The Pulmonary Circulation

Question 1

What are the 2 types of circulatory system

Answer 1

Systemic and pulmonary

Question 2

What is the arterial pressure in the systemic system

Answer 2

120/80mmHg

Question 3

What is the arterial pressure of the pulmonary circuit

Answer 3

20/8mmHg

Question 4

What is unusual about the pulmonary artery

Answer 4

its the only artery that carries deoxygenated blood

Question 5

What is the purpose of the pulmonary system

Answer 5

Bring air and blood in very close contact to allow gas exchange

Question 6

Why is the low pulmonary circulation pressure important

Answer 6

the separating membrane between the blood and air is very thin. high pressure would leak fluid into the alveoli

Question 7

What is the only organ to receive the entire cardiac output

Answer 7

lungs

Question 8

What are the respiratory functions of the pulmonary circuit

Answer 8

gas exchange
re-oxygenate blood
eliminate CO2

Question 9

What are the non-respiratory functions of the pulmonary circuit

Answer 9

• Aid in lung fluid balance
• Site of Angiotensin converting enzymes ACE, converts AT1 to AT2
• Supplies nutrients to lung tissue
• Blood reservoir

Question 10

What are some special properties of the pulmonary blood vessels

Answer 10

Much thinner walls than systemic as need to withstand less pressure
Vessels distend more than systemic ones

Question 11

How are pulmonary vessels able to keep the blood pressure low

Answer 11

Dilating

Recruiting other normally closed vessels

Question 12

How can alveoli affect surrounding capillaries

Answer 12

increase alveolar pressure can compress the capillaries, increase resistance and reduce blood flow

Question 13

What is different between the arterial and venous pressures in the systemic and pulmonary circulations

Answer 13

Systemic = big difference (driving pressure)
Pulmonary = small drop, small change can make considerable change to driving pressure

Question 14

How and when can the vessels of the pulmonary circulation act as a blood reservoir

Answer 14

Vessels = very compliant
Can serve as reservoir when left ventricular output momentarily exceeds venous return
Cardiac output can be rapidly increased by drawing upon pulmonary blood volume, lungs can be referred to as accessory heart

Question 15

Which circulation supplies blood to the structures of the lungs including the upper respiratory tract

Answer 15

systemic circulation

Question 16

What is a massive pulmonary embolism

Answer 16

When 50% or more of the pulmonary circulation is obstructed by a clot

Question 17

In what conditions of ventilation and perfusion is gas exchange optimal

Answer 17

When the ventilation is closely matched to blood flow/perfusion.
Where fraction of alveolar ventilation is matched to the fraction of cardiac output perfusing that alveolus.

Question 18

What is an ideal ventilation/perfusion ratio (V/Q ratio) for the whole lung

Answer 18

0.8-1.0

Question 19

Name 3 things that influence the distribution of blood flow

Answer 19

Gravity
Alveolar Gas Pressure
Hypoxic Pulmonary Vasoconstriction

Question 20

What almost entirely determines the systemic circulation blood flow in the organ

Answer 20

The high resistance arterioles that regulate blood flow through the capillary beds

Question 21

Do the alveoli at the base or apex receive more ventilation

Answer 21

Base receives about twice as much

Question 22

How can the distribution of blood flow in the lungs be assessed

Answer 22

Similar to method to assess distribution of ventilation

Xe133 in saline solution injected into the pulmonary artery with radiation detectors placed outside chest

Question 23

Does the apex or base of lungs receive more blood flow

Answer 23

On average base receives about 4 times more blood flow per unit lung volume than apex

Question 24

Going from rib 1 to the bottom one, how does the V/Q ratio change

Answer 24

At the base the lung receives excess perfusion relative to ventilation so V/Q is less than 1.0
The apex has an excess ventilation to perfusion so V/Q is greater than 1.0

Question 25

How do systemic arteries react to hypoxia and why

Answer 25

They vasodilator to increase the delivery of oxygen.

Question 26

How do arterioles in the lungs react to hypoxia and why

Answer 26

They vasoconstrict to direct blood away from under ventilated parts of the lungs and is important to maintain V/Q matching.

Question 27

How does Hypoxic pulmonary vasoconstriction tend to affect V/Q

Answer 27

tends to promote optimum V/Q ratio for the lungs as a whole by increasing the V/Q in areas of the lungs where it is lower than normal