Topic 13: Respiratory System - External + Internal Respiration and Oxygen Transport

Question 1

What occurs in external respiration? (2)

Answer 1

• oxygen from alveoli to blood
• CO2 from blood to alveoli

Question 2

What is external respiration aided by? (3 steps, 5 points)

Answer 2

1) thin respiratory membrane (2 cells + basement mem)
2) large surface area - capillaries, alveoli
- RBC single file in capillaries so max RBC exposure to gases
3) Blood velocity slow compared to gas diffusion
- RBC have time to pick up/release gases

Question 3

What occurs in internal respiration? (2)

Answer 3

• oxygen from blood to cells
• CO2 from cells to blood

Question 4

What is partial pressure of gases? (2)

Answer 4

• the pressure exerted by a single gas in a mixture of gases
  ex. O2 = 21% of air
  partial p = 0.21 x 760 mmHg = 160 mmHg
  written as PO2, PCO2, etc

Question 5

What promotes gas movements? (3)

Answer 5

• pressure gradients
• air to blood, blood to cells
• gas moves from high to low pressure

Question 6

What are the 2 ways that oxygen is carried?

Answer 6

1) dissolved in plasma (1.5%) = PO2
2) Bound to hemoglobin (98.5%)

Question 7

How is oxygen carried in the plasma? (2 points, 7 steps)

Answer 7

1) at lung capillaries (external resp.)
- O2 moves from high pressure (105 mmHg in lungs/alveoli) to low pressure (40 mmHg in the capillary)
2) At tissue capillaries (internal resp.)
- Arterial PO2 = 95 mmHg
- resting venous + ISF PO2 = 40 mmHg
- so ICF PO2 is less than 40 mmHg
- then O2 diffuses down CG from: capillary to ISF to cell

Question 8

How is oxygen carried when bound to Hb? (4)

Answer 8

• each Hb can bind 4 O2 molecules (1O2/Fe)
• deoxyHb + O2 <-> HbO2 (oxyHb)
• relationship between PO2 and %Hb saturation shown on O2-Hb dissociation curve
• shows how much O2 is ob Hb for a given amount of dissolved O2

Question 9

What is the plateau of the O2-Hb dissociation curve? (2)

Answer 9

• between 60 and 100 mmHg PO2
• range of PO2 in lungs at which Hb picks up O2 (H 97% saturated)

Question 10

What occurs during plateau of the dissociation curve if alveolar PO2 decreases below normal? (2)

Answer 10

• little change in Hb saturation
• at high altitude, if alveolar Po2 is above 60 mmHg, Hb carries normal amount of O2

Question 11

What is the steep portion of the dissociation curve?

Answer 11

• range of PO2 in tissues, so O2 unloaded from Hb

Question 12

What occurs in the steep portion if at rest? (3)

Answer 12

ISF PO2 = 40 mmHg
- Hb is 75% saturated (97-75% = 22% unloaded to cells)
- allows holding of breath

Question 13

What occurs in the steep portion if high metabolism ie. during exercise? (2)

Answer 13

• ISF PO2 = 20 mmHg
• so Hb = 40% saturated (97-40% = 57% or more O2 unloaded easily)

Question 14

What does it mean if there is a shift to the right on the O2-Hb dissociation curve? (2)

Answer 14

• for a given PO2, you get less Hb saturation
• O2 unloads more easily/ and loads less easily
  in lecture he said it occurs in tissues

Question 15

Why does a shift to the right occur? (6)

Answer 15

1)when increased PCO2
2) decreased pH (related to increased CO2 and lactic acid)
- decreased ability of oxygen to bind to hemoglobin when H+ is bound to globin = BOHR EFFECT
3) increased temp
4) all occur when increase in cell metabolism like exercise, since Hb releases more O2

Question 16

What does it mean if there is a shift to the left of the dissociation curve? (3)

Answer 16

• for a given PO2, you get more Hb saturation
• O2 loads more easily and unloads less easily
• conditions at lungs (decreased temp due to evap. cooling)

Question 17

When does a shift to the left occur?

Answer 17

1) when decrease in PCO2
2) higher pH
3) decreased temp (due to evap. cooling)