lecture 26

Question 1

what are the mix of gases we breath?

Answer 1

78% nitrogen
21% oxygen
0.033% CO2

Question 2

dalton’s law

Answer 2

the total pressure exerted by a mixture of gases equals the sum of pressures exerted by all individual gases

Question 3

partial pressure of O2 in atmosphere

Answer 3

160 mm Hg

Question 4

partial pressure of CO2 in atmosphere

Answer 4

0.25 mm Hg

Question 5

Hypoventilation

Answer 5

• decreasing our ventilation rate below 12 breaths/min
• PO2 will decrease because we slow down breathing
  PCO2 will increase because we’re blowing out less CO2 (CO2 will build up)

Question 6

hyperventilation

Answer 6

• increasing our ventilation rate below 12 breaths/min
• PO2 will increase because your bringing in more
• PCO2 will decrease because your blowing out more CO2

Question 7

Alveolar partial pressures and explain the reasoning behind it

Answer 7

PO2: 100 mm Hg
PCO2: 40 mm Hg
- because stale air and anatomical dead space and diffusion happens right away

Question 8

O2 and CO2 diffuse across_________________

Answer 8

alveolar epithelial cells (type 1) and capillary endothelial cells

Question 9

rate of diffusion is governed by ficks law

Answer 9

Rate of diffusion is directly proportional to:
1. Surface Area (A)
2. Membrane permeability (D= diffusion constant)
3. Partial pressure gradient (P)

Rate of diffusion is inversely proportional to
1. Diffusion distance (T): membrane thickness and interstitial fluid
- T is squared

Question 10

Gases diffusing down there partial pressure gradient

Answer 10

Pulmonary circulation:
- alveolar PO2 > venous PO2 (100>40)
- alveolar PCO2 < venous PCO2 (40<46)

Systemic circulation:
- arterial PO2 > tissue PO2 (100>40)
- arterial PCO2 < tissue PCO2 (40<46)

Question 11

Hypoxia

Answer 11

Oxygen depleted state

Question 12

Factors that decrease the amount of O2 reaching alveoli

Answer 12

1. low O2 content in atmosphere
2. Low alveolar ventilation
   - decreased lung compliance (loose elasticity or compliance can impair O2 uptake
   - increased airway resistance (bronchoconstriction, paracrine factors, autonomic control
   - CNS depression (drugs, alcohol overdose)
3. Rate and depth of breathing
4. Adequate perfusion of alveoli

Question 13

What can impair rate of gas exchange

Answer 13

1. Emphysema
2. Asthma
3. Fibrotic lung disease
4. Pulmonary edema

Question 14

Emphysema

Answer 14

• is distruction of alveolar wall which decreases surface area for gas exchange
• loss of elastance
• happens when u smoke a lot
  Result: Decrease surface area available for gas exchange which decreases diffusion rate and potentially lead to hypoxia

Question 15

Asthma

Answer 15

• local or systemic release of broncoconstrictors which increase resistance in air ways
• not enough air getting into lungs in the first place
• partial pressure gradient decreases
  Result: partial pressure of O2 will be much less than 100 mm Hg because O2 isn’t getting into the alveoli in the first place

Question 16

Fibrotic lung disease

Answer 16

• build up of scar tissue which can be result from exposure of asbestos
• the dense fibrous tissue is neither elastic or compliant. If lungs are becoming fibrotic they are not as compliant therefore it will become difficult to fill lungs with air which will reduce the partial pressure gradient and the scar tissue will increase thickness

Question 17

Pulmonary edema

Answer 17

• when there is a build up of fluid between alveolar epithelial cells and capillary endothelial cells which is called interstitial fluid
• often a result of heart failure
• increase the thickness
  Result decrease in rate of diffusion which decreases oxygen uptake and can lead to hypoxia