Lecture 14- Special Circulation Flashcards
1
Q
name 6 special circulations
A
pulmonary
cerebral
coronary
skeletal
cutaneous
2
Q
blood supply to the lungs
A
- bronchial circulation
- pulmonary circulation
3
Q
Bronchial circulation
A
Part of systemic circulation
Meets the metabolic requirements of the lungs (e.g. provides oxygen)
4
Q
Pulmonary circulation
A
Blood supply to alveoli
Required for gas exchange
5
Q
pulmonary circulation must be carefully adapted to accept the
A
entire cardiac output
6
Q
at rest CO is
A
5 L/min
7
Q
maximum CO
A
20-25 L/min
8
Q
adaptations of pulmonary ciruclation
A
- Works at low pressure and low resistance
- Mean arterial pressure 12-15 mmHg
- Mean capillary pressure 9-12 mmHg
- Mean venous pressure 5mmHg
- Short, wide vessels
- Lots of capillary (many parallel elements)
- Arterioles have relatively little smooth muscle
9
Q
A
10
Q
adaptions of the alveoli to promote efficient gas exchange
A
- High density of capillaries in alveolar wall – large capillary surface area
- Short diffusion distance
- Thin layer of tissue separating gas phase from plasma
- 0.3um
- Large surface area and short diffusion distance produce high O2 and CO2 transport capacity
11
Q
perfusion ration (V/Q ratio)
A
For efficient oxygenation- need to match ventilation of alveoli with perfusion of alveoli
12
Q
optimal V/Q ratio
A
0.8
13
Q
to maintain the optimum V/Q ratio what must occur
A
diverting blood from alveoli which are not well ventilated
14
Q
Hypoxic pulmonary vasoconstriction
A
- Ensures optimal ventilation/ perfusion ration
- Hypoxic pulmonary vasoconstriction is the most important mechanism regulating pulmonary vascular tone
- Alveolar hypoxia results in vasoconstriction of pulmonary vessels
- Ensure perfusion matches ventilation
- Poorly ventilated alveoli are less well perfused
- Ensure optimal gas exchange
15
Q
However… Chronic hypoxic vasoconstriction can cause
A
right ventricular failure
16
Q
how can Chronic hypoxic vasoconstriction cause right ventricular failure
A
- Chronic increase in vascular resistanceà chronic pulmonary hypertension
- Increased afterload (the resistance the heart has to pump against)à right ventricular heart failure (hypertrophy due to having to pump harder)
17
Q
when does chronic hypoxic vasoconstriction occur
A
Can occur at altitude or as a consequence of lung disease such as emphysema
18
Q
Low pressure pulmonary vessels are strongly influenced by
A
gravity
In upright position there is greater hydrostatic pressure on vessels in the lower part of the lungs
19
Q
when patients lie down
A
more vessels across the whole lung become distended
20
Q
Effect of exercise on pulmonary blood flow
A
- Increased CO
- Small increase in pulmonary arterial pressure
- Opens apical capillaries
- Increased oxygen uptake by lungs
- As blood flow increases capillary transit time is reduced
- At rest transit time is 1s
- Can fall to 0.3s without compromising gas exchange
21
Q
formation of tissue fluid is determined by
A
starling forces
22
Q
starling forces
A
Hydrostatic pressure of blood within the capillary forces fluid out of the capillary
Oncotic pressure is the pressure exerted by large molecules such as plasma proteins (albumin) àdraws fluid into the capillary
23
Q
in systemic circulation capillary hydrostatic pressur is more influenced by
A
venous pressure
(hypertension does not usually result in peripehral oedema)
24
Q
what minimised the formation of lung lymph
A
low capillary pressure (lower than systemic capillaries) and oncotic pressure of tissue fluid (oncotic pressure is higher in the lungs)
25
increased capillary pressure causes
more fluid to filter out- oedema
26
Low capillary pressure
prevents pulmonary oedema ---\> pulmonary pressure usually low (only a small amount of fluid leaves)
27
what can cause pulmonary oedema (caused by capillary pressure increase)
if left atrial pressure rises to 20-25 mmHg
## Footnote
Mitral valve stenosis
Left ventricular failure
28
pulmonary oedmea forms mainly ....... when upright
at the base
29
pulmonary oedema forms throughout the lungs when
lying down
30
why is pulmonary oedema dangerous
impairs gas exchange
31
what can be used to help relieve the symtoms of pulmonary oedema
diuretic
32
the brain has a high demand for
oxygen
33
how much of CO does the brain receive
15%
34
O2 consumption by grey matter accounts for .......of total body consumption at rest
20%
35
why must the brain have a secure supply of oxygen
* Neurones sensitive to hypoxia
* Loss of consciousness within a few second of cerebral ischaemia
* Irreversible damage to neurone in 4 minutes
E.g. interruption to blood supply e.g. stroke causes neuronal death
36
how does cerebral ciruclation meet the high demand for O2
* **High capillary density**
* Large SA for gas exchange
* Reduced diffusion distance
* **High basal flow rate**- X10 average for whole body
* **High O2 extraction** (35% above average)
37
structurally how is a secure blood supply ensured
Anastomoses between basilar and internal carotid arteries
38
functionally how is secure blood supply to the brain ensured?
Myogenic autoregulation maintains perfusion during hypotension
Metabolic factors control blood flow
Brainstem regulates other circulations
39
regional activity produces local increases in blood flow
Neurones with increases neurones activity have increase blood flow
40
Signals of increased neuronal activity
* Increased pCO2
* increased [K+]
* Increased adenosine (strongest vasodilator of cerebral arterioles)
Strong **vasodilators**
* decrease in oxygen
41
myogenic autoregulation- increased blood pressre
vasoconstriction
42
myogenic autoregulation- decreased blood pressure
vasodilation
43
Cerebral resistance vessels have a well developed myogenic response to changes in transmural pressure.
Maintains cerebral blood flow when BP changes
Will fail below 50 mmHg
44
panic hyperventilation can lead to
hypocapnia and cerberal vasoconstirction leading to dizziness or fainting
45
Cushing’s reflex
Rigid cranium protects the brain- but does not allow for volume expansion.
* Increases in intracranial pressure impairs cerebral blood flow (e.g. cerebral tumour or haemorrhage)
* Impaired blood flow to vasomotor control regions of the brainstem increase sympathetic vasomotor activity
* Increases arterial BP
* Maintains cerebral blood flow
46
cushings reflex ensures
The Cushing reflex helps save braintissues during periods of poor perfusion.
47
48
coronary ciruclation must
* Must deliver oxygen at a high basal rate
* Must meet increased demand à can work at a rate increased 5-fold
49
where do the right and left coronary arteries arise from
right and left aortic sinuses
50
when does flow in the left coronary artery mainly occur
during diastole
51
Adaptations in coronary circulation
* **High capillary density** (3000/mm2, compared to 400/mm2 in skeletal muscle) facilitates efficient oxygen delivery
* Diffusion distance **\<9um**
* **Continuous production of NO** by coronary endothelium **maintains a high basal flow**
52
coronary blood flow increases with
myocardial oxygen demand
53
Vasodilation of coronary arterys causes
metabolic hyperaemia- excess of blood in the vessels supplying an organ
54
vasodilaotrs of coronary circulation
adenosine
potassium
decreased pH
55
Coronary arteries are functional
end arteries
56
functional end arteries
an artery that is the only supply of oxygenated blood to a portion of tissues. Arteries that don’t anastomose with neighbours
57
where there are few anastosomes
prone to atheroma
* Narrowed coronary arteries leads to angina on exercise (increase O2 demand)
* Blood flow mostly during diastole
* Diastole is reduced as heart rate increases (due to exercise)
58
what can cause coronary vasoconstirction and angina
stress and angina
59
Sudden obstruction by thrombus causes
myocardial infarction
60
during exerise skeletal muscle requires
increased O2 and nutrient delivery and removal of emtabolites
61
skeletal muscl plays an importnant role in helping to
regulate arterial blood pressure
62
Adaptations of skeletal muscle circulation
* **Capillary density depends on muscle type**
* Postural muscles- in constant use- have higher capillary density
* **Very high vascular tone**
* Permits lots of dilatation
* Flow can increase \>20 times in active muscle
* At rest only half capillaries are perfused at any one time--\> allows for increased recruitment
* **Opening of precapillary sphincters allows more capillaries to be perfused**
* Increased blood flow and reduces diffusion distance
63
increased flow causes metabolic hyperaemia in skelteal muscle ciruclation. Which agents act as vasodilators
* Increased potassium
* Increased osmolarity
* Inorganic phosphates
* Adenosine
* Increased hydrogen
* Adrenaline
* Through B2 receptors
* Vasoconstrictor response via NA on alpha1
64
what is cutaenous circulation
The circulation and blood supply of the skin
65
cutaneous circulation has a special role in
temp regulation (core temp 36.5 to 37.5 degrees)
- skin is main dissipating surface
66
cutaneous circulation also plays a role in
Vasoconstriction in cutaneous circulation maintains BP
67
Apical skin has specialised structures called
arteriovenous anastomoses (AVA)
68
arteriovenous anastomoses (AVA)
AVAs are low-resistance connections between the small arteries and small veins that supply and drain the skin. These allow the shunt of blood directly into the venous plexus of the skin, without it passing through capillaries. Since AVAs contain no capillary section, they are not involved in transport of nutrients to/from the tissues, but instead play a major role in temperature regulation.
69
AVAs are not regulated by
Not regulated by local metabolised
70
AVAs are under
Under neural sympathetic control (vasoconstrictor fibres)
Reduced vasomotor drive to AVA allows them to dilate- diverts blood to veins near surface
71
Decrease core temp increases sympathetic tone in AVA
Decrease in blood flow to apical skin
72
increased core temp
opens AVAS
