Respiratory Physiology Lecture 5 Part 21: Gas Exchange and the pulmonary circulation

Question 1

What determines arterial levels of gas?

Answer 1

Partial pressure of gas in alveoli determines arterial levels

Question 2

P_o2 and % of capillary length relationship for healthy and diseased

Answer 2

As capillary length increases there reaches an equilibrium for which concentration of oxygen reaches.

• Occurs within first 1/3 of capillary length which is good especially if you are in a diseased condition the extra length of time is advantageous
  
  • Continues to increase for diseased person. PO2 will not reach 100 but around 80 which may be sufficient enough to deliver O2 to peripheral tissues

Question 3

Cardiac Output

Answer 3

CO

The volume of blood pumped by the heart per minute (mL blood/min)

Question 4

Flow system circulation = ??

Answer 4

Flow Pulmonary circulation

Question 5

Systemic circulation

Answer 5

high pressure system necessary to deliver blood in peripheral tissue (Brain) and overcome high resistance system

• LV generates a lot of pressure to go against gravity and to deliver oxygen to the whole body

Question 6

Pulmonary circulation

Answer 6

low pressure system, needs to deliver blood only to lungs and high pressures are risky (Lung edema)

• Does not need to travel far from RV and need it to be low pressure since the respiratory system is fragile

Question 7

Blood circulation

Answer 7

Question 8

System formation of pulmonary circulation

Answer 8

Low-pressure system:

• Needs to pump blood only to the top of the lung
• Important for avoiding rupture of respiratory membrane and edema formation

Low resistance system:

• R is less than 1/10 of that in the systemic circulation due to:
  
  • Shorter and wider vessels

High compliance vessels:

• Higher number of arterioles with a low resting tone
• Due to the thin walls and the paucity of smooth muscle can accept large amounts of blood so large expansion of vessels
• Can dilate in response to modest increases in arterial pressure
• Increased CO can load respiratory system with more blood

Question 9

Equation for resistance

Answer 9

poiseuille’s law

Question 10

What is compliance?

Answer 10

the property of a material of undergoing elastic deformation or (of a gas) change in volume when subjected to an applied force. It is equal to the reciprocal of stiffness.

Question 11

Pulmonary blood volume = ??

Answer 11

450 mL (220 - 900 mL)

• About 0.5 L but this amount can vary dramatically due to the high compliance

Question 12

Pulmonary capillary blood volume = ??

Answer 12

70 mL at rest, up to 200 mL during exercise

Question 13

Describe the gas exchange surface of the pulmonary capillaries

Answer 13

There are 280 billion highly anastomosing capillary segments, creating a gas exchange surface of 50 - 100 m2 (~ Size of a tennis court)

• Very large surface area of the respiratory membrane

Question 14

What is anastomosis in capillaries?

Answer 14

An anastomosis is a connection or opening between two things that are normally diverging or branching, such as between blood vessels, leaf veins, or streams. Such a connection may be normal or abnormal; it may be acquired or innate; and it may be natural or artificial

Question 15

How fast does blood passes through the pulmonary capillaries?

Answer 15

in about 0.75 sec at rest and can be reduced to 0.3 sec when the cardiac output increases