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Physiology 1 : cardiovascular > Properties of Special Circulation > Flashcards

Properties of Special Circulation Flashcards

1
Q

What are the 5 special circulations?

A 
→ Cerebral
→  Pulmonary 
→ Skeletal Muscle 
→ Renal 
→ GI
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2
Q

What are the 3 characteristics to consider with 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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3
Q

Where do the two coronary arteries originate from?

A

→ The left side of the heart at the beginning (root) of the aorta just after it exits the left ventricle

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4
Q

Where do cardiac veins carry deoxygenated blood?

A

→ From the myocardium to the right atrium

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5
Q

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

A

→ Returns through the coronary sinus

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6
Q

What are the special requirements of the coronary circulation?

A

→ Needs a high basal supply of O2

→ 20 x that of skeletal muscle

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7
Q

Why does the coronary circulation have a high capillary density?

A

→ Large surface area for O2 transfer

→ Reduces the diffusion distance to the myocytes

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8
Q

What is diffusion time proportional to?

A

→ Distance squared

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9
Q

What is the blood flow of the coronary circulation during normal activity?

A

→ High blood flow

→ x10 of the flow per weight of the rest of the body

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10
Q

What is the sympathetic innervation like in the coronary circulation?

A

→relatively sparse

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11
Q

What is O2 extraction like during normal activity?

A

→ High O2 extraction 75%

→ average in the body 25%

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12
Q

How does the production of vasodilators change during increased demand?

A

→ Production of vasodilators out-compete relatively low sympathetic vasoconstriction

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13
Q

Why does adrenaline dilate coronary vessels?

A

→ Abundance of Beta 2 adrenoreceptors

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14
Q

How is 75% of the oxygen able to be unloaded to the myocardium during normal activity?

A

→ Coronary sinus blood returning to the right atrium from myocardial tissue has a greater CO2 content

→The high CO2 and low pH has shifted the curve to the right

→Hb has less affinity for O2 and more O2 is given up to myocardial tissues.

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15
Q

How does increased O2 requirement produce increased blood flow?

A

→Extraction is near maximum during normal activity
→ To provide more O2 during demand blood flow must increase
→ Myocardium metabolism generates metabolites to produce vasodilation which increases blood flow.

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16
Q

Describe ischaemic heart disease

A

→Coronary arteries are functional end-arteries and therefore decreased perfusion produces major problems
→The heart is very susceptible to sudden and slow obstruction

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17
Q

What does suddden ischaemic heart disease produce?

A

→ acute thrombosis

→ Myocardial infarction

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18
Q

What can lead to slow ischaemic heart disease?

A

→ Atheroma
→ Chronic narrowing of lumen - produces angina
→ Systole obstructs coronary flow

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19
Q

What does occlusion of the Left Anterior Descending Coronary Artery in thrombosis lead to?

A

→ obstruction of blood flow to anterior left ventricle

20
Q

What does myocardial infarction lead to?

A 
→Ischemic tissue 
→Acidosis 
→Pain (stimulation of C-fibres) 
→Impaired Contractility 
→Sympathetic activation 
→Arrhythmias 
→Cell death (necrosis)
21
Q

In a normal heart what is the resistance like?

A

Resistances are in series - they add together

22
Q

During exercise what happens to the resistances in a normal heart?

A

→Metabolic vasodilation of arterioles
→reduces total R
→Increased blood flow to meet increased O2 demands
→Total R reduced

23
Q

What is the resistance like in the heart of someone with angina (Resting) ?

A

→Stenosis in large coronary artery
→Increases resistance
→Metabolic hyperaemia occurs at rest, so blood flow meets needs

24
Q

What is the resistance like in the heart of someone with angina (exercise) ?

A

→During exercise, arterioles further dilate to reduce resistance
→total resistance is still too high due to dominance of stenosis
→O2 demand cannot be met, so angina develops

25
Q

What are the mechanical factors that reduce coronary flow?

A

→Shortening diastole
E.g. high heart rate

→Increased ventricular end-diastolic pressure
E.g. heart failure (aortic stenosis, stiffening of ventricle)

→Reduced diastolic arterial pressure
E.g. hypotension
Aortic regurgitation

26
Q

What are the special properties of cutaneous circulation?

A

→Defence against the environment

→Lewis triple response to trauma (increased blood flow)

27
Q

How is temperature regulated?

A

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

28
Q

What does skin temperature depend on?

A

Skin blood flow

Ambient temperature

29
Q

What is the function of Arterio-Venous Anastomoses (AVAs)?

A

→Direct connections of arterioles and venules expose blood to regions of high surface area
→Convection, conduction, radiation, evaporation

30
Q

What do sympathetic vasoconstrictor fibres do?

A

→ Release noradrenaline acting on alpha 1 receptors

31
Q

What do sudomotor vasodilator fibres do and what are they driven by?

A

→ AcH acting on endothelium to produce NO

→ Driven by temperature regulation nerves in the hypothalamus

32
Q

What are the special functional features of the cutaneous circulatory system?

A

→Responsive to ambient and core temperatures
→Help heat loss
→Increased ambient temperature causes vaso- and venodilation
→Help to conserve heat
→Decreased ambient temperature causes vaso- and venoconstriction

33
Q

What happens in severe cold?

A

→Severe cold causes “paradoxical cold vasodilation”

→Core temperature receptors in the hypothalamus control sympathetic activity to skin and hence skin blood flow

34
Q

What is cold-induced vasoconstriction and what is the reason for it?

A

→Conserve heat
→Sympathetic nerves react to local cold by releasing noradrenaline
→binds to α2 receptors on vascular smooth muscle in the skin
→α2 receptors bind to noradrenaline at lower temperatures than α1 receptors

35
Q

What is paradoxical cold vasodilation for and what does long term exposure to it cause?

A

→Protects against skin damage
→Caused by paralysis of sympathetic transmission
→Long-term exposure leads to oscillations of contraction/relaxation

36
Q

What happens with increased cutaneous perfusion ?

A

→Stimulate warmth receptors in anterior hypothalamus 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

37
Q

Where is blood directed to following loss of BP?

A

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

38
Q

What is blood redirection mediated by?

A

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

39
Q

What happens if you warm up the body quickly during 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

40
Q

What happens during emotional communication?

A

Blushing (sympathetic sudomotor nerves)

41
Q

What happens in response to skin injury?

A

The Lewis triple response

42
Q

What are the three stages of the Lewis Triple Response?

A

→Local redness
Site of trauma

→Local swelling
Inflammatory oedema (wheal)

→Spreading flare
Vasodilation spreading out from the site of trauma

43
Q

What mediates the flare to trauma?

A

C-fibre axon reflex mediates the flare to trauma

44
Q

What happens at the site of damage regarding pathogens?

A

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

45
Q

What happens during prolonged obstruction of flow by compression?

A

→Severe tissue necrosis
→Bed sores
→Heels, buttocks, weight bearing areas

46
Q

What is postural hypotension and what are the symptoms?

A

→Often standing for long periods in hot weather will decrease central venous pressure (hypotension)

→As well as increased capillary permeability (oedema)

→You feel faint, rings of fingers can be tighter

Physiology 1 : cardiovascular (18 decks)

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