5.3 Pulmonary Circulation

Question 1

Pressure in pulmonary vs systemic circulation

Answer 1

Pulmonary is much lower (about 25/10mmHg)

Question 2

Cardiac output in pulmonary vs systemic circulation

Answer 2

The same

Question 3

Pulmonary artery vs systemic artery wall thickness

Answer 3

Pulmonary arteries are much thinner

Question 4

In the systemic circulation, the windkessel effect enables relatively constant blood flow. Is this the case in the pulmonary circulation?

Answer 4

No

(Systole, full on, diastole, low, systole, full on, diastole, low)

Question 5

The main factor that modulates resistance in the systemic circulation is at the level of the arterioles. Is this the same in the pulmonary circulation?

Answer 5

• No
• In the pulmonary circulation, it is at the level of the capillaries
• How many? How dilated are they? Etc

Question 6

What factors influence the resistance of the pulmonary circulation (other than capillaries)?

Answer 6

• Lung volume
• Vascular smooth muscle tone
• Alveolar hypoxia
• Pulmonary intravascular pressure

Question 7

Using ohms law, work out how pulmonary circulation pressure can remain constant in response to an increase in blood flow. How does this happen?

Answer 7

• Decrease in resistance
• Distension of pulmonary capillaries
• Recruitment of previously narrowed capillaries

Question 8

List two pathological processes which can lead to a ventilation/perfusion ratio of zero. What is the result of this?

Answer 8

• Peripheral oedema
• Pneumonia

Result: hypoxemia

Question 9

What is a pulmonary shunt?

Answer 9

Passage of the blood from the right side to the left side of the heart without being oxygenated

Question 10

Describe the perfusion of zone 1 of the lungs during standing

Answer 10

No blood flow; alveolar pressure is higher than the pressure in the arteries

Question 11

Describe the perfusion of zone 2 of the lungs during standing posture

Answer 11

Blood flow in systole, when arterial pressure is sufficient. No blood flow in diastole, as arterial pressure in insufficient.

Question 12

Describe the perfusion of zone 3 of the lungs during standing posture

Answer 12

Constant flow of blood, as arterial pressure is always sufficient

Question 13

How does long volume influence pulmonary vascular resistance?

Answer 13

High resistance at low volumes: large vessels are not held open by stretched alveoli

High resistance at high volumes: small vessels are compressed by stretched alveoli

Goldilocks zone: FRC

Question 14

List three chemical factors that can increase pulmonary vascular resistance

Answer 14

• Endothelin 1; potent vasoconstrictor
• Catecholamines
• Thromboxane

Question 15

List some substances that can decrease pulmonary vascular resistance

Answer 15

• Nitric oxide; potent vasodilator
• Substance P
• Prostacyclin
• Adenosine

Question 16

What is the precursor to endothelin1 ?

Answer 16

Pro-endothelin 1

Question 17

What receptors does endothelin bind to?

Answer 17

ETA and ETB

Question 18

What is the precursor to nictric oxide?

Answer 18

L-arginine

Question 19

How does Nitric oxide dilate blood vessels?

Answer 19

Activates an enzyme, which facilitates a chemical reaction that results in vasodilation

Question 20

What is the precursor to prostacyclin, and what receptor does it bind to? What is the result?

Answer 20

Precursor: arachidonic acid
Receptor: IP receptor
Result: Vasodilation