pulmonary circulation

Question 1

what are the 2 circulation systems in the lungs

Answer 1

1. bronchial circulation
2. pulmonary circulation

Question 2

what does the bronchial circulation do

Answer 2

supplies O2 and nutrients to meet the metabolic requirements of the lungs

Question 3

what does the pulmonary circulation do

Answer 3

carries deoxygenated blood away from the heart to the lungs’ alveoli to undergo gas exchange and returns oxygenated blood back to the heart

Question 4

describe movement of deoxygenated blood

Answer 4

• leaves the right ventricle through the pulmonary valve
• enters the pulmonary trunk - this divides into the right and left pulmonary arteries

Question 5

how does blood become oxygenated in the lungs

Answer 5

• arteries divide further into smaller capillaries at the alveoli
• allows gas exchange
• Oxygen diffuses from the alveoli into the pulmonary capillaries
• carbon dioxide diffuses from the capillaries into the alveoli

Question 6

describe movement of oxygenated blood

Answer 6

• leaves lungs through the pulmonary veins to the heart’s left atrium, completing the pulmonary cycle.
• the blood is then distributed around the body via the systemic circulation.

Question 7

why must the pulmonary circulation be able to accept the entire cardiac output

Answer 7

because the right heart can’t work without the left heart

both the right and left ventricle must have the same cardiac output to prevent blood from building up in either the systemic or pulmonary circulation

Question 8

why does the pulmonary circulation need adaptations

Answer 8

to facilitate high volumes of blood flowing through it

Question 9

what are the adaptations of pulmonary circulation

Answer 9

• low pressure
• low resistance

adaptations of pulmonary capillaries for gas exchange

• large SA
• short diffusion distance
• hypoxic pulmonary vasoconstriction

Question 10

why is pulmonary circulation a lower pressure system

Answer 10

it is lower than systemic circulation

because the pulmonary arteries have thin vascular walls and high compliance, allowing them to carry more blood

Question 11

why is pulmonary circulation a lower resistance system

Answer 11

• pulmonary vessels are shorter and wider compared to systemic vessels
• pulmonary capillaries run in parallel, rather than in series like the systemic circulation
• relatively little smooth muscle in the arterioles - helps to reduce arterial tone.

These properties allow the pulmonary circulatory system to operate at a lower resistance.

Question 12

how do pulmonary capillaries achieve a large SA

Answer 12

due to the branching structure of the pulmonary tree.

Question 13

how do pulmonary capillaries achieve a short diffusion distance

Answer 13

the very high density of capillaries also means that the alveolar wall is always close to a capillary

Question 14

what is hypoxic pulmonary vasoconstriction

Answer 14

an important mechanism which responds to low alveolar oxygen levels to increase the efficiency of gas exchange

Question 15

what is an optimal V/Q ratio

Answer 15

0.8-1.0

Question 16

why is it important that the ventilation of the alveoli is matched by their perfusion

Answer 16

for efficient oxygenation of the blood

Question 17

how is optimal V/Q ratio maintained

Answer 17

• blood must be diverted away from poorly ventilated alveoli and directed towards better-ventilated alveoli.
• ensured by hypoxic pulmonary vasoconstriction, whereby small pulmonary arteries constrict to redirect blood flow from poorly ventilated areas of the lung to better-ventilated lung areas.

Question 18

what determines fluid formation in tissues

Answer 18

starling forces

The increased hydrostatic pressure of the blood in the capillaries pushes fluid out of the vessels at the arterial end. In contrast, oncotic pressure (exerted by large molecules such as plasma proteins) draws fluid back into the capillary at the venous end.

Question 19

what minimises fluid formation in the lungs

Answer 19

the low capillary pressure of the pulmonary vessels - means that only a small amount of fluid leaves the capillaries, and nearly all of this is reabsorbed.

a protective mechanism against fluid formation in the lungs

Question 20

role of bronchial arteries

Answer 20

• receive blood from the thoracic aorta and the upper intercostal arteries.
• they enter the lung at the hilum and branch at the main bronchus

Question 21

what do one portion of bronchial arteries supply

Answer 21

the lower trachea, extrapulmonary airways, and supporting structures

drains into the superficial bronchial veins

These veins join the azygous (from the right lung), the accessory hemizygous or intercostal vein (from the left lung), before reaching the inferior vena cava to enter the right heart.

Question 22

what do the other portion of bronchial arteries supply

Answer 22

the intrapulmonary airways up to the level of the terminal bronchioles, where they form extensive anastomoses with the pulmonary vasculature.

drains via deep bronchial veins within the lung and joins the pulmonary veins to travel to the left heart.

Question 23

what is pulmonary vascular resistance

Answer 23

the resistance against blood flow from the pulmonary artery to the left atrium

Question 24

what causes pulmonary hypertension

Answer 24

in chronic hypoxia, there is widespread vasoconstriction of the pulmonary vessels due to (the normally protective) hypoxic pulmonary vasoconstriction.

causes a chronic increase in vascular resistance, leading to pulmonary hypertrnsion

Question 25

what causes pulmonary oedema

Answer 25

If the pressure inside the pulmonary capillaries rises, then more fluid will leave the capillaries.

can occur if the left atrial pressure rises (such as in mitral valve stenosis or left ventricular failure).

Not all of this extra tissue fluid will be reabsorbed, and therefore builds up in the lung tissue.

Question 26

how does pulmonary oedema impair gas exchange

Answer 26

by increasing the length of the diffusion pathway.

Question 27

4 main causes of hypoxaemia

Answer 27

• hypoventilation
• diffusion abnormlaity
• V/Q mismatch
• shunt