e.g. adenosine, lactate, Co2, K+ from active cells causes vasodilation

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5
Q

How does nitric oxide contribute to blood flow?

A

Shear stress from increased blood flow in arteries and arterioles causes their lining endothelial cells to release EDRF which leads to vasodilation

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6
Q

What are some the longer term control mechanisms that exist to regulate blood flow?

A

Capillary density changes (certain organs can grow more capillaries e.g. skeletal muscle. Muscle mass increases, so oxygen demands increase, capillaries are grown to match the demand)

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7
Q

What is autoregulation?

A

The intrinsic ability of an organ to maintain a constant blood flow despite changes in BP

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8
Q

What are the two mechaisms of autoregulation?

A

Metabolic and myogenic

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9
Q

Describe the metabolic mechanism

A

Diffusion of metabolic products (e.g. adenosine, lactate, Co2, K+) from active cells causes vasodilation

oxygen removal from blood by active cells reduces local blood oxygen, also leading to vasodilation

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10
Q

Describe the myogenic mechanism of autoregulation

A

Stretch induces a reflex in vascular smooth muscle constriction (prominent in the arterioles).

The muscles can recoild/dilate/restrict to maintain the BP of the vessels they surrounde/supply

Does not require SNS or metabolic input and is a rapid mechanism for larger arteries and arterioles

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11
Q

How much can autoregulation adjust BP by?

A

Up to 100mmHg

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12
Q

Total systemic blood flow is the sum of all blood flow to organs ONLY IF….

A

1: organ circulations are arranged in parallel
2: CO is the sum of all organ blood flows

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13
Q

if systemic blood flow increases or decreases, what happens to the blood flow to the brain?

A

Nothing. it stays the same. Percentage of overall flow may be different but the raw value always stays the same

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14
Q

What is vasomotion?

A

Blood flow regulation at the tissue level.

Rhythmic distribution of blood flow in a tissue driven by changes in metabolism

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15
Q

What is a mechanism that exists to regulate capillary blood flow (e.g. when skeletal muscles ar at rest and capillary flow only acts to meet nutrient demand)

A

Pre-capillary sphincters

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16
Q

What are the three variables relating to stroke volume that can be altered?

A

Preload, afterload and contractility

17
Q

What is preload? Why is it relevant?

A

Preload is the amount of blood that fills the heart before it contracts.

18
Q

Why does increasing sarcomere length increase the tension of the next contraction?

A

Placing the sarcomere under more tension increases the sensitivity of troponin C to Ca2+

In other words it increases the efficiency of E-C coupling in cardiomyocytes

19
Q

What is preload proportional to?

A

the volume of the ventricle at the end of diastole (EDC)

20
Q

What does a high EDV lead to?

A

increased cardiomyocyte stretch and increased force of contractionQ

21
Q

What is the Frank-Starling mechanism?

A

If venous return increases, stroke volume and therefore CO, increases to match

22
Q

How can you increase venous return e.g.during exercise to maintain a higher CO

A

Skeletal muscle pump: contraction of muscles helps to squeeze the veins and propel blood back to the heart

Respiratory pump: inhalation moves the diaphrgam and causes the vena cava to constrict.On exhalation, the vena cava relaxes

23
Q

What is afterload?

A

The pressure the heart has to work against during ejection.

It is analagous to the force that a skeletal muscle works against when it shortens

24
Q

What is the law of LaPlace? How does it apply to ventricles?

A

Wall stress = pressure x radius / 2 x wall thickness

Ventricular muscle is roughly a sphere shape, s the force it has to oppose when contracting is the wall stress

25
Q

How can afterload be altered?

A

Systolic pressure of the ventricle e.g.hypertension

Radius of the ventricle e.g. dilated cardiomyopathy

Wall thickness e.g. ventricular hypertrophy as a compensatory mechanism

26
Q

What is contractility (inotropy)?

A

The performance of the ventricle at a given preload and afterload

27
Q

What is the main difference between contractility and preload/afterload?

A

Contractility is INDEPENDENT of these factors, that partially depend on the properties of the vasculature

28
Q

How is contractility regulated?

A

SNS

Circulating catecholamines e.g. adrenaline increasing more Ca2+

medications

force frequency

29
Q

Describe the neural inputs to the SA node

A

SNS: accelerator nerve, increases heart rate

PNS: vagus nerve: decreases heart rate

30
Q

If the intrinsic firing rate of the SA node is 100 bpm, why is resting heart rate usually 60bpm?

A

The HR is under PNS control at rest

31
Q

How would you increase HR?

A

Decrease vagal tone, then increase SNS activation

32
Q

What are two other ways to modify heart rate?

A

Stretch the SA node or stretch the atria

33
Q

How does stretching the SA node modify HR?

A

mechanical stretching of the SA node increases HR by up to 15% by causing an increase in venous return to the atria, increasing filling volume

34
Q

How does stretching the atria modify HR?

A

Creates a reflex in HR known as the Bainbridge reflex.

when activated, stretch receptors activate the ANS to increase HR

Bainbridge reflex prevents blood building up in the great veins and pulmonary circulation

35
Q

Under normal conditions, CO is principally controlled by venous return. what 3 mechanisms contribue?

A

Frank-Starling mechanism: acting on SV

Effect of preload on SA node stretch: acting on HR

Bainbridge reflex: acting on HR

36
Q

What if the limit of CO is reached but the tissues still need more flow? e.g. if the tissue demands increase to approch the norml max or CO is impaired in heart failure

A

Even if arterioles begin to dilate, BP will fall and flow will not increase.

Blood supply then has to be limited to some organs

37
Q

How does SNS innervation of vasculature regulate and maintain BP?

A

Decrease radius of arteriole, increasing resistance and decreasing flow

Decrease radius of vein, decreasing volume

38
Q

What are the local and SNS manifestations of limited CO?

A

Local: arteriolar vasodilation happens to tr and increase flow. This wins out in critical organs.

SNS: arterial and arteriolar vasoconstriction if BP starts to fall. This wins out in non-critical organs e.g. skin, gut and kidneys

CAM201 Physiology (4 decks)

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