Special Circulatioms Flashcards
(39 cards)
What are the two types of blood supplies going to the lungs ?
- Bronchial circulation
2. Pulmonary circulation
What is the bronchial circulation ?
The metabolic requirement of the lungs is supplied by the bronchial circulation which is part of the systemic circulation.
What is the pulmonary circulation ?
It is required for gas exchange between the alveolar air and the blood.
What are two features of the pulmonary circulation?
- Low pressure -
2. Low resistance due to lots of capillaries , short and wide vessels and arterioles have little smooth muscle.
What are adaptations of the pulmonary circulation that promote efficient gas exchange?
- Very High density of capillaries in the alveolar wall ( a high number of capillaries very close together ). This means that the surface of the alveoli in the lungs are covered in capillaries , providing a large surface area over which gas exchange can take place.
- Very short diffusion distance
- Low pressure due to large number of capillaries.
What is the ventilation- perfusion ratio ?
The ratio between the volume of air coming in and out of the lungs and the volume of blood flowing past the lungs into the pulmonary circulation.
For efficient oxygenation of the alveoli of the lungs , what needs to happen with the V/Q ratio ?
The ventilation must match the perfusion of the alveoli. The optimal ratio is 0.8. Eg 4L/min : 5L/min.
How is the V/Q ratio maintained ?
The body must be able to divert blood away from the poorly ventilated alveoli and towards better ventilated alveoli. This is done via hypoxia pulmonary vasoconstriction.
What is hypoxic pulmonary vasoconstriction?
When the alveoli are poorly ventilated , the air in them isn’t being refreshed leading to a low partial pressure or oxygen and a high partial pressure of Carbon dioxide. The body responds by causing vasoconstriction of the pulmonary vessels to direct blood away from the poorly ventilated alveoli and towards the better ventilated alveoli to maintain V;Q.
How can chronic hypoxic vasoconstriction occur ?
Due to chronic lung disease such as emphysema or if at high altitudes for long periods of time.
What are the consequences of chronic hypoxic vasoconstriction?
Right ventricular failure
This is because due to vasoconstriction of the pulmonary vessels , there would be a chronic increase in vascular resistance. This would lead to chronic pulmonary hypertension.
There would be a high afterload on the right ventricle which can lead to right ventricle heart failure
What are the effects of exercise on pulmonary blood flow ?
- increased cardiac output
- Small increase in arterial pulmonary pressure
- Opens apical capillaries ( at the top of the lungs )
- Increased o2 uptake by lungs
- Capillary transit time is reduced
How is tissue fluid formed ?
High hydrostatic pressure of blood within the capillary which pushes fluid out of the capillary.
And oncotic pressure in the capillary is pressure exerted by large molecules such as plasma proteins which draws fluid into the capillary.
The balance between these two is what determines how much fluid leaves the capillary into the interstitium
.
Is capillary hydrostatic pressure more influenced by arterial pressure or venous pressure ?
VENOUS pressure in the systemic circulation
What is the difference between oncotic / hydrostatic pressures in the lungs compared to other parts of the body ?
Oncotic pressure of tissue fluid in lungs is greater than in periphery
Capillary hydrostatic pressure in the lungs is lower than in the systemic capillaries
Plasma Oncotic pressure is the same
Filtration and reabsorption of fluid in the lungs is more or less the same so much less formation of lung fluid occurs.
What are benefits of there being low capillary pressure in the lungs ?
Pulmonary capillary pressure is normally low which means only a small amount of fluid leaves the capillaries.
How can pulmonary oedema arise ?
When capillary pressure is increased
Due to left atrial pressure increase . This could be the case in mitral valve stenosis or left ventricular heart failure.
What are the consequences of pulmonary oedema ?
It impairs gas exchange and is affected by posture.
When the patient is standing , the fluid in the lungs pools at the base. When the patient is lying down , the fluid spreads out throughout the lungs. This fills the alveoli with fluid and causes impairment of gas exchange leading to breathlessness.
What percentage of cardiac output does the cerebral circulation receive ?
15% of cardiac output.
But only accounts for 2% of body mass.
How does the cerebral circulation meet the high demand for O2 ?
- High capillary density : large surface area for gas exchange. And reduced diffusion distance.
- High basal flow rate
- High o2 extraction
Why is O2 supply to the brain vital ?
Neurones are very sensitive to hypoxia. Loss of consciousness after a few seconds of cerebral ischameia. And you begin to get irreversible damage to neurones in 4 minutes.
How is a secure blood supply ensured to the cerebral circulation ?
- Structural features : anastomoses between basilar and internal carotid arteries.
- Function features : myogenic autoregulation maintains perfusion during hypotension.
Metabolic factors control blood flow
Brain stem regulates other circulations
What is myogenic autoregulation ?
This is where cerebral arteries will change their diameter in response to changes in systemic pressure . This ensures cerebral, blood flow remains at the same rate even where there are increases and decreases in systemic pressure.
For example , if the blood pressure is increased , there is vasoconstriction of the arteries to prevent too much blood flowing to the brain,
If blood pressure is decreased , the. Vasodilation occurs so enough blood enters cerebral circulation.
Give an example of how metabolic factors help to ensure blood flow to cerebral circulation ?
At high levels of Co2 ( hyper cap is) in the brain : vasculature in the brain results in vasodilation to increase blood flow to restore to the normal co2 levels.
Hypocapnia ( low Co2 levels ) : brain vasculature results in vasoconstriction to decrease the blood flow and increase PCo2 in the brain.
