Term
| Why is the pulmonary circulation called the lesser circulation? |
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Definition
- Goes into the lungs & alveoli
- Has lesser physical distribution, lower pressures, & lower resistances than the systemic circulation
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Term
| What two circulations do the lungs require? |
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Definition
- Pulmonary circulation
- Bronchiole circulation (part of the greater circulation)
- Has distribution & the arteries carry unoxygenated blood
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Term
| Describe the pulmonary circulation. |
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Definition
- Resistances much lower than systemic circulation
- Pulmonary capillaries hold 10% of the pulmonary circulation
- Lung capillary volume is about equal to the stroke volume of the right ventricle
- The right ventricle is its pump
- The amount of blood that flows through the pulmonary circulation is about equal to the amount of blood that flows through all other organs & tissues
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Term
| What type of pump is the right ventricle? Why? |
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Definition
- Volume pump
- It pumps a large volume at a low pressure
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Term
| What is the absolute intravascular pressure? |
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Definition
- The pressure inside a vessel relative to air
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Term
| What is transmural pressure? |
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Definition
- The pressure across the wall of a vessel
- Very important in the lungs
- Extra-alveolar (like capillaries) share walls with alveolar vessels
- Alveolar vessels are affected by alveolar pressure
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Term
| What is driving pressure? |
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Definition
- The pressure that pushes fluid through a tube
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Term
| What is pulmonary wedge pressure? |
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Definition
- The pressure measured in a pulmonary artery distal to an occlusion of that artery
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Term
| List 2 things that can go wrong with the pulmonary circulation pressures and the consequences. |
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Definition
- Obstruction in the arteriole system (like a blood clot)
- Increased capillary pressure (transmural capillary pressure exceeds capillary oncotic pressure)
- Pulmonary edema (water leaves the capillaries & enters the alveoli)
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Term
| Which side of the heart has more pressure? |
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Definition
- Left side of the heart is a pressure pump and has much greater pressure than the right
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Term
| What are the effects of gravity on the pulmonary circulation? |
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Definition
- Significant impact of gravity
- Dorsal/ventral in quadrupeds
- Superior/inferior in bipeds
- In the lungs, the pressure is lower, so hydrostatic pressure plays a greater role in perfusion
- Remember hydrostatic pressure is caused by the height of fluid in the column, in this case blood
- Higher up, the pressure is lower; Farther down, the pressure is higher
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Term
| What happens to the pressure inside the alveolus (Palv) when the diaphragm contracts/relaxes? |
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Definition
- Contraction of diaphragm (flattening): Palv becomes negative
- Relaxation of diaphragm (dome): Palv becomes positive
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Term
| How is a capillary perfused? |
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Definition
- Good perfusion = Pa > Pv > Palv
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Term
| Describe the hydrostatic pressure in the top and bottom parts of the lungs. |
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Definition
- Hydrostatic pressure in the top of the lungs is low
- In the bottom of the lungs, its high
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Term
| Describe the perfusion of the top, middle, and bottom parts (zones 3, 2, & 1) of the lungs. |
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Definition
- Top part of the lungs has very poor perfusion b/c the hydrostatic pressure is so low
- Bottom part of the lung has good perfusion b/c the hydrostatic pressure is high
- Middle part of the lung has intermittent flow. When alveolar pressure is positive, the flow goes down. When alveolar pressure is negative, the flow goes up.
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Term
| What happens if you exert too much energy on the re-breathing bag & blow up the alveoli? |
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Definition
- Blood flow is cut off b/c you're squeezing the capillaries b/w the alveoli
- When this happens, pressure in the right ventricle increases from blood backing up
- This forces fluid out into the alveoli because you are increasing Pc at the arterial end
- Causes pulmonary edema
- With right side heart block, pressure in the PA goes up, but systemic pressure goes down
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Term
| What are the 2 types of pulmonary resistance alterations? |
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Definition
- Passive alterations
- Active alterations
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Term
| What are passive alterations? |
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Definition
- No smooth muscle contraction
- Recruitment & distention
- Capillaries that were not open will open (recruitment)
- Open capillaries will increase in diameter (distention)
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Term
| Why is an increase in pressure from resistance bad? |
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Definition
- Forces fluid into alveoli to cause edema
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Term
| When there is inspiratory movement, vessels increase in length and width. Why does this not increase resistance? |
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Definition
- Increasing length alone would increase resistance.
- However, increasing the width decreases resistance & the effects of increasing width are greater than those of increasing length
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Term
| How does surfactant help open alveoli? |
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Definition
- The alveoli are essentially bubbles
- The surfactant-air interface in the alveoli causes the bubbles to contract
- When that happens, capillaries between the alveoli are pulled open & wide
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Term
| When pulmonary artery pressure goes up, what happens to resistance? Why? |
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Definition
- As pulmonary artery pressure goes up, resistance goes down
- Due to passive alterations
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Term
| What are active alterations to pulmonary vascular resistance? |
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Definition
- Smooth muscle contraction
- Hypoxia is a powerful vasoconstrictor locally in the lungs (not globally)
- Parenchymal tissue must be present to prevent hypoxemia by shunting blood away from unventilated alveoli
- Depends on vasoconstrictive chemicals (H+, K+, etc)
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Term
| Why would you want vasoconstriction in the lungs with hypoxia? |
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Definition
- If a local area of the lungs becomes hypoxic, you want to shunt blood flow away to areas of the lungs where it can actually pick up oxygen
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Term
| Give 2 reasons why arterial pO2 is not equal to alveolar pO2. |
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Definition
- Right to left shunts
- Ventilation/perfusion mismatches (most common)
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Term
| What are right to left shunts? |
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Definition
- All the blood in the lung doesn't come into contact with O2
- This blood will mix with O2 rich blood to lower the overall O2
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Term
| What are ventilation/perfusion mismatches? |
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Definition
- Ventilation is good at the top & poor at the bottom of the lung
- Perfuion is poor at the top & good at the bottom of the lung
- Somewhere in the middle is a good ventilation/perfusion ratio
- VA/Q (ventilation of the alveolus/flow of blood) of 1 is ideal ratio
- Anything less than 1 is a mismatch
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Term
| What is venous admixture? |
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Definition
- Alveoli are perfused but not ventilated
- Blood stays venous blood
- VA/Q is less than 1 and can be 0
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Term
| What is alveolar dead space? |
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Definition
- Alveoli that are ventilated but not perfused
- High VA/Q ratio that can be infinity
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Term
| What is an absolute shunt? |
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Definition
- Blood never comes into contact with an alveolus
- Stays venous blood
- Can reduce pO2 of blood that leaves the lungs
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Term
| How is water dealt with in the lungs by pressures? |
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Definition
- Oncotic pressure is higher than hydrostatic pressure
- Hydrostatic pressure is so low that water is always moving into the capillary
- If water gets into the alveolus, it will be reabsorbed
- Good b/c you need the alveoli to be dry
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