Pulmonary circulation Flashcards
what are the two physical circulations in the lung
- pulmonary and bronchial
what is the bronchial circulation part of
systemic circulation
What does the bronchial circulation supply oxygenated blood to
- the trachea
- the bronchi
these are conducting airways
what does the bronchial venous drainage drain
the bronchial Venus drainage is partly into the bronchia veins to the right atrium but mainly to the pulmonary veins that go to the left atrium
what is the pulmonary circulation
- it is the output from the right heart blood into the lungs
describe the bronchial circulation
- Arises from the aorta.- branch of early part of the descending aorta , travel along the main bronchi to supply oxygenated blood to the tissues of the bronchi and bronchioles
- Part of systemic circulation.
- Receives about 2% of left ventricular output.
describe the pulmonary circulation
- Arises from Right Ventricle.
- Receives 100% of right heart cardiac output
where do the bronchial arteries travel down to
- they travel down the bronchi and. branch at the various branch points
what do bronchial arteries supply
- supply capillary beds in the bronchi and bronchial smooth muscle
describe the bronchial veins
- Venus blood drains in to this
- travel back to the right side of the heart
what can anastomoses
- various arterial or Venus shunts between the bronchial and pulmonary ciruclation
right heart output…
must always match left heart output
how long does it take for blood to pass through the lungs
5 seconds
how many capillaries does the pulmonary circulation have
280billion supplying 300 million alveoli
what is the surface area for gas exchange in the pulmonary circulation
50-100m2
what are the anatomical features of the pulmonary circulation
The pulmonary arteries are thin walled. They have far less smooth muscle than systemic arteries.
They have a larger diameter than systemic arteries.
Vessels are highly distensible and compressible
Because of high compliance, pulmonary arteries stretch during systole: this smooths the blood flow through the lungs
How do you work out blood flow
pressure gradient / resistance
what drives blood flow
- oressure gradient drives blood flow
- the mean pulmonary artery pressure is low therefore resistance is low
-
what happens if pulmonary arterial resistance rises
- creates pulmonary arterial hypertension
- this is when the pulmonary arteries constrict causing extra work on the right hand side of the heart, this causes the heart to enlarge and therefore it can cause heart failure eventually on the right side of the heart
what is the pulmonary artery pressure
15mmHg
what is the nerve supply to the lungs
- somatic
- sympathetic
- parasympathetic
where is the somatic nerve supply to the lungs
- carries pain and touch sensation from the lungs to the spinal cord segments T2-T6
where is the sympathetic nerve supply to the lungs
- from spinal nerves T2 to T4-6
- post ganglionic nerves from the paravertebral sympathetic ganglia pass into the lungs plexi around pulmonary arteries and arterioles
what do sympathetic fibres innervate
- smooth muscle within the walls of bronchi and small pulmonary vessels
what is the action of the sympathetic nervous system
- bronchodialtion and vasodilation
- bronchial smooth muscle relaxes and dilates via adrenergic beta receptors - bronchial muscle relaxation due to sympathetic nerves which is augmented by circulating adrenaline
describe how the parasympathetic innervates the lungs
- supply to the lungs via the vagus
- vagus nerve contains afferent and efferent fibres
what is the action of the parasympathetic nervous system on the lungs
- bronchoconstriction and stimulate secretion of mucus in the bronchi
where does the gas exchange occur
- gas exchange occurs in the alveolar ducts and alveoli and a small part of exchange takes place in the respiratory bronchioles
what is the mean pulmonary pressures when standing of..
- Pulmonary artery
- lung apex
- lung base
Pulmonary artery = 15mmHg
Lung apex = 2 mmHg
Lung base = 25 mmHg - higher due to gravity
describe blood flow and airflow to the apices of the lungs
- no blood flow to the apices as alveolar pressure is greater than capillary pressure therefore the alveolar pressure squashes the capillaries and blocks them
- flow only ceases during expiration when the pressure in the lungs is maximal there is some flow during inspriation
- total cessation of flow only happens when a person is ventilated with positive pressure or haemorrhage - apical blood vessels completely collapse and blood doesn’t flow to these regions
describe blood flow and airflow to the middle part of the lungs
- this part of the lungs is 3cm above the heart to the apices
- the flow is pulsatile and fluctuates during inspiration and expiration due to changes in alveolar pressure
- average flow increases nearer the base as Pa increases
what does pulsatile mean
means that it varies with breathing
describe the blood flow and airflow to the lungs in the base
- blood flow occurs continuously as pulmonary arterial and Venus pressure always exceeds alveolar pressure therefore the capillaries open
- this zone has the best gas exchange
what are the zones of the lung
Zone 1 - apices
Zone 2 - middle
Zone 3- base
Zone 4 - small and often present at the lung bases
how do you measure the distribution of blood flow in the lungs
- measured using radioactive xenon
- injected into venous blood and evolves into alveolar gas from the pulmonary capillaries
- radiation counters measure the amount of xenon passing through each lung zone
what is lung compliance
lung compliance is a measure of stretchability of the lungs
- it is the change in volume per unit pressure change
what is the equation of compliance
dV/dP
where is compliance on the volume pressure curve
on the straight slope upwards
compliance is….
different at the base and apex of the lung
- it is higher in the base which means the base is better ventilated per unit lung volume than apices
- this helps compensate for the poor perfusion of the apices
the basal alveoli are…
more ventilated than the apical alveoli
- basal alveoli has a higher compliance and therefore a bigger volume charge per unit pressure change
describe compliance at the base of the lungs
- both blood flow and ventilation are higher
- therefore compliance is higher
what is the ventilation perfusion ratio
- ratio of gas flow and blood flow
- V/Q
describe the ventilation perfusion ratio in apex of the lung
- greater ventilation that perfusion
- larger ventilation perfusion ratio
- greater than 1
describe the ventilation perfusion ratio in the base of the lung
- lower ventilation perfusion ratio
- lower than 1
describe the oxygen and carbon dioxide concentration in the apex of the lung
- high oxygen saturation
- low carbon dioxide saturation
- slows that it has good gas exchange but low blood flow
describe the oxygen and carbon dioxide concentration in the base of the lung
- low oxygen saturation
- high carbon dioxide saturation
- slows that it has less good gas exchange but greater blood flow
what happens to the V/Q during airway obstruction
- V/Q is lower than normal
- if always are blocked completely then ventilation is O, if blood flow is normal than the V/Q ration is O whatever the perfusion
- no gas exchange in a lung that is perfused but not ventilated therefore the oxygen saturation and carbon dioxide saturation of pulmonary venous blood from the affected lung will approach that of mixed venous blood
what happens to the V/Q during blood flow obstruction
- ratio is higher than normal
- blood flow is O and if ventilation is normal than V/Q is infinite
- there is no gas exchange in a lung that is ventilated but not perfuse therefore oxygen and carbon dioxide saturation of alveolar gas will approach that of inspired air
what does pulmonary hypoxia cause
vasoconstriction
- this is food as it diverts blood away from the poly ventilated hypoxic regions of the lungs towards the well ventilated regions
what does systemic hypoxia cause
vasodilation
what happens to the pulmonary circulation system during exercise
- cardiac output increases
- pulmonary arterial pressure does not change
- pulmonary arterial resistance decreases during exercise
what are the mechanism of pulmonary arterial changes during exercise
- pulmonary arteries and arterioles are thin walled and they become distended when the cardiac output from the right heart rises at the start of exercise, the stretching generates a reflex relaxation of the arterial smooth muscle so the vessels relax and enlarge which reduces the vascular resistance
- increased ventilation that occurs at the start of exercise increases the oxygen saturation in the alveoli
- the high oxygen level increases arteriolar dilation to a maximum - arteriovenous shunts open in the lungs during exercise this allows blood to go directly into the pulmonary veins, shunts can also open between the pulmonary and bronchial circulations
describe foetal pulmonary circulation
- pulmonary vascular resistance is high because of generalised hypoxic vasoconstriction in the foetal lungs, therefore blood flow through foetal lungs is low
- most blood entering right foetal heart is shunted via the foramen ovale and ductus arteriosus to the right side of the heart
what happens when a baby takes its first breath
- pulmonary vascular resistance decreases
- alveoli of the neonate becomes better oxygenated
- pulmonary blood flow is equal to cardiac output
what is the foramen ovale
- hole in the arterial wall between the left and right atria
- allows blood to shut across to left heart instead of going into the right ventricle
- output of right ventricle is therefore less than left ventricle
- closes after birth normally
what is the arteries ductus
- joins the aorta and pulmonary artery
- allows blood from right ventricle to shunt directly to the aorta and bypasses the lung
- shuts immediately after birth
