Session 8.1 Flashcards
(25 cards)
What are the two circulations of the lungs?
Bronchial circulation
- part of systemic circulation
- meets metabolic requirements of the lungs
Pulmonary circulation
- required for gas exchange
- works at low pressure and low resistance
What are the features of the pulmonary circulation?
Low pressure
Low resistance
- short, wide vessels
- lots of capillaries (lots of different routes = less resistance)
- arterioles have relatively little smooth muscle
What adaptations are there for efficient gas exchange?
- high density of capillaries =large SA
- short diffusion distance
- narrow capillaries
What’s the ventilation perfusion ratio?
For efficient oxygenation, need to match ventilation of alveoli with perfusion of alveoli
Optimal V/Q ratio = 0.8
Maintaining this means diverting blood from alveoli which aren’t well ventilated
How can the V/Q ratio be maintained?
Hypoxia pulmonary vasoconstriction
- alveolar hypoxia leads to constriction of pulmonary vessels
- this ensures perfusion matches ventilation
- poorly ventilated alveoli are less well perfumed
- helps optimal gas exchange
What are the downsides of hypoxia pulmonary vasoconstriction maintaining V/Q ratio?
- If chronic, can cause right ventricular heart failure
- chronic can occur at altitude or as a consequence of lung disease such as emphysema
If high pressure is consistent = RV hypertrophy and RV heart failure
What’s the effect of exercise on pulmonary blood flow?
- Increases cardiac output
- Small increase in pulmonary arterial pressure
- Opens apical capillaries
- Increased o2 uptake by lungs
- As blood flow increases capillary transit time is reduced
How does gravity influence pulmonary vessel pressure?
Upright = greater hydrostatic pressure on vessels in the lower part of the lung below the level of the heart
Will be distended during diastole as a result
How does low capillary pressure prevent pulmonary oedema?
Lower hydrostatic pressure = less fluid leaves capillaries
How can mitral valve stenosis cause pulmonary oedema?
- harder for blood to flow from LA to LV = increased pressure in LV = more pressure in pulmonary veins = pulmonary oedema
Can also get left ventricular failure
What are the effects of Pulmonary oedema?
Impairs gas exchange
- affected by posture
- forms mainly at base when upright
- forms throughout lung while lying down (patient often sleeps with several pillows)
- use diuretics to relieve symptoms
- treat underlying cause if possible e.g if caused by mitral valve stenosis, treat than
What is the high o2 demand in the brain met by??
High capillary density
High basal flow rate
High o2 extract
Why is a supply of O2 to the brain essential?
- neurones sensitive to hypoxia
- loss of consciousness after a few seconds of cerebral ischaemia
- begin to get irreversible after 4 mins
- cerebral infarction = stroke
What is the role of myogenic autoregulation in the brain?
Maintains perfusion during hypotension
Increased blood pressure = vasoconstriction
Decreased blood pressure = vasodilation
Fails if BP falls below 50mmHg
How is cerebral blood supply secured by metabolic regulation?
Cerebral vessels v sensitive to changes in arterial Pco2
Hypercapnia = High Pco2 = vasodilation so region of brain is better perfumed
Hypocapnia = Low Pco2 = vasoconstriction
Panic hyperventilation can cause hypocapnia and cerebral vasoconstriction leading to dizziness or fainting
How does regional activity in the brain influence blood flow?
Areas with increased neuronal activity have increased blood flow
Vasodilation =
Increased Pco2
Increased k+
Increased adenosine
What is cushings reflex?
- Rigid cranium protects brain but doesn’t allow volume for expansion
- Increases in intracranial pressure impairs central blood flow = cerebral tumour/haemorrhage
- Impaired blood flow to vasomotor activity = increase arterial BP and helps maintain cerebral blood flow
Where do the right and left coronary arteries arise from?
The right and left aortic sinuses
What are the adaptations for an efficient coronary circulation?
- high capillary density
- short diffusion distance
- continuous production of NO by coronary endothelium = maintains high basal flow
What vasodilators are used for coronary arteries?
Adenosine, increased potassium, lower ph
Coronary arteries are functional end arteries. What does this mean?
Prone to atheromas
Narrowed = lead to angina on exercise
Blood flow is mainly during diastole and if HR increased diastole reduced
Stress and cold can cause sympathetic coronary vasoconstriction and angina
Sudden obstruction by thrombus can cause myocardial infarction
What does opening of pre capillary sphincters allow?
More capillaries to be perfumed = increases blood flow and reduced diffusion distance
What is the role of the Cutaneous circulation?
Temperature regulation
Skin is the main heat dissipating surface, regulated by cutaneous blood flow
Also role in maintaining BP
Vasoconstriction here is to maintain BP
What are arteroveous anatosomes?
In the apical skin
a separate bridge between venue and arteriole end of the blood vessel
Can be constricted/dilated
