Gas Exchange

Question 1

What is the pressure of the thoracic cavity compared to atmospheric air?

Answer 1

-ve pressure

Question 2

What is the elastic property of lung tissue?

Answer 2

Wants to collapse/deflate

Question 3

What structures bound the thoracic cavity?

Answer 3

Ribs, sternum, diaphragm

Question 4

What keeps the lungs semi-inflated even during exhalation?

Answer 4

-ve pressure

Question 5

What does high lung compliance indicate?

Answer 5

A small change in pressure leads to a large change in volume

Question 6

How is compliance defined mathematically?

Answer 6

Change in volume/change in pressure

Question 7

What substance increases lung compliance?

Answer 7

Surfactant

Question 8

What are the benefits of surfactant in the lungs?

Answer 8

• Reduced energy needed to inflate lungs
• Prevents transudate (fluid) coming out of capillaries

Question 9

What type of cells produce surfactant?

Answer 9

Type II pneumocytes

Question 10

What disease states can alter lung compliance?

Answer 10

• Lack of surfactant (e.g., respiratory distress syndrome)
• Increase in connective tissue (e.g., fibrosis)
• Reduced lung elastic tissue (e.g., emphysema)

Question 11

What type of process is inspiration?

Active or passive?

Answer 11

Active process

Question 12

What happens during inspiration to lower pressure?

Answer 12

Increases volume of the thorax

Question 13

What are the steps involved in inspiration?

Answer 13

• Diaphragm contracts and flattens
• External intercostal muscles contract to aid ribs opening
• Increased thoracic volume lowers pressure
• Lungs expand, increasing lung volume
• Air is drawn into the alveoli

Question 14

What type of process is expiration at rest?

Active or passive?

Answer 14

Passive process

Question 15

What occurs during passive expiration?

Answer 15

• Diaphragm relaxes, reducing thorax volume
• Thoracic wall and ribs return to resting position
• Elastic lung recoils, expelling air

Question 16

What muscles are involved in active expiration?

Answer 16

• Internal intercostal muscles
• Accessory muscles (e.g., abdominal muscles)

Question 17

How does ventilation differ in the horse?

Answer 17

• Firm thoracic wall shows biphasic inspiration and expiration
• Active and passive phases

Question 18

What does partial pressure Px refer to?

Answer 18

Pressure exerted by a single gas

Question 19

What is the principle of gas movement related to partial pressure?

Answer 19

Gas moves from area of high Px to low Px

Question 20

What is the ultimate goal of respiration?

Answer 20

To keep correct concentrations of certain molecules in the tissues for correct function: O2, CO2, H+

These molecules are essential for cellular metabolism and maintaining homeostasis.

Question 21

How are gases exchanged during respiration?

Answer 21

Via simple diffusion from alveolus to blood (external respiration) and from blood to tissue (internal respiration)

This process relies on concentration gradients.

Question 22

What does Fick’s Law describe?

Answer 22

Factors influencing the rate of diffusion of a gas across a membrane, including:
* SA of membrane
* Membrane thickness
* Partial pressure difference
* Diffusion coefficient

Fick’s Law is crucial for understanding gas exchange efficiency.

Question 23

What can affect gas diffusion according to Fick’s Law?

Answer 23

Diseases affecting:
* Alveolar destruction (SA)
* Fibrosis or edema (thickness)
* Ventilation disturbances
* Perfusion disturbances

Diseases like emphysema or pulmonary fibrosis can significantly impair gas exchange.

Question 24

Describe external respiration for O2.

Answer 24

Diffusion of O2 from alveolus into blood follows pressure gradient

Rapid equilibriation occurs between capillary and alveolar PO2.

Question 25

How does the rate of O2 diffusion change during external respiration?

Answer 25

Slower rate as PO2 difference gets smaller ## Footnote This is due to the decreasing gradient as O2 diffuses into the blood.

Question 26

Describe external respiration for CO2.

Answer 26

Diffusion of CO2 from blood to alveolus ## Footnote PCO2 in blood varies depending on metabolic activity in different body regions.

Question 27

What is internal respiration?

Answer 27

Diffusion down the pressure gradient of O2 from blood to interstitial fluid, and vice versa for CO2 ## Footnote This process is crucial for cellular respiration.

Question 28

How is O2 primarily transported in the blood?

Answer 28

Most is transported by hemoglobin within RBCs ## Footnote O2 has low solubility in blood, making hemoglobin essential for transport.

Question 29

What is the role of iron-based haem groups in hemoglobin?

Answer 29

Haem binds to molecular oxygen ## Footnote Each hemoglobin molecule contains 4 haem groups.

Question 30

What happens when the first O2 binds to hemoglobin?

Answer 30

Causes a conformational change in hemoglobin ## Footnote This change increases the affinity for subsequent O2 binding.

Question 31

What does the Oxygen Dissociation Curve represent?

Answer 31

The relationship between PO2 and hemoglobin saturation ## Footnote It illustrates how hemoglobin's affinity for O2 changes with different partial pressures.

Question 32

When is hemoglobin's affinity for O2 low?

Answer 32

When PO2 is low, such as in tissues ## Footnote This encourages hemoglobin to release O2 where it is needed most.

Question 33

How is CO2 transported in the blood?

Answer 33

As: * dissolved in plasma * bound to amine group of hemoglobin * as bicarbonate ions (HCO3) ## Footnote This transport is crucial for maintaining acid-base balance.

Question 34

What is the significance of bicarbonate (HCO3) in the blood?

Answer 34

Contributes to the bicarbonate buffer system, helping to buffer dramatic changes to pH ## Footnote This system is vital for maintaining acid-base homeostasis.

Question 35

Why is carbon monoxide (CO) considered poisonous?

Answer 35

Binds to hemoglobin with 200-300x greater affinity than O2 ## Footnote This binding is 'irreversible' and displaces O2, leading to hypoxia.