Special Circulations Part 2

Question 1

how does cerebral circulation meet the high demand for oxygen

Answer 1

High capillary density (large sa and reduced diffusion distance)
High basal flow rate
High oxygen extraction
Neurones continually use oxygen to maintain high conc Grad

Question 2

Why is secure oxygen supply to brain vital

Answer 2

Neurones very sensitive to hypoxia
Loss of consciousness after a few seconds of cerebral ischeamia
Irreversible neurone damage after 4 mins
Stroke causes neuronal death

Question 3

how is a secure cerebral blood supply ensured

Answer 3

Structurally- anastomoses between basilar and internal carotid arteries

Functionally- myogenic auto regulation maintains perfusion during hypotension, metabolic factors, brain stem

Question 4

What is myogenic auto regulation

Answer 4

Cerebral resistance vessels have a myogenic response to changes in transmural pressure

Maintains cerebral blood flow when BP changes

Question 5

What happens in myogenic auto regulation when there is raised blood pressure

Answer 5

Vasoconstriction

Question 6

What is hypercapnia

Answer 6

Increased partial pressure of carbon dioxide

Question 7

What happens in hypercapnia

Answer 7

Vasodilation to increase blood supply

Question 8

Panic hyperventilation can cause

Answer 8

Hypocapnia and cerebral vasoconstriction leading to dizziness or fainting

Question 9

What causes local cerebral increases in blood flow

Answer 9

Regional activity - areas with increased neuronal activity

Question 10

What is a powerful vasodilator of cerebral arterioles

Answer 10

Adenosine

Question 11

What leads to cerebral vasodilation

Answer 11

increased partial pressure of carbon dioxide, increased potassium, increase adenosine, decreased partial pressure of oxygen due to ATP breakdown

Question 12

What is Cushing’s reflex

Answer 12

Rigid cranium protects the brain but does not allow for volume expansion

increases in inter cranial pressure impair cerebral blood flow

Impaired blood flow to vasomotor control regions of the brain stem increase sympathetic vasomotor activity

Question 13

What happens when sympathetic vasomotor activity is increased

Answer 13

Increases arterial BP
Maintains cerebral blood flow
Increased bP causes reflex bradycardia
Bradycardia and acute hypertension - hallmark of space occupying legion

Question 14

what must coronary circulation do

Answer 14

Deliver oxygen at high basal rate

Meet increased demand

Question 15

Right and left coronary arteries arise from

Answer 15

Right and left aortic sinuses

Question 16

Flow in the left coronary artery occurs mainly during

Answer 16

Diastole

Question 17

Features of coronary circulation

Answer 17

high capillary density facilitates efficient oxygen delivery, diffusion distance short, continuous production of NO by coronary endothelium maintains a high basal flow

Question 18

What happens to coronary blood blood with increased myocardial oxygen demand

Answer 18

Supplied by increased blood flow
Almost linear relationship
Small increase in oxygen extraction ]
Vasodilation due to metabolic hyperaemia
vasodilators = adenosine (up potassium and down pH)

Question 19

How are coronary arteries functional end arteries

Answer 19

Few arterio-arterial anastomoses
Prone to atheromas
Narrowed leads to angina
Blood flow mostly during diastole

Question 20

Stress and cold can cause

Answer 20

Sympathetic coronary vasoconstriction and angina

Question 21

Sudden obstruction by thrombus caused

Answer 21

Myocardial infarction

Question 22

Skeletal muscle circulation key features

Answer 22

Must increase oxygen and nutrient delivery and removal of metabolites during exercise

Helps regulate arterial blood pressure

resistance vessels have rich innervation by sympathetic vasoconstrictor fibres (baroreceptor reflex maintains bp)

Question 23

What makes skeletal muscle circulation effective

Answer 23

Capillary density depends on muscle type
Very high vascular tone (permits lots of dilation)
At rest only 1/2 perfused at one time (allows for increased recruitment)
Opening of precapillary sphincters allows more capillaries to be perfused

Question 24

What agents act as vasodilators during hyperaemia

Answer 24

Increased potassium 
Increased osmolarity 
Inorganic phosphates 
Adenosine 
Increased hydrogen 

Adrenaline in arterioles in skeletal muscle through beta 2

Question 25

Problems associated with skeletal muscle circulation

Answer 25

Atheroma formation 
Intermittent claudication (pain in calf or buttocks when you walk)

Question 26

Cutaneous circulation key points

Answer 26

Special role in temperature regulation
Skin is main heat dissipating surface
Vasoconstriction maintains BP

Question 27

Acral (apical) skin has specialised structures called

Answer 27

Arterovenous anastomoses (AVAs)

Question 28

what do AVAs do

Answer 28

regulate heat loss from apical skin

High sa:v
Neural control (sympathetic vasoconstrictor fibres)
Not regulated by local metabolites

Question 29

Increased core temperature

Answer 29

Opens AVAs

Question 30

Reduced vasomotor drive allows AVAs to

Answer 30

Dilate- diverts blood to veins near surface

Question 31

What happens in non-apical skin to increase blood flow to lose heat

Answer 31

Sympathetic cholinergic fibres activate sweat glands that may in turn release vasodilators such as bradykinin

Question 32

Problems associated with cutaneous circulation

Answer 32

Decreased blood flow due to pressure e.g. pressure ulcers
Reynaud’s - XS vasoconstriction in response to cold, hands and feet
XS vasodilation in response to heat can cause postural hypotension