Term
| How do the pulmonary artery endothelial cells prevent blockages? |
|
Definition
1. Fibrinolysis
2. Activate inflammatory cascade
3. Cause leakage of plasma into the lung's interstitial tissue |
|
|
Term
| What happens when the small pulmonary arteries and arterioles become blocked? |
|
Definition
| They prevent air, thrombi, and fat from reaching the systemic vascular beds. This prevents arterial obstruction and tissue ischemia/infarction of the cerebral, coronary, renal, or intestine cierculations. Air emboli are absorbed within the pulmonary capillaries. Fat and amniotic fluid emboli may cause acute inflammation within lung tissue, leading to hypoxemia. |
|
|
Term
| How is metabolic activity activated and deactivated in the endothelial cells of the pulmonary circulation? |
|
Definition
Activation - Angiotensin I is converted to II by ACE, which is located on the surface of pulmonary capillary endothelial cells
Inactivation - bradykinin, serotonin, prostaglandins E1, E2, and F2a, and norepinephrine are inactivated by the pulmonary capillary endothelial cells.
Note: epinephrine, vasopressin, and histamine pass through unchanged ( no effect) |
|
|
Term
| How much blood is contained in the pulmonary circulation at any given time? |
|
Definition
| 500 mL or 10% of the total blood volume |
|
|
Term
| Is the pulmonary or systemic circulation higher in resistance? |
|
Definition
|
|
Term
| How do pulmonary arteries compare to systemic ones? |
|
Definition
| They have thinner walls, less musculature, less connective tissue, and are more compliant compared to systemic vessels. They also have less capacity for vasoconstriction compared to systemic vessels. |
|
|
Term
| How is resistance determined? |
|
Definition
R = Delta P/Q
Pressure gradient in the pulmonary circulation divided by flood flow
R = (Mean PAP - LAP)/Cardiac Output |
|
|
Term
| How does the change in resistance of the pulmonary circulation differ from that of the systemic? |
|
Definition
In the pulmonary, about 60% of the pressure drop occurs pre-capillary, indicating that the arteries and veins contributre about equally to the resistance to blood flow through the lungs.
In the systemic circ, vascular resistance occurs mostly at the level of the arterioles.
The pulmonary resistance is 10 fold lower than the systemic |
|
|
Term
| How do cardiac output and pulmonary artery pressure (PAP) affect resistance when elevated? |
|
Definition
An increase in the cardiac output and PAP will cause a decrease in the pulmonary vascular resistance (PVR)
Note: this differs from the systemic system, where an increase in flow and pressure (MAP) are associated with and increase in systemic vascular resistance |
|
|
Term
| Why does an increase in flow Q cause a decrease in the pulmonary vascular resistance? |
|
Definition
There are 2 mechanisms:
1. Capillary recruitment - when CO and PAP are at normal levels, many capillaries are partially or completely collapsed b/c of the low perfusion pressure. Increased Q causes the collapsed capillaries to open, leading to a decreased resistance.
2. Capillary distension - due to the capillary walls been thin and highly compliant, their lumens will extend with an increase in Q, further decreasing resistance |
|
|
Term
| What happens to pulmonary vascular resistance as pulmonary arterial pressure rises? Why is this important? |
|
Definition
| PVR falls. This is important to prevent the development of pulmonary edema |
|
|
Term
| What happens to extra-alveolar vessels in terms of pulmonary vascular resistance during inspiration? |
|
Definition
| There is a decrease in pleural pressure causing an increase in transmural pressure. As lung volume increases, so does the radial traction on the connective tissues surrounding the arteries, arterioles, venuoles, and veins. This causes a decrease in pulmonary vascular resistance. |
|
|
Term
| What happens to alveolar capillaries in terms of pulmonary vascular resistance during inspiration? |
|
Definition
| With inspiration,, the lung volume will increase causing the alveoli to increae in size and the capillaries to stretch. The capillary lumen will decrease in diameter, leading to an increae in vascular resistance. |
|
|
Term
| What is functional residual capacity? |
|
Definition
| This is when pulmonary vascular resistance is at its lowest because neither alveolar nor extra alveolar vessels are compressed. |
|
|
Term
| How is resistance increased at low lung volumes? What about at high lung volumes? |
|
Definition
Low volumes - compression of extra-alveolar vessels by increases in pleural pressure and decreased traction on the vessels by connective tissue
High volumes - due to increased size of alveoli and compression of alveolar capillaries |
|
|
Term
| What does hypoxic pulmonary vasoconstriction help relieve? |
|
Definition
| It reduces the effect of poorly ventilated alveoli on oxygen and CO2 exchange. It helps match perfusion to alveolar ventilation |
|
|
Term
| What is global hypoxia? What conditions is it commonly found? |
|
Definition
| It is generalized pulmonary arteriole constriction leading to a significant rise in pulmonary vascular resistance (PVR) and pulmonary artery pressure (PAP). It is seen at high altitudes with reduced barometric pressure and ambient partial pressures of oxygen. Also seen in chronic lung diseases |
|
|
Term
| What are 5 fluid forces that regulate movement into capillaries? |
|
Definition
Hydrostatic pressure
Colloid osmotic pressure
Alveolar Surface tension
Capillary permeability
Pulmonary Edema |
|
|
Term
| What are four causes of pulmonary edema? |
|
Definition
1. Increased pulmonary capillary hydrostatic pressure due to left ventricular failure (e.g. mitral stenosis, aortic valve stenosis)
2. Damage to type II alveolar pneumocytes, which decreases surfactant and leads to increase surface tension
3. Decreased colloid osmotic pressure
4. Diffuse lung injury |
|
|
