West's 9th ed - Chapter 4 - Blood Flow and Metabolism (1)

Question 1

How many pulmonary veins drain into the left atrium?

Answer 1

Four.

Question 2

What is the mean pressure in the pulmonary artery?

Answer 2

15mmHg (25 systolic and 8 diastolic)

Question 3

What happens to the interior of the extra-alveolar pulmonary blood vessels during inspiration?

Answer 3

Both arteries and veins fill with blood during inspiration, because the elastic lung parenchyma surrounding them is expanding and pulling the vessels open by radial traction.

Question 4

What happens to the interior of the alveolar capillaries if alveolor pressure increases?

Answer 4

The capillaries are compressed if alveolar pressures increase enough.

Question 5

As pulmonary vascular pressures are raised (e.g. with increasing blood flow), what happens to pulmonary vascular resistance?

Answer 5

PVR decreases as pulmonary vascular pressures are raised, and as blood flow rises. This is due to both RECRUITMENT and DISTENSION.

Question 6

What is recruitment? (with regard to pulmonary capillaries)

Answer 6

Recruitment is the opening of previously closed capillaries. Recruitment contributes to a decrease in pulmonary vascular resistance.

Question 7

What is distension? (with regard to pulmonary capillaries)

Answer 7

Distension is the widening of the lumen of capillaries. Distension contributes to a decrease in pulmonary vascular resistance.

Question 8

What happens to the vascular resistance of extra-alveolar pulmonary vessels as lung volumes expand?

Answer 8

As lung volumes expand (from zero), pulmonary vascular resistance decreases. The elastic tissue of the stretching lung parenchyma actually pulls these extra-alveolar vessels open. As the lung volume increases past FRC and past tidal breathing volumes, PVR starts to increase, and continues to increase as lung volumes increase to Vital Capacity.

Question 9

What is critical opening pressure?

Answer 9

This refers to the high PVR at low lung volumes. If the lung is completely collapsed, the extra-alveolar vessels are also somewhat collapsed (narrowed), and the PVR is high (because the arteries and veins have smooth muscle and elastic tissue in their walls, which has to be overcome in order to distend the vessels). The pressure in the arteries has to be risen above the critical opening pressure in order to allow any blood flow at all.

Question 10

Which parts of the lung are perfused more in the upright lung?

Answer 10

The lower parts. Perfusion (like ventilation) is greater in dependent regions (e.g. in the posterior lung when a person is lying supine)

Question 11

What happens to pulmonary circulation when alveolar gas is hypoxic? How low does the alveolar PO2 have to be for this to happen?

Answer 11

Small pulmonary arterioles will constrict if they are in contact with alveoli containing a PO2 of less than 100mmHg, to an exponentially increasing degree as the alveolar PO2 drops further. This phenomenon is called Hypoxic Pulmonary Vasoconstriction.

Question 12

What is the usual PO2 of the blood in pulmonary arterioles? And in alveoli? And in the blood of pulmonary veins?

Answer 12

Pulmonary arterioles: 40mmHg
Alveolar gas: 100mmHg
Pulmonary veins: 100mmHg

Question 13

What role does the autonomic nervous system play in pulmonary vasoconstriction to hypoxic parts of the lung?

Answer 13

Very little. Hypoxic Pulmonary Vasoconstriction is largely due to direct effects of the surrounding PO2.

Question 14

What happens to Angiotensin I in the lungs?

Answer 14

As Angiotensin I passes through the pulmonary capillaries, the enzyme ACE, lying in the endothelium of the capillaries, converts it to Angiotensin II, which is a potent vasoconstrictor.

Question 15

Name some of the substances that are inactivated by the lungs, as they pass through the pulmonary circulation. (Substances are inactivated either by uptake and storage, or by enzymatic degradation).

Answer 15

Bradykinin (inactivated by ACE).
Serotonin
Prostaglandins E1, E2, F2alpha
Norepinephine (but only up to 30%)
Leukotrienes

Question 16

How does the pressure surrounding pulmonary capillaries compare to the pressure surrounding pulmonary arteries and veins?

Answer 16

The capillaries are exposed to alveolar pressures, and can therefore be squashed if alveolar pressures are high. The larger vessels are extra-alveolar, and the pressures surrounding them are lower.

Question 17

What happens to pulmonary vascular resistance when cardiac output increases?

Answer 17

PVR falls even lower than its usual low level during exercise and times of increased cardiac output.

Question 18

What happens to the pulmonary circulation at birth?

Answer 18

Whilst in utero, the fetal pulmonary circulation is subject to significant hypoxic pulmonary vasoconstriction. At birth, this is dramatically reversed, and the pulmonary blood flow increases enormously.

Question 19

What determines whether fluid will move across the pulmonary capillary endothelium into the interstitium?

Answer 19

The Starling equilibrium. It is to do with the difference in colloid oncotic pressures, and the difference in hydrostatic pressures.

Question 20

What happens to pulmonary vascular resistance if you increase pulmonary arterial pressure? What happens to PVR if you increase pulmonary venous pressure?

Answer 20

PVR decreases as you increase the pressure in either pulmonary arteries and/or pulmonary veins.