Week 7

Question 1

Def: Convection

Answer 1

Bulk flow of gases goes through movement of medium

Question 2

Oxygen transport pathway

Answer 2

1. Air flow via convection into alveoli (Pulmonary Ventilation)
2. Diffusion of O2 across respiratory epithelium
3. Circulation of Oxygen through circulatory system via convection
4. Diffusion of O2 into cells

Question 3

Why do the partial pressure of O2 and CO2 decrease along the path of flow at each diffusion step?

Answer 3

There has to be a pressure difference at point of diffusion for process to occur

Question 4

Purpose of lungs

Answer 4

Provides the interface for gas exchange between the air and the blood

Question 5

Pulmonary Ventilation

Answer 5

Brings fresh air and O2 into contact with the gas-exchange surface and expels CO2

Question 6

Purpose of Alveoli

Answer 6

Provide an interface for diffusion between air and blood

Question 7

Characteristics of Air-blood interface

Answer 7

• large surface area
• very thin

Question 8

Ideal Gas Law

Answer 8

PV=nRT
- where n is the number of moles of the gas, V is its volume, Tis its temperature (in K), and R is the gas constant

Question 9

What is total barometric pressure

Answer 9

760mmHg or 760 Torr

Question 10

How do you calculate total barometric pressure

Answer 10

= sum of partial pressures of each gas in a volume

Question 11

Fraction of N2 in dry air

Answer 11

79%

Question 12

fraction of O2 in dry air

Answer 12

21%

Question 13

fraction of CO2 in dry air

Answer 13

0.03%

Question 14

Partial pressure of gases in liquid

Answer 14

The partial pressure of gas that is dissolved in a liquid is equal to the partial pressure of that gas in the air phase with which the fluid is in equilibrium

Question 15

How to calculate concentration of a dissolved gas

Answer 15

= Partial pressure x solubility

Question 16

O2 and CO2 partial pressure through the circulatory system

Answer 16

1. Atmospheric air and alveolar
   - Alveolar partial pressures are very different from outside air
   - 160 mmHg O2 atmospheric
   - 0.3 mmHg CO2 Atm
   - 104 mmHg O2 alveolar
   - 40 mmHg CO2 Alv
2. Pulmonary Veins
   - Partial pressures are very similar in alveolar air and the blood leaving the lungs (slightly less in blood)
   - 104 mmHg O2
   - 40 mmHg CO2
3. Systemic Arteries
   - Partial pressures are the same in blood leaving the lungs and entering the systemic capillary beds
   - 104 mmHg O2
   - 40 mmHg CO2
4. Cells
   - Partial Pressure in cells are very different from blood
   - less than 40 mmHg O2
   - more than 46 mmHg CO2
5. Systemic Veins and Pulmonary Arteries
   - Partial pressures are the same in venous blood leaving the systemic capillaries and blood entering the pulmonary capillary beds
   - 40 mmHg O2
   - 46 mmHg CO2

Question 17

Flow Down Gradients

Answer 17

Diffusion of gases from one point to another is driven by partial pressure gradients between two points
- move from low pressure to high pressure

Question 18

Def: diffusion capacity

Answer 18

an index of the conductance of a gas across the diffusion surface

Question 19

Ficks law of the rate of diffusion

Answer 19

Diffusion flux rate = D x change in pressure

Question 20

What factors determine diffusion capactiy

Answer 20

• Solubility and diffusivity of the gas (+)
• Area of diffusion surface (+)
• Thickness of diffusion surface (-)
• Properties of ventilation and/or perfusion of diffusion surface
• Temperature (+)

Question 21

How and why does the O2 diffusion rate change along pulmonary capillaries

Answer 21

diffusion rate decreases along capillaries as blood O2 partial presure increases because the difference in pressures decreases

Question 22

What factors determine venous PO2?

Answer 22

• Effects of diffusion
• Blood flow (convection) (+)
• Tissue metabolism (O2 consumption) (-)

Question 23

Mass Balance

Answer 23

The contents of material in any body compartment is determined by the inputs and the outputs from that compartment
Accumulation = input + generation - output - consumption
- equation refers to absolute mass in a compartment or to rates of change
- in steady state conditions equation equals 0

Question 24

Mass balance for O2 in tissues

Answer 24

• Input = Q x CaO2
• Generation = 0
• Output = Q x CvO2
• Consumption = VO2
  VO2 = Q x (CaO2-CvO2)

Question 25

Mass balance across O2 transport pathway

Answer 25

VO2
= O2 inhaled - O2 exhaled (in lungs)
= Lung O2 diffusion
= Q x (CaO2 - CvO2)
= Tissue O2 diffusion
= Mitochondrial O2 Consumption

Question 26

What limits maximal capacity for aerobic metabolism?

Answer 26

maximal rate of O2 transport

Question 27

Determinant of VO2

Answer 27

Occurs at the intersection between mass balance curve and fick’s law curve because the rate of O2 removal from the circulation must equal the rate of diffusion into the tissue
- determined by Q and O2 diffusing capacity

Question 28

What determines the O2 diffusing capacity of a tissue

Answer 28

• Capillary density (surface area)
• Properties of blood flow

Question 29

Mass Balance graph

Answer 29

x- axis: Venous PO2
y- axis: VO2
as the venous PO2 increases VO2 decreases

Question 30

Fick’s Law graph

Answer 30

X- Axis: Venous PO2
y- Axis: VO2
As the venous PO2 increases VO2 increases
P cap increases VO2 increases, translates to increase venous PO2