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Cardiovascular System > Control Of The Circulation > Flashcards

Control Of The Circulation Flashcards

1
Q

Why do we need to control the circulation

A

To maintain blood flow
To maintain arterial pressure
To distribute blood flow
Auto-regulation/homeostasis
To function normally
To prevent catastrophe
To maladapt in disease

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2
Q

Characteristics of arteries

A

Low resistance conduits
Elastic
Cushion systole
Maintain blood flow to organs during diastole

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3
Q

Where is the principle site of resistance of vascular flow

A

Arterioles

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4
Q

What is TPR

A

Total arteriolar resistance

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5
Q

What is TPR determined by

A

Local, neural and hormonal factors

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6
Q

What are 2 major roles of arterioles

A

Major role in determining arterial pressure
Major role in distributing flow to tissue/organs

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7
Q

What determines the radius of the arterioles

A

Vascular smooth muscle

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8
Q

What happens if the vascular smooth muscle contracts

A

The radius decrease so the resistance increases and the flow decreases

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9
Q

What happens when vascular smooth muscle relaxes

A

When the vascular muscle relaxes the radius increases which causes the resistance to decrease and the flow to increase

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10
Q

Why does vascular smooth muscle never completely relaxed

A

Myogenic tone

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11
Q

What does the slow flow of capillaries allow

A

It allows time for nutrients and waste to be exchanged

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12
Q

How is flow determined inside the capillaries

A

Arteriolar resistance
Number of open pre-capillary sphincters

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13
Q

Characteristics of veins

A

Compliant
Low resistance conduits
Valves present to aid venous return against gravity
Skeletal muscle/respiratory pump aids venous return
Vasoconstriction maintains venous return/pressure

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14
Q

How is cardiac output calculated

A

Heart rate X stroke volume

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15
Q

How is blood pressure calculated

A

Cardiac output X Total peripheral resistance

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16
Q

How is pulse pressure calculated

A

Systolic - diastolic pressure

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17
Q

How is mean arterial pressure calculated

A

Diastolic pressure + 1/3 pulse pressure

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18
Q

What governs flow

A

Ohms law and poiseuilles law

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19
Q

What is ohms law

A

Flow = pressure gradient/resistance

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20
Q

What is poiseuille’s equation

A

Flow = radius to the power of 4

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21
Q

What is the frank starling mechanism

A

Stroke volume increases as end diastolic volume increases, due to the length-tension relationship of muscle the end diastolic volume would increase so the stretch would increase along with the increased force of contraction. At rest the cardiac muscle is not at its optimum length. Increased vascular resistance increases end diastolic volume which increases stroke volume and increased cardiac output even if heart rate is constant

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22
Q

What is the goal of control of circulation

A

Maintain blood flow
CO = SV X HR
This needs pressure to bush blood through the peripheral resistance

23
Q

What is blood pressure

A

Blood pressure is the pressure of blood within and against the walls of the arteries

24
Q

When is systolic blood pressure the highest

A

It is highest when the ventricles contract

25
Q

When is diastolic blood pressure the lowest

A

It is lowest when the ventricles relax

26
Q

How is blood pressure measured

A

Using the brachial artery

27
Q

Why is the brachial artery used to measure blood pressure

A

Convenient to compress, and it is at the level of the heart

28
Q

In what ways can blood pressure be controlled

A

Auto regulation
Local mediators
Humoral factors
Baroreceptors
Central (neural) control

29
Q

What is myogenic auto regulation

A

Myogenic autoregulation of the blood vessels is when the smooth muscle of the blood vessel stretches under the pressure of the blood within the lumen, so when this decreases the vessel will contract until the diameter normalises or is slightly reduced in normal size

30
Q

Why does autoregulation vary

A

It is an intrinsic ability of an organ and so will have constant flow despite perfusion pressure changes

31
Q

Where has excellent autoregulation

A

Renal, cerebral and coronary

32
Q

Where has moderate levels of autoregulation

A

Skeletal muscle/splanchnic

33
Q

Where has poor autoregulation

A

Cutaneous vessels

34
Q

How is blood flow maintained to vital organs such as the brain and heart

A

Intrinsic control

35
Q

What is examples of a vasoconstrictor

A

Endothelin-1
Internal blood pressure/myogenic contraction

36
Q

What are examples of vasodilators

A

Hypoxia
Bradykinin
Tissue breakdown products

37
Q

What is essential for control of the circulation

A

Endothelium

38
Q

What are examples of circulating hormonal vasoconstrictors

A

Epinephrine - skin
Angiotensin II
Vasopressin

39
Q

What are examples of circulating hormonal vasodilators

A

Epinephrine- muscle
Atrial natriuretic peptide

40
Q

Where are primary baroreceptors found

A

Carotid sinus and aortic arch

41
Q

Where are secondary baroreceptors found

A

Veins
Myocardium
Pulmonary vessels

42
Q

How do baroreceptors respond to increased blood pressure

A

Blood pressure increase is detected which results in increased firing which results in a decreases in cardiac output so reduces blood pressure

43
Q

What are the role of arterial baroreceptors in the short term

A

Key role in short term regulation of blood pressure is minute to minute control in response to exercise or haemorrhage

44
Q

What happens to baroreceptors if the arterial pressure deviates from norm for more than few days

A

The baroreceptors would adapt to a new baseline pressure which would be seen in hypertension

45
Q

What is a major factor in long-term blood pressure control

A

Blood volume

46
Q

What are the main neural influences on the medulla

A

Baroreceptors
Chemoreceptors
Hypothalamus
Cerebral cortex
Skin
Changes in blood oxygen and carbon dioxide

47
Q

What does stimulation of the anterior hypothalamus causes on cardiovascular reflexes

A

Decreased blood pressure and heart rate

48
Q

What is important in the regulation of skin blood flow in the response to temperature

A

Hypothalamus

49
Q

How can the cerebral cortex affect blood flow and pressure

A

Stimulation of the cerebral cortex can usually cause increased vasoconstriction
Emotion can increase vasodilation and depressor responses

50
Q

Where are central chemoreceptors found

A

In the medulla

51
Q

How is short term blood pressure changes controlled

A

Baroreceptors

52
Q

How is long term blood pressure change controlled

A

Volume of blood
Na+
H2O
Renin-angiotensin-aldosterone
ADH

53
Q

What are the key central effectors

A

These are peripheral
Blood vessel vasodilation and vasoconstriction
Heart rate and contractility
Kidneys fluid balance in longer term control

Cardiovascular System (12 decks)

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