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CVS > Properties of special circulation > Flashcards

Properties of special circulation Flashcards

1
Q

What 3 characteristics need to be considered for special circulations?

A

Special requirements are met by circulation

Special structural or functional features of the circulation

Specific problems relating to that circulation

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2
Q

Where do the two coronary arteries originate from?

A

Two coronary arteries originate from the left side of the heart at the beginning (root) of the aorta, just after it exits the left ventricle

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3
Q

What do cardiac veins carry?

A

Cardiac veins carry blood with a poor level of oxygen, from the myocardium to the right atrium.

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4
Q

Where does most of the blood of the coronary veins return through?

A

Most of the blood of the coronary veins returns through the coronary sinus

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5
Q

What does the heart need a high supply of?

A

Needs a high basal supply of O2 – 20x resting skeletal muscle

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6
Q

What are the structural features of the heart?

A
  • High capillary density
  • Large surface are for O2 transfer
  • Time proportional to d^2
  • Cardiac muscles contain high number of fibres and capillaries giving rise to shorter diffusion paths
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7
Q

Blood flow during normal activity

A

High blood flow – x10 the flow per weight of rest of the body

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8
Q

Sympathetic innervation during normal activity

A

Relatively sparse sympathetic innervation

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9
Q

What is released during normal activity

A

High NO released during vasodilation

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10
Q

What is there a high extraction of?

A

High O2 extraction(75%)

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11
Q

What increases during increased demand?

A

Coronary blood flow increases in proportion to demands

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12
Q

What is produced during increased demand?

A

Production of vasodilators (adenosine, K+, acidosis) out-compete relatively low sympathetic vasoconstriction

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13
Q

What does circulating adrenaline do during increased demand?

A

Circulating adrenaline dilates coronary vessels due to abundance of β2-adrenoreceptors

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14
Q

What blood has a greater CO2 content and due to what reason?

A

Coronary sinus blood returning to the right atrium from myocardial tissue has a greater CO2 content
Due to high capillary density, surface area and small diffusion distance

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15
Q

What does high CO2 and low pH do to the bohr curve and what affect does this have?

A
  • The high CO2 and low pH has shifted the curve to the right meaning that haemoglobin has less affinity for oxygen and more O¬2 is given up to the myocardial tissues
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16
Q

What percentage of oxgen does myocardium extract from haemoglobin compared to other tissue?

A
  • The myocardium is able to extract 75% of the oxygen as opposed to typically 25% in other tissues
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17
Q

What does an increased O2 requirement produce?

A

Increased O2 Requirement Produces Increased Blood Flow

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18
Q

What does myocardium metabolism generate in order to increase blood flow?

A
  • Myocardium metabolism generates metabolites to produce vasodilation which increases blood flow (metabolic hyperaemia)
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19
Q

What is there an increase of in order to increase blood flow?

A
  • There is also an increase in pCO2, H+, K+ levels
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20
Q

What are human coronary arteries?

A
  • Coronary arteries are functional end-arteries and therefore decreased perfusion produces major problems
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21
Q

Example of suden obstruction

A

o Acute thrombosis, produces myocardial infarction

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22
Q

Example of slow obstruction

A 
o	Atheroma (sub-endothelium lipid plaques)
o	Chronic narrowing of lumen, produces angina
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23
Q

What can thrombosis result in?

A

total occlusion of the left anterior descending coronary artery

24
Q

What can occlusion lead to and result in?

A
  • Occlusion leading to obstruction of blood flow to anterior (front) left ventricle
    and can lead to MI
25
Q

How do you calculate total resistance in series?

A

Add them together

26
Q

What happens to total resistance during exercise and how is this brought about?

A

exercise, metabolic vasodilation of arterioles reduces total R

27
Q

What leads to angina?

A
  • Stenosis in large coronary artery
28
Q

Effect of stenosis on resistance

A

o Increases resistance

29
Q

What causes angina to develop?

A

total resistance is still too high due to dominance of stenosis
o O2 demand cannot be met, so angina develops

30
Q

What is restricted during diastole?

A

Coronary Blood Flow Is Restricted During Diastole

31
Q

What are the mechanical factors reducing coronary flow?

A
  • Shortening diastole
  • Increased ventricular end-diastolic pressure
  • Reduced diastolic arterial pressure
32
Q

What are special properties of the cutaneous circulation?

A

Defence against the environment

- Lewis triple response to trauma (increased blood flow)

33
Q

Temperature regulation in cutaneous circulation

A

Temperature regulation
o Blood flow delivers heat from body core
o Radiation (proportional to skin temperature)
o Conduction to skin – convection from skin (skin temperature)
o Sweating (latent heat of evaporation)
o Skin is an organ
o Skin temperature can rage from 0 o C to 40 o C (briefly) without damage
 Poikilothermic rather than homeothermic

34
Q

What does skin temperature depend on in cutaneous circulation?

A
  • Skin temperature depends on
    o Skin blood flow
    o Ambient temperature
35
Q

What does direct connections of arterioles and venules (AVAs)expose?

A
  • Direct connections of arterioles and venules expose blood to regions of high surface area
36
Q

What does the sympathetic vasoconstrictor fibres release and act on?

A
  • Release noradrenaline acting on α1 receptors
37
Q

What does acetylcholine act on and produces what in sudomotor vasodilator fibres?

A
  • Acetylcholine acting on endothelium to produce NO
38
Q

What does a cold temperature induce?

A

Induces vasoconstriction

39
Q

How do sympathetic nerves react to local cold?

A
  • Sympathetic nerves react to local cold by releasing noradrenaline which binds to α2 receptors on vascular smooth muscle in the skin
    o α2 receptors bind to noradrenaline at lower temperatures than α1 receptors
40
Q

What does paradoxical cold vasodilation protect?

A

-Protects against skin damage

41
Q

What is paradoxical cold vasodilation caused by?

A

Caused by paralysis of sympathetic transmission

42
Q

What does long-term exposure to cold eventually lead to?

A

Long-term exposure leads to oscillations of contraction/relaxation

43
Q

What happens to cutaneous perfusion as temperature increases?

A

Increased cutaneous perfusion with increased core temperature

44
Q

What does an increased core temperature stimulate?

A

Stimulate warmth receptors in anterior hypothalamus

45
Q

What does the stimulation of warmth receptors in anterior hypothalamus cause?

A

CAUSING…
Sweating
Increased sympathetic activity to sweat glands mediated by acetylcholine

Vasodilation
Increased sympathetic sudomotor activity such that acetylcholine acts on endothelium to produce NO
NO dilates arterioles in extremities

46
Q

When is blood directed to more vital organ/tissue?

A

Blood directed to more important organs/tissues during loss of BP following haemorrhage, sepsis, acute cardiac failure

47
Q

What is vasoconstriction of skin blood vessels mediated by?

A

Mediated by sympathetic vasoconstrictor fibres + adrenaline + vasopressin + angiotensin II

48
Q

What may reduce when the body is warmed up to quickly during a haemorrhage?

A

During a haemorrhage, warming up the body too quickly may reduce cutaneous vasoconstriction and be potentially dangerous
Blood flows to the skin and not to the vital organs

49
Q

What is blushing mediated by?

A

blushing (sympathetic sudomotor nerves)

50
Q

What is the lewis triple response?

A

Response Of Skin To Trauma

51
Q

What are the 3 responses?

A 
Local redness
       Site of trauma
Local swelling
       Inflammatory oedema (wheal)
Spreading flare
       Vasodilation spreading out from the site of trauma
52
Q

What mediates the flare to trauma?

A

The C-fibre axon reflex mediates the flare to trauma

53
Q

What is there an increased delivery of to site of damage?

A

Increased delivery of immune cells & antibodies to the site of damage to deal with invading pathogens

54
Q

What can prolonged obstruction of flow by compression cause?

A

Severe tissue necrosis

55
Q

Where do bed sores usually occur?

A

Heels, buttocks, weight bearing areas

56
Q

How are bedsores avoided?

A

Shifting position/turning which causes reactive hyperaemia (on removal of compression

High skin tolerance to ischemia

57
Q

What can standing for long periods decrease?

A

Often standing for long periods in hot weather will decrease central venous pressure (hypotension)
As well as increased capillary permeability (oedema)

CVS (17 decks)

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