Pulmonary Circulation

Question 1

How does the pressure in the pulmonary circulation differ from the systemic circulation?

Answer 1

The pressure in the pulmonary circulation is MUCH LOWER than in the systemic circulation

Question 2

State a key difference in the structure of the pulmonary arteries compared to the systemic arteries.

Answer 2

The pulmonary arteries have a greater lumen: wall thickness ratio meaning that they are more distensible/compliant

Question 3

How does the mean arterial blood pressure vary between the systemic and pulmonary circulation?

Answer 3

MABP in the pulmonary circulation is 15% that of the systemic circulation

Question 4

How does the pressure gradient differ between the systemic and pulmonary circulation?

Answer 4

10% of systemic

Question 5

How does the resistance differ between the systemic and pulmonary circulation?

Answer 5

10% of systemic

Question 6

Where is ACE expressed?

Answer 6

In the lung endothelium and in the kidneys

Question 7

What does ACE do?

Answer 7

Converts Angiotensin I to Angiotensin II

Breaks down bradykinin

Question 8

Describe the protective role of the pulmonary circulation.

Answer 8

The pulmonary circulation filters out small clots that could reach the brain or heart and cause sudden death. It filters the blood before it reaches the systemic circulation.

Question 9

State and describe three pulmonary shunts.

Answer 9

Bronchial Circulation - branches off the aorta and returns to the pulmonary veins. It goes through the left side of the heart twice before the right side of the heart and so it bypasses the lungs.
Foramen Ovale and Ductus Arteriosus - Foetal Shunts - provide a low resistance path for the blood from the right side of the heart to enter the left side of the heart without going through the lungs.

Question 10

Give two examples of congenital heart defects.

Answer 10

ASD/Patent Foramen Ovale

VSD

Question 11

How does the pulmonary circulation respond to an increase in cardiac output?

Answer 11

The pulmonary arteries are fairly compliant and so they can dilate to increase perfusion without causing much of a change in MABP and hence preventing pulmonary oedema.

Question 12

Describe the perfusion across the lungs at rest when standing up.

Answer 12

The base of the lungs is more perfused that the apex - due to gravity and the fact that blood follows the path of least resistance.

Question 13

Describe and explain the effects of increasing ventilation on pulmonary
resistance.

Answer 13

Ventilation increases pulmonary resistance at the EXTREMITIES
When it is near residual volume (forced expiration), the intrathoracic pressure presses on the extra-alveolar arteries thus increasing resistance.
When it is near TLC, the expansion of the alveolus presses on the alveolar arteries thus increasing resistance.

Question 14

How do the systemic and pulmonary circulation differ in their response to hypoxia?

Answer 14

Systemic - vasodilation to increase perfusion to match metabolic demand
Pulmonary - vasoconstriction

Question 15

What channel is response for this response to hypoxia?

Answer 15

Oxygen sensitive potassium channel

Question 16

Give an example of a situation in which the response of the pulmonary circulation to hypoxia is USEFUL.

Answer 16

Foetal Development - prevent blood from flowing through the lungs

Question 17

Give an example of a situation in which the response of the pulmonary circulation to hypoxia is DETRIMENTAL.

Answer 17

COPD - obstruction leads to hypoventilated airways causing vasoconstriction
This increases the resistance of the pulmonary circulation leading to pulmonary hypertension and right ventricular hypertrophy. This can lead to congestive heart failure.

Question 18

State three causes of pulmonary oedema.

Answer 18

Increase in hydrostatic pressure (e.g. due to pulmonary hypertension as a result of left ventricular failure)

Infection - proteins and white blood cells accumulate in the interstitium thus increasing the interstitial oncotic pressure

Lymphatic Obstruction - can’t clear away the net 1 mm Hg that enters the interstitium