Special Circulations: coronary; cerebral; pulmonary; skeletal Flashcards
(62 cards)
1
Q
Where do the left/right coronary arteries arise from?
A
- base of the aorta
- at the aortic sinuses
- in the aortic (semilunar) valve
2
Q
Where does most coronary venous blood drain into?
A
- coronary sinus (into right atrium)
3
Q
Where does coronary heart disease commonly occur?
A
- left side (anterior surface) of heart
4
Q
Name 3 special adaptations of coronary circulation
A
- high capillary density (exchange of O2/nutrients helps oxygenate cardiac muscle)
- high basal blood flow
- high O2 extraction
5
Q
Describe O2 extraction by the heart
A
- heart extracts ~75% of O2 from blood (compared to 25% whole body average) under resting conditions
6
Q
Can the heart increase O2 extraction (to increase oxygenation of cardiac muscle)?
A
- no (heart already extracts so much O2, cannot manage any more!)
7
Q
How can oxygenation of the heart be improved (if we can’t extract more oxygen from the blood?)
A
- increase coronary blood flow
8
Q
Name the intrinsic mechanism of controlling coronary blood flow
A
- decreased PO2 (hypoxia): vasodilation of CA
- metabolic hyperaemia (increased blood flow): matches flow to O2 demand
- adenosine (from ATP breakdown): potent vasodilator
9
Q
Name the extrinsic mechanisms of controlling coronary blood flow
A
- sympathetic vasoconstrictor nerves supply coronary arterioles (THIS IS NOT WANTED)
- metabolic hyperaemia overcomes vasoconstriction
- this occurs as a result of increasing HR + SV (>CO)
- circulating adrenaline is released from adrenal cortex
- adrenaline activates beta 2 adrenoceptors
- this causes vascular smooth muscle dilation (similar to sympathetic effect on bronchial smooth muscle)
10
Q
What is the sympathetic process of coronary vasodilaton called?
A
- function sympatholysis
11
Q
Does sympathetic stimulation on alpha adrenoceptors improve coronary blood flow?
A
- no (vasoconstrictor = reduces blood flow)
12
Q
What causes metabolic hyperaemia?
A
- increased cardiac work (SV/HR)
13
Q
What metabolites are released as a result of metabolic hyperaemia?
A
- K+
- Co2
- H+
14
Q
When does peak LEFT coronary blood flow occur?
A
- during diastole
- left CA is situated near left ventricle
- systole = high pressure in LV (+ left CA)
coronary blood flow falls during systole
15
Q
Describe peak RIGHT coronary blood flow
A
- right CA situated close to RV
- systole: RV squeezed
- lower pressure in RV than LV
- blood flow to right CA not reduced as much
- blood flow between systole + diastole remains similar
16
Q
What is the effect of shortening diastole on coronary blood flow?
A
- reduced diastole
- reduced coronary blood flow
- ischaemia
- chest pain
17
Q
What can cause reduced diastole?
A
- tachycardia
18
Q
What supplies arterial blood to the brain?
A
- internal carotids
- vertebral arteries
19
Q
Describe the effect of hypoxia on grey matter in the brain
A
- grey matter = very sensitive to hypoxia
- unconsciousness after a few seconds of ischaema
- irreversible necrosis (cell damage) within ~3mins
20
Q
Give an alternative (latin) name for the circle of Willis
A
Circulus Arteriosus Cerebri
21
Q
What is the circle of Wilis?
A
- anastomotic system of arteries that lies at the base of the brain
- formed when the internal carotid artery enters the cranial cavity (bilaterally) and divides into the anterior cerebral + middle cerebral arteries
22
Q
Describe the branching of the anterior cerebral artery
A
- anterior cerebral arteries are united by anterior communicating arteries
- these connections form the anterior half of the circle of Willis
23
Q
Describe the posterior branches of the circle of Willis
A
- posteriorly, the BASILAR artery is formed by the left/right vertebral arteries
- basilar arteries branch into a left/right posterior cerebral artery
- posterior cerebral arteries complete the circle of Willis by joining the internal carotid system anteriorly via the posterior communicating attires
24
Q
How is cerebral perfusion maintained?
A
- via function of circle of Willis
- even if the carotids are obstructed, perfusion can be maintained via the other cerebral arteries
25
How is ischaemia caused in the brain?
- obstruction of one of the smaller branch arteries in the circle of Willis
26
Name the 2 main types of stroke
- ischaemic
| - haemorrhagic
27
What can cause an ischaemic stroke?
- atherosclerotic obstruction
- thrombus
- embolus
ATRIAL FIB
28
What is auto regulation?
- guard against cerebral blood flow when changes in MAP occur (within the range 60-160 mm Hg)
29
What is the effect of the following on cerebral blood flow? a) sympathetic stimulation b) baro receptors
a) little overall effect
| b) negligible (don't want cerebral vasoconstriction/dilation in response to baroreceptor stretch)
30
When does auto regulation fail?
- if MAP < 60 mmHg or >160 mm Hg
31
What happens in cerebral blood flow if MAP rises?
- resistance vessels CONSTRICT
| - limits cerebral blood flow
32
What happens in cerebral blood flow if MAP falls?
- resistance vessels DILATE
| - maintains cerebral blood flow
33
Symptoms of a MAP <50 mmHg?
- fainting
- confusion
- brain damage
34
How can we calculate MAP?
- diastole + 1/3 x (systole-diastole)
35
What are the following effects on cerebral blood flow? a) increasing CO2 b) decreasing CO2
a) cerebral vasodilation
| b) cerebral vasoconstriction
36
Why does hyperventilation lead to fainting?
- blowing off CO2
- decreased CO2
- cerebral vasoconstriction
- decreased blood flow
37
What is regional hyperaemia?
- blood flow increases to active parts of the brain
| - due to K+ efflux from repetitively active neurones (?)
38
What % of the skull is?
a) brain
b) blood
c) cerebro-spinal fluid (CSF)
a) 80%
b) 12%
c) 8%
39
What is the normal intracranial pressure? (ICP)
8-13 mm Hg
40
What is the equation for cerebral perfusion pressure? (CPP)
CPP = MAP - ICP
41
What is the effect of increased ICP?
- decreased cerebral perfusion pressure
- opposes cerebral blood flow
- failure of auto regulation
42
What conditions increase ICP?
- head injury
| - brain tumour
43
Describe the blood-brain barrier?
- cerebral capillaries have very tight intracellular junctions allowing selective movement of substances across
44
What can pass the BBB?
- O2; CO2
| - glucose (by facilitated diffusion using carrier molecules) (brain has obligatory glucose requirement)
45
What can't pass BBB?
- hydrophilic substances
e. g. ions/catecholamines/proteins
- helps to protect brain from fluctuating levels of ions in blood
46
Where does the entires cardiac output flow into from the right ventricle?
- pulmonary circulation
47
How are the metabolic needs of the airway met?
- via systemic bronchial circulation (bronchial arteries = branch of thoracic aorta)
48
What % of total systemic circulation is pulmonary circulation?
- about 10%
49
What is the typical pulmonary artery BP?
20-25 (systole)
| 6-12 (diastole)
50
What is the pulmonary capillary resistance (in mmHg)? How does this differ from systemic capillary resistance?
- pulmonary capillary resistance is low (8-11 mm Hg)
| - systemic capillary resistance is around 17-25 mm Hg
51
What adaptation of pulmonary circulation protects you from pulmonary oedema?
- absorptive forces exceed filtration forces
52
What is the effect of hypoxia on a) pulmonary arterioles b) systemic arterioles?
a) vasoconstriction
| b) vasodilation
53
Why is the effect of hypoxia opposite for pulmonary and systemic circulation?
- vasoconstriction of pulmonary arterioles helps to divert blood from poorly ventilated areas of lung
- diverts blood from poorly oxygenated area to area that is in higher demand of oxygen
- occurs to maintain V/Q balance
54
What % of total body mass is skeletal muscle?
- 40%
55
How does skeletal muscle impact blood pressure?
- resistance of skeletal muscle vascular bed has large impact on BP
56
What maintains resting blood flow?
- sympathetic vasoconstrictor tone
57
Describe the changes that occur in skeletal circulation during exercise
- local metabolic hyperaemia overcomes sympathetic vasoconstrictor activity
- circulation adrenaline acts on beta 2 adrenoceptors to cause vasodilation
- increased cardiac output = increased skeletal blood flow during exercise
58
Where is the skeletal muscle pump situated?
- in large limbs
59
What does the skeletal muscle pump do?
- contraction of muscle aids venous return
| - one way venous valves allow blood to move forward toward the heart
60
What does the skeletal muscle pump protect against?
- postural hypotension + fainting
61
What is a blood pool?
- collections of blood in the lower limb veins if venous valves become incompetent
- these venous blood pools are called varicose veins
62
Do varicose veins lead to a reduction in CO? (reduced venous return; decreased SV; decreased CO?)
- no
- causes a compensatory increase in blood volume
- maintains normal CO
